Free Flip-Book Zoology Class 11th & 12th by Study Innovations

Body Fluids and Circulation

the heart. muscle.

(2) The impulse of contraction originates from nervous (2) The impulse of contraction originates itself in the heart.
system.

(3) The heart normally stops beating immediately after (3) The heart removed from the body continues to beat
removal from the body. Therefore, heart transplantation is for some time. Therefore, heart transplantation is possible.
not possible.

(4) Examples : Hearts of some annelids and most (4) Examples : Hearts of molluscs and vertebrates.
arthropods.

(b) Origin and conduction of heart beat : Initiation of heart beat is under special bundles of cardiac
of right atrium below the opening of superior vena
cava. This is the place where sinus venosus is
incorporated in the wall of right atrium in the
embryo. S.A. node is the main tissue of heart and has
highest degree of autrohythmicity (generates beating
impulse at the rate of 70-80 times/minute) but least
conductivity. The rhythmic impulses produced are
called as Sinus rhythmia. In frog S.A. node is present
in sinus venosus.

(ii) Atrio-ventricular node or A.V. node :
Also called reserve pacemaker, node of Twara and

cAschoff. Discovered by Lewis Kent. It lies in the right
muscles called nodal tissue. The cardiac muscles have less actin and myosin. So, structurally they become more a
nerve than muscle and functionally they are similar to neurons.

(1) Morphology of nodal tissue : The nodal tissue consists of the following –

(i) Sinu-auricular or S.A. node : Also called as pacemaker, node of keith and flack, heart of heart, brain of
heart, pulsation centre. It is located in the right wall

SINU-AURICULAR LEFT ATRIUM
NODE
AURICULO
RIGHT ATRIUM VENTRICULAR NODE
INTERNODAL
BUNDLE OF HIS
PATHWAY
INTERVENTRICULAR
RIGHT SEPTUM
BUNDLE OF
PURKINJE LEFT VENTRICLE
LEFT BUNDLE OF
FIBRES

atrium near the junction of interauricular and RIGHT VENTRICLE PURKINJE FIBRES

interventricular septum close to the opening of Fig. – Conducting system of rabbit's heart (ventral view)
coronary sinus. It is concerned with the conduction of

cardiac impulses generated by S.A. node, but it can also RIGHT VAGUS
generate the impulse at the rate of 40-60/minute. These PARASYMPATHETIC
impulses produced are rhythmic and called nodal rhythmia. In
LEFT VAGUS
(PARASYMPATHETIC)

frog, A.V. node is absent. SYMPATHETIC
GANGILA

(iii) Bundle of His or A.V. bundle : Discovered by SINUATRIAL AURICULO
His. It arises from A.V. node, descends in the interventricular NODE VENTRICULAR
septum and bifurcates into two branches innervating the wall
NODE

of right and left ventricle respectively. The myocardium of ACCELERATOR
atria and ventricles are discontinuous and this bundle is the NERVES

only muscular connection between the two. It is concerned Fig. – Innervation of human heart by autonomic nerves
with the conduction of impulse from atria to the tip of

Chapter 11 247

Body Fluids and Circulation

ventricle but can also generate impulse at the rate of 35-40/minute. The impulses produced are non-rhythmic.
(iv) Purkinje fibres : Numerous, modified muscle fibres which act as sympathetic nerve fibres. They arise

from branches of bundle of His and provide impulse to myocardium of ventricles. They can also generate non-
rhythmic impulse at a rate of 30-35/minute.

(2) Working of nodal tissue : S.A. node spontaneously initiates a wave of contraction which is conducted
along the tracts of special muscle fibres called internal pathways over both the auricles at a rate of 1m/sec. The
impulse generated travels first in the right atrium than in left atrium. So, right atrium contracts first but the
contraction ends simultaneously in both atria. As the musculatures of atria and ventricles are discontinuous and are
separated by a septum of fibrous connective tissue, called annular pad in mammals, the wave of contraction is
received by A.V. node from myocardium of atria and is provided to bundle of His. The impulses reach the A.V.
node about 0.03 seconds after their origin from S.A. node. The A.V. node generates a fresh wave of contraction
which passes over both the ventricles along the bundle of His and its ramifications at the rate of 1.5 to 4 m/sec. The
Purkinje fibres bring about the contraction of ventricles from the apex of heart which passes quickly towards the origin
of pulmonary and systemic arches forcing blood into them.

S.A. node not only acts as pacemaker but also establishes the basic rhythm at which the heart beats. In case of
degeneration of S.A. node, A.V. node can generate impulse but it will lead to abnormal beating (arrhythmia). The
failure of atrial impulse to pass into ventricles for a few seconds to few hours is called ventricular escape or stokes-
adams syndrome leading to delayed pick up of heart beat. In such conditions, artificial pacemaker (Lithium Battery)
is placed underneath the patient’s chest.

Ectopic pacemaker : If any cardiac muscle other than the conducting tissue (nodes) generates impulse, then
extra beats are heard. Such muscles are called Ectopic pacemaker.

In mammals, conducting system of the heart has S.A. node, A.V node and complicated system of conducting
fibres. But in frog, it has only S.A. node and system of conducting fibres is simple.

cHeart beat rate : Heart beat/minute or number of cardiac cycles/minute. Example – frog-64/min., rabbit-

200/min., human-70-80/min. Females have higher heart rate than males.

Normal heart beat rate → Rhythmia

Abnormal heart rate → Arrhythmia

Decrease in heart rate → Bradycardia

Increase in heart rate → Tachycardia

(c) Regulation of heart beat : The centre controlling the heart rate (cardiac centre) is present in medulla
oblongata of brain and possess chemoreceptors sensitive for CO2, O2 and also for blood pressure. This centre is
under the influence of hypothalamus which is the controller of autonomic activities.

(1) Nervous control : Brain receives two sets of nerve fibres : Sympathetic and para sympathetic or vegal.

When there is increase in blood CO2, the sympathetic nerve fibres stimulate S.A. node by producing
sympathin (adrenaline + noradrenaline). This compound induces impulse generation by inducing entry of

Chapter 11 248

Body Fluids and Circulation

Ca2+ into cardiac muscles. So, heart beat and force of contraction increase (Tachycardia). After action,
sympathin is destroyed by sympathenase, COMT (catechol orthomethyl transferase) and MAD (Mono Amino
Oxidase).

When there is increase in blood O2, the parasympathetic or vagal (10th cranial) nerve inhibits S.A. node by
producing acetylcholine. This compound increases contraction time and hence, heart beat is decreased
(Bradycardia). After action, acetyl choline is destroyed by enzyme acetyl choline esterase (AchE). This chemical
regulation of heart beat on behalf of nerves was discovered by Otto Loewi.

Vagus escape : Stimulation of vagus nerve decreases the heart rate but its continuous stimulation shows no
further decrease. This phenomenon is called Vagus escape.

(2) Hormonal control : Hormones from adrenal medulla adrenaline and nor adrenaline accelerate the heart
beat, the latter under normal conditions and the former at the time of emergency.

Pounding : Very fast heart beat during some conditions like anger and love.

Thyroxine hormone also increases the heart beat by increasing energy production.

(d) Factors affecting heart rate
• Heart rate increases with increase in basal metabolic rate (BMR).
• Heart increases as the size of the animals body decreases.
• Decrease in pH also increases heart rate.
• Heart rate increases with increase in temperature.
• Increase in Na+ ions in blood or in cardiac muscles, increase heart rate.
• Increase in Ca2+ ions in blood increase heart beat but if they are injected in cardiac muscles, heart stops in

contracted phase which is called Systolic Arrest.

c• Injection of K+ ions in heart muscles stop impulse generation. So, heart stops in diastolic or Relax phase.

• H+ ions reduce force of contraction of heart.
• Increased inspiration, muscular exercise, low oxygen tension, injection of adrenaline, thyroxine, sympathin

– all increase heart rate.
• Increased expiration, during sleep, injection of acetylcholine decrease heart rate.
• Stenosis – Narrowing of valve is called stenosis.
Cradiac cycle

A regular sequence of three events :

(i) Auricular systole (0.1 sec)

(ii) Ventricular systole (0.3 sec)

(iii) Joint Diastole or complete cardiac diastole (0.4 sec)

Chapter 11 249

Body Fluids and Circulation

During the completion of one heart beat is called as cardiac cycle. These events are repeated in a cyclic
manner during each heart beat.

(i) Auricular systole : The atria contract due to wave of contraction stimulated by S.A. node contraction of
auricles drives most of their blood into respective ventricles as the A.V. valves are open. There is no backflow of
blood into the large veins as the contraction begins at the upper end and passes towards ventricles and moreover,
the valves present at the opening of these veins close. Also, blood is already present in large veins which offers
resistance to the blood that may return from the atria. At the end of a atrial systole, there starts the relaxation of
auricles (auricular diastole) and contraction of ventricles (ventricular systole) simultaneously. Atrial systole takes 0.1
second while atrial diastole is of about 0.7 seconds.

(ii) Ventricular systole : The ventricles begin to contract due to a wave of contraction stimulated by A.V.
node. Due to ventricular systole, the pressure of blood in ventricles immediately rises above that in the auricles.
With this pressure, the bicuspid and tricuspid valves close rapidly to prevent the backflow of blood. This closure of
A.V. valves at the start of ventricular systole produces first heart sound called “Lubb” or Systolic sound. The
semilunar valves are also close at this time. When the pressure of blood in the ventricles exceeds that in the great
arteries, the semilunar valves open and blood enters into the great arteries. This marks the end of ventricular systole
which takes about 0.3 seconds. Now the ventricles start relaxing (ventricular diastole which lasts for about 0.5 sec.)

(iii) Joint diastole : The ventricles and auricles are in the diastolic phase simultaneously. As the ventricular
diastole progresses, the pressure in the ventricles falls below that in the great arteries. So, to prevent backflow of
blood from great arteries into ventricles, the semilunar valves close rapidly. This rapid closure of semilunar valves at
the beginning of ventricular diastole produces second heart sound “Dup” or diastolic sound.

During joint diastole, blood from great veins and coronary sinus flows into the atria and some blood also
passes from auricles into the respective relaxing ventricles due to less pressure in ventricles. This phase takes only
0.4 seconds and is also called as blood receiving period of heart. Thus a cardiac cycle is completed in 0.8 seconds.

cCardiac output : Volume of blood pumped from heart (left ventricle) into the systemic aorta in one minute is

called cardiac output. It is also called minute volume. It is calculated as the product of stroke volume (amount of
blood pumped by left ventricle each time it contracts) and rate of heart beat.

i.e. Cardiac output = Stroke volume × Rate of heart beat

= 70 ml × 75 times/minute = 5040 ml/minute ≃ 5 litres/minute
Total amount of blood in human body is about 6.8 litres (7% of body weight). During mild exercise, the
cardiac output rises to about 11 litres. Cardiac output is directly proportional to the size of the organism, metabolic
rate etc. but is inversely proportional to age.

(i) Fractions of cardiac output : Amount of pure blood going to an organ per minute is called as fraction of
the organ.

• Cardiac fraction – 200 ml/min.

• Hepatic fraction – 1500 ml/min. (28% of blood as liver is the busiest organ of body and has maximum
power of regeneration).

• Renal fraction – 1300 ml/min (25% of blood)

Chapter 11 250

Body Fluids and Circulation

• Myofraction – 600-900 ml/min.
• Cephalic organs – 700-800 ml/min.

• Remaining organs – Remaining blood.

(ii) Cardiac index : Cardiac output per square metre of body surface area per minute. As area of normal
young adult is 1.7 metre square, so, cardiac index is 3 litres/min/square metre.

(iii) Cardiac reserve : Maximum amount of blood that can be pumped by left ventricle under the conditions
of maximum needs. In this condition, heart beat can go upto 250 and stroke volume can go upto 100 ml per
systole. Cardiac reserve is 25-30 litres which is about 5-6 times of cardiac output.

(iv) End diastolic volume : Amount of blood present in left ventricle at the end of diastole. It is the
maximum volume of the cavity of left ventricle and is equal to 120-130 ml.

(v) End systolic volume : Amount of blood present in left ventricle at the end of systole. It is the least
volume of the cavity of left ventricle and is equal to 50-60 ml.

(vi) Stroke volume : (70 ml) is equal to the difference between the end diastolic volume and end systolic volume.

(vii) Venous return : Amount of impure blood returning to righ atrium per minute is called venous return and
is equal to 5.25 litres. The venous return is due to many factors –

(a) Little blood pressure in the veins.

(b) Skeletal muscle pump : Veins usually pass through skeletal muscles which, on contraction, exert
milking action on veins. So, there is upward movement of blood.

(c) Respiratory pump : Due to the movement of diaphragm during breathing, blood moves upward in the
veins.

(d) Pressure difference in venae cavae and right atrium. The negative pressure created in right atrium due to
the atrial diastole results in sucking up of blood from venae cavae into the atrium.

cHeart sounds
In normal heart, four sounds are heard. First and second sounds have audible frequencies, so, they can be
heard very easily. 3rd and 4th sounds are having very less frequency (less than 20 Hertz). So, they can’t be heard
easily. Third heart sound is running water sound. Fourth heart sound is also called Atrial sound as it appears when
blood flows from atria into ventricles due to atrial contraction.

Differences between first and seconds heart sounds

First heart sound (Lubb) Second heart sound (Dup)

(1) It is produced by closure of bicuspid and tricuspid (1) It is produced by closure of semilunar valves at the

valves at the start of ventricular systole. start of ventricular diastole.

(2) It is low pitched, less loud and of long duration. (2) It is higher pitched, louder, sharper and of short
duration.

(3) It lasts for 0.15 seconds. (3) It lasts for 0.1 second.

(4) Its principal frequencies are 25 to 45 cycles per (4) Its principal frequency is 50 cycles per second.
second.

Chapter 11 251

Body Fluids and Circulation

Heart sounds can be heard by an instrument called stethoscope by placing its receiver on left side of the chest
at the fourth intercostal space. Hearing of sound with the help of stethoscope is called Auscultation. The quality of
heart sounds indicates the state of the heart valves. Defective or damaged heart valves lead to the backflow of blood
either from ventricles to auricles or from aortae to ventricles. Such defects are detectable as abnormal hissing sound
called “Murmur”.. Defective valves may be replaced or repaired surgically. Syphilis and Rheumatic fever cause
Murmur. The instrument used to magnify and record the heart sound is called Phonocardiogram.

Electrocardiogram (ECG)

A graphic record of electrical events occuring during a cardiac cycle is called Electrocardiogram. The
PT

c0
instrument used for rcording the heart’s electrical variations is called Electrocardiograph in which the potential
differences of heart muscles are recorded by a galvanometer. In ECG, there are 2 types of waves :

(i) Depolarisation waves : They represent the generation of the potential difference. These waves appear
only when both electrodes of galvanometer are in different fields. When both the electrodes are in same field, there
is no deflection and wave drops down to base line.

(ii) Repolarisation waves : They appear when depolarisation is over and the muscle fibre is returning to its
original polarity. When both electrodes are in same polarity (means 100% repolarisation and 100% depolarisation),
there is no deflection.

A normal ECG has 5 deflection waves – P, Q, R, S and T. Out of them – P, R and T waves are above the base
line and are called positive waves. The Q and S waves are below base line and are called negative waves. The port
of the base line between any 2 deflections is called Interval.

T (sec)

0 0.4 0.8 1.2 1.6 2.0 2.4 2.8 3.2 3.6 4.0
R RR R

Normal PT PT PT

QQ QQ R

S SS S

–1

Fig. – Normal electrocardiogram

P wave : Indicates impulse of contraction generated by S.A. node P T
and its spread in atria causing atrial depolarisation. The interval PQ
represents atrial contraction and takes 0.1 second.

QRS complex : Indicates spread of impulse of contraction from QS
A.V node to the wall of ventricles through bundle of His and pukinje
fibres causing ventricular depolarisation. This complex also represents ATRIAL DEPOLARISATION
repolarization of S.A. node. VENTRICULAR DEPOLARISATION

The RS of QRS wave and ST interval show ventricular contraction VENTRICULAR REPOLARISATION
(0.3 seconds). QRS is related to ventricular systole.
Fig. – Normal ECG deflections, Depolarisation
and repolarisation

T wave : Indicates repolarisation during ventricular relaxation.

Chapter 11 252

Body Fluids and Circulation

Any abnormality in the working of heart alters the wave pattern of ECG. Thus, ECG is of great diagnostic
value in cardiac diseases. ECG also indicates the rate of heart beat.

If S.A. node is degenerated, the P wave disappears. This condition is called Heart fail. Atrial repolarisation
wave is not seen in normal ECG because at this time, the depolarisation wave of ventricles is being recorded. When
there is degeneration of bundle of His, the P to R interval increases. This is called Wenckebach phenomenon.

