5.THE CARDIOVASCULAR SYSTEM

 Right atrioventricular valve (tricuspid valve) has 3 flaps
or cusps.

 Left atrioventricular valve (mitral valve) has 2 cusps.

 Flow of blood in the heart is one way – blood enters the
heart via the atria and passes into the ventricles below.

 The valves between the atria and ventricles open and
close passively according to changes in pressure in the
chamber.



Cont.

 The valves are prevented from opening upwards into
the atria by tendinous cord, called chordae tendineae
which extend from the inferior surface of the cusps to
little projections of myocardium into the ventricles,
covered with endothelium, called papillary muscles.



Epicardium Visceral layer of serous pericardium
Comprised of mesothelial cells and fat and
connective tissues

Myocardium Muscle layer
Comprised of cardiomyocytes

Endocardium Lines inner surface of heart chambers and
valves
Comprised of a layer of endothelial cells,
and a layer of subendocardial connective
tissue

Clinical Endocarditis
relation











14 Steps of Blood Flow Through the
Heart

 1) body –> 2) inferior/superior vena cava –> 3)
right atrium –> 4) tricuspid valve –> 5) right
ventricle –> 6) pulmonary arteries –> 7) lungs –>
8) pulmonary veins –> 9) left atrium –> 10)
mitral or bicuspid valve –> 11) left ventricle –>
12) aortic valve –> 13) aorta –> 14) body.



Blood flow

Function of the Coronary Arteries

 Coronary arteries supply blood to the heart muscle. Like
all other tissues in the body, the heart muscle needs
oxygen-rich blood to function.

What are the different coronary arteries?

 Left main coronary artery (LMCA).

 Right coronary artery (RCA).

 The left main coronary artery supplies blood to
the left side of the heart muscle (the left
ventricle and left atrium). The left main coronary
divides into branches:

1. The left anterior descending artery branches off
the left coronary artery and supplies blood to
the front of the left side of the heart.

cont

2. The circumflex artery branches off the left
coronary artery and encircles the heart muscle.
This artery supplies blood to the outer side and
back of the heart.

Right coronary artery (RCA).

 supplies blood to the right ventricle, the right atrium,
and the SA (sinoatrial) and AV (atrioventricular) nodes,
which regulate the heart rhythm.

 The right coronary artery divides into smaller branches,
including the right posterior descending artery and the
acute marginal artery.

 Together with the left anterior descending artery, the
right coronary artery helps supply blood to the middle
or septum of the heart.

Why are the coronary arteries
important?

 any coronary artery disorder or disease can have
serious implications by reducing the flow of oxygen
and nutrients to the heart muscle.

 This can lead to a heart attack and possibly death.
Atherosclerosis (a buildup of plaque in the inner
lining of an artery causing it to narrow or become
blocked) is the most common cause of heart disease.

Conducting system of the heart

 The heart possesses the autorhythmicity - means
it generate own electrical impulses and beats
independently of nervous or hormonal control.

 Supplied with sympathetic and parasympathetic
nerve fibres, which increase and decrease
respectively the intrinsic heart rate.

 Heart responds to a number of circulating
hormones, including adrenaline (epinephrine) and
thyroxine.

SINOATRIAL NODE (SA NODE)

 SA node or sinus node is a group of cells located in the
wall of the right atrium of the heart.

 These cells have the ability to spontaneously produce an
electrical impulse (action potential), that travels through
the heart via the electrical conduction system causing it
to contract.

 In a healthy heart, the SA node continuously produces
action potential, setting the rhythm of the heart and so
is known as the heart's natural pacemaker.

 The rate of action potential production (and therefore
the heart rate) is influenced by nerves that supply it.

SA NODE

 The sinoatrial node is a banana-
shaped structure that varies in
size, usually between 10-30
millimeters (mm) long, 5–7 mm
wide, and 1–2 mm deep

 located in the wall (myocardium)
of the right atrium, laterally to the
entrance of the superior vena cava





ATRIOVENTRICULAR NODE (AV Node)

 Situated near the atrioventricular valves.
 Secondary pacemaker function – if there is problem with

SA node, or with the transmission of impulses from the
atria.
 Its intrinsic firing rate, slower than SA node (40-60 beats
per minute).

Nerve supply to the heart

 The heart is influenced by autonomic (sympathetic and
parasympathetic) nerves.

1. Vagus nerve (parasympathetic) supply mainly the SA
and AV node and atrial muscle. Vagal stimulation
reduced the rate at which impulses are produced,
decreasing the rate and force of the heartbeat.

2. Sympathetic nerves supply – increase the rate

The cardiac cycle

 At rest, healthy adult heart
beat at a rate of 60 – 80 beats
per minute (b.p.m).

 During each heartbeat or
cardiac cycle, the heart
contracts (systole) and then
relaxes (diastole).









Heart sound

 Heartbeat can be heard if the ear, or diaphragm of a
stethoscope is placed on the chest wall a little below the
left nipple and slightly near the midline.

 There are 4 heart sound:
1. The first two are most easily distinguish.
2. Sound through stethoscope like ‘lub dup’.
 Lub- fairly loud, due to the closure of the

arterioventricular valves.
 Dup- softer,due to closure of the aortic and pulmonary

valves.

