Download Cardiovascular System

Cardiovascular System
Physiology
Cardiac Muscle
Cardiac muscle cells are elongated, branching
cells that contain one or occasionally two
centrally located nuclei.
 CM cells contain myosin and actin organized into
sarcomeres which join end to end to form
myofibrils.
 The arrangement of actin and myosin gives the
striations.
 Striations of cardiac muscle are less regularly
arranged and less numerous than skeletal.
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Diagram of muscle contraction and relaxation.
The same mechanism exists in skeletal muscle.
Cardiac Muscle Continued
Another characteristic is the intercalated
disks; these are specialized cell junctions –
they work to increase contact between the
cells.
 This also serve to allow the cardiac muscle
contract in waves to “massage” the blood
out of the heart.
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Contraction
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Adenosine triphosphate (ATP) provides the
energy for cardiac muscle contraction, and
, as in other tissues, ATP depends on
oxygen availability. Cardiac muscle cannot
develop a large O2 debt. A large oxygen
debt would result in muscular fatigue and
the heart would eventually cease beating.
What organelle must be present in large
numbers?
Contraction
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Action potentials are conducted through two nodes that
are made of modified cardiac muscle cells. The two
nodes are contained in the walls of the right atrium and
are named according to their position in the atrium.
The SA (Sinoatrial) node is medial to the opening of the
superior vena cava.
The AV (atrioventricular) node is medial to the right
atrioventricular valve. The AV node gives rise to a
conducting bundle of the heart (the atrioventricular
bundle). Within the septum, this bundle divides into the
right and left bundle branches.
Contraction
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Cardiac muscle cells have the ability to generate spontaneous action
potentials, but cells of the SA node do this at an increased
frequency – PACEMAKER.
Action potentials that are produced spread from the SA node to
adjacent cardiac muscle fibers of the atrium. Action potentials are
conducted from the SA node to the AV node really fast.
Action potentials get conducted from the AV node to the bundle
branches and then the velocity of the action really speeds up. It
passes through the right and left bundle branches and penetrates
the myocardium of the ventricles. Ventricular contraction begins at
the apex and proceeds toward the base of the heart. During this
process, the distance between the base and the apex decreases –
shortening the heart.
CONTRACTION IS SYSTOLE. VENTRICULAR SYSTOLE CAUSES
EJECTION OF BLOOD FROM THE HEART.
Cardiac Cycle
VD – Pressure decreases in the atria. As the AV valves
open, blood flows into the ventricles.
2/3rds of the way through filling, the SA node
depolarizes (the action potential is spread over the atria)
the atria contracts causing AS.
 VS – Ventricular contraction causes the ventricular
pressure to increase – AV valves close. Pressure rises
until the ventricular pressure exceeds the pressure in the
blood vessels. Isometric contraction: AV valve is closed
and the SL is not yet open (pressurizes the chambers).
When the ventricular pressure exceeds the pressure in
the vessels, the SL’s open and ejection begins.
Ventricular volume decreases during ejection (VD).
Shockwave
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