5.THE CARDIOVASCULAR SYSTEM

THE CARDIOVASCULAR
SYSTEM

AAP2013
PN WAN

CARDIOVASCULAR SYSTEM

 Cardio – heart

 Vascular – blood vessel

 Divided for

 The heart – pumping action ensures constant
circulation of the blood

 Blood vessel –form a lengthy network through
which the blood flows.

Cont,

 The heart pumps blood into:
1. Pulmonary circulation
2. Systemic circulation.

Cont.

 The right side of the heart pumps blood to the lungs
(the pulmonary circulation) where gas exchange
occurs

 The blood collect O2 from the airsacs and excess
carbon dioxide diffuse into the airsacs for exhalation.

 The left side of the heart pumps blood into the
systemic circulation, which supplies the rest of the
body.

Cont.

 Cardiovascular system ensures a continuous flow
of blood to all body cells – continual physiological
adjustments to maintain an adequate blood
supply.

 If inadequate supply of oxygen and nutrients to
body cells – tissue damage occurs and cell death
may follow.



BlOOD VESSEL

 LEARNING OUTCOMES
1. Describe the structures and functions of arteries, veins,

and capillaries
2. Explain the relationship between the different types of

blood vessel
3. Indicate the main factors controlling blood vessel

diameter
4. Explain the mechanisms by which exchange of nutrients,

gases and wastes occurs between the blood and the
tissues.

ARTERIES AND ARTERIOLES

 These blood vessels transport blood away from the
heart.

 Their wall consist of three layers of tissue;
1. Tunica adventitia/outer layer of fibrous tissue
2. Tunica media/middle layer of smooth muscle and

elastic tissue
3. Tunica intima/inner lining of squamous epithelium
➢ Arteries have ticker walls than veins to wishstand the

high pressure of arterial blood.

Anastomoses and end-arteries

 Anastomoses- arteries that form a link between
main arteries suppliying an area, ex:arterial supply
to the palms of the hand, and sole of the feet.

 End-arteries : the sole source of blood to a tissue,
ex: the branches from the circulus arteriosus (circle
of Willis) in the brain or the central artery to the
retina of eye.

Capillaries and sinusoids

 The smallest arterioles break up into a number of
minute vessels called capillaries.

 Capillaries walls consist of a single layer of
endothelial cells sitting on a very thin basement
membrane, through which water and other small
molecule can pass.

 Blood cells and large molecules such as plasma
proteins do not normally pass through capillary walls.

 Capillaries form a vast network of tiny vessels that
link the smallest arterioles to the smallest venules.

Cont.

 In certain places including the liver and bone
marrow, the capillaries are significantly wider and
leakier than normal.

 These capillaries are called sinusoids.

 Their walls are incomplete and their lumen is
much larger than usual, blood flows through them
more slowly under less pressure, can come
directly into contact with cells outside the
sinusoid wall.

Capillary refill time

 When an area of skin is pressed firmly with a
finger, it turns white (blanches) because the blood
in the capillaries under the finger has been
squeezed out.

 Normally take less than 2 second to refill once the
finger is removed, and for the skin to turn pink
again.

 In children – capillary refill time suggests poor
perfusion or dehydration.

Veins and venules

 Veins return blood at low pressure to the heart. The walls
of the veins are thinner than arteries but have the same
three layers of tissue.

 They are thinner because there is less muscle and elastic
tissue in the tunica media, as veins carry blood at lower
pressure than arteries.

 When cut, the veins collapse while the thicker-walled
arteries remain open.

 When an artery is cut blood spurts at high pressure.

 Some veins posses valves –prevent backflow of blood,
ensuring that it flows towards the heart.

 Smallest veins are called venules.



Cont.

 Veins are called capacitance vessels because they
are distensible, have capacity to hold a large of
proportion of the body’s blood.

 In haemorrhage, veins can constrict, helping to
prevent a sudden fall in blood pressure.

Blood supply

 The outer layers of tissue of thick-walled blood
vessels received their blood supply via a network
of blood vessels called the vasa vasorum.

 Thin walled vessels and the endothelium of the
others receive oxygen and nutrients by diffusion
from the blood passing through them.

Control of blood vessel diameter

 The smooth muscle in the tunica media of veins
and arteries is supplied by nerves of the
autonomic nervous system.

 These nerves arise from the vasomotor centre in
the medulla oblongata and they change the
diameter of blood vessels, controlling the volume
of blood they contain.

Blood vessel diameter and blood flow

 Resistance to flow of fluids along a tube is
determined by three factors:

1. The diameter of the tube

2. The length of the tube

3. The viscosity of the fluid.

 Blood vessel diameter is regulated by the smooth
muscle of the tunica media, which is supplied by
sympathetic nerves of the autonomic nervous
system.

Cont.

 Sympathetic activity generally constrict blood
vessel smooth muscle and therefore narrow the
vessel (vasoconstriction) – increasing the pressure
inside.

 Decreased nerve stimulation relaxes the smooth
muscle, thinning the vessel wall and enlarging the
lumen (vasodilation) – increased blood flow under
less pressure.