If bundle of His is completely cut, the P-R interval becomes infinite as the bundle of His is to transmit the

cardiac impulses. It is called total heart fail or total heart block. In arborisation heart block, the defect lies in purkinje fibres. In

heart attack, T waves become negative. When there is decrease in blood supply to a part of heart, there occurs

death of myocardium. This condition is called Myocardial infarction (MI). It is acute heart attack. The ST part of
ECG is depressed when heart muscles receive insufficient oxygen and is elevated in acute MI. When there is
degeneration of myocardium and deposition of fibres, the condition is called fibrillation during which, ECG
obtained is bizzare or non-decipherable.
arterioles further divide into smaller vessels called meta-arterioles (70 µm) which divide into capillaries. At the

cbeginning of capillary, the arterioles posses circular muscles called precapillary sphincter which regulates flow of
Vector cardiogram : Represents the direction of transmission of impulse.

History of ECG : The ECG was first recorded by Waller in frog. First human ECG was prepared by
Einthoven who also discovered the electrocardiograph and discussed the principles of ECG. Hence, he is commonly
called “Father of Electrocardiography”.

Blood vessels

The study of blood vessels is called Angiology. The blood vessels are of following types :

(i) Arteries (ii) Capillaries (iii) Veins

Vasa vasorum : Supply blood to the wall of large blood vessels.

(i) Arteries : Thick walled, carrying oxygenated blood (deoxygenated in pulmonary artery) from heart to
various parts of body. These blood vessels are grouped as Aorta which branches to form arteries which further

divides into thinner branches called arterioles inside the organ. Average diameter of arteriole is 120 µm. the

blood into the capillaries which is called vasomotion.

Muscleless end of meta-arteriole is called thoroughfare channel or preferential channel.

The largest artery is dorsal / abdominal aorta (systemic aorta).

Elastic or conducting arteries receive blood from heart and do not provide it to any organ rather they provide

blood to other atreries and are pressure reservoirs of blood.

Muscular arteries show vasoconstriction and vasodilation and provide blood to the organs.

Anastomosis : If more than one arteries are supplying to one organ then branches of these arteries unite to

form a network called Anastomosis. It provides many collateral or alternate pathways of blood supply. So, if there is

blocking of any artery, it will not lead to necrosis.

End arteries : In organs like heart, branches of different arteries do not unite rather they terminate due to

which the alternate pathways are not available. In such cases, blocking of any artery leads to necrosis of related part

of organ. To develop alternate pathway in such conditions is called as By pass surgery.

(ii) Capillaries : Smallest blood vessels, discovered by Marcello Malpighl (also layered nucleated squamous
epithelial cells called endothelium resting on a basement membrane. Diameter of capillary is about 8µ. These are

Chapter 11 253

Body Fluids and Circulation

also called as exchange vessels as they are the site of exchange of material between blood and tissue because of
least barrier in them. The capillaries can be grouped into two categories :

(a) Arteriolar capillary : Which supplies nutrition, respiratory gases etc. to the body cells.

(b) Veinular capillaries : Which collect the metabolic wastes from the body cells.

Capillaries possess abour 5% of total body blood and are present near almost all cells of body in the
intercellular spaces. The tissues which are devoid of intercellular spaces are also devoid of capillary. They are called
avascular tissues.

Capillaries are surrounded by cells of connective tissue called pericapillary cells. Some of these cells are
contractile and phagocytic in nature and are called Rouget cells or pericytes.

Continuous capillaries are without fenestra/aperture, hence are less permeable. These are present in organs
such as lungs, muscles, connective tissues and brain tissues.

Fenestrated capillaries possess apertures/fenestra and are found in those organs where there is maximum need
of permeability such as endocrine glands, intestinal villi, cavities of brain, kidney, ciliary body of eye.

Sinusoids are irregularly dilated capillaries found in organs where there is decrease in flow rate such as liver,
spleen, bone marrow, parathyroid, pituitary gland. In liver, sinusoids are branches of venules and open into venules
while in other organs, they originate from arteriole and unite to form venules.

(iii) Veins : These are thin walled, carrying deoxygenated blood (oxygenated in pulmonary vein) from tissues
to the heart. Venules, smallest branches, unite to form veins which in turn unite to form vena cava. The largest vein
is inferior vena cava/post caval. Varicose veins is stout, blood filled painful veins specially of the limbs due to
defective watch pocket valves.
TUNICA
(a) Histology of arteries and veins : TUNICA EXTERNAINTERNA

ENDOTHELIUM TUNICA MEDIAcLUMEN

DIRECTION OF BLOOD FLOW VEIN ARTERY

CAPILLARY

ENDOTHELIUM

TUNICA EXTERNA

VENOUS TUNICA MEDIA
VALVE TUNICA INTERNA

VEINS (A) (B) (C)

Fig. – (A) Venous valves, (B-D) Histology of the blood vessels (D)

(1) Tunica externa or tunica adventitia : Outermost, fibrous, made up of collagen rich connective tissue
and less elastin fibres. The collagen fibres give strength to the blood vessels and prevent their overdilation.

Chapter 11 254

Body Fluids and Circulation

(2) Tunica media : Middle, thickest, made up of smooth involuntary muscle fibres and elastin fibres. This
layer is very much variable because number of elastin fibres and muscle fibres depend upon the position of blood
vessels from the heart.

(3) Tunica interna or tunica intima : Innermost, thinnest, made up of inner, single layer of simple
squamous epithelial cells called endothelium resting on a basement membrane and outer layer of elastic (yellow
fibrous) connective tissue. The hollow space in the blood vessel is called lumen.

Differences between arteries and veins

S.No. Characters Arteries Veins

(1) Wall Thick, more elastic, non collapsible. Thin, less ealstic, collapsible.
(b) Blood pressure : The pressure exerted by the blood on the wall of the blood vessels in which it is present
(2) Tunica externais called blood pressure. It is usually measured in brachial artery by an instrument called sphygmomanometerLess developed, so less strong.More developed, so more strong.
(3) Tunica media More muscular and has many elastic Less muscular and only a few elastic
c(invented by Riva-Rocci). Arterial blood pressure is of 2 types :fibres.fibres.
(4) Tunica interna Endothelial cells more elongated. Elastic Endothelial cells less flat. Elastic
membrane more developed. membrane less developed.
(5) Lumen Narrow Wider
(6) Position Deep seated except wrist, neck etc. Superficial
(7) Valves Without valves. With valves to prevent back flow.
(8) Direction of blood flow From heart to body organs From body organs to heart
(9) Nature of blood Oxygenated except pulmonary artery. Deoxygenated except pulmonary vein
(10) Blood pressure More, generally 120/80 mm of Hg. Less, generally 0 mm of Hg.
(11) Speed of blood Fast Slow
(12) After death Becomes empty Contain blood
(13) Amount of blood 15% at any given time. 64% at any given time
(14) Colour Pink Dark red
(15) Disintensibility Less More

(1) Systolic blood pressure : It is the pressure exerted by blood on the walls of the blood vessels due to the

systole of ventricles and is equal to 120 mm Hg. During ventricular systole, there is expansion in the artery due to

the uncoiling of elastic layer. Hence, the pressure is maximum in arteries but gradually decreases in capillaries and veins.

(2) Diastolic blood pressure : It is the pressure exerted on walls of blood vessels when the ventricles are
relaxed. During ventricular diastole, the uncoiled elastic layer recoils leading to normalization of artery. Hence,
blood pressure drops down to 80 mm Hg. Thus, blood pressure in normal person is systolic/diastolic pressure i.e.
120/80 mm Hg.

(3) Pulse pressure : The difference between systolic and diastolic pressures is called pulse pressure and its
normal value is 120 – 80 mm Hg = 40 mm Hg. It provides information about the condition of arteries.

(4) Mean arterial pressure : It is the average pressure of systolic and diastolic pressures. As the blood
remains in the systolic phase for shorter period and in the diastolic phase for longer period, the mean pressure of
blood lies near the diastolic pressure.

This value varies at different levels of circulation being maximum (100 mm Hg) in the aorta and minimum (0
mm Hg) in the venae cavae under normal conditions.

Chapter 11 255

Body Fluids and Circulation

Pulse : It is the pressure wave of distension and recoiling felt in the radial artery due to the contraction of left
ventricle which force about 70-90 ml of blood in each cardiac cycle to aorta. This perssure wave of contraction
travels down to the wall to the arteries and is called the pulse.

The pulse is measured in the radial artery in the wrist but can be felt in the temporal artery over the temporal
bone or the dorsal pedis artery at the bind of ankle. The pulse normally travels at the rate of 5-8 m/second.

Since each heart beat generates one pulse in the arteries so the pulse rate per minute indicates the rate of
heart beat. So the normal pulse rate in a normal adult person is 72/minute.

The normal ratio of systolic pressure to diastolic pressure to pulse pressure is about 3 : 2 : 1.
Important Tips

• There is an inverse relationship between heart rate and blood pressure. The process is called Marey’s law of heart.

• During measurement of blood pressure, a sound is heard in the cubital artery with the help of stethoscope. This sound is called Karot
Koff sound.

• Blood pressure means arterial blood pressure.

(c) Factors affecting blood pressure :

(1) Age : With the advancing age, BP increases after the age of 60 years, it is calculated as 100 + age of the person.

(2) Cardiac output : BP increases with the increase in cardiac output.

(3) Elasticity of blood vessels : BP is inversely related to the elasticity of the blood vessels.

(4) Total peripheral resistance : Constriction of the blood vessels increases BP whereas dilation of the
blood vessels decreases BP.

Hypotension : Low blood pressure with systolic below 110 mm Hg and diastolic below 70 mm Hg. It is

ccaused by low metabolic rate, starvation, anaemia, chronic vasodilation of arterioles, lower pumping activity of

heart, loss of blood in haemorrhage, valvular defects, nervous disorders and Addison’s disease. It may cause fainting.

Hypertension : Persistent high blood pressure with systolic more than 140 mm Hg and diastolic more than
90 mm Hg. It is caused by decrease in extensibility of the artery due to atherosclerosis and arteriosclerosis. Sclerosis
means hardening and narrowing of blood vessels which may be due to the deposition of cholesterol or calcium or
lipid or any other compound in the wall of the arteries and arterioles.

In atherosclerosis deposition is mainly in tunica interna of the blood vessels which prevents their dilation. The
atherosclerosis is, infact, the beginning of thickening and hardening of blood vessels but later, the deposition of
cholesterol and other compounds takes places in both tunica media and tunica interna leading to arteriosclerosis.

Hypertension caused by hormones (epinephrine, aldosterone, renin) is called secondary hypertension, other
forms of hypertension are known as primary or essential hypertension.

A blood pressure of 220/120 mm Hg may cause internal haemorrhage due to rupturing of some blood vessels.
Cerebral haemorrhage due to rupturing of some blood vessels cerebral haemorrhage or complete cessation or great

Chapter 11 256

Body Fluids and Circulation

decrease in blood supply to some part of brain causes stroke or CVA (Cerebrovascular accident). Hypertension is
commonly called as silent killer.

High density lipoproteins (HDL) are responsible for excretion of cholesterol and thus, reduce the risk of
coronary heart diseases. Low density lipoproteins (LDL) and very low density lipoproteins (VLDL) cause deposition
of cholesterol in the wall of the arteries and thus, increase the risk of coronary heart diseases. The blood pressure
was first measured by Stephen Halls in horse. Highest blood pressure is recorded in giraffe.

Types of blood circulation in human
The physiology of blood circulation was first described by Sir William Harvey in 1628. The blood circulation in

our body is divisible into 3 circuits –

(i) Coronary circulation : It involves blood supply to the heart wall and also drainage of the heart wall.

Coronary arteries : One pair, arising from the aortic arch just above the semilunar valves. They break up
into capillaries to supply oxygenated blood to the heart wall.

Coronary veins : Numerous, collecting deoxygenated blood from the heart wall and drains it into right
auricle through coronary sinus which is formed by joining of most of the coronary veins. But some very fine
coronary veins, called venae cordis minimae open directly in the right auricle by small sized openings called
foramina of Thebesius.

(ii) Pulmonary circulation : It includes circulation between heart and lungs. The right ventricle pumps
deoxygenated blood into a single, thick vessel called pulmonary aorta which ascends upward and outside heart gets
divided into longer, right and shorter, left pulmonary arteries running to the respective lungs where oxygenation of
blood takes place. The oxygenated blood from lungs is returned to the left auricle by four pulmonary veins. Left auricle

cpumps this blood into the left ventricle.

Chapter 11 257

Body Fluids and Circulation

(iii) Systemic circulation : In EXTERNAL CAROTID LEFT COMMON
this, circulation of blood occurs INTERNAL CAROTID CAROTID
between heart and body organs. The
left ventricle pumps the oxygenated LEFT SUBCLAVIAN

blood into systemic arch which supplies VERTEBRAL

it to the body organs other than lungs RIGHT COMMON CAROTID PULMONARY ARTERIES
through a number of arteries. The RIGHT SUBCLAVIAN PULMONARY TRUNK
deoxygenated blood from these organs

is returned to the right auricle through BRANCHIOEPHALIC CORONARY ARTERY
two large veins (precaval and post AORTA INFERIOR PHRENIC
caval). Right auricle pumps this blood
into the right ventricle. Thus, the AXILLARY COELIAC
sytemic circulation involves two circuits HEART LEFT RENAL
–
BRACHIAL GENITAL
(a) Arterial circulation or Arterial SUPERIOR INFERIOR
system MESENTRIC
RIGHT RENAL MESENTERIC
(b) Venous circulation or Venous LUMBAR ULNAR
system COMMON RADIAL
ILIAC INTERNAL
Time taken by blood to circulate ILIAC
in the body from heart to heart to heart EXTERNAL ILIAC
is called circulation time. The amount FEMORAL
of blood flowing per minute in POSTERIOR TIBIAL DEEP FEMORAL
pulmonary and systemic circulation is
same. POPLITEAL

(a) Arterial system : It involves ANTERIOR
aorta, arteries, arterioles and meta-
arterioles. It supplies oxygenated blood cTIBIAL
to all parts of the body except lungs.

The left ventricle of the heart

pumps the oxygenated blood into a

single, question marked shaped, long

vessel called left carotid-systemic aorta.

It is the largest blood vessel of the

body. The initial part of systemic aorta Fig. – Arterial system in human body
is dilated and is called aortic sinus. It

possess some baroreceptors and some CO2 sensitive cells. Barroreceptors are supplied with 9th cranial nerve
(glossopharyngeal).

After ascending from the heart, the systemic aotra turns and descends down to the level of lower border of

fourth lumbar vertebra. At its distal extremity, it bifurcates into right and left common iliac arteries. The sytemic

aorta has following parts –

(1) Ascending aorta : It gives off left and right coronary arteries.

Arch of aorta : It gives – Innominate or Brachiocephalic artery left common carotid artery left subclavian artery.

Chapter 11 258

Body Fluids and Circulation

(2) Descending aorta : The aorta turns towards the back of heart and finally converts into dorsal aorta.
While dorsal aorta is in thorax, it is called thoracic aorta; when it goes down into diaphragm, it is called abdominal
aorta. Mammals have left systemic arch while birds have right systemic arch.

Arterial System

Ascending Descending
artery artery

Right side Left side Thoracic region Abdominal region

Brachiocephalic cPancreoduodenal Jejunal Iliac IliocolicRight commonLeftLeft common PerichrodialMediastermal Superior
innominate carotid subclavian carotid phrenic

Right subclavian Oesophageal Intercostal

External & Subcostal

carotid Internal External Internal

carotid carotid carotid

Vertebral Axillary

Ulnar Radial

Inferior phrenic Coelic artery Superior mesenteric Renal Lumbar Sacral Inferior mesenteric Common iliac

Left Common Splenic
gastric hepatic

Internal External
iliac iliac

(1) Ascending aorta

(i) From convexity of the arch of aorta

(a) Brachiocephalic (innominate) : Unpaired, largest branch of the aorta divides into right subclavian
towards right side and right common carotid towards left side. Right subclavian gives off vertebral artery (supplies to
head and part of right shoulder) and then enters into right arm, now called axillary artery or brachial artery, which
divides into ulnar and radial arteries in the region of elbow. The right common carotid, enters into head and divides
into external and internal carotids which supply the right parts of head by their tributaries.

(b) Left common carotid : Unpaired artery, enters into head and divides into left external and internal
carotids which supply the left parts of the head by their tributaries.

(1) The external carotids of both sides provide blood to thyroid gland, tongue, throat, face, ear, scalp.

(2) The internal carotids of both sides supply to brain, eye, inner part of nose and forehead. These internal
carotids go upward and enter skull through foramen magnum and unite at the base of brain along with the vertebral

Chapter 11 259

Body Fluids and Circulation

arteries of both sides. So, there is formation of a ring shaped artery called as “Circle of willis”. From this circle,
many branches or arteries arise which go to different parts of brain.

In frog, the internal carotid has at its base, carotid labyrinth (spongy mass of non-contractile fibro-elastic tissue)
which acts as a sensory organ to detect blood pressure in artery.

(ii) Left subclavian artery : Unpaired artery, it gives off a left vertebral artery (supplies to head and part of
left shoulder) and then enters into left arm, now called left axillary artery or left brachial artery which divides into
ulnar and radial arteries in the region of elbow.

(2) Descending aorta : The descending dorsal aorta divided into thoracic and abdominal aorta.

