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HEART : A DUAL PUMP |FINDYOURSELF
HEART
The
Cardiac Muscle
• Branched
• Centrally
located nucleus
• Muscle
cells of the heart-more 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.
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”)
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 co-ordinated
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