Local regulation of blood flow

 Example :
 Blood flow through the gastrointestinal tract increasing

after a meal to allow for increased activity in the tract, and
adjustment to blood flow through the skin in the control of
body temperature.
 The main mechanism associated with this local of blood
flow include:
1. Release of metabolic waste product, e.g CO2 and lactic

acid. Active tissue release more wastes than resting tissue,
so increased levels of waste increase blood flow into the
area.

Cont.

2. Tissue temperature : a rise in metabolic activity
increase tissue temperature, causes vasodilation

3. Hypoxia stimulates vasodilation and rise in blood flow
through the affected tissue.

4. Release of vasodilator chemicals. Inflamed and
metabolically active tissues produce a number of
vasodilators, which increase blood supply to the area.

5. Action of vasoconstrictors. The sympathetic hormone
adrenaline (epinephrine), released from the adrenal
medulla, is powerful vasoconstrictor. Others include
angiotensin.



Capillary Exchange.
Exchange Of Gases.

 Internal respiration is the process by which gases area
exchanged between capillary blood and local body
cells.

 Oxygen is carried from the lungs to the tissues in
combination with haemoglobin as oxyhaemoglobin.

 Carbon dioxide is one of the waste products of cell
metabolism, and towards the venous end of the
capillary.

Cont.

 Blood transport co2 to the lungs for excretion by three
different mechanism:

 Dissolve in the water of the blood plasma -7%
 In chemical combination with sodium in the form of

sodium bicarbonate -70%
 Reminder in combination with haemoglobin -23%

Exchange of other substances

 Nutrients, including glucose, amino acids, fatty
acids, vitamins and mineral salts required by all
body cells are transported round the body in the
blood plasma.

 They diffuse through the semipermeable capillary
walls into the tissues.

 Water exchange freely between the plasma and
tissue fluid by osmosis.

HEART

Learning outcomes

1. Describe the structure of the heart and its position
within the thorax.

2. Trace the circulation of the blood through the heart and
the blood vessel of the body.

3. Outline the conducting system of the heart

4. Relate the electrical activity of the cardiac conduction
system to the cardiac cycle.

5. Describe the main factors determining heart rate and
cardiac output.

Heart

 Roughly cone-shaped hollow muscular organ.
 About 10cm long and is about the size of the owner’s fist.
 Weighs about 225g in women and is heavier in men about

310g

Position

1. The heart lies in the thoracic cavity in the mediastinum
(the space between the lungs).

2. Lies obliquely, little more to the left than the right, and
presents a base above and an apex below.

3. The apex is about is 9cm to the left of the midline at
the level of the 5th intercostal space, i.e; a little below
the nipple and slightly nearer the midline.

4. The base extends to the level of the 2nd rib.





Organs associated with the heart

Inferiorly –apex rest Superiorly – the great Posteriorly-
on the central tendon blood vessel oesophagus, trachea,

of diaphragm (aorta,svc,pa,pv) Lt & Rt bronchus,
descending aorta, ivc,

thoracic vertebrae.

Laterally- lungs Anteriorly – sternum,
ribs and intercostal

muscles.







STRUCTURE





PERICARDIUM

 -outermost layer, made up of 2 sacs.
 Outer sacs (fibrous pericardium) consists of

fibrous tissue
 Inner sacs (serous pericardium) continuous double

layer of serous membrane.
 Fibrous pericardium is continuous with the tunica

adventitia of the great vessels above and
adherent to the diaphragm below.
 Its inelastic, fibrous nature prevents
overdistention of the heart.





PERICARDIUM

 The serous membrane consists of flattened
epithelial cells.

 It secretes serous fluid, called pericardial fluid,
into the space between the visceral and parietal
layers – allow smooth movement between them
when the heart beats.

 The space between the parietal and visceral
pericardium is only a potential space.



MYOCARDIUM

 Composed of specialised cardiac muscle found only in
the heart.

 Striated like skeletal muscle, but not under voluntary
control.

 Each fibre (cell) has a nucleus and one or more
branches.

 Running through the myocardium is also the network
of specialised conducting fibres responsible for
transmitting the heart’s electrical signals.

MYOCARDIUM

 -thickest at the apex and thins out towards the
base.

 Reflects the amount of work each chamber
contributes to the pumping of blood.

 Thickest in the left ventricle, which has the
greatest workload.

 Specialised muscle cells in the walls of the atria
secrete atrial natriuretic peptide.



Fibrous tissue in the heart

 Myocardium is supported by a network of fine fibres
that run through all the heart muscle. This is called
the fibrous skeleton of the heart.

 Atria and the ventricles are separated by a ring of
fibrous tissue, which does not conduct electrical
impulses.

 When a wave of electrical activity passes over the
atrial muscle, it can only spread to the ventricle
through the conducting system that bridges the
fibrous ring from atria to ventricle.

Endocardium

 This line the chambers and valves of the heart.

 It is a thin, smooth membrane to ensure smooth
flow of blood through the heart.

 Consist of flattened epithelial cells, and it is
continuous with the endothelium lining the blood
vessels.

Interior of the Heart

 The heart is divided into a right and left side by
the septum.

 After birth, blood cannot cross the septum from
one side to the other.

 Each side is divided by an atrioventricular valve
into the upper atrium and the ventricle below.

 The atrioventricular valves are formed by double
folds of endocardium strengthened by a little
fibrous tissue