(i) From thoracic segment of aorta : Several pairs of small arteries arise in this region to supply various
parts such as pericardium (pericardial artery); lungs and bronchi (bronchial artery); oesophagus (oesophageal
artery); mediastinal organs and thymus (mediastinal artery); intercostal muscles and mammary glands (intercostals
and subcostal arteries); upper surface of diaphragm (superior phrenic artery).

(ii) From abdominal region of aorta : In the abdominal region, abdominal aorta gives off several pairs of
arteries. Some of the major ones are as follows

(a) Inferior phrenic artery : Right and left to supply the lower surface of the diaphragm.

(b) Coeliac artery : Unpaired, divides into three branches

(1) Left gastric artery : To stomach.

(2) Common hepatic artery : To pylorus, pancreas, gall bladder, liver, cystic duct, hepatic ducts etc.

(3) Splenic artery : To pancreas, stomach and spleen.

(c) Superior mesenteric : Unpaired, supplies various parts of small intestine (except superior part of
duodenum part of colon and caecum). Its sub branches are

c(1) Pancreo duodenal artery : To pancreas and duodenum.

(2) Jejunal artery : To jejunum.

(3) Ilial artery : To ileum and jejunum.

(4) Iliocolic artery : To ileum and colon.

(d) Supra renal artery : Supplies the adrenal glands.

(e) Renal arteries : One pair, supply to kidney.

(f) Lumbar arteries : 4 pairs, supply the skin, muscles, joints, vertebrae, meninges, spinal cord etc. in the
lumbar region.

(g) Sacral artery : Supplies the tissues of sacral region.

(h) Inferior mesenteric artery : Unpaired, supplies most part of colon, rectum and anal canal.

(i) Common iliac arteries : Two, right and left, formed by bifurcation of aorta at its lower end. Each
common iliac artery divides into external and internal iliac arteries. The internal iliac (hypogastric) artery supplies

Chapter 11 260

Body Fluids and Circulation

lies viscera and wall of pelvic region, perineum and gluteal regions. The external iliac artery enters into the leg now
called femoral artery continues down the thigh, now called popliteal artery which bifurcates into anterior and
posterior tibial arteries, at about the level of knee.

Inguinal canal : Connects abdominal cavity with the cavity of scrotum. So, through this canal, spermatic
artery (testicular artery), subclavian vein and sperm duct pass.

(b) Venous system : It originates in tissues by union of capillaries and ends in the atrium of heart. It includes
two major veins – superior and inferior vena cava which drain the deoxygenated blood into the right atrium.

Venous System

Superior vena cava Inferior vena cava Pulmonary vein

Branchiocephalic Inter jugular Subclavian External jugular Azygous & cHepaticvein
vein vein vein
vein Hemi azygous vein

Internal Inferior Left superior Cephalic Axillary
vein
thoracic vein thoracic vein intercostal vein

Common Lumbar vein Genital vein Renal vein Supra renal Inferior
iliac vein vein phrenic

External Internal
iliac iliac

Anterior Posterior Popliteal Large Small
tibial tibial saphenous saphenous

(1) Superior vena cava (pre caval) : Single, formed by the union of right and left brachiocephalic
(innominate) veins. It collects blood from head, neck, arms and chest region. It involves the following veins –

(i) Brachiocephalic veins : Two, each is formed by the union of an outer subclavian vein and medial
internal jugular vein. Each vein also receives blood from different thoracic parts of its sides through three main
veins.

(a) Internal thoracic vein : From some muscles and mammary glands.

(b) Inferior thyroid vein : From thyroid gland.
(c) Left superior intercostal vein : From upper part of thorax.
(ii) Internal jugular vein : Two, right and left. Each one is formed by the union of numerous sinuses and
veins of the cranial cavity, superior part of the face and some part of neck and collects blood from these regions.
(iii) Subclavian veins : Two, right and left, formed in the shoulder region by union of cephalic and axillary
veins of respective sides.

(a) Axillary veins : Two, right and left, present in the respective arms and collect blood from these regions.

Chapter 11 261

Body Fluids and Circulation

(b) Cephalic veins : Two, right and left, collect blood from respective arms and shoulder region.

(iv) External jugular veins : Two, right and left, open into respective subclavian vein. They collect the blood
from parotid gland, facial muscles and superficial parts of cranium.

(v) Azygos and hemiazygos veins : Azygos vein originates in lumbar region towards right side of
mediastinum and ascends upwards small veins from lumbar and thoracic parts of backbone, oesophagus,

mediastinum, pericardium etc. empty into it.

Towards the left side of the body RIGHT LEFT
originates hemiazygos and accessory EXTERNAL JUGULAR EXTERNAL JUGULAR
hemiazygos collects blood from
oesophagus, mediastinum, intercostal RIGHT cLEFTEXTERNAL
muscles, mammary glands etc. and drains INTERNAL JUGULAR JUGLAR
into Azygos which in turn opens into RIGHT SUBCLAVIAN LEFT
superior vena cava. Accessory SUBCLAVIAN
hemiazygos drains blood into left BRACHIOEPHALIC LEFT AXILLARY
innominate vein. SUPERIOR
VENA CAVA CORONARY
(2) Inferior vena cava : It is the INFERIOR
largest vein, originated in inferior lumbar HEART PHRENIC
region by the union of right and left HEPATIC LEFT CEPHALIC
common iliac veins and opens into right HEPATIC PORTAL
atrium by separate opening. It collects RIGHT SUPRARENAL LIVER
blood from all body structures below the RIGHT RENAL INFERIOR
diaphragm. It involves following veins – RIGHT TESTICULAR VENA CAVA
LUMBAR
(i) Common iliac veins : Two, LEFT
right and left. Each one is formed by union COMMON ILIAC SUPRARENAL
of external and internal iliac veins.
EXTERNAL ILIAC LEFT RENAL
(ii) External iliac vein : This is the FEMORAL
continuation of femoral vein which LEFT
collects blood from leg. Femoral vein in GREAT SAPHENOUS TESTICULAR
turn is formed by the union of anterior
tibial vein, posterior tibial vein, popliteal INTERNAL
vein, large saphenous vein, small ILIAC
saphenous vein, etc. which collect blood FEMORAL
from different parts of leg. External iliac
vein also collects blood from pubic region POPLITEAL
and parts of pelvis through number of
small veins. Last saphenous vein is the POSTERIOR TIBIAL
longest vein of the body.
ANTERIOR TIBIAL
(iii) Internal iliac (Hypogastric)
Fig. – Venous system in male human being

Chapter 11 262

Body Fluids and Circulation

veins : Two, right and left. Each one is formed by union of number of small veins, which collect blood from pelvis,
pelvic viscera, pelvic girdle, sacrum, rectum, ureter, urinary bladder, uterus, vagina, prostate glands, seminal vesicle,
penis, scrotum etc. (i.e. number of reproductive organs).

(iv) Lumbar veins : Four pairs, which collect blood from muscles, skin and vertebrae of lumbar region and
drains it into inferior vena cava.

(v) Genital veins : In man, right testicular vein collects blood from male organs and inguinal regions and

drains it into inferior vena cava. Left testicular vein drains the blood into left renal vein. In woman, the right ovarian

vein drain blood from ovaries, uterus etc. and empties into inferior vena cava. The left ovarian vein opens into left

renal vein.

(vi) Renal veins : Two, right and left collects blood from respective kidneys and opens into inferior vena
cava. The left renal vein is about three times longer than the right one.

(vii) Suprarenal vein : Two, right and left, collects blood from adrenal glands. Right one opens into inferior
vena cava whereas left one opens into left renal vein.

(viii) Inferior phrenic veins : These veins drain the blood from lower surface of diaphragm. The right one
ends in post caval. The left one is often doubled with its one branch ending in left renal or suprarenal vein and the
other in post caval.

(ix) Hepatic veins : They drain blood from liver into the post caval. Urea is maximum in hepatic vein while it
is minimum in renal vein.

Portal system

It is a part of venous circulation which is present between two groups of capillaries i.e. starts in capillaries and
ends in capillaries. The vein which drains blood into organs other than heart is called portal vein.

Types of portal system : It is of following types :
(i) Hypothalamo-hypophysial portal system
(ii) Hepatic portal system

c(iii) Renal portal system
(i) Hypothalamo-hypophysial portal system :

Present in higher vertebrates (amphibia, reptiles,

birds and mammals). Blood from hypothalamus is OPTIC CHIASMA
collected by hypophysial portal vein which ends in HYPOTHALAMUS

anterior lobe of pituitary gland. The superior INFUNDIBULUM CAPILLARIES
hypophysial artery which bring blood into circle of ARTERY TO BRAIN
willis bifurcate outside the lobe; one branch supplies
HYPOPHYSIAL PORTAL VEIN

the lobe itself, but the other one supplies the

hypothalamus. The vein that drain the blood from NEUROHYPOPHYSIS ARTERY TO
hypothalamus then runs into pars distalis and divide (POSTERIOR LOBE) ADENCHYPOPHYSIS

into capillaries. Thus this is a portal vein called VEIN ADENCHYPOPHYSIS
hypothalamo-hypophysial portal vein. (ANTERIOR LOBE)

Function : This portal system enables the SECONDARY CAPILLARY
releasing factors and inhibiting factors from PLEXUS

Fig. – Human hypophysial portal system

Chapter 11 263

Body Fluids and Circulation

hypothalamus to reach upto anterior pituitary.

(ii) Hepatic portal system : Found in all chordates. In mammals, there is a single vein called hepatic portal
vein, formed by the union of four main veins, which drain venous blood from different parts of alimentary canal

(digestive system) into the liver. These veins are :

(a) Posterior mesenteric vein : Collect blood from rectal wall and anal region. This vein possess maximum
diluted blood. Posterior mesenteric made up of by joining of 4 small veins that is rectal vein, sigmoid vein, left
colonic vein and it opens into the splenic vein.

(b) Anterior mesenteric vein : Collect blood from wall of colon, caecum and small intestine. This vein

possesses largest concentration of nutrients (glucose, amino-acid and vitamins). This vein formed by the joining of
right colonic vein, ileocolic vein and appendicular vein.

(c) Splenic vein : Collect blood from spleen and pancreas splenic vein possess free haemoglobin in large amount.
(a) The blood which comes
from the alimentary canal contains(d) Right gastric vein : Receives blood from stomach and duodenum.
digested food like glucose and
amino acids. The excess of glucose
is converted into glycogen which is

cstored in the liver for later use.
Posterior mesenteric vein open into splenic vein and splenic, anterior mesenteric, right gastric fused to form
hepatic portal vein, which leads to blood in the liver.

In amphibians (example – frog), hepatic portal system is formed of single hepatic portal vein and single
anterior abdominal vein. The latter collects blood from leg region and drains it into the left lobe of liver.

Significance of hepatic portal system : The hepatic portal system has following significance.

RIGHT GASTRIC OESOPHAGUS
VEIN STOMACH
SPLEEN
INFERIOR
VENA CAVA

HEPATIC VEIN

LEFT LOBE
OF LIVER

When an individual feels deficiency HEPATIC PORTAL SPLEENIC VEIN
of food, the glycogen is converted VEIN PANCREAS
into glucose and is transferred to the
SUPERIOR MESENTRIC
VEIN

blood stream via hepatic veins. RIGHT COLONIC DUODENUM
VEIN
(b) Harmful nitrogenous waste INFERIOR
like ammonia is converted into urea ILEOCOLIC MESENTERIC VEIN
which is later removed by kidneys. VEIN
Thus the blood is detoxified DESCENDING
(purified) of harmful nitrogenous DESCENDING COLON
waste. COLON
CAECUM LEFT COLONIC
VEIN
APPENDICULAR VEIN
SIGMOID VEIN

(c) Liver produces blood APPENDIX SIGMOID COLON
proteins which are put into blood RECTAL VEIN RECTUM
circulation.
Fig. – Human hepatic portal system

Chapter 11 264

Body Fluids and Circulation

(iii) Renal portal system : It is well developed in fishes and amphibians it is reduced in reptiles and birds
and is absent in mammals. This system carries blood from the posterior region of the body to the kidneys by renal
portal veins, thence its name. The kidneys remove the waste products from the blood and then the blood is passed
to the post caval by renal veins. Why renal portal system is absent in mammals ? The mammals have no renal
portal system due to the following facts :

(a) It is an Evolutionary trend that fishes and amphibians have well developed renal portal system, while in
reptiles and birds this system gets reduced. Finally in mammals it ultimately disappears.

(b) The heart of mammals is four chambered.
c(i)Lymph : Lymph can be defined as blood minus RBC's. In addition to the blood vascular system all
(c) Due to the four chambered heart in mammals there is total separation of oxygenated and deoxygenated blood.

(d) Posterior portion of body gets oxygenated blood from the heart and after oxidation process, etc. the blood
does not get so much impurities that it should go to the kidneys first for filtration as happens in fishes and
amphibians.

Renal portal system in frog consists of one pair of renal portal vein, each one formed by the union of formal
vein and sciatic vein. It collects blood from leg region and drains it into kidney. It also collects blood from dorsal part
of lumbar region through dorsolumbar vein.

Function : Renal portal system helps in blood filtration by draining it into kidney which filters the blood.

Lymphatic system

It is a part of greater circulation which begins in the tissue fluid with lymphatic capillaries which are always
terminally closed. This system terminates into venous system near heart. The main components of this system are :

(i) Lymph (ii) Lymphatic system in frog

(iii) Lymphatic system in human (iv) Lymphatic organ

vertebrate possess a lymphatic system. It is colourless or yellowish fluid present in the lymph vessels. It

is a mobile connective tissue like blood and is formed by the filtration of blood. This process involves

the diffusion of substances from blood capillaries into the interstitial space which is, thus, the primary

site of lymph formation. Two forces bring about a steady filtration of plasma fluid into the tissue

spaces : capillary pressure (30-35 mm Hg) and colloid osmotic pressure in tissue fluid (8 mm Hg).

Most of the compounds come out by filtration and few such as glucose come out by diffusion. These

compounds get collected in the intercellular space as Tissue fluid or Interstitial fluid which is, infact, a

part of blood. So, it must return to blood otherwise blood volume will decrease. For this, the outflux

of plasma fluid into capillaries is prevented by colloid osmotic pressure in plasma (28 mm Hg) which

counteracts the above two forces. When the blood flows from arteriolar to venous part of the

capillaries, the capillary pressure falls to 10-15 mm Hg due to which the blood capillaries absorb

waste material and CO2 from filtered blood. Thus, at the side of veinlets, net diffusion pressure = 28
– 15 = 13 mm Hg. After absorption by veins, a small amount of CO2 and waste material still remains
in the tissue fluid which is absorbed in the lymphatic capillaries as lymph. So, we can say that lymph

is modified tissue fluid.

Chapter 11 265

Body Fluids and Circulation

Differences between lymph and blood

S.No. Characters Blood Lymph

(1) RBC Present Absent

(2) Blood platelets Present Absent

(3) WBC Persent, generally 7000/cu mm Persent, generally 500-75000/cu mm

(4) Plasma Present Present

(5) Albumin : globulin Albumin > Globulin Albumin > Globulin

(6) Fibrinogen More Less

c(ii) Lymphatic system in frog : In frog, all(7) Coagulation propertyMoreLess

(8) Direction of flow Two way, heart to tissues and tissues to heart One way, tissues to heart

(9) Rate of flow Fast Slow

(10) Glucose, urea and CO2 Less More

Hence, lymph can be represented as :

Lymph = Blood – [RBC + platelets + plasma proteins of high molecular weight]

Composition of lymph : Microscopic examination of lymph depicts that is contains a large number of

leucocytes (mostly lymphocytes) ranging from 500 to 75,000 per cubic mm. No blood platelets present. The

composition of the non cellular part of lymph (fasting) is as follows :

(1) Water 94% (2) Solids 6%

(a) Proteins : Protein content is roughly half of the plasma and varies from 2.0 – 4.5%. It varies according to

the part of the body from which is collected, i.e. in liver 6%, in limb 2% of intestinal part 4%. The varieties of

proteins are found – albumin, globulin and fibrinogen. In addition to this, traces of prothrombin, fibrinogen.

(b) Fats : In fasting condition fat content is low but after a fatty diet it may be 5.0 – 15%.

(c) Carbohydrates : Sugar, 132.2 mgm per 100 ml.

(d) Other constituents : Urea, creatinine, chlorides, phosphorus, calcium, enzymes and antibodies.

• Normally the rate of lymph formation is equal to the rate of its return to the blood stream.

lymph capillaries empty into large, irregular lymph LATERAL SINUS DORSAL SINUS

FEMORAL SINUS

spaces called lymph sinuses. The latter are lined by a CRURAL SINUS
membranous squamous epithelium and occur in all

parts of body. The major lymph sinuses are :

(a) Subcutaneous lymph sinuses : These are

several sinuses located beneath skin and separated CONNECTIVE SUBMAXILLARY
from each other by thin septa of connective tissue TISSUE SEPTA SINUS
(figure). Major subcutaneous sinuses are brachial
lymph sinuses in forelimbs, dorsal and lateral trunk ABDOMINAL PECTORAL
SINUS SINUS

sinuses and pelvic lymph sinuses in posterior part of Fig. – The subcutaneous lymph sinuses

trunk, and crural or femoral lymph sinuses in

hindlimbs.

