CARDIAC MUSCLE
Dr. Ayisha Qureshi
Assistant Professor,
MBBS, MPhil
Location of the Heart:
The Pericardium &
the Pericardial Sac:
The heart is enclosed in the double-walled,
membranous pericardial sac (peri means
“around”). The sac consists of two
layers—a tough, fibrous covering and a
secretory lining.
The outer fibrous covering of the sac
attaches to the connective tissue partition
that separates the lungs. This attachment
anchors the heart so that it remains
properly positioned within the chest.
The sac’s secretory lining secretes a thin
pericardial fluid, which provides
lubrication to prevent friction between the
pericardial layers as they glide over each
other with every beat of the heart.
Pericarditis, an inflammation of the
pericardial sac that results in a painful
friction rub between the two pericardial
layers, occurs occasionally because of viral
or bacterial infection.
Heart walls are composed of 3 distinct layers:
1. ENDOCARDIUM (inner): thin layer of
endothelium that lines the entire circulatory
system (endo means “within”)
2. MYOCARDIUM (middle): composed of
cardiac muscle that forms the bulk of heart
wall (myo means “muscle”)
3. EPICARDIUM (outer): thin external
membrane covering the heart (epi means “on”)
The Cardiac
Muscle
• Branched
• Centrally located nucleus
• Muscle cells of the heartmore commonly called
myocytes or myofibrils.
• Outside membrane is
called sarcolemma.
• Cardiac muscles have the
same arrangement of actin
and myosin, and the same
bands, zones and Z discs as
skeletal muscles forming
sarcomeres.
• They do have less
sarcoplasmic reticulum
than skeletal muscles and
require Calcium from extra
cellular fluid for
contraction as T-tubules
are not well organized.
Arrangement of
the heart muscles
The myocardium consists
of interlacing bundles of
cardiac
muscle
fibers
arranged spirally around
the circumference of the
heart.
What is the advantage of
the spiral arrangement?
When the cardiac muscle
contracts & shortens, a
wringing effect is
produced, efficiently
pushing blood upwards
towards the exit of the
major arteries of the heart.
Intercalated Discs
Although the cardiac muscles interdigitate & branch,
there is no anatomical continuity b/w the individual
muscle fibers.
• Cardiac muscle are branched, have a single nucleus
and are interconnected to each other, end to end by
specialized structures called as INTERCALATED
DISCS. The intercalated discs are further composed
of:
1. Gap Junctions
2. Desmosomes
HEART AS A DUAL
PUMP:
Even thought the heart is a
single organ, the left and the
right side of the heart is
anatomically and functionally
separate.
This is done with the help of
the interventricular spetum.
It ensures that the blood
from the left and right side of
the heart does not mix.
Although the left and the
right sides are separated, the
heart contracts in a coordinated fashion: the atria
contract together and the
ventricles contract together….
O2 poor blood returns from the body thru the
Superior & Inferior Vena Cava
↓
Enters the Right atrium
↓
Right ventricle
↓
Pulmonary artery
↓
Lungs
↓
Blood is Oxygenated
↓
Pulmonary Veins
↓
Left Atrium
↓
Left Ventricle
↓
Aorta
↓
Circulated to the body