Structure & Function of Heart and its parts. Heart walls, pericardium, heart valves, septa, nodal tissues, coronary circulation, blood vessels of heart, AV bundle, bundle of his, purkinje fibers, myogenic nature of heart, action potential generation.

1. SRTRUCTURE OF HEART

2. Human Circulatory
System
Human circulatory system,
also called the blood
vascular system consists of
a muscular chambered
heart, a network of closed
branching blood vessels
and blood, the fluid which
is circulated.

3. The Heart
• Heart is a muscular organ that
pumps blood received from the
veins into the arteries, thereby
maintaining the flow of blood
through the entire circulatory
system.
• Mesodermally derived organ.
• Situated in the thoracic cavity, in
between the two lungs, slightly
tilted to the left.
• Size of a clenched fist.

4. The Pericardium
• It is protected by a
double walled
membranous bag,
pericardium, enclosing
the pericardial fluid.
• Function - to restrict
excessive movements of
the heart as a whole and
serve as a lubricated
container in which
different parts of heart
can contract.
R Removal of a section of pericardium
Heart enclosed in pericardium

5. Heart Walls
1. Epicardium – visceral layer of the serous pericardium. outer protective
layer.
2. Myocardium – cardiac muscle layer forming the bulk of the heart. It is
the middle layer of the heart. Fibrous skeleton of the heart –
crisscrossing, interlacing layer of connective tissue.
3. Endocardium – endothelial layer of the inner myocardial surface. It is
the deepest layer of the heart. It has the smooth lining to reduce
friction of blood flow.

6. The Heart Chambers
Our heart has 4 chambers 
1. Two relatively small upper chambers called atria
2. Two larger lower chambers called ventricles
• The right atrium receives blood from the body. This
blood is low in oxygen. This is the blood from the
veins.
• The right ventricle pumps the blood from the right
atrium into the lungs to pick up oxygen and remove
carbon dioxide.
• The left atrium receives blood from the lungs. This
blood is rich in oxygen.
• The left ventricle pumps the blood from the left
atrium out to the body, supplying all organs with
oxygen-rich blood.

7. Blood Vessels Of Heart
These bring blood to the lungs, where
oxygen enters the bloodstream, and then
to the body:
• The inferior and superior vena cava bring
deoxygenated blood from the body into
the right atrium.
• The pulmonary artery channels oxygen-
poor blood from the right ventricle into the
lungs, where oxygen enters the
bloodstream.
• The pulmonary veins bring oxygen-
rich blood to the left atrium.
• The aorta channels oxygen-rich blood to
the body from the left ventricle.

8. Coronary Circulation
Coronary circulation is the circulation of
blood in the blood vessels that supply
the heart muscle (myocardium).
Coronary arteries supply oxygenated
blood to the heart muscle, and cardiac
veins drain away the blood once it has
been deoxygenated.
• Two coronary arteries arise from
the aorta just beyond the semilunar
valves; supply blood into the musculature
of the heart.
• Deoxygenated blood is returned to the
chambers of the heart via coronary veins;
most of these converge to form the
coronary venous sinus, which drains into
the right atrium.

9. The Septa
• A thin, muscular wall called the
interatrial septum separates the
right and the left atria.
• Whereas a thick-walled, the
inter-ventricular septum,
separates the left and the right
ventricles.
• The atrium and the ventricle of
the same side are also separated
by a thick fibrous tissue called the
atrio-ventricular septum.
Atrio-ventricular septum
Interatrial Septum
Interventricular septum

10. Heart Valves
Each of the septa are provided with an
opening through which the two chambers
of the same side are connected.
• The opening between the right atrium &
the right ventricle is guarded by a valve
formed of 3 muscular flaps or cusps, the
tricuspid valve.
• A bicuspid/mitral valve guards the opening
b/w the left atrium & the left ventricle.
• The openings of the right and the left
ventricles into the pulmonary artery and
the aorta are provided with the semilunar
valves.
The valves in the heart allows the flow of
blood only in one direction, i.e., from the
atria to the ventricles and from the
ventricles to the pulmonary artery or aorta.
These valves prevent any backward flow.

11. Myogenic Nature Of Heart
A myogenic heart is capable of
generating a cardiac contraction
independent of nervous input. In a
myogenic heart contraction is initiated
by the myocyte cell itself instead of an
outside occurrence or stimulus such as
nerve innervation.
Reason-
• A specialized cardiac musculature called
the nodal musculature is distributed in
the heart.

12. The Nodal Tissue
1. A patch of this tissue is present in the right
upper corner of the right atrium-sino-atrial
node (SAN).
2. Another mass of this tissue is seen in the
lower left corner of the right atrium close
to the atrio-ventricular septum-atrio-
ventricular node (AVN).
3. Bundle of nodal fibers, atrioventricular
bundle (AV bundle) continues from the
AVN, passes through the atrio-ventricular
septa to emerge on the top of the
interventricular septum and immediately
divides into a right and left AV bundle.
4. These branches give rise to minute fibers
throughout the ventricular musculature of
the respective sides and are called purkinje
fibers.

13. • The nodal musculature has the ability to generate action potentials
without any external stimuli, i.e., it is auto excitable.
• However, the number of action potentials that could be generated in
a minute vary at different parts of the nodal system.
• The SAN can generate the maximum number of action potentials, i.e.,
70-75 min–1 , and is responsible for initiating and maintaining the
rhythmic contractile activity of the heart.
• Therefore, SAN is called the pacemaker.
• Our heart normally beats 70-75 times in a minute (average 72 beats
min–1).

14. Actional Potential Generation

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