(b) Subvertebral lymph sinus (= cisterna magna) : This is a single large lymph sinus located beneath

vertebral column throughout the length of the trunk. Kidneys are lodged in this sinus.

A number of lymph capillaries empty into the body cavity or coelem also. This proves that the coelomic fluid is

also lymph, and the coelom is a large lymph sinus.

Chapter 11 266

Body Fluids and Circulation

Lymph hearts : Two pairs of small, sac-like structures, one pair 1ST PAIR OF BRACHIAL
located behind the transverse processes of third vertebra, and the other in HEARTS SINUS
the region of urostyle, are closely connected with lymph sinuses in frog

(figure). These have thin, but muscular walls. by contraction of their walls,

these regularly pulsate and pump the lymph of sinuses into veins. DORSAL LATERAL
Obviously, these are “lymph heart”. The anterior lymph heatrs pump the SINUS SINUS

lymph into subscapular veins and the posterior ones into femoral veins. 2ND PAIR OF
(iii) Lymphatic system in human HEARTS
(a) Lymph capillaries : Small, thin, lined by endothelium resting
FEMORAL
on a basement membrane and fine whose one end is blind and other end SINUS
unites to form lymphatic ducts. These are present almost throughout the
cPELVIC
body but are absent in brain, eyeball, spinal cord, internal ear, bone
marrow etc. Lymph capillaries in the region of small intestine in villi are SINUS
called “lacteals” which collect chyle which is Fig. – Lymph hearts of frog
milky white in colour due to absorbed fat.
Lacteals help in the absorption of digested fat. CERVICAL NODES
LEFT SUBCLAVIAN VEIN
Lymphatic ducts or vessels : RIGHT THORACIC
Numerous, present in various parts of body. LYMPH DUCT AXILLARY NODES
These vessels are like veins as they have all LEFT THORACIC
the three layers – tunica externa, tunica media RIGHT LYMPH DUCT
SUBCLAVIAN
INTERCOSTAL NODES
VEIN CYSTERNA CHYLI

and tunica interna, and are provided with LUMBAR NODES

watch pocket or semilunar valves but valves

are more in number than veins.

(c) Flow of lymph in lymphatics :
Pulsations of lymph hearts in frog create
sufficient force to maintain a steady flow of

lymph in the lymphatic system. In mammals, ILIAC NODES
the credit for maintaining onwards flow of

lymph goes to (i) the “squeezing force” INGUINAL NODES

created by the muscles of body wall and

internal organs, (ii) the breathing movements

of diaphragm and thoracic cage, (iii) mild

peristalsis created by smooth muscles of the

wall, of lymphatics themselves, and (iv) the

pressure created by increasing amount of

lymph in the lymphatics. Certain compounds

like fats increase the rate of lymph flow and

are called lymphata gogue. Blocking of lymph

flow causes oedema. Fig. – Lymphatic system of mammals shown in man (ventral view)

(d) Types of lymphatic ducts : Two

Chapter 11 267

Body Fluids and Circulation

main types :

(1) Right lymphatic duct : It is the smallest lymphatic duct with the length of approximately 1.25 cm. Its
one end is blind and other one opens into right subclavian vein at the junction of right internal jugular vein. It
collects lymph from one-fourth of the body (right part of head, neck, thoracic cavity and right arm).

(2) Left lymphatic duct/thoracic duct : It is the longest lymphatic duct with the length of
approximately 38-45 cm. It originates from cisterna chyli and empties into left subclavian vein. It collects lymph
from three-fourth part of the body i.e. complete posterior part through cisterna chyli, left part of head, neck,
thoracic cavity and left arms.

Lymphadenitis : During infection, central part of follicle

cshows rapid division and formation of plasma cells. hence, this
(3) Cisterna chyli receptaculum chyli : It is a dilated sac like structure present below the diaphragm in
lumbar region at the level of second lumbar vertebra. It collects lymph from posterior part of body i.e. abdomen,
pelvic region and hind limbs and drains it in the left lymphatic duct.

It shows inflation and deflation due to the movement of diaphragm which is a passive movement. Hence, it is
also called as passive lymphatic artery. It is also called as second heart.

(4) Lymph nodes or lymph glands : These are the masses of lymphatic tissue and connective tissue
(reticular tissue) and are located on the capillaries either solitary or in cluster. Where they are present solitary and in
few number, such tissues are called diffused lymphatic tissues and where they are in clusters, they are called tonsils.

Lymph nodes are covered by capsule of white collagen TRABECULUS AFFERENT LYMPH VESSELS
tissue. Outer region of lymph node is called cortex and inner SUBCAPSULAR
region is called medulla. In medulla, there are medullary cords, SINUS
(cord like arrangement of lymphocytes). Cortex possess follicles
(clusters of lymphocytes), outer part of which possess T-cells
and macrophages while the inner part possess B-cells.

part is also called reaction centre. The inflammation of lymph

nodes in such condition is called Lymphadenitis. MEDULLARY CORDS BLOOD VESSELS
EFFERENT LYMPH VESSEL
Some of the common lymph nodes are – Axillary nodes
(in armpits), genital (Inguinal) nodes (in pubic region), cervical Fig. – Scheme to show some features of the structure
of a lymph node

nodes (in neck region), intercostal nodes (in chest region), lumbar nodes (in lumbar region), iliac nodes (in pelvic

region) and payer’s patches (in small intestine). Besides these lymphatic nodes, a number of them are also present

near major blood vessels (arteries), specially dorsal aorta.

Tonsils : Clusters of lymph nodes. They are very often called as policemen. Various tonsils are – Normal
tonsils (in pharynx), adenoid tonsils (in nasopharynx), abdominal tonsils (in vermiform appendix) and policeman of
intestine (in lamina propria of ileum). Adenoid tonsils are present upto 7 years of age, then they are degenerated.
Their swelling is called adenoid. Inflammation of tonsils is called Tonsilitis.

Haemal lymph node : In many animals some lymph nodes are found to possess red colour, due to the
presence of blood in them. In man they are found in the retroperitoneal tissues and also in the mediastinum. In
these nodes some of the so-called lymphatic channels contain blood, while the rest of the nodes possesses the same

Chapter 11 268

Body Fluids and Circulation

structure as the typical lymph node. Spleen may be regarded as the modified haemal lymph (haemolymph) node.
Lymph nodes are located at intervals along its course.

Function of lymph nodes :

(i) They produce and supply lymphocytes to the blood and as a supportive function the trabeculae carry blood
vessels which supply the node.

(ii) They make screening of the lymph by means of phagocytic activity.

(iii) They serve a great defensive role against bacterial infections.

(iv) They temporarily stop the spread of cancer cells as those cells have to penetrate through the lymph vessels

to the lymph nodes from where they spread in the body.
(v) They act as mechanical filters to resist the entrance of poisonous substances into circulation.
(vi) They carry out immunological responses. They help in elaboration of antibodies and in the development of immunity.

(vii) Lymph nodes produce γ-globulin.
(iv) Lymphatic organs : The lymphatic organs present in our body are chiefly spleen (haemolymphatic
organ) and thymus (endolymphatic organ).

(a) Spleen : In frog, a small and spherical, dark red organ, called spleen, is found attached, by means of a
fold of peritoneum, to the anterior part of large intestine in rabbit, the spleen is some what flattened and elongated,
and attached to the hind border of stomach.
c(2) Trabeculae : Narrow fold like septa or
Structure of spleen : Spleen is madosermal in origin. Spleen is the largest solid mass of reticulo-endothelial
tissue in the body. Histologically it is formed by following structure –

(1) Capsule : It is the outer covering of spleen MESOTHELIAL CELL LINING RED PULP TRABECULA CAPSULE
formed of elastic fibrous connective tissue and smooth CENTRAL
muscles. The outer layer of the capsule is the serous ARTERY
coat formed of visceral peritoneum.
VENOUS SINUSES
IN RED PULP

GERMINAL CENTRE

trabeculae extend inwards from the capsule, dividing (SECONDARY MODULE)

the spleen tissue into several incomplete lobules. These CORTEX OF ARTERIOLE IN VEIN IN
are better developed in rabbit and other mammals WHITE PULP TRABECULAR BY RED PULP TRABECULA
than in frog.
ARTERY SURROUNDED

LYMPHOCYTES

Fig. – Histological structure of spleen (Diagrammatic)

(3) Splenic pulp : The reticulo-endothelial

tissue is called splenic pulp. It contains a denser network of blood capillaries, small sinuses and fine blood vessels.
The meshes of this network are studded with numerous splenic cells, red, blood corpuscles, macrophages and
lymphocytes. The splenic pulp is of two distinct types –

(i) White pulp (ii) Red pulp

Chapter 11 269

Body Fluids and Circulation

(i) White pulp : The white pulp is the ACCORDING TO 'CLOSED THEORY' ARTERIAL CAPUSLE MESOTHELIAL CELL LINING
accumulation of lymphatic tissue surrounding ARTEROLE OPENING DIRECTLY CAPILLARY PENICILLAR
a major arterial vessels of the spleen. This INTO SPLENIC SINUSOIDS ARTERY

lymphatic tissue is comprised of lymphocytes, SPLEENIC VENOUS RED PULP
plasma cells, macrophages or other free cell SINUSES ARTERIOLE

lying in the meshwork of reticular fibres at RED PULP ELLIPSOLD
(SHEATHAL ARTERIOLE)

various points along the course of the vessels GERMINAL CENTRE

where the infiltration of lymphocytes is CENTRAL ARTERIOLE SPLEENIC NODULE TO
greater, it forms spherical or ovoid nodules CENTRAL ARTERY WHITE PULP

TRABECULAR PERI ARTERIAL
VEIN LYMPH SHEATH
OF WHITE PULP
TRABECULAR
ARTERY
c(a) Its macrophages engulf (= phagocytize) and destroy wornout blood corpuscles, dead and live pathogens,which are called as splenic nodules of white
pulp. The splenic nodules may have typical
germinal centres.

(ii) Red pulp : It is a modified ACCORDING TO 'OPEN THEORY'
lymphatic tissue and is mostly infiltrated with ARTEROLE OPENING INTO PULP ON
cells of the circulating blood. It consists of two (MESH) BETWEEN SPLENIC SINUSAL
components –
Fig. – Anatomy of circulation in a splenic lobule showing
(a) Splenic sinuses or sinusoids. both closed circulation and open circulation (Diagrammatic)

(b) Splenic cords or Billroth cords [big blood sinuses]. It is raddish due to excessive number of RBCs. Red pulp
of spleen contains reticular fibres, erythrocytes, lymphocytes, macrophages, monocytes etc.

In mammal embryos the red pulp contains myelocytes, erythroblast and also megakaryocytes. These types of
cells are not present in adult spleen except in certain pathological condition.

Function : Although located close to the alimentary canal, the spleen has nothing to do with digestive system.
it is, in fact, an important constituent of the reticuloendothelial system of body and performs the following functions:

cell debris, pigment granules and other useless particulate materials, thus regularly cleaning the blood of its impurities.

(b) It is active haemopoietic organ. In foetal life, the red pulp possess myeloblast, erythroblast and
megakaryocytes. Hence, in foetus, it produces blood. In adults, the red pulp possess macrophages, plasma cells and
lymphocytes. So, in adults, it is not producing blood rather it is screening blood.

(c) In adults, it also serves as a sort of “blood bank”. Its sinuses act as “reservoirs of blood”. When required,
their blood is squeezed into general circulation. Similarly, RBCs stored in spleen are also released into general
circulation when required.

(d) Many lymphocytes of spleen produce antibodies.

(e) Spleen also acts as Grayeyard or Slaughter house of worn out RBCs.

(f) Haemolysin is formed in spleen.

(g) Haemoglobin is broken down into haem and globin by spleen. The haem is further split into iron and
pigment haematoidin, which becomes bilirubin of plasma. Iron first stored is splenic pulp then transferred into liver
and bone marrow. After splenectomy this storage function suffers and more iron is lost.

Chapter 11 270

Body Fluids and Circulation

Besides all these functions, the primary function of spleen is that it assists liver and helps in maintaining the
composition of blood.

(b) Thymus : It is a bilobed mass of lymphiod tissue which is situated in the upper chest near front side of
heart. It is prominent in children but begins to degenerate in the adults. It stimulates the development and
differentiation of T-lymphocytes, which produce antibodies, thus, increasing the resistance to infection.
Important Tips

• Lymphatic system in class amphibia is of open type.
• Lymph sinuses are the large spaces containing lymph. These are present in frog but absent in mammals.
• Lymph heart – The heart which collects lymph.
• In frog, lymph hearts are two pairs – an anterior pair and a posterior pair which collect lymph from respective regions. There are no

lymph hearts in mammals.
• The process of lymph formation is called Transudation.
• Lymph serves to return the interstitial fluid to the blood.
• Oedema (Edema) or Dropsy – A local swelling due to the accumulation of tissue fluid in tissues caused by the defective circulation of

blood or lymph.
• Lymph nodes are secondary lymphatic organs because they harbour lymphocytes. Primary lymphoid organs are bone marrow and thymus.
• Lymph nodes are maximum in armpits and groin.
• Spleen is called “first reservoir” of blood while liver is called “second reservoir” of blood.
• Spleen, liver and kidneys – all are called filter apparatus of blood.
• Diseasess where there is more destruction of RBCs such as malaria, banti disease, there is enlargement of spleen called as

splenomegaly.
• Thymus is concerned with the immunological reactions.
• In AIDS, there occurs generalised swelling of all lymph nodes.
• Spleen is absent in cyclostomes.

c• Cardiology – Study ofheart.

• Pericarditis – Inflammation of pericardium.
• Endocarditis – Inflammation of endocardium, generally caused due to the rheumatic fever.
• Frank-Starling law – Within certain physiological limits, the heart pumps all the blood that comes in it.
• Largest sized heart is found in Blue whale.
• Papillary muscles of ventricles are found only in the heart of mammals.
• Valves in heart were first reported by Fabricious.
• World’s first heart transplant was performed by Dr. Christian Barnard on 55-year old Louis Wash kansky in Cape town, South

Africa in the year 1967.
• India’s first heart transplant was conducted by cardiac surgeon Dr. P. Venu Gopal in a 42-year old man Mr. Devi Ram on 3rd August,

1994 at AIIMS, Delhi.
• Cardiomegaly – Enlargement of heart.
• Myocardial Ischaemia – Deficient blood supply to heart muscle leading to angina pectoris.
• Angina pectoris – Severe but temporary heart pain of short duration which is usually felt in front of the chest and may pass into the arms.
• Coronary thrombosis – Formation of blood clot in coronary arteries of heart causing death of tissue and leading to heart attack or MI.

Chapter 11 271

Body Fluids and Circulation

• Coronary sclerosis – Narrowing of coronary arteries leading to severe chest pain (Angina pectoris).
• Rheumatic heart Disease (RHD) – Defects in heart valve due to toxins produced by throat infection caused by streptococcus leading

to rheumatic fever.
• Coronary angiography – X-ray of the arteries, supplying the heart, after injecting them with radio-opaque material.

c

Chapter 11 272

Excretory Products and their Elimination

Introduction : The component structural and functional units of the bodies of all organism are cells which
have been looked as "miniature chemical factories" because of continuous metabolism taking place in these. It yields
certain waste products which are, not only useless, but harmful to the cells and the body. Cells, therefore, throw out
these wates, by diffusion, into their surrounding medium. Finally, these wastes are eliminated by the body into its

external environment. This is, thus an important vital activity of all organism. It is called excretion.

Besides removing the metabolic wastes and impurities from the blood, the kidney also perform the important

function of osmoregulation by regulating the amount of water in body fluids. The normally functioning kidneys

produce a large volume of dilute urine when more water is taken, and a small volume of concentrated urine when

water intake by the body is poor.

(iii) Coelenterates : Hydra also lacks special excretory organs. The nitrogenous waste products like ammoniaExcretory organs of different organism.

care removed through the general surface of the body by diffusion. Some nitrogenous waste products are also(i) Protozoans : In protozoans like AmoebaANETWORK OFB
and Paramecium carbon dioxide and ammonia are SPONGIOME COLLECTING
mostly excreted out by diffusion through general SPONGIOME
body surface. It is considered that the contractile TUBULES TUBULES TUBULE

vacuoles also play some role in the removal of
excretory products.

(ii) Sponges : In sponges, the nitrogenous CONTRACTILE AMPULLA
metabolic waste (ammonia) leaves the body in the VACUOLE
outgoing water current by diffusion. SPONGIOME
SPONGIOME TUBULES AND
Most of the sponges are marine and have no VESICLES
problem of surplus water in their cells. A few VESICLES
sponges lie in hypotonic fresh water and have C
contractile vacuoles in most of their cells.

thrown along with indigestible matter through the mouth.

(iv) Platyhelminthes : Planaria, liverfluke and tapeworm possess a large number of excretory cells called the
flame cells (solenocytes) and long excretory ducts (also called canals of vessels). The flame cells open into the

ductules which in turn open into the excretory duct.

