Cvs 1. functional anatomy

Cardiovascular Physiology
by
Prof. R. K. Marya
Functional Anatomy
of the Heart

CARDIOVASCULAR SYSTEM
Introduction
• The cardiovascular system consists of a pump,
the heart, and a series of distributing and
collecting tubes, i.e. arteries and veins, and
capillaries.
• Capillaries serve the most important function of
rapid exchange of materials between the blood
and extracellular fluid bathing the tissue cells.

Overview of functions of CVS
• The cardiovascular system constitutes a
transportation System.
• It delivers to all the tissues materials
necessary for their normal functions (e.g. O2,
nutrients, hormones, etc.), as well as, removes
the waste products produced by cellular
metabolism (e.g. CO2, uric acid, urea, etc.).

Overview of functions of CVS
• A number of defense systems against
infection (e.g. leukocytes, immunoglobulins,
etc.) also circulate in the bloodstream.
• Cardiovascular system helps to regulate the
body temperature by transporting heat,
generated by metabolic processes to the
areas where it can be dissipated.

The Heart
The wall of the heart consists of:
i. Epicardium, that is the visceral layer of serous
pericardium.
ii. Myocardium, the thick middle layer composed of
cardiac muscle fibers.
iii. Endocardium, the innermost layer formed by the
endothelial cells and subendothelial connective
tissue.

The Heart: Structure

Heart: Functional Anatomy
• The human heart consists of four The atria are
receiving chambers.
• The ventricles are ejecting chambers.
• An interatrial septum separates the two atria,
whereas an interventricular septum separates the
two ventricles.

Myocardium
• Left ventricle and interventricular septum are
thickest (about 10 mm).
• The thickness of the right ventricular wall is
about one-third of left ventricular wall.
• The walls of the two atria are still thinner (<2
mm).
• The thickness of cardiac chamber may be
correlated with the peak pressure generated in
each chamber during contraction (systole).

Flow of blood in the Heart

Atrioventricular valves
• The atrioventricular orifices are large oval-
shaped apertures between an atrium and the
respective ventricle.
• The right AV orifice is guarded by the tricuspid
valve (it has three cusps),
• Left AV orifice is guarded
by the mitral valve (also
called bicuspid valve, since
it consists of two cusps).

• The AV valves allow the blood to flow in
one direction only, i.e. from the atria to
the ventricles.
• During ventricular contraction, the
tendency of blood to flow back to the
respective atria is prevented by the closure
of the valve
Atrioventricular valves

Papillary muscles
• The papillary muscles are conical muscular
projections arising from the ventricular walls.
• From their apices arise tendinous cords (chordae
tendineae) which are attached to the border and
inferior surfaces of the cusps of AV valves.

Function of Papillary muscles

• During ventricular contraction, the papillary muscles
also contract and help to
(i) draw the cusps of AV valves together so as to
close the AV orifice and prevent regurgitation of
blood back into the atria.
(ii) prevent the membranous cusps from prolapsing
into the atria.
• During atrial contraction, blood passes through the
AV orifice, pushing the cusps of AV valve aside like a
curtain.
Function of Papillary muscles

Aortic valve
Semilunar valves
• The aortic and pulmonary orifices are rounded
apertures, smaller than the respective AV
orifices.
• They are guarded by the aortic and pulmonary
valves, respectively.
• These valves are also known as the
semilunar valves
since each consists of
three halfmoon-
shaped cusps

• These cusps allow the blood to flow from the
ventricle to the respective arterial trunk
(aorta or pulmonary artery) during ventricular
contraction by getting aside to the wall.
• When the ventricles relax, the tendency of the
blood to flow back into the ventricles is
prevented by the three cusps, which by opening
like pockets, close the orifice.
Semilunar valves

Cardiac Muscle: Structure
• Cardiac muscle fibers are striated like skeletal
muscle fibers, but have centrally located nuclei.
• Cardiac muscle cell contains actin and myosin
filaments, the sarcotubular system, and other
organelles seen in the skeletal muscle.
• Mitochondrial content of cardiac muscle is much
larger than that of the skeletal muscle.

Cardiac/Skeletal muscle histology

THE CARDIAC MUSCLE
• The most characteristic histological feature of the
cardiac muscle is a syncytium-like appearance.
• (A syncytium is a multinucleated mass of
cytoplasm which is not divided by end-
membranes into individual cells.)
• Cardiac muscle fibers seem to divide and reunite
with the adjacent muscle fibers.

