Cardiovascular System - Vessels and Heart Outline
I. Cardiovascular System
A. Overall functions and basic components - There are three components of the cardiovascular
or circulatory system - the blood vessels, the heart and blood. These components function to
transport oxygen, nutrients, waste, and hormones throughout the body. Additionally, they are
responsible for keeping you healthy via the white blood cells. Blood vessels can vary their size
to aid in temperature regulation.
B. Blood Vessels - The tubes that carry blood are the blood vessels. There are three basic types
of blood vessels.
1. Arteries
a. Definition - An artery carries blood away from the heart. With one
exception (the pulmonary artery), arteries carry bright red oxygenated
blood. These arteries deliver oxygen to tissues from head to toe.
b. Walls of arteries - The walls are very muscular and thick. The
smooth muscle can contract to push blood along. Tiny arteries can
even close due to intense constriction.
c. Pulse - As the heart beats, it pumps blood into the arteries. The push
of the blood as the heart beats can be felt peripherally as a pulse. The
heart provides an excellent driving force for the blood and therefore
arteries have high pressures pushing the blood along. A normal resting
pulse is 60-80 beats per minute.
2. Veins
a. Definition - Veins return blood back to the heart. With one exception
(the pulmonary vein), the blood in veins is dark red/blue in color and is
deoxygenated.
b. Walls of veins - The walls are quite thin in comparison to arteries.
The veins do not have the benefit of the pump forcing blood through
them because they are at the end of the circuit, far away from the
benefit of the pump. Thus, the pressures in veins are lower than in
arteries and no pulse can be felt.
c. Valves - Since the veins have low driving pressure and thin muscle
in their walls, they have a difficult time moving blood through them.
Therefore, veins have a series of one-way valves to prevent backflow of
blood. Thus, if blood travels in a vein from your ankle to your knee, it
won't go back to your ankle because of the valves. Veins also course
through your skeletal muscle and movement results in "milking" of
blood through the veins.
3. Capillaries
a. Definition - These are the tiniest of all blood vessels. They connect
the arteries and veins. Blood leaves the heart through arteries, which
become tiny arteries, which become capillaries, which become tiny
veins, which become big veins returning blood to the heart.
b. Walls of capillaries - The wall is very thin. In fact, it is only one cell
layer.
c. Diffusion - Because of the thin wall, the capillary is the site of
diffusion. Oxygen can diffuse (high concentration in blood to low
concentration in surrounding tissues) out of the blood into the
surrounding tissues and carbon dioxide, which is waste from the
tissues, diffuses from the tissues into the bloodstream.
4. Lymph vessels (not part of cardiovascular system) -- Since we are talking about
blood vessels, lymph vessels travel next to veins and carry fluids similar to blood
but without red blood cells. Eventually lymph vessels dump their fluids into large
veins. Lymph vessels carry substances that are too large or too abundant to be
initially carried by the bloodstream. Along the way, lymph vessels filter their
contents through lymph nodes.
C. Heart (cardia-) - The heart is the pump that pushes the blood through the blood vessels. It is
located in the center (just a bit to the left) of the chest cavity. It is surrounded by lungs on either
side.
1. Striated involuntary muscle - The heart is basically a big muscle. Recall, that it is
striated under the microscope and not under voluntary control.
2. 4 chambers or cavities are inside of the heart and filled with blood. Then, as the
heart beats, the blood is squeezed from chamber to chamber to artery. The four
chambers are:
a. Left and Right Atrium -( Atria pl.) - These are the two upper
chambers of the heart.
b. Left and Right Ventricle - These are the two lower chambers of
the heart.
3. Valves - Four one-way valves in the heart keep