Excretory canals are present on each lateral side or the collecting tubules of which one is dorsal and the other
ventral. In the last proglottid, they join to form a pulsatile caudal vesicle, which is open to a exterior by excretory
pore.

Excretory materials diffuse from the surrounding tissues into the flame cells. Vibrations of the cilia cause these
materials to remove in the excretory ducts. The walls of the ducts reabsorb useful substances and remaining
excretory materials (e.g., ammonia) are expelled out through the excretory pores.

(v) Aschelminthes : The round worms such as Ascaris have H-shaped excretory system. It is made up of a
single Renette cell. It consists of two longitudinal excretory canals connected anteriorly by a network of transverse

canals. A short terminal duct opens outside via excretory pore. Ascaris is excretes both ammonia and urea.

Chapter 12 274

Excretory Products and their Elimination

GLOBULES OF TERMINAL EXCRETORY
EXRETION DUCT PORE
ANTERIOR
GRANULES BASAL NUCLEUS CANAL
CELL LUMEN GRANULES
SMALLER
DUCTULE CILIA (FLAME) NUCLEI
EXCRETORY
NETWORK OF
PORE TRANSVERSE

CANALS

EXCRETORY POSTERIOR LATERAL
DUCT LONGITUDINAL

EXCRETORY CANALS

Fig. – Flame cell of Platyhelminthes Fig. – Renette cell of Ascaris
clateral ducts and a single renal sac. Each green gland consists of an end
(vi) Annelids : In annelids like Nereis, earthworm, leech, etc., the

tubular coiled structures, the nephridia are excretory organs. A typical ANTERIOR DISTAL TWISTED LOOP
nephridium starts from a rounded ciliated funnel, the nephrostome CANAL LIMB
which opens into coelom (body cavity). The nephrostome leads into a
nephridial tubule with ciliated cells. A typical nephridium opens outside NEPHROSTOME PROXIMAL
the body through a small aperture called nephridiopore. However, in LIMB
CILIATED
CANALS

earthworm three types of nephridia are found. The septal nephridia FUNNEL TERMINAL
situated on the septa (behind 15th segment) and pharyngeal nephridia ( DUCT

in three pairs of bundles in the 4th, 5th, and 6th segments) open into the Fig. – Septal nephredium of
alimentary canal and pour their excretory materials there. It is an Earthworm

adaptation for conservation of water. The integumentary nephridia (found scattered in the body wall in each

segement except the first two segments) open directly on the body surface. Excretory materials help the earthworm in

keeping the skin moist for cutaneous respiration. RENAL BLADDER
URETER PORES

(vii) Arthropods : (a) The excretory system of the adult Prawn END SAC GREEN
(crustacean) consists of a pair of antennary or green glands, a pair of LABYRINTH GLAND

sac, labyrinth (glandular plexus) and bladder. The end sac extracts LATERAL DUCT

nitrogenous waste products and excess water from the blood. The TRANSVERSE
CONNECTIVE

excretory fluid is transferred from the sacs to the labyrinth in which useful

materials are absorbed and carried to the blood. The remaining RENAL SAC

excretory fluid called urine, flows from the labyrinth to the bladder. The

excretory fluid also comes here from the renal sac. Urine is temporarily

stored in the bladders. Later on urine is expelled out through ureters and

renal pores.

Fig. – Antennary gland of Prawn

(b) Most insects, centipedes and millipedes, possess Malpighian

tubules as their principal excretory organs. They are fine, spiral or convoluted, thread-like tubules which are

attached to the alimentary canal. The distal closed end of each Malpighian tubule float freely in the haemolymph

(blood). These tubules extract metabolic wastes like potassium and sodium urate, water and carbon dioxide from

the blood. In the Malpighian tubules bicarbonates of potassium and sodium, water and uric acid are formed. A large

amount of water and bicarbonates of potassium and sodium are reabsorbed by the cells of Malpighian tubules and then

Chapter 12 275

Excretory Products and their Elimination

transferred to the blood (haemolymph). Uric acid is carried to the alimentary canal of the insect and is finally passed out
through anus.

(c) Spiders and scorpions possess Malpighian tubules or GUT
coxal glands or both for excretion.
FACES URIC+H2O+BICARBONATES OF
K+&Na+
ACID

(viii) Molluscs : They have one or two pairs of kidneys RECTUM MALPIGHIAN TUBULE
which discharge excretory matter into the mantle cavity which is
finally passed out of the body along with the out flowing water. HAMEOLYMPH
(BLOOD)
(ix) Echinoderms : Specialized excretory organs are absent
FURTHER WATER
REABSORPTION

in echinoderms (e.g., Starfish). The excretory products, chieflyBLADDER BODY WALL
ammonia, are eliminated by diffusion through dermal branchae ANUS
(primitive gills) and tube feet. V VI Fig. – Malpighian tubule of insecta
EXCRETORY PORE
SACCULE DIAPHRAGM EFFERENT POSTERIOR
cFig. – Coxal gland or ScorpionOR VESSICLE LABYRINTH RENAL VEIN RENAL CHAMBER

EFFERENT INTESTINE
RENAL VEIN

ENTERIOR
RENAL CHAMBER

ENTERIOR

RENAL SINUS

APERTURE INTO

POSTERIOR RENAL

CHAMBER AURICLE AORTIC
RENO-PERICARDIAL PERICARDIUM AMPULLA

APERATURE VENTRICLE

Fig. – Organ of Bojanus
(Pila – mollusca)

Excretory organs of different organisms

S.No. Phylum Excretory/osmoregulatory Function Example
Organ/Organelle and

principal N2-waste

I. Invertebrates

(1) Protozoa Contractile vacuole Ammonotelic Amoeba

Ammonia Osmoregulatory Paramecium

(2) Porifera General surface of body Ammonotelic Sycon, Leucon

(3) Coelenterata Ammonia, General surface of body Ammonotelic Hydra

(4) Platyhelminthis flame cells (=Solenocytes) Ammonotelic Taenia, fasciola

form the protonephridial system

(5) Nematoda H-shaped excretory organ, Renette cells Ammonotelic Ascaris

(6) Annelida Nephridial system, Ammonotelic Pheretima

(Metameric), various types

(7) Arthropoda

a. Class-Insecta Malpighian tubule Uricotelic Periplaneta

Chapter 12 276

Excretory Products and their Elimination

(Uric acid)

b. Class crustacea Antennary (=green) gland Uricotelic Palaemon

Uric acid

c. Class Arachnida Coxal glands Uricotelic Spider

Malpighian tubule

Hepato pancreas

Nephrocytes

(8) Mollusca (a) Kidney (=organ of Bojanus) or Renal organ Pila

(b) Keber's organ

Aquatic forms excrete

Ammonia RIGHTAmmonotelic Pulmonate
Terrestrial forms KIDNEY Mollusc
Excrete uric acid Uricotelic Limax
(9) Echinodermata Dermal branchiae (primitive gills) tube feet, cRIGHTURETERAmmonotelic Cucumaria
body surface (Ammonia) Asterias

Excretory system of man. INFERIOR VENA DORSAL AORTA
CAVA
Mammalian (human) urinary system consists of a pair of
kidneys, a pair of ureter, a urinary bladder and a urethra. RENAL SUPRARENAL GLAND
ARTERY LEFT KIDNEY
(i) Kidneys : The kidneys are dark-red, bean-shaped
organs about 11 cm long, 5 cm wide and 3 cm thick, each weight RENAL PELVIS
about 150 gm in an adult male and about 135 gm in adult VEIN
female. They are placed against the back wall of the abdominal
cavity just below the diaphragm, one on either side opposite the LEFT
last thoracic and first three lumber vertebrae. The lower two pairs URETER
of ribs protect them.
URINARY
The kidneys are covered by peritoneum on the front BLADDER
(ventral) side only. thus, they are retroperitoneal. The right kidney

is attached more anterior than the left in rabbit. This asymmetry is TRIGONIUM OPENING OF
just the reverse of that found in man. VESICAE URETER

URETHRA

In man left kidney occurs at a slightly higher level than the

right one, because right side has prominent right liver lobe. In Fig. – Human urinary system

rabbit the condition is little differ due to quadropedilism i.e. left kidney is in normal position while the right kidney

shift ached to provide place for stomach below it.

In mammals, the kidney is bean-shaped i.e. concavo convex. The center of concave inner surface is called as
hilum or hilus which gives out a ureter. From this hilus surface the renal artery enters into the kidney, the renal vein
comes out and the renal nerves enter into the kidney.

Chapter 12 277

Excretory Products and their Elimination

(a) Structure of kidney : The kidneys are metanephric in MINOR MAJOR
mammals. The kidney is divisible into two parts outer-cortex and CALYX CALYX

inner-medulla. CORTEX

Renal pyramids or medullary pyramids : The medulla

is subdivided into 10 to 12 conical masses – the renal pyramid,

each having broad base towards the cortex and a narrow end RENAL PAPILLAE
called renal papilla towards the pelvis.

Renal columns of bertini : Between the pyramids, the PELVIS

cortex extends into the medulla or renal columns of bertini. HILUS

lac nephron). In frog each kidney bears aboutCalyx : Each renal papilla projects into the cavity of a
2 thousand nephron.
minor calyx, minor calyx join to form major calyx. The major URETER
(b) Structure and types of nephron :
calyx open into a wide funnel like structure, the pelvis. The latter
cA nephron or uriniferous tubules is made of
leads into the ureter. In rabbit, the pelvis is unbranched hence, it MEDULLARY RENAL COLUMNS
is without calyx. PYRAMIDS OF BERTINI

In frog ventral surface of each kidney has many ciliated Fig. – H.L.S. of human kidney
funnels called nephrostomes. They drain wastes from body cavity

(coelom) and connect to renal veins in frog or to uriniferous tubules in tadpoles.

Histology of kidney : Histologically a kidney is made of innumerable thin, long, much convoluted tubular

units called uriniferous tubule or nephron. DISTAL CONVOLUTED RENAL CAPSULE
Nephron is the structural and functional TUBULE

unit of kidney. One human kidney may PROXIMAL PERITUBULAR
contain about one million (10 lac nephron) CONVOLUTED CAPILLARY NET

TUBULE WORK

nephron (In rabbit each kidney bear about 2

MALPIGHIAN RENAL
CORPUSCLE CORTEX

CORTICAL
NEPHRON

two parts – BRANCH OF

(1) Malpighian body : The proximal RENAL ARTERY

end of each nephron forms a blind or closed, BRANCH OF JUXTAGLOMERULAR
enlarged and double walled cup, the RENAL VAIN NEPHRON
Bowman's capsules in the cortex. (name
Bowman's capsule is based on english THICK SEGMENT OF PYRAMID OF
physiologist and histologist William Bowman). ASCENDING LIMB OF RENAL MEDULLA

Each capsule contains a network of HENLE'S LOOP COLLECTING
VASA RECTA TUBULE

blood capillaries the glomerulus which THIN SEGMENT OF BRANCH OF
receives blood through afferent arteriole and ASCENDING LIMB OF COLLECTING
the blood comes out through the efferent
arteriole .The diameter of the efferent arteriole HENLE'S LOOP TUBULE

DESCENDING LIMB OF DUCT OF BELLINI
HENLE'S LOOP (=PAPILLARY DUCT)

is comparatively lesser. (Bowman's capsule VASA RECTA RENAL
and glomerulus receives about 20 – 25% of PELVIS PAPILLA

the cardiac out put (blood) at rest. Fig. – Position, structure and blood supply of cortical and
The composite structure of Bowman's juxtamedullary nephrons is a mammalian kidney

Chapter 12 278

Excretory Products and their Elimination

capsule and glomerulus is known as Malpighian body or Malpighian corpuscles after the Italian microscopist Marcello
Malpighi.

(2) Tubule : The tubule is differentiated in to 3 parts P.C.T., Henle's loop and D.C.T.

The Bowman's capsule opens into a proximal convoluted tubule (P.C.T.) the anterior part of the P.C.T. is more

coiled where as its posterior part is almost straight. The P.C.T. opens into a Henle's loop. The Henle's loop is a U-

shaped structure which has a distinct descending limb and an ascending limb. The ascending limb opens in to the

distal convoluted tube. The D.C.T. is a coiled structure. Many D.C.T. unit to form a collecting duct. The collecting

ducts of one pyramid unit to form a duct of Bellini. The duct of Bellini lead into the pelvis part.

Arrangement of nephron : The malpighian body and a part of P.C.T. and D.C.T. are situated in the cortex.

Most of the part of P.C.T. and D.C.T., Henle's loop and collecting ducts are found in the medulla.
c2. Aresmallinsize.
Vasa recta : The efferent arteriole of juxta-glomerular nephron forms a peritubular capillary system around

the Henle's loop which is called vasa recta. Each of the vasa recta makes U turn at the inner most part of the

medulla and return to the venous circulation near the junction of medulla and cortex. The efferent arteriole and

peritubular capillaries technically constitute a renal portal system. In all amniotes as reptiles, birds and mammals

have a renal portal system.

Types of nephron : Nephrons are of two types cortical and juxtamedullary, with regard to their location

in the kidney. The cortical nephrons form about 80% to 90% of total nephron. They lie in the renal cortex and

have very short loops of Henle that extend only little into the medulla.

The juxta medullary nephron have their Bowman's capsule close to (Juxta) the junction of the cortex and

the medulla and have very long loops of Henle, extending deep into the medulla. This type of nephron is

present in only birds and mammals. The cortical nephrons control the plasma volume when water supply is

normal. The juxtamedullary nephrons regulate the plasma volume when water is in short supply (In advarse

condition).

Differences between cortical and Juxtamedullary nephrons

Cortical Nephrons Juxtamedullary Nephron

1. Form 80% of total nephrons. 1. Form only 20% of total nephrons.

2. Are large in size.

3. Lie mainly in the renal cortex. 3. Have Bowman's capsules in the cortex near its junction

with the medulla.

4. Henle's loops are very short and extend only a little into the medulla 4. Henle's loop are very long and extend deep into the medulla.

5. Control plasma volume when water supply is normal. 5. Control plasma volume when water supply is short.

(c) Histology of nephron NUCLEUS OF A
Glomerulus : Glomerulus is a network of up to 50 parallel ENDOTHELIAL CELLPODOCYTE
branching and anastomosing capillaries covered by endothelium,
basement membrane and epithelium made of podocytes which has OF GLOMERULAR
slit pores that restrict passage of colloids. However, small molecules CAPILLARY
and water can easily pass through them in to the P.C.T.
Bowman's capsule : The podocytes forming the inner wall PODOCYTE
of the Bowman's capsule have gaps (about 25 nm wide) the slit
pores. FINGER LIKE PODOCYTE NUCLEUS
The outer wall of the Bowman's capsule consists of PROCESSES OF
unspecialized squamous epithelium (flattened).
Proximal convoluted tube : P.C.T. is made up of simple PODOCYTES

Fig. – A glomerular capillary entwined
by processes of three podocytes

Chapter 12 279

Excretory Products and their Elimination

columnar epithelium. It has microvilli so it is also known as brush border epithelium.

Loop of Henle : The epithelium of descending limb of loop of Henle is very thin and composed of squamous

epithelium and ascending limb is lined by cuboidal epithelium. The ascending limb is impermeable to water and

permeable to NaCl.

Distal convoluted tube : It is made up of

cuboidal epithelium which is glandular in nature.

Collecting ducts : The collecting ducts are lined

by cuboidal and columnar epithelium in different regions. GLOMERULAR
At intervals, the cuboidal cells are ciliated. EPITHELIUM

Juxta-glomerular apparatus : This specialized JUXTAGLOMERULAR
cellular apparatus is located where the distal convoluted CELLS
tube passes close to the Bowman's capsule and afferent
arteriole. Cells of the D.C.T. epithelium in contact with AFFERENT
ARTERIOLE
corgan of hypothetical primitive kidneys. EFFERENT
ARTERIOLE

afferent arteriole are denser than other epithelial cells

known as maculla densa. Maculla densa has special Lacis SMOOTH MACULA INTERNAL
cell or Polkisson's cell. These cells secrete renin hormone MUSCLE CELLS DENSA
that modulate blood pressure and thus renal blood flow ELASTIC
LAMINA

and G.F.R. are regulated. DISTAL BASEMENT
(d) Origin and types of kidneys in different TUBULE MEMBRANE

vertebrate : Kidney tubules (nephrons) arise in the Fig. Juxta glomerular apparatus

embryo in a linear series from a special part of mesoderm

called mesomeare or nephrotome.

Number, complexity and arrangement of Nephrons are BOWMAN'S MALPIGHIAN
differ in different groups of vertebrates. A nephron is CAPSULE CORPUSCLE
differentiated into three parts – peritoneal funnel, tubule and
malpighian body. Peritonial funnel (nephrostome) are normally JUXTAGLOMERULAR GLOMERULUS
APPARATUS

present in embryos and larvae and considered as vestigeal

Archeonephros kidney : Archeonephros is the name NECK PROXIMAL CONVOLUTED
TUBULE
given to the hypothetical primitive kidney of ancestral

vertebrate. It is also called as holonephros or complete kidney.