Electrical changes in the heart

 What controls the timing of your heartbeat?
1. Heart rate, which is the number of times your heart beats

per minute.
2. Heart rhythm, which is the synchronized pumping action of

your four heart chambers.
➢ Your heart's electrical system should maintain:
1. A steady heart rate of 60 to 100 beats per minute at rest.

The heart's electrical system also increases this rate to
meet your body's needs during physical activity and lowers
it during sleep.
2. An orderly contraction of your atria and ventricles (this is
called a sinus rhythm).

Electrical changes in the heart

 Body tissue and fluids conduct
electricity well, so the electrical
activity in the heart can be recorded
on the skin surface using electrodes
positioned on the limbs and the
chest.

 This recording called an
electrocardiogram (ECG).

 Normal ECG tracing shows five
waves which named P, Q, R, S and T.

Cont.

 The P wave arise when the impulse from the SA node
sweep over the atria (atrial depolarisation).

 The QRS complex represents the very rapid spread of
the impulse from the AV node through the AV bundle
and the Purkinje fibres and the electrical activity of
the ventricular muscle (ventricular depolarisation).

Cont.

 T wave presents the relaxation of the ventricular muscle
(ventricular repolarisation).

 Atrial repolarisation occurs during ventricular
contraction, and not seen because the larger QRS
complex.

 The ECG described above originates from the SA node is
called sinus rhythm.

 Sinus rhythm is 60-100 b.p.m
 Faster heart rate – tachycardia
 Slower heart rate - bradycardia

The heartbeat happens as follows:

1. The SA node (called the pacemaker of the heart) sends
out an electrical impulse.

2. The upper heart chambers (atria) contract.
3. The AV node sends an impulse into the ventricles.
4. The lower heart chambers (ventricles) contract or

pump.
5. The SA node sends another signal to the atria to

contract, which starts the cycle over again.

When the SA node sends an electrical
impulse, it triggers the following process:

1. The electrical signal travels from your SA node
through muscle cells in your right and left atria.

2. The signal triggers the muscle cells that make your
atria contract.

3. The atria contract, pumping blood into your left and
right ventricles.

How does your body control your heart
rate?

 The sympathetic and parasympathetic nervous
systems, which have nerve endings in the heart.

 Hormones, such as epinephrine and norepinephrine
(catecholamines), which circulate in the
bloodstream.

Cardiac output

 -is the amount of blood ejected from each ventricle
every minute.

 The amount expelled by each contraction of each
ventricle is the stroke volume

 -expressed in litres per minute (L/min) and is
calculated by multiplying the stroke volume by the
heart rate (measured in beats per minute):

Cardiac output = stroke volume x heart rate

Cont.

 In a healthy adult at rest, the stroke volume is
approximately 70ml and if the heart rate is 72 b.p.m
the cardiac output is 5L/min

 -can increased to meet the demands of exercise to
around 25L/min.

 -athletes, up to 35L/min

 Increasing during exercise is called the cardiac
reserve.

Stroke volume

1. Determined by the volume of blood in the ventricles
immediately before they contract (preload).

2. Increase preload lead to stronger myocardial
contraction, and more blood is expelled.

3. The heart always pumps out all the blood that it
receives, allowing it to adjust cardiac output to match
body needs.

4. Cardiac output decreases – the heart begins to fail.

5. Other factors that increased myocardial contraction,
sympathetic nerve activity and circulating hormones, e.g
adrenaline (epinephrine), noradrenaline
(norepinephrine) and thyroxine.

Arterial blood pressure

 This affects stroke volume – create resistance to
blood being pumped from the ventricles into the
great arteries.

 This resistance called afterload

 Increasing afterload increases the workload of the
ventricles – because it increase the pressure
against which they have to pump.



Blood volume

 Kept constant by the kidneys.

 Blood volume fall through sudden haemorrhage –
cause stroke volume, cardiac output and venous
return to fall.

 The body’s compensatory mechanism will tend to
return these values towards normal, unless the
blood loss is too sudden or severe for
compensation.

Venous return

 Contraction of the left ventricle ejecting blood
into the aorta is not sufficient to push the blood
through the arterial and venous circulation and
back to the heart.

 Other factors are involved:

1. The position of the body

2. Muscular contraction

3. Respiratory pump

Heart rate
Main factors determining heart rate:

1. Autonomic nervous 6. Gender.
system. 7. Age.
8. Temperature.
2. Circulating 9. Baroreceptor reflex.
chemicals.

3. Position.

4. Exercise.

5. Emotional states.

Blood pressure

 Def: force or pressure that blood exerts on the walls of
blood vessels.

 Systemic arterial blood pressure maintains the essential
flow of blood into and out of the organs of the body.

 If BP too high, blood vessel can damaged, causing clots
or bleeding from sites of blood vessel rupture.

 If too low, blood flow may be inadequate – dangerous
for essential organs such as the heart, brain or kidneys.

Cont.

 BP varies according to the time of day, the
posture, gender, and age.

 BP falls at rest and during sleep.
 Increase with age and usually higher in women

than in men.

Systolic and diastolic pressures.

 Systolic blood pressure – left ventricles contracts
and pushes blood into the aorta.

 In adults it is about 120mmHg or 16kPa.
 Diastolic blood pressure – heart is resting

following the ejection of blood.
 In adult is about 80mmHg or 11kPa
 Arterial BP is measured with sphygmomanometer.

Factor determining blood pressure

1. Cardiac output
2. Peripheral or arteriolar resistance
3. Autoregulation