This lecture help the students such as medical ,nursing , and any health care provider to understand the basic information about Cardiac system anatomy.

1. THE CARDIOVASCULAR
SYSTEM
DR. LUMA ALZAMEL

3. Heart
The heart is a roughly cone-shaped hollow muscular
organ. It is about 10 cm long and is about the size of the
owner's fist. It weighs about 225 g in women and is
heavier in men (about 310 g).
Position
The heart lies in the thoracic cavity in the mediastinum
between the lungs. It lies obliquely, a little more to the left
than the right, and presents a base above, and an apex
below. The apex is about 9 cm 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. The base extends to
the level of the 2nd rib.

4. Organs associated with the heart
Inferiorly — the apex rests on the
central tendon of the diaphragm.
Superiorly — the great blood vessels,
i.e. the aorta, superior vena cava,
pulmonary artery and pulmonary veins.
Posteriorly — the oesophagus, trachea,
left and right bronchus, descending
aorta, inferior vena cava and thoracic
vertebrae.
Laterally — the lungs — the left lung
overlaps the left side of the heart.
Anteriorly — the sternum, ribs and
intercostal muscles.

5. Structure
The heart is composed of three layers of
tissue:
pericardium, myocardium and endocardium.
Pericardium
• The pericardium is made up of two sacs. The
outer sac consists of fibrous tissue and the
inner of a continuous double layer of serous
membrane. The space between the parietal
and visceral pericardium is only a potential
space. In health the two layers are in close
association, with only the thin film of serous
fluid between them.

6. Myocardium
The myocardium is composed of specialised
cardiac muscle found only in the heart. It is
not under voluntary control but, like skeletal
muscle, cross-stripes are seen on microscopic
examination. Each fiber (cell) has a nucleus
and one or more branches. The ends of the
cells and their branches are in very close
contact with the ends and branches of
adjacent cells.
Endocardium
This forms the lining of the myocardium and
the heart valves. It is a thin, smooth,
glistening membrane which permits smooth
flow of blood inside the heart. It consists of
flattened epithelial cells, continuous with the
endothelium that lines the blood vessels.

7. Interior of the heart
The heart is divided into a right and left side by the
septum, a partition consisting of myocardium
covered by endocardium. After birth blood cannot
cross the septum from one side to the other. Each
side is divided by an atrioventricular valve into an
upper chamber, the atrium, and a lower chamber,
the ventricle. The atrioventricular valves are formed
by double folds of endocardium strengthened by a
little fibrous tissue. The right atrioventricular valve
(tricuspid valve) has three flaps or cusps and the left
atrioventricular valve (mitral valve) has two cusps.

8. The valves between the atria and
ventricles open and close passively
according to changes in pressure in the
chambers. They open when the pressure in
the atria is greater than that in the
ventricles. During ventricular systole
(contraction) the pressure in the ventricles
rises above that in the atria and the valves
snap shut preventing backward flow of
blood. The valves are prevented from
opening upwards into the atria by tendinous
cords, called chordae tendineae, which
extend from the inferior surface of the cusps
to little projections of myocardium covered
with endothelium, called papillary muscles.

9. Conducting system of the
heart
The heart has an intrinsic system whereby the
cardiac muscle is automatically stimulated to
contract without the need for a nerve supply from
the brain.
However, the intrinsic system can be stimulated or
depressed by nerve impulses initiated in the brain
and by circulating chemicals including hormones.
There are small groups of specialized
neuromuscular cells in the myocardium which
initiate and conduct impulses causing coordinated
and synchronized contraction of the heart muscle.

10. Sinoatrial node (SA node)
This small mass of specialised cells is in the wall of the right atrium near the
opening of the superior vena cava. The SA node is the 'pace-maker' of the heart
because it normally initiates impulses more rapidly than other groups of
neuromuscular cells.
Atrioventricular node (AV node)
This small mass of neuromuscular tissue is situated in the wall of the atrial
septum near the atrioventricular valves. Normally the AV node is stimulated by
impulses that sweep over the atrial myocardium. However, it too is capable of
initiating impulses that cause contraction but at a slower rate than the SA node.

11. Atrioventricular bundle (AV bundle or bundle of His)
This is a mass of specialised fibres that originate from the AV node. The AV
bundle crosses the fibrous ring that separates atria and ventricles then, at the
upper end of the ventricular septum, it divides into right and left bundle
branches. Within the ventricular myocardium the branches break up into fine
fibres, called the Purkinje fibres.AV bundle convey electrical impulses from the
AV node to the apex of the myocardium where the wave of ventricular
contraction begins, then sweeps upwards and outwards, pumping blood into the
pulmonary artery and the aorta.

12. Nerve supply to the heart
In addition to the intrinsic impulses generated within the conducting system described
above, the heart is influenced by autonomic nerves originating in the cardiovascular
centre in the medulla oblongata which reach it through the autonomic nervous system.
These consist of parasympathetic and sympathetic nerves and their actions are
antagonistic to one another.
The vagus nerves (parasympathetic) supply mainly the SA and AV nodes and atrial
muscle. Parasympathetic stimulation reduces the rate at which impulses are produced,
decreasing the rate and force of the heart beat.
The sympathetic nerves supply the SA and AV nodes and the myocardium of atria and
ventricles. Sympathetic stimulation increases the rate and force of the heart beat.

13. Factors affecting heart
rate
 Autonomic nervous system.
 Circulating chemicals. The hormones adrenaline and noradrenaline, secreted by
the adrenal medulla, have the same effect as sympathetic stimulation, i.e. they
increase the heart rate. Other hormones including thyroxine increase heart rate
by their metabolic effect. Some drugs, dissolved gases and electrolytes in the
blood may either increase or decrease the heart rate.
 Position. When the person is upright, the heart rate is usually faster than when
lying down.
 Exercise. Active muscles need more blood than resting muscles and this is
achieved by an increased heart rate and selective vasodilatation.
 Emotional states. During excitement, fear or anxiety the heart rate is increased.
Other effects mediated by the sympathetic nervous system may be present.
Gender. The heart rate is faster in women than men.
 Age. In babies and small children the heart rate is more rapid than in older
children and adults.

14. Good Luck