(It extended entire length of coelom) It tubules are segmentally DISTAL CONVOLUTED
arragned and nephrostome is present. Glomerulus is external TUBULE

(without capsule). It duct is called as archeonephric duct. Ex.

Larva of myxine.

Modern vertebrates exhibits three different kinds of adult LOOP OF HENLE;
kidney Pronephros, Mesonephros and Metanephros. THICK ASCENDING LIMB

(1) Pronephros : It originates from the anterior part of

the nephrotome. It is also termed head kidney due to its LOOP OF HENLE;
anterior position. There are only 3 pronephrine tubule THIN DESCENDING LIMB

(nephron) in frog embryo, 7 in human embryo, and about 12

in chick embryo which are segmentary arranged. Nephrostome DUCT OF BELLINI
present, glomerulus is external and unite to form glomus in
COLLECTING DUCT

some cases. Duct is pronephric duct or mullerian duct. Fig. – Juxtamedullary nephron and epithelial cells in
the wall of its various parts

Chapter 12 280

Excretory Products and their Elimination

Pronephros is functional in all embryos and larval stages. It is mostly transitory and soon replaced by the next stage
or mesonephros.

Example – Adult myxine and petromyzones (cyclostomes) and some fishes but non urinary and lymphoid in
function.

(2) Mesonephros : It originates from the middle part of the nephrotome. Duct is mesonephric or Wolffian
duct. Nephrostome is absent except some embryos of anamniotes. Example – In amniotes (reptiles, birds and
mammals) mesonephros is functional only in the embryos, replaced by metanephros in the adult. In anamniotes
(fishes and amphibian) mesonephros is functional in both embryo as well as adults.

Note :  In shark and caeccilians, tubules extend posteriorly throughout the length of coelom. So it is also called

posterior or opisthonephric kidney.
lined by transition epithelium which has great power of

cstreaching. The neck of bladder is guarded by two
 In frog mesonephric duct is also known as Bidder's canal which carry sperm and urine both.

(3) Metanephros : It originates from the posterior part of the nephrotome. When metanephric tubules

develop, all the mesonephric tubules disappear except those associated with the testes in male and forming vasa

efferentia. Nephrostome absent. A thin, U-shaped loop of Henle forms between P.C.T. and D.C.T. which is

incomplete in Reptiles and Birds and well developed in mammals. Duct is metanephric or ureter. Reproductive duct

is separate. The kidney is highly compact which possesses innumerable nephrons. Example – All amniotes –

Reptile, Birds and mammal.

(ii) Ureters : From the hilum of each kidney emerges a whitish tube the ureter. The ureters are about 28 cm

long. Their wall consists of transitional epithelium surrounded by a layer of muscle fibres. Openings of the two

ureters in the bladder are separate, but closely placed. These are oblique, so that the urine cannot regurgitate into

the ureters when the bladder contracts. Peristalsis of ureters also cheeks regurgitation of urine.

(iii) Urinary bladder and Urethra : The urinary bladder is pear-shaped which is made up of smooth and

involuntary muscles. The muscles is also known as detrusor muscles (muscles that has the action of expelling a

substance). The lower part or neck of the bladder leads into the urethra. There is a smooth triangular area, called

trigonium vesicae. The lumen of the urinary bladder is

URETER

sphincters, inner is involuntary controlled by spinal reflex

and outer is voluntary controlled by cerebral cortex. A INNER LINING OPENINGS OF WALL OF
person feels the sensation of micturation when the OF BLADDER URETERS BLADDER
quantity of urine in the bladder is about 300 c.c.

Urethra : The urinary bladder leads into the

urethra. In a female, it is quite short, only about 3 to 5 cm TRIGONE INTERNAL
long, and carries only urine. It opens by urethral orifice, or SPHINCTER

urinary aperture in the vulva infront of the veginal or URETHRAL EXTERNAL
genital aperture. In a male urethra is much longer, about ORIFICE SPHINCTER
20 cm and carries urine as well as spermatic fluid. It URETHRA

passes through the prostate gland and the penis. It opens Fig. – Parts of ureters, trigone of the
out at the tip of the penis by urinogenital aperture. bladder, sphincters and urethra

Differences between male and female urethra

Male urethra Female urethra

1. It is about 20 cm long. 1. It is just 3 – 5 cm long.

Chapter 12 281

Excretory Products and their Elimination

2. It has 3 regions : prostatic urethra (3–4 cm), membranous 2. It is not differentiated into regions.

(1 cm) and penial (15 cm)

3. It opens out at the tip of the penis by urinogenital aperture. 3. It opens into the vulva by urinary aperture.

4. It carries urine as well as semen to the exterior. 4. It carries only urine to the exterior.

5. It has 2 sphincters. 5. It has a single sphincter.

Physiology of excretion.

Major nitrogenous excretory substance in frog, rabbit and human is urea, i.e. these are ureotelic animals. The
excretory physiology in these animals may be considered under two phases, viz urea synthesis and formation and
excretion of urine.

(a) Deamination : The amino acid is oxidised using oxygen. This result in removal of the amino groupProtein Digestioncainnaallimentary → Amino acid Aibnstoesrptintioen → Blood circulation

c(NH2 ) and leaves pyruvic acid. the pyruvic acid can enter the Krebs cycle and be used as a source of energy in cellUseful aminoHarmful amino
acid acid

Assimillation Enter in liver
in cells and form urea

(i) Synthesis of urea in liver : Urea is formed in liver by two processes.

(a) Deamination (b) Ornithine cycle

respiration. The amino group is converted to ammonia (NH3 ) during deamination. Deamination is also known as

oxidative deamination.

CH3 CH3

||
1
CH − NH2 + 2 O2 → CO + NH3
| |

COOH COOH

(Amino acid ) (Pyruvic acid )

With the help of a number of enzymes and energy of A.T.P. two molecules of ammonia are combined with
CO2 to form urea according to the following cycle.

(b) Ornithine cycle (Kreb-Henseleit cycle) : In liver one molecule of CO2 is activated by biotin and
combines with two molecule of NH2 in the presence of carbamyle phosphate synthatase enzyme (C.P.S.) and 2
ATP to form carbamyle phosphate and one molecule of H 2O release. Carbamyle phosphate react with ornithine

Chapter 12 282

Excretory Products and their Elimination

and form citrulline. Citrulin combines with another molecule of ammonia and form arginine. Arginine is broken into
urea and arnithine in the presence of an enzyme arginase and water.

2NH 2 + CO2 Arginase → NH 2 − CO − NH 2 + H 2O
(Urea)

H2O ASPARTIC ACID
Pi
BIOTIN CO2+NH3 1 C.P.S. CARBAMYL CITRULLINE + ATP
ACTIVATOR PHOSPHATE
+
2 ATP 2 ADP 3 AMP+PPi
+NH3
2
H2O OXALOSUCCINIC ACID

ARGINOSUCCINIC
ACID
Liver cells, thus, continuously remove ammonia and some CO2 from blood and release urea into the blood.ORNITHINE

Kidneys continuously remove urea from the blood to excrete it in urine.54
(ii) Urine formation : Urine formation occurs in the kidneys. It involves three processes glomerular filtration,
NH 2 ARGININE +
reabsorption and tubular secretion. C=O H2O FUMARIC ACID
(a) Ultra filtration or (Starlin hypothesis)
(1) It is passive process which takes place from the glomerulus into the Bowman's capsule. The glomerularNH 2

cepithelium has various micropores (diameter = 0.1 UREA Fig. – Ornithine cycle

µ) which increase the rate of filtration. AFFERENT ARTERIOLE

(2) The non colloidal part of the plasma as GHP→65-75 MM HG EFFERENT ARTERIOLE
urea, water, glucose, and salts are forced out from

the glomerular capillaries into the Bowman's capsule

by the high pressure of the blood in the glomerular

capillaries. The pressure is high because the

glomerular capillaries are narrower than the afferent BCOP→30 MM HG 15-25 MM HG EFP
renal arteries.

(3) The effective filtration pressure that causes

ultrafiltration is determined by three pressures.

Glomerular hydrostalic pressure : The 10 MM HG

G.H.P. is the blood pressure in glomerular capillaries CHP 20 MM HG 10 MM HG

due to the efferent arteriole is narrower than afferent

arteriole. It is the chief determinent of effective

filtration pressure, i.e. the main driving force to cause Fig. – Ultra filtration
filtration.

G.H.P. = +70 mm Hg.

Chapter 12 283

Excretory Products and their Elimination

Blood colloidal osmotic pressure : The B.C.O.P. is the osmotic pressure created in the blood ofG.F.R.
glomerular capillaries due to plasma proteins (mainly albumin). It resists the filtration of fluid from the capillaries.R.P.F.

B.C.O.P. = – 30 mm Hg.
Capsular hydrostatic pressure : C.H.P. is the pressure caused by fluid (filtrate) that reaches into Bowman's
capsule and resists filtration.
C.H.P. = –20 mm Hg.
Effective filtration pressure : E.F.P. is glomerular hydrostatic pressure minus the colloidal osmotic pressure
of blood and capsular hydrostatic pressure.
E.F.P. = G.H.P. – (B.C.O.P. + C.H.P.)

= 70 mmg – (30 mmg Hg + 20 mm Hg)
= 70 – 50
E.F.P. = 20 mm Hg

Note :  Net opposing filtration pressure (N.O.F.P.) = B.C.O.P.+C.H.P.

= 50 mm Hg.
Glomerular filtrate : The plasma fluid that filters out from glomerular capillaries into Bowman's capsule of

nephrons is called glomerular filtrate. It is a non colloidal part and possess urea, water, glucose, amino acid,

vitamins, fatty acid, uric acid, creatin, creatinine, toxins, salts etc.

R.B.Cs, W.B.Cs platelets and plasma proteins are the colloidal part of the blood and do not filtered out from

glomerulus. Glomerular filtrate is isotonic to blood plasma.

Glomerular filtrate or Nephric filtrate = Blood – (Blood cells + Plasma protein)
or

= Blood – (R.B.Cs + W.B.Cs+platelets + plasma protein)
or

= Plasma – Protein

Gomerular filtration rate (G.F.R.) : G.F.R. is the amount of filtrate formed per minute in all nephrons of

the paired kidney. There is a sexual difference. In male the rate is 125 ml/min, in female it is 110 ml/min. G.F.R. is

affected by volume of circulating blood, neural activity, stretch response to pressure of the wall of the arteriole.

c180 litre of filtrate is formed per day, out of it, only 1.5 litre of urine is produced per day which is 0.8% of the

total filtrate.

Renal plasma flow : About 1250 ml (25% of cardiac output or total blood) blood circulates through kidneys
each minute and of this blood, about 650 ml is the plasma. The latter is called the renal plasma flow (R.P.F.)

R.P.F. = 650 ml.
Filtration fraction : This is the ratio of G.F.R. to R.P.F., and it is called filtration fraction.
Filtration fraction =

(b) Selective reabsorption : Discovered by Richard and supporters.

P.C.T. : P.C.T. is the pivotal site for reabsorption.

Glucose, amino acid and Na + , K + ions are reabsorbed by active transport.

Cl − are reabsorbed by passive transport following the positively charged ions.

Active uptake of ions reduces the concentration of the filtrate and an equivalent amount of water passes into

the peritubular capillaries by osmosis. (Here 80% water is reabsorbed by passive transport. It is also known as

( )obligatory water reabsorption). Most of the important buffer bicarbonate HCO3− is also reabsorbed from the filtrate.

Chapter 12 284

Excretory Products and their Elimination

P.C.T. absorb nearly 80–90% of filtered bicarbonate. Some urea is reabsorbed by diffusion. The rest reman in the filtrate

for removed in the urine.

Henle's loop : See counter current mechanism.

D.C.T. : When the level of plasma water falls, the posterior pituitary lobe release the antidiuretic hormone (ADH)

which increases the permeablity of the distal convoluted tubule and the collecting duct to water. Water is reabsorbed

from the filtrate by osmosis and a reduced amount of concentrated urine is produced (Here 13% water is reabsorbed by

facultative reabsorption)

The distal convoluted tubule and the collecting duct actively reabsorbed sodium from the filtrate under influence

of the adrenal hormone aldosteron which makes their walls permeuble to ions. The reabsorption of Na+ brings about

the uptake of an osmotically equivalent amount of water. But duct of Bellini is relatively impermeable to water.
Bicarbonate ions are also reabsorbed in D.C.T.

(c) Tubular secretion : It occurs as under –
 Creatinine, hippuric acid and foreign substances (pigments, drugs including penicillin) are actively secreted

into the filtrate in the PCT from the interstitial fluid. Hydrogen ions and ammonia (NH3 ) are also secreted into the PCT.
Non threshold substances : They
are not reabsorbed. Example – Uric acid. Potassium, hydrogen,NH+andHCO3−ions are secreted by active transport, into the filtrate in the DCT.
4
cDiuretic substances : Normally, the
 Urea enters the filtrate by diffusion in the thin region of the ascending limb of Henle's loop.

Removal of H+ and NH + from the blood in the PCT and DCT helps to maintain the pH of the blood
4

between 6 to 8. Any variation from this range is dangerous.

Tubular secretion probably plays only a minor role in the function of human kidneys, but in animals, such as

marine fish and desert amphibians which lack glomeruli and Bowman's capsules, tubular secretion is the only mode

of excretion. When the blood pressure, and consequently the filtration pressure, drop below a certain level, filtration

stops and urine is formed by tubular secretion only.

High threshold substances : Such substances are absorbed almost all. Example – Sugar, amino acids,

vitamins etc.

Low threshold substances : They are absorbed in low concentration. Example – Urea, creatinine, phosphate.

PROXIMAL DISTAL
CONVOLUTED
GLOMERULUS ACTIVE CONVOLUTED ACTIVE
REABSORPTION TUBULE
TUBULE
REABSORPTION

amount of urine formed depends on the

intake of water, dietary constituents, ISOTONIC HYPERTONIC OR ISOTONIC
environmental temperature, mental and

physiological states of the person. However, PASSIVE PASSIVE COLLECTING DUCT
REABSORPTION REABSORPTION
there are some substances which increase
ISOTONIC ISOTONIC
the volume of urine to be excreted, these
HYPERTONIC DESCINDING ASCINDING
substances are called diuretic substances. LOOP OF HENLE LIMB LIMB
Exmaple – Tea, Coffee, alcohal etc.
HYPERTONIC
(iii) Mechanism of urine
concentration (Counter current FREELY IMPERMEABLE VARIABLY
mechanism of urine concentration) : PERMEABLE TO TO WATER PERMEABLE
Mammals form hypertonic urine. The urine TO WATER
is made hypertonic with the help of counter WATER
current multiplier system. This process takes
place in the Henle's loop and vasa recta Fig. – Counter current multiplier in Henle's loop

Chapter 12 285

Excretory Products and their Elimination

and it involves mainly Na + and Cl − . In P.C.T. urine is isotonic. The descending limb of loop of Henle is permeable

to water. Its surrounding tissue fluid is hypertonic. Hence, the water moves out and the Na + and Cl − moves in the
descending limb by passive transport. Therefore, the filtrate in the descending limb finally becomes hypertonic.

The ascending limb of the Henle's loop is impermeable to the water. The Na + and Cl − moves out by active

transport. Hence the filtrate finally becomes hypotonic. The Na + and Cl − re-enter into the descending limb of the
Henle's loop. The collecting duct always passes through the hypertonic tissue fluid. Hence, water comes out
osmotically making the filtrate hypertonic. Now in collecting duct glomerular filtrate is known as urine. Term urine
first time use in collecting duct.

Summary of events occurring in a nephron

Materials transferred Nephron region Process involved Mechanism
1. Glucose, Amino acids, Vitamins, Bowman's capsule Glomerular filtration Ultrafiltration
Hormones, Na+, K+, Mg2+, Ca+2, H2O,
Urea, Uric Acid, Creatinine, Ketone Bodies. Proximal convoluted tubule Reabsorption Active transport
2. Glucose, Amino Acids, Hormones,
Vitamins, Na+, K+, Mg2+, Ca+2 Proximal convoluted tubule Reabsorption Passive transport
3. Cl– Proximal convoluted tubule Reabsorption Osmosis
4. Water Proximal convoluted tubule Reabsorption Diffusion
5. Urea Narrow region of descending limb of Reabsorption Omosis
6. H2O Henle's loop
Narrow region of ascending limb of Reabsorption Diffusion
7. Na+,K+,Mg+2,Ca+2,Cl– Henle's loop
Wide part of ascending limb of Henle's Reabsorption Active transport
8.Inorganic ions as above loop
Distal convoluted tubule, collecting tubule, Reabsorption with Osmosis
9.H2O collecting duct ADH Help
Distal convoluted tubule, collecting tubule, Reabsorption with cActive transport
10. Na+ collecting duct aldosterone help
reabsorption secretion

11. Urea Last part of collecting duct Reabsorption with Diffusion
aldosterone help
reabsorption secretion

12. Creatinine, Hippuric Acid, Foreign Proximal convoluted tubule Reabsorption with Active transport
substances aldosterone help
reabsorption secretion

13. K+, H+ Distal convoluted tubule Reabsorption with Active transport
aldosterone help
reabsorption secretion

14. NH3 Distal convoluted tubule Reabsorption with Diffusion
aldosterone help
reabsorption secretion

15. Urea Ascending limb of Henle's loop (Thin part) Reabsorption with Diffusion
aldosterone help
reabsorption secretion

Urine.