Cardiac muscle cells ( diagrammatic)

THE CARDIAC MUSCLE
• Early histologists described the cardiac muscle as
an anatomical syncytium.
• Electron microscopic studies have revealed that
the dense partitions seen under light microscopy,
and called intercalated discs are actually end
membranes that separate one muscle cell from
another.
• Intercalated discs are desmosomes which provide
a strong junction between the adjacent cardiac
muscle cells

• Intercalated discs have areas of low electrical
resistance.
• At the outer border of the intercalated disc, the
adjacent cell membranes contain proteinaceous
tunnels called connexions or gap junctions.
• Electrical resistance in these gap junctions is 400
times less than in other parts of the cell
membrane
The intercalated discs

The intercalated discs

Cardiac muscle is a functional syncytium
• Electrical impulse arising in one cardiac muscle
fiber spreads to the next through the gap
junctions.
• In this way, the cardiac impulse spreads
throughout the muscle mass quickly, resulting in
a coordinated contraction of the whole muscle
mass.
• Therefore, the cardiac muscle behaves as a
functional syncytium, although anatomically it is
not so.

Conduction system of the Heart
• For the heart to pump efficiently and the
systemic and pulmonary circulations to
operate in synchrony, the two halves of the
heart must beat in a coordinated manner.
• Besides the myocardium described above, the
heart also contains a conduction system,
which facilitates this coordination.

• The conduction system is composed of modified
cardiac muscle cells ( not neural tissue).
• The specialized conduction system is responsible
for automatic and rhythmic origin of cardiac
impulse and its spread throughout the heart.
• It consists of SA node, AV node, Bundle of His and
its right and left branches and Purkinje tissue
Conduction system of the Heart

Conduction system of the heart

Sinoatrial (SA) Node
• The sinoatrial node is a small strip of
specialized cardiac muscle tissue, measuring
25 mm × 2 mm.
• It is located in the right atrial wall immediately
anterior and lateral to the opening of the
superior vena cava.
• The muscle fibers of SA node are 3–5 μm in
diameter in contrast to 15–20 μm diameter of
the surrounding atrial muscle

Sinoatrial (SA) Node
• SA node acts as pace-maker of the heart.
• The SA node also contains parasympathetic
autonomic ganglia and postganglionic
sympathetic and parasympathetic fibers.
• The autonomic nerves modulate the activity of
SA node.

Internodal Pathways
• These are three bundles of Purkinje type fibers
which connect SA node with AV node.
• The bundles are called the anterior, middle and
posterior intermodal tracts.
• Their physiological role is controversial.

Atrioventricular (AV) Node
• The AV node, measuring 20 mm × 3 mm, is
located in the wall of right atrium at the
right posterior portion of the interatrial
septum.
• The atrioventricular node is situated
subendocardially, in contrast to the
subepicardial location of the SA node.
• It consists of specialized muscle fibers
resembling those of the SA node.

Bundle of His
• The myocardium consists of two muscle
masses attached to a fibrous ring.
• Atrial muscle mass is attached to the upper
surface of the fibrous ring.
• The ventricular muscle mass is attached to the
lower surface of the fibrous ring.
• The bundle of His is the only electrical link
between the atrial muscle mass and the
ventricular muscle mass.

The His-Purkinje system
• The His-Purkinje system consists of bundle of His and
its branches.
• It contains modified muscle fibers with diameter of
70–80 μm.
• His-Purkinje system’s conduction velocity is 4 m/sec
as compared to 1.0 m/sec in the typical myocardial
fiber.
• The faster conduction velocity helps to spread the
wave of excitation rapidly over the two ventricles, so
that the two contract simultaneously.

• The bundle of His begins from the AV
node, passes through the fibrous AV
ring into the top of interventricular
septum.
• Almost immediately it divides into the
right and left bundle branches, which
supply the right and the left ventricles,
respectively
Bundle of His

His bundle branches
• The left bundle branch further divides into
anterior and posterior fascicles.
• The anterior branch is thinner of the two and
supplies the anterior wall of the left ventricle.
• The thicker posterior branch supplies the
posterolateral wall of the left ventricle.
• The right bundle branch supplies the right
ventricle

His bundle branches& Purkinje fibers

His bundle branches
• The His bundle branches run sub-
endocardially on the respective sides of the
septum.
• At the apex of the heart, these bundle
branches divide further into a large number
finer branches that spread into the
subendocardial region of the respective
ventricles.

Reference
Marya, R.K. Medical Physiology, 4th Edi.
CBS publishers New Delhi, 2016

Cvs 1. functional anatomy

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