Download Cardiac Physiology

Cardiac Physiology
Chapter 9
The circulatory system has
three main components:
• The heart establishes a pressure
gradient to pump the blood
• The blood vessels are passageways
for the distribution of pumped blood
throughout the body.
• The blood is a transport medium,
serving the needs of body cells.
– The pulmonary circulation is a loop of
blood vessels between the heart and the
lungs.
– The systemic circulation is the circuit of
blood vessels between the heart and other
body systems.
The heart is a muscular organ,
about the size of a closed fist.
– It is located in the thoracic cavity, between the sternum and
vertebrae. The base of the heart lies to the right of the
sternum. The apex lies to the left of the sternum.
– By its location the blood can be manually driven from the
heart by CPR.
• The heart is a dual pump.
– The atria are its two upper chambers. They receive blood
returning to the heart. They transfer blood to the ventricles.
– The ventricles are the two lower chambers. They pump
blood from the heart.
– Veins are blood vessels that carry blood from the tissues to
the heart. Arteries are blood vessels that carry blood from
the heart to the tissues.
– A septum separates the low-oxygen blood on the right side
of the heart from the high-oxygen blood on the left side.
The right side of the heart receives blood from
the systemic circulation. The heart pumps
blood into the pulmonary circulation.
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The venae cavae are veins returning
blood to the right atrium. Oxygen has
been extracted from this blood. Carbon
dioxide has been added to it. This blood
is pumped from the right ventricle through
the pulmonary artery to the lungs.
The lungs add oxygen to this blood
received from the right side of the heart.
Carbon dioxide is taken away from this
blood. This blood flows through
pulmonary veins to the left atrium of the
heart. This high-oxygen is pumped from
the left ventricle through the aorta, a large
artery.
Therefore, the left side of the heart
receives blood from the pulmonary
circulation. It pumps it into the systemic
circulation.
The systemic circulation is a series of
parallel pathways. Parts of it are
distributed to different body regions.
Each region receives a fresh blood
supply. Depleted blood (low oxygen, high
carbon dioxide) returns to the right side of
the heart.
• The right and left pumps can be compared.
– Oxygen-poor blood on the right side soon becomes the
same volume of oxygen-rich blood pumped from the left
side.
– The pulmonary circulation is low pressure and low
resistance. The systemic circulation is the opposite.
– Pressure is the force exerted by pumped blood on a vessel
wall. Resistance is the opposition to blood flow.
The action of heart valves ensure that blood
flows in the proper direction.
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The AV valves are the tricuspid on the right and bicuspid on the left.
They allow blood to flow from the atria into the ventricles. This occurs
when atria pressure is greater than ventricular pressure, during
ventricular filling.
During ventricular emptying, when ventricular pressure exceeds atrial
pressure, the AV valves close. This prevents the blood from flowing
backwards. The AV valves are anchored by chordae tendineae to
papillary muscles.
The other pair of valves are the semilunar, pulmonary on the right and
aortic on the left. They are forced open when the ventricular pressures
exceed the pressures in the pulmonary arteries and aorta.
The semilunar valves close when the pressure in the ventricles falls
below the pressures in these vessels. This prevents the blood from
flowing backwards.
A fibrous skeleton separates the atria from the ventricles.
– See Figures 9-5 and 9-6
The heart wall consists of
three layers.
– The endocardium is the inner layer of
epithelium.
– The myocardium is the middle layer of
cardiac muscle tissue.
– The epicardium is the external membrane.
• Cardiac muscle fibers are
interconnected by intercalated discs.
They form a functional syncytia.