Chapter 12 286

Excretory Products and their Elimination

The fluid and dissolved waste substances excreted by the kidneys constitute urine.

Quantity : An adult man normally passes about 1 to 1.8 litres of urine in 24 hours. The volume of urine
depends upon (i) the fluid intake, (ii) level of physical activity, (iii) type of food taken and (iv) environmental
temperature increase urine output. Less fluid intake and profuse sweating due to heavy physical work and high
temperature reduce urine output. Certain substances, such as tea, coffee and alcohol, increase urine output. These
are said to be diuretic.

(i) Physical properties : Urine is transparent yellowish fluid, its shade depending on its concentration. Its
colour is due to a pigment urochrome derived from the breakdown of haemoglobin from the worn-out RBCs.
Colour of the urine is altered by certain materials taken such as beet, vitamin B complex and some drugs. It is
hypertonic to blood plasma. Its specific gravity ranges between 1.003 and 1.04, being slightly higher than that of
water. Its pH is 6. It depends on the diet. High protein food and fruits increase acidity whereas vegetables increase
alkalinity. Urine has a characteristic unpleasant odour. If allowed to stand, urea is degraded by bacteria to ammonia
which imparts a strong smell to urine.

(ii) Chemical composition : Urine consists of water and organic and inorganic substances. Water alone
forms about 95% of it, other substances form only 5%. The organic substances are mainly nitrogenous organic
compounds include urea, uric acid, creatinine and hippuric acid. Of these, urea is the principal component of
human urine. The non nitrogenous organic compounds include vitamin C, oxalic acid, phenolic substances include
ammonia, and mineral salts such as chlorides, sulphates and phosphates of sodium, potassium, calcium and
magnesium. Sodium chloride is the principal mineral salt of the urine. Urine also contains some other substances,
such as pigments and drugs, and some epithelial cells and leucocytes.

(iii) Abnormal materials : Presence of proteins (albumins), bile salts, bile pigments, ketone bodies, blood,
pus, microbes and more than a trace of glucose in the urine is pathological condition. Presence of glucose, protein,

cblood, ketone bodies and pus in the urine is called glucosurea, proteinuria, haematuria, ketonuria and pyuria respectively.
(iv) Renal threshold : A negligible amount of glucose is present in the urine. The highest concentration of a
substances in the blood upto which it is fully reabsorbed from the glomerular filtrate is called its threshold. If its
concentration in the blood exceeds its renal threshold, some of the filtered out substance is not reasborbed and is
excreted in the urine. For example, the renal threshold of glucose is 180 mg. per 100 ml. of blood. If its blood level
exceeds 180 mg., some of the filtered out glucose is not reabsorbed and is passed in urine.

(v) Conduction of urine and Micturition : Urine is produced and drained continuously by the nephrons
into the renal pelvis. From here, it is carried down the ureters by peristaltic waves into trigonum vesicae and then
into the body of the urinary bladder. The bladder serves to store the urine temporarily and also to pass it out at
suitable intervals. The process of passing out urine from the urinary bladder is called urination or micturition, As
urine collects, the muscular walls of the bladder distend to accommodate it. Distension of its walls stimulates the
sensory nerve endings in the bladder wall and this sets up reflexes, which cause an urge to pass out urine. During
the discharge of the urine, the bladder and urethral sphincters relax and the smooth muscles of the bladder wall
gradually contract. This slowly drives the urine from the bladder through the urethra to the exterior. Reflux of the

Chapter 12 287

Excretory Products and their Elimination

urine into the ureters is prevented because the terminal parts of the ureters pass obliquely through the bladder wall
and are consequently closed when the bladder wall contracts around them. Relaxation and contraction of the
urinary bladder are caused by impulses from the sympathetic and parasympathetic nerve fibres.

Micturition may be voluntarily postponed for some time until the pressure in the bladder rises too high to
control. Micturition may also be voluntarily achieved even before sufficient urine has accumulated in the bladder.
Normally an urge for micturition starts when the bladder is a little more than halffull of urine.

Urine constituents in man (in gram)

1. Total volume 1,200 ml – per 24 h c
2. Water 1,140 ml
3. Total solids 50 gm

4. Glucose 0
5. Protein 0
6. Ketones 0

7. Urea 30 gm
8. Creatinine 1.6 gm

9. Creatine 0.1 gm
10. Hippuric acid 0.7 gm
11. Urobilinogen 0.4 mg

12. Porphyrins 50 – 300 µg
13. Uric acid 0.7 gm
14. NaCl 15.0 gm
15. K 3.3 gm
16. Ca 0.3 gm
17. Mg 0.1 gm
18. Fe 0.1 gm
0.2 0.005 gm

19. SO4 2.5 gm
20. PO4 2.5 gm

• pH of urine = 6

• Yellow colour of urine is due to Urochrome pigment.

• volume of urine is one day = 1 litre – 1.5 litre per day

• Specific gravity = 1 – 1.04

Urine constituants in man (in %)

1. Water 96%

2. Urea 2%

3. Uric acid 0.2%

4. NH3 0.25%
5. Creatinine 0.5%

6. Hippuric acid 0.025%

Chapter 12 288

Excretory Products and their Elimination

7. Salt 1%

Hormonal control of renal function.
Hormonal controls of the kidney function by negative feedback circuits can be identified :

(i) Control by antidiuretic hormone (ADH) : ADH, produced in the hypothalamus of the brain and
released into the blood stream from the pituitary gland, enhances fluid retention by making the kidneys reabsorb

more water. The release of ADH is triggered when osmoreceptors in the hypothalamus detect an increase in the

osmolarity of the blood above a set point of 300 mosm L–1. In this situation, the osmoreceptor cells also promote

thirst. Drinking reduces the osmolarity of the blood, which inhibits the secretion of ADH, thereby completing the

feedback circuit. cDRINKINGREDUCES

(ii) Control by Juxtaglomerular apparatus (JGA) : THIRST BLOOD
JGA operates a multihormonal Renin-Angiotensin-
Aldosterone System (RAAS). The JGA responds to a OSMOLARITY
decrease in blood pressure or blood volume in the afferent + TO SET POINT
arteriole of the glomerulus and releases an enzyme, renin into –
the blood stream. In the blood, renin initiates chemical
reactions that convert a plasma protein, called BLOOD OSMOLARITY
angiotensinogen, to a peptide, called angiotensin II, which
works as a hormone. Angiotensin II increases blood pressure INCREASES ABOVE
by causing arterioles to constrict. It also increases blood SET POINT
volume into ways : firstly, by signaling the proximal +
convoluted tubules to reabsorb more NaCl and water, and
secondly, by stimulating the adrenal gland to release PITUITARY
aldosterone, a hormone that induces the distal convoluted
tubule to reabsorb more Na+ and water. This leads to an GLAND
increase in blood volume and pressure, completing the
feedback circuit by supporting the release of renin. (a) Na+ AND H2O COLLECTING

REABSORPTION INCREASED DUCT HIGHER BLOOD
+ VOLUME

OR PRESSURE

+
ALDOSTERONE

D.C.T. LOW BLOOD
VOLUME OR
PRESSURE

MALPIGHIAN – ADRENAL
BODY ARTERIOLE GLAND
RENIN
PRODUCTION + CONSTRICTION + AFFERENT
RENIN ARTERIOLE

EFFERENT ARTERIOLE

ANGIOTENSINOGEN ANGIOTENSIN II

Fig. – Regulation of renal function by feedback
circuits : (a) control by ADH: (b) Control by RAAS

(iii) Parathormone : The hormone increases blood Ca++ (Hypercalcium) and decreases PO4 accordingly, it
increases absorption of Ca+, increases excretion of PO4.

(iv) Thyrocalcitonin : It increases excretion of Ca++ in the kidney.

(v) Prostaglandin : The renal pyramids produce fatty acids of prostaglandins (P.G.) which participates in
blood pressure regulation.

(vi) Erythropoiotin : It is secreted by juxtaglomerular apparatus and plays an important role in erythropoiosis
(blood production).

Differences between Rennin and Renin

S.No. Rennin Renin

1. It is secreted by peptic (zymogen) cells of gastric It is secreted by specialised cells in the afferent

glands into the stomach. arterioles of the kidney cortex.

2. Its secretion is stimulated by food. Its secretion is stimulated by a reduction of Na+ level
in tissue fluid

Chapter 12 289

Excretory Products and their Elimination

3. It is secreted as an inactive form prorennin which is It is secreted as renin.
activated to rennin by HCl.

4. It is a proteolytic enzyme. It is a hormone that acts as an enzyme

5. It helps in the digestion of milk protein casein. It converts the protein angiotensinogen into
angiotensin.

Homeostatic regulatory functions of kidneys

By continuously eliminating metabolic wastes and other impurities, and even the surplus quantity of useful
materials from blood plasma in the form of urine, kidneys play a vital role in homeostasis. Kidneys also operate
certain other homeostatic regulatory mechanisms. Proper maintenance of the internal environment is knows as
homeostasis. All regulatory functions of kidneys can be enumerated as follows –

(i) Osmoregulation : Being the universal solvent, water is the actual vehicle in ECF to transport materials
between various parts of body. Water volume in ECF tends to vary considerably due to several reason, such as
drinking, perspiration, diarrhoea, vomiting, etc. As described in previous pages, the kidneys maintain the water
balance in ECF by diluting or concentrating urine.

(ii) Regulation of osmotic pressure : Osmolality of cytoplasm is mainly due to proteins and potassium and
phosphate ions, whereas that of the ECF is mainly due to sodium, chloride and bicarbonate ions. Inspite of marked
difference in chemical composition, the two fluids – intracellular (cytoplasm) and extracellular (interstitium) – must
be isotonic, because if ECF becomes hypotonic, cells will absorb water, swell retaining apropriate number, mainly of
sodium and chloride ions, kidneys maintain the normal osmolality of ECF.

(iii) Regulation of pH : Concentration of hydrogen ions (NaH2 PO4) in ECF is to be regulated at a constant
value usually expressed as pH (minus log of H+). The normal pH of ECF is about 7.4. A low pH, i.e. a high H+
concentration causes acidosis, while a high pH, i.e. a low H+ concentration causes alkalosis. Both of these
conditions severely affect cellular metabolism. Several special control systems, therefore, operate in the body to
prevent acidosis and alkalosis. These system are called acid-base buffer system. Kidneys play a key role in

cmaintenance and operation of these systems. Further, the kidneys regulate hydrogen ion concentration in ECF by

excreting acidic or basic urine.

(iv) Regulation of electrolyte concentrations in ECF : The kidneys regulate, not only the total
concentrations of water and electrolytes in ECF, but also the concentrations of individual electrolytes separately.
This regulation is complex and is accomplished by tubular reabsorption and secretion under the control of
hypothalamic and adrenal hormones.

(v) Regulation of RBC-count in blood : In oxygen deficiency (hypoxia), kidneys secrete an enzyme into the
blood. This enzyme reacts with plasma globulin to form erythropoietin. The latter substance stimulates bone marrow
to produce more RBCs for enhancing O2-intake in lungs.

(vi) Regulation of renal body flow : See (R.A.A.S.).

Excretory products in different organisms.

(i) Waste products of protein metabolism

Chapter 12 290

Excretory Products and their Elimination

(a) Amino acids : These are end products of protein digestion absorbed into the blood from small intestine.
Certain invertebrates, like some molluscs (eg Unio, Limnae, etc.) and some echinoderms (eg Asterias) excrete
excess amino acids as such. This is called aminotelic excretion or aminotelism.

( )(b) Ammonia or : In most animals, excess amino acids are deaminated, i.e. degraded into their
NH + NH 3
4

keto and ammonia groups. The keto groups are used in catabolism for producing ATP, whereas ammonia is

excreted as such or in other forms. Ammonia is highly toxic and highly soluble in water. Its excretion as such,

therefore, requires a large amount of water. That is why, most of the aquatic arthropods, bony and freshwater

fishes, amphibian tadpoles, turtles, etc excrete ammonia. This type of excretion is called ammonotelic excretion or

ammonotelism.

(c) Urea CO (NH 2 )2 : This is less toxic and less soluble in water than ammonia. Hence, it can stay for some

time in the body. Many land vertebrates (adult amphibians, mammals) and such aquatic animals which cannot
afford to lose much water (e.g. elasmobranch fishes), turn their ammonia into urea for excretion. This type of
excretion is called ureotic excretion or ureotelism.

(d) Uric acid : Animals living in dry (arid) conditions, such as land gastropods, most insects, land reptiles
(snakes and lizards), birds etc have to conserve water in their bodies. These, therefore, systhesize crystals of uric acid
from their ammonia. Uric acid crystals are nontoxic and almost insoluble in water. Hence, these can be retained in
the body for a considerable time before being discharged from the body. Uric acid is the main nitrogenous excretory
product discharged in solid form. This excretion is called uricotelic excretion or uricotelism.

(e) Trimethylamine oxide : Certain marine molluscs, crustaceans and teleost fishes first form trimethylamine
from their ammonia by a process known as methylation. Then, the trimethylamine is oxidised to trimethylamine
oxide for excretion.This oxide is soluble in water, but nontoxic.

(f) Guanine : Spiders typically excrete their ammonia in the form of guanine. Some guanine is also formed in
amphibians, reptiles, birds and earthworms. It is insoluble in water. Hence, no water is required for its excretion.

(ii) Wasteproducts of nucleic acid metabolism : As a result of nucleic acid digestion, nitrogenous organic

cbases – purines (adenine and guanine) and pyrimidines (cytosine, thymine and uracil) – are absorbed from intestine
into the blood. Most of these are excreted out. About 5% of the total excretion of body accounts for these

substances. In man, purines are changed to uric acid for excretion. In most other mammals, nitrogenous organic

bases are excreted in the form of allantoin. Insects, amphibians, reptiles and birds also excrete these bases in the

form of uric acid. Some freshwater molluscs and crustacean arthropods excrete these in the form of ammonia.

(iii) Some sundry excretory substances (Others excretory products)

(a) Hippuric and ornithuric acids : Sometimes food of rabbit and other mammals may contain traces of
benzoic acid, or this acid may be formed in small amounts during fat metabolism. It is highly toxic. As it is absorbed
in blood, it is combined with glycine and changed into less toxic hippuric acid for excretion. In birds, benzoic acid is
combined with ornithine and changed into ornithuric acid for excretion.

(b) Creatine and creatinine : Muscle cells contain molecules of creatine phosphate, which are high energy
molecules and serve for storage of bioenergy like ATP. It is synthesised by 3 amino acids (G.A.M.) (Glycine,
Argenine and Methionine). Excess amount of this phosphate is, however, excreted out as such, or after being
changed into creatinine.

Chapter 12 291

Excretory Products and their Elimination

Differences between ammonotelism, ureotelism and uricotelism

S.No. Ammonotelism Ureotelism Uricotelism

1. Means excretion of nitrogenous waste Means excretion of nitrogenous waste Means excretion of nitrogenous waste

mainly as ammonia. mainly as urea. mainly as uric acid.

2. Uses very little energy in forming Uses more energy in producing urea. Uses far more energy in producing uric

ammonia. acid.

3. Its product is very toxic. Its product is less toxic. Its product is least toxic.

4. Causes considerable loss of body's water. Causes less loss of body's water. Causes least loss of body's water

5. Occurs in aquatic animals. Occurs in aquatic as well as land Occurs in land animals.

Disorders of kidneys. animals.

(i) Artificial kidney : Artificial kidney, called
haemodialyser, is a machine that is used to filter the
blood of a person whose kidneys are damaged. The
process is called haemodialysis. It may be defined as the
separation of small molecules (crytalloids) from large
molecules (colloids) in a solution by interposing a
semipermeable membrane between the solution and
water (dialyzing solution). It works on the principle of
dialysis, i.e. diffusion of small solute molecules through a

csemipermeable membrane (G. dia = = through, lyo =
6. Examples : Amoeba, Scypha, Hydra, Examples : Earthworm, Cartilaginous Examples : Insects, land crustaceans,

Earthworm, Unio, Prawn, Salamander, fishes, frog, turtles, alligators, mammals land snails, land reptiles birds.

Tadpole or frog, bonyfish. (man).

7. Animals excreting NH3 are called Animals excreting urea are termed Animals excreting uric acid are called

ammoniotelic. uroetelic. uricotelic.

RADIAL BLOOD
ARTERY PUMP

SAPHENOUS CELLOPHANE
VEIN MEMBRANE
BUBBLE
TRAP

separate). Haemodialyser is a cellophane tube

suspended in a salt-water solution of the same COMPRESSED FRESH CONSTANT USED
composition as the normal blood plasma, except that no CO2 AND AIR DIALYZING TEMPERATURE DIALYZING
urea is present. Blood of the patient is pumped from one SOLUTION SOLUTION
of the arteries into the cellophane tube after cooling it to BATH
0oC and mixing with an anticoagulant (heparin). Pores
Fig. – Flow of blood through an artificial kidney for haemodialysis

of the cellophane tube allow urea, uric acid, creatinine, excess salts and excess H+ ions to diffuse from the blood

into the surrounding solution. the blood, thus purified, is warmed to body temperature, checked to ensure that it is

isotonic to the patient's blood, and mixed with an antiheparin to restore its normal clotting power. It is then pumped

into a vein of the patient. Plasma proteins remain in the blood and the pores of cellophane are too small to permit

the passage of their large molecules. The use of artificial kidney involves a good deal of discomfort and a risk of the

formation of blood clots. It may cause fever, anaphylaxis, cardiovascular problems and haemorrhage. Kidney

transplant is an alternative treatment.

C.A.P.D. : Continuous ambulatory peritoneal dialysis.

Chapter 12 292

Excretory Products and their Elimination

(ii) Kidney (Renal) Transplantation
Meaning : Grafting a kidney from a compatible donor to restore kidney functions in a recipient suffering from
kidney failure is called renal transplantation.
History : First kidney transplant was performed between identical twins in 1954 by Dr. Charles Hufnagel, a
Washington surgeon, India's first kidney transplant was done on December 1, 1971 at Christian Medical College,
Vellore, TamilNadu. The recipient was a 35 years old person Shaninughan.
Eligibility : All patients with terminal renal failure are considered eligible for kidney transplantation, except
those at risk from another life-threating disease.
Donors : A living donor can be used in a kidney transplant. It may be in identical twin, a sibling, or a close
relative. If the living donors are not available, a cadaveric donor may be used (cadaver is a dead body). Over half of
the kidney transplants are from cadavers.
Success rate : A kidney transplant from an identical twin, called isogeneic graft or isograft, is always
successful. A renal transplant from a sibling or a close relative or a cadaver, termed allogeneic graft or homograft, is
usually successful with the use of an immunosupressant that prevents graft rejection by body's immune response.
Many renal transplant recipients are known to have retained functional grafts for over 20 years. Earlier, renal
transplantation was limited to patients under 55 years. Now, however, with better techniques, kidney grafting has
been done in selected patients in the 7th decade of life.

Pretransplant preparation : It includes haemodialysis to ensure a relatively normal metabolic state, and
provision of functional, infection-free lower urinary tract.

Donor selection and kidney preservation : A kidney donor should be free of hypertension, diabetes, and
malignancy. A living donor is also carefully evaluated for emotional stability, normal bilateral renal function,
freedom from other systematic disease, and histocompatibility. Cadaveric kidney is obtained from previously
healthy person who sustained brain death but maintained stable cardiovascular and renal function. Following brain
death, kidneys are removed as early as possible, flushed with special cooling solutions, such as mannitol and stored
in iced solution. Preserved kidneys usually function well if transplanted within 48 hours.

Recipient-Donor Matching : Recipient and donor are tested for 3 factors :

c Blood groups : Recipient's blood group should be compatible with donor's blood group.

 Human leucocyte antigen (HLA) : It is a genetic marker located on the surface of leucocytes. A person
inherits a set of 3 antigens from the mother and three from the father. A higher number of matching antigens
increases the chances that the kidney graft will last for a long time.

 Antibodies : Small samples of recipient's and donor's blood are mixed in a tube. If no reaction occurs, the
patient will be able to accept the kidney.

Transplant procedure : Transplantation is done under general anaesthesia. Operation takes 3 or 4 hours.
Cut is given in the lower abdomen. Donor's kidney is transplanted retroperitonealy in the iliac fossa. Artery and vein
of new kidney are connected to the iliac artery and vein of the recipient. Ureter of the new kidney is connected to
the urinary bladder of the recipient. Often the new kidney starts producing urine as soon as blood flows through it,
but sometimes it may take a few weeks before it starts working. A week's stay in the hospital is necessary to recover
from surgery, and longer if there are complications.

The new kidney takes over the work of two failed kidneys. Unless they are causing infection or high blood
pressure, the old kidneys are left in place.

Chapter 12 293

Excretory Products and their Elimination

Immunosupression : Immunosupression means to depress the immune response of the recipient to graft
rejection. Prophylactic immunosuppressive therapy is started just before or at the time of renal transplantation. An
ideal immunosuppressant suppress immunity against foreign tissue but maintains immunity against infection and
cancer. The drug, named cyclosporin, in such an immunosupressant. Use of antiserum to human lymphocytes is
equally useful. It destroys T-cell mediated immune responses, but spares humoral antibody responses.

(iii) Kidney diseases
Pyelonephritis : It is an inflammation of renal pelvis, calyces and interstitial tissue (G.pyelos = trough, tub;
nephros = kidney; itis = inflammation). It is due to local bacterial infection. Bacteria reach here via urethra and
ureter. Inflammation affects the countercurrent mechanism, and the victim fails to concentrate urine. Symptoms of
the disease include pain the back, and frequent and painful urination.

Glomerulonephritis : It is the inflammation of glomeruli. It is caused by injury to the kidney, bacterial
toxins, drug reaction, etc. Proteins and R.B.Cs pass into the filtrate.

Cystitis : It is the inflammation of urinary bladder (G.kystis = bladder, –itis = inflammation). It is caused by
bacterial infection. Patient has frequent, painful urination, often with burning sensation.

Uremia : Uremia is the presence of an excessive amount of urea in the blood. It results from the decreased
excretion of urea in the kidney tubules due to bacterial infection (nephritis) or some mechanical obstruction. urea
poisons the cells at high concentration.

Kidney stone (Renal calculus) : It is formed by precipitation of uric acid or oxalate. It blocks the kidney
tubule. It causes severe pain (renal colic) in the back, spreading down to thighs. The stone may pass into the ureter
or urinary bladder and may grow, and cause severe pain of blackade. When in bladder, the patient experiences
frequent and painful urination and may pass blood in the urine. Surgery may be needed to remove stone and
relieve pain.

Kidney (Renal) failure (RF) : Partial or total inability of kidneys to carry on excretory and salt-water
regulatory functions is called renal or kidney failure. Result kidney failure leads to (i) uremia, i.e., an excess of urea

cand other nitrogenous wastes in the blood (G.ouron = urine, haima-blood); (ii) Salt-water imbalance; and (iii)

stoppage of erythropoietin secretion.

Causes : Many factors can cause kidney failure. Among these are tubular injury, infection, bacterial toxins,
glomerulonephritis (inflammation of glomeruli) arterial or venous obstruction, fluid and electrolyte depletion,
intrarenal precipitation of calcium and urates, drug reaction, heammorrhage, etc.

Accessory excretory organs
(i) Skin : Many aquatic animals, such as Hydra and starfish, excrete ammonia into the surrounding water by

diffusion through the body wall. In land animals, the skin is often not permeable to water. This is an adaptation to
prevent loss of body's water. Mammalian skin retains a minor excretory role by way of its sudoriferous, or sweat,
glands and sebaceous, or oil glands.

(a) Sweat gland : Sweat glands pass out sweat. The latter consists of water containing some inorganic salts
(chiefly sodium chloride) and traces of urea and lactic acid. It also contains very small amounts of amino acids and
glucose. Sweat resulting from heavy muscular exercise contains a lot of lactic acid. The latter is produced in the
muscles by glycolysis. Loss of salt by sweating produces no immediate problem because water is also lost, and the
salt concentration of body fluids is not much changed. However, taking a lot of water after heavy sweating dilutes

Chapter 12 294

Excretory Products and their Elimination

the tissue fluid, causing 'electrolyte imbalance'. This may cause muscle cramps. A dilute salt solution should be taken
in case of heavy sweating.

(b) Sebaceous glands : Oil glands pass out sebum that contains some lipids such as waxes, sterols, other
hydrocarbons and fatty acids.

(ii) Lungs : Carbon dioxide and water are the waste products formed in respiration. Lungs remove the CO2
and some water as vapour in the expired air. Lungs have access to abundant oxygen and oxidise foreign
substances, thus causing detoxification and also regulate temperature.

(iii) Liver : Liver changes the decomposed haemoglobin of the worn-out red blood corpuscles into bile
pigments, namely, bilirubin and biliverdin. These pigments pass into the alimentary canal with the bile for
elimination in the faeces. The liver also excretes cholesterol, steroid hormones, certain vitamins and drugs via bile.
Infected or damaged liver does not remove bile pigments which accumulate in the blood and cause jaundice. The
bile pigments impart yellowish tinge to the skin and mucosa (known as jaundice). Liver deaminates the excess and
unwanted amino acids, producing ammonia, which is quickly combined with CO2 to form urea in urea or ornithine
cycle. Urea is less toxic than ammonia. It is removed by the kidneys.

(iv) Large intestine : Epithelial cells of the colon transfer some inorganic ions, such as calcium, magnesium
and iron, from the blood into the cavity of the colon for removal with the faeces.

(v) Saliva : Heavy metals and drugs are excreted in the saliva.
(vi) Gills : Gills remove CO2 in aquatic animals. They also excrete salt in many bony fish.
Osmoregulation.

The regulation of solute movement, and hence, water movement, which follows solutes by osmosis, is known
as osmoregulation. Osmosis may be defined as a type of diffusion where the movement of water occurs selectively
across a semipermeable membrane. It occurs whenever two solutions, separated by semipermeable membrane (the
membrane that allows water molecules to pass but not the solutes) differ in total solute concentrations, or
osmolarity. The total solute concentration is expressed as molarity or moles of solute per litre of solution. The unit of

cmeasurement for osmolarity is milliosmole per litre (mosm L–1). If two solutions have the same osmolarity, they are

said to be isotonic. When two solutions differ in osmolarity, the solution with higher concentration of solute is called
hypertonic, while the more dilute solution is called hypotonic. If a semipermeable membrane separates such
solutions, the flow of water (osmosis) takes place from a hypotonic solution to a hypertonic one.

Osmoconformers are the animals that do not actively control the osmotic condition of their body fluids.
They rather change the osmolarity of body fluids according to the osmolarity of the ambient medium. All marine
invertebrates and some freshwater invertebrates are strictly osmoconformer. Osmoconformers show an excellent
ability to tolerate a wide range of cellular osmotic environments.

Osmoregulators, on the other hand, are the animlas that maintain internal osmolarity, different from the
surrounding medium in which they inhabit. Many aquatic invertebrates are strict or limited osmoregulators. Most
vertebrates are strict osmoregulators, i.e. they maintain the composition of the body fluids within a narrow osmotic
range. The notable exception, however, are the hagfish (Myxine sp., a marine cyclostome fish) and elasmobranch
fish (sharks and rays).

Chapter 12 295

Excretory Products and their Elimination

Osmoregulators must either eliminate excess water if they are in hypotonic medium or continuously take in
water to compensate for water loss if they are in a hypertonic situation. Therefore, osmoregulators have to spent
energy to move water in or out and maintain osmotic gradients by manipulating solute concentrations in their body fluids.

(i) Water and solute regulation in freshwater environment : Osmolarity of freshwater is generally much
less than 50 mosm L–1 while the freshwater vertebrates have blood osmolarities in the range 200 to 300 mosm L–1.
The body fluids of freshwater animals are generally hypertonic to their surrounding environment. Therefore,
freshwater animals constantly face two kinds of osmoregulatory problems : they gain water passively due to osmotic
gradient, and continuously lose body salts to the surrounding medium of much lower salt content.

However, the freshwater animals prevent the net gain of water and net loss of body salts by several means,
Protozoa (Amoeba, Paramoecium) have contractile vacuoles that pump out excess water. Many others eliminate
water from the body by excreting large volume of very dilute urine. As a general rule, animals do not drink water,
including freshwater fish do not drink water to reduce the need to expel and salt loss are minimised by a specialised
body covering (subcutaneous fat layer of scaleless fish and scales over the body of fish or crocodile). Freshwater
animals have remarkable ability to take up salts from the environment. The active transport of ions takes place
against the concentration gradient. Specialised cells, called ionocytes or chloride cells in the gill membrane of fresh
water fish can import Na+ and Cl– from the surrounding water containing less than 1mM NaCl, when their plasma
concentration of NaCl exceeds 100 mM.

(ii) Water and solute regulation in marine environment : Sea water usually has an osmolarity of about
1000 mosm L–1. Osmolarity of human blood is about 300 mosm L–1. The osmoregulatory problems in marine
situation are opposite to those in freshwater environment. Marine bony fish have the body fluids hypotonic to
seawater, and thereby, they tend to lose water from the body through permeable surfaces (gill membranes, oral and
anal membranes). To compensate for the water loss, marine bony fish drink seawater. However, drinking seawater
results in a gain of excess salts. The ionocytes or chloride cells of the gill membrane of marine bony fish help to
eliminate excess monovalent ions from the body fluid to the seawater. Divalent cations are generally eliminated with
faeces. Hilsa, salmon and other fish that migrate between seawater and freshwater, when in ocean, drink and

cexcrete excess salt through the gill membrane. A number of hormones play a key role in this switching over process.
In general, the body fluids of marine invertebrates, ascidians and the hagfish are isotonic to seawater. In
elasmobranch fish (sharks and rays) and coelocanths (lobefin fish), osmolarity of the body fluids is raised by
accumulating certain organic substances (osmolytes). Retention of osmolytes in body fluids reduces the
osmoregulatory challenges. The best known examples of such organic osmolytes are urea and trimethylamine oxide
(TMAO). Body fluids of sharks and coelocanths are slightly hyperosmotic to seawater due to retention of urea and
TMAO while hypoionic to seawater as they maintain far lower concentration of inorganic ions in the body fluids.

(iii) Water and solute regulation in terrestrial environment : Land animals are always subject to osmotic
desiccation, like the marine animals. Air-breathing animals constantly lose water through their respiratory surfaces.
However, animals utilise various means to minimise this water loss. Good examples are the waxy coatings of the
exoskeletons of insects, the shell of the land snails and the multiple layers of dead, keratinised skin cells covering
most terrestrial vertebrates. Despite such protective measures, a considerable amount of water is lost through oral,
nasal and respiratory surfaces. This may even be fatal for the animal concerned. Humans, for examples, die if they
lose around 12 per cent of the body water. Therefore, water loss must be compensated by drinking and eating moist
food. Desert mammals are well adapted to minimise water loss. Kangaroos rats, for example, lose so little water that

Chapter 12 296

Excretory Products and their Elimination

they can recover 90 percent of the loss by using metabolic water (water derived from different cellular metabolic
processes.) The nasal countercurrent mechanism for conserving respiratory moisture is also important. Behavioural
adaptations, such as nervous and hormonal mechanisms that control thirst, are important osmoregulatory
mechanisms in terrestrial animals. Many desert animals are nocturnal to avoid the heat of day-time, another
important behavioural adaptation that minimises dehydration. The camels, however, reduce the chance of
overheating by orienting to give minimal surface exposure to direct sunlight. They produce dry faeces and
concentrated urine. When water is not available, the camels do not produce urine but store urea in tissues and
solely depend on metabolic water. When water is available, they rehydrate themselves by drinking up to 80 litres of
water in 10 minutes.
Important Tips

• Anuria – Failure of kidney to form urine.

• Oligourea – is less urine output.

• Cystitis – Inflammation of urinary bladder.

• Filtration fraction – Ratio between GFR (glomerular filtration rate) and RPF (renal plasma flow).

• Gout – Painful great toe (arthiritis) due to deposition of uric acid.

• Haematuria – Presence of blood cells in urine.
• Oedema – Increased volume of interstitial fluid.

• Polynephritis – Inflammation of large number of nephrons.

• Renal stone – Stone formation in the nephrons of kidney due to accumulation of mainly calcium oxalates some phosphates and uric acid.

• Trimethylamine – Excretory product of marine teleosts (bony fishes).

• Uraemia – High concentration of urea (about 10 times) in blood.

• Chloragogen cells – Found in coelomic fluid of earthworm and are analogous (functionally similar) to human liver as are excretory in
function.

• Contractile vacuole – Osmoregulatory apparatus of fresh-water protozoans like Amoeba, Parmaecium etc. So contractile vacuole is

cfunctionally analogous to vertebrate kidney.

• Glomerulonephritis – Chronic inflammation of glomeruli due to streptococcal infection.

• Aminoaciduria – Urine with amino acids like cystine, glycine, etc.

• Polyuria – Increased urine volume.

• Allantoin and allantoic acid are nitrogenous excretory products formed during embryonic development of amniotes with shelled eggs.
Allantoin is also called embryonic waste by allantoic acid is stored in allantois foetal membrane.

• Chances of infection of urinary tract are more in women due to shroter urethra.

• Urate cells – These are excretory cells of fat body of insects. These store excretory waste permanently called storage excretion.

• Bright disease – Characterised by nephritis caused by streptococal infection.

• Ptosis – Displacement of kidney.
• Dysuria – Painful urination.

Certain animals are both ammonotelic and ureotelic e.g. Ascaris, earthworm, lung fish (African toad), etc.

• Aminotelism – Expelling of amino acids as nitrogenous waste e.g. molluscs like Unio, Echinoder like Asterias, etc.
• Chordate with flame cells is Branchiostoma (also called Amphioxus).

• Nocturia – Increased volume of urine at night.

Chapter 12 297