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CARDIOVASCULAR SYSTEM
Heart is enclosed by a membrane
(pericardium)
Wall of Heart:
Epicardium: visceral
pericardium = protection by
reducing friction
Myocardium: cardiac muscle
Endocardium: inner layer of
epithelium & elastic and
collagenous connective tissue
The heart has 4 chambers
top = atria (right and left)
bottom = ventricles (right, left)
Ear-like projections = auricles
Right & left side separated by the
septum.
Atrioventricular (AV) valves
Right side tricuspid valve-3 cusps
Left side bicuspid valve-2 cusps
The cusps of the valves are
attached to strong fibrous
strings (chordae tendinae) that
prevent cusps from swinging
back into the atrium. The valves
only allow blood to flow in one
direction (atrium to ventricle).
The right ventricle has a thinner
wall- pumps blood to the lungs
The left ventricle has thicker walls
because it must pump blood to
the entire body.
Heart sounds-lubb- AV valves
close. Ventricles contract
dubb-pulmonary & aortic valves
close. Ventricles relax.
Normal and abnormal EKGs and
heart sounds
www.bioscience.org/atlases/heart/
Right Side-blood low in oxygen
returns to the heart via
superior & inferior vena cava.
As the right atrium relaxes, a
vacuum is created, drawing
in venous blood.
The right atrium contracts,
forcing blood through the
tricuspid valve into the right
ventricle.
The ventricle contracts closing
the tricuspid valve & blood is
sent through the pulmonary
valve into the pulmonary
arteries, where it is carried to
the lungs to eliminate CO2
and pick up fresh O2 .
Left Side-oxygenated blood
enters the heart on the left
side through the pulmonary
veins. The left atrium
contracts, forcing blood
through the bicuspid valve into
the left ventricle. The left
ventricle contracts, closing the
bicuspid valve and opening the
aortic valve into the aorta.
Cardiac Conduction System
SA Node (sinoatrial node) –
special cardiac tissue near
opening of the superior vena
cava. It is responsible for the
rhythmic activity of the heart by
initiating an impulse that
spreads into the myocardium
and stimulates contraction.
The SA node is called the
pacemaker, initiating 70-80
impulses per minute.
AV Node (atrioventricular node)located in the inferior portion of
the upper septum. Impulses
flow slowly through fibers from
the SA node to the AV node,
then quickly through the AV
bundle.
AV Bundle – large bundle of fibers
whose branches give rise to
purkinje fibers which spread down
the septum to the base of the heart,
then upward through the lateral
walls of the heart. This causes the
heart to contract from the bottom
upward, forcing blood into the
aorta and pulmonary arteries.
Vascular System– blood vessels
1. Arteries – strong, elastic walls
adapted for carrying blood at
high pressure. Arteries subdivide into thinner vessels
called arterioles.
The inside layer is the endothelium
which is a smooth surface to
prevent blood clotting. It secretes
substances that dilate and
contract blood vessels. Arteries
carry blood away from the heart.
2. Capillaries – smallest blood
vessels. They connect arterioles
and venules. They have thin
walls, allowing substances in
blood & tissue to be exchanged.
Capillaries carry blood with high
levels of O2 & nutrients.
3. Veins – carry blood back to the
heart. Path parallels the arteries.
Veins have thinner walls and less
elastic tissue than arteries. Veins
have valves which keep blood
flowing toward the heart. Veins
subdivide into venules which
can’t carry high pressure blood.
Blood Pressure : is the force of
blood against the inner walls of
the blood vessels.
During contraction of ventricles,
arterial pressure (systolic
pressure) is the highest.
During ventricle relaxation, arterial
pressure (diastolic pressure) is
the lowest.
Normal blood pressure is below
120/80.
120/80 to 140/90 is
prehypertensive.
Normal heart rate is about 72 beats
per minute.
Blood pressure depends on:
1. Blood volume (5 L in adults)
2. Blood viscosity (ease of flow)
3. Resistance to flow (friction
between blood and vessel walls
4. Stroke volume-volume of blood
discharged from left ventricle with
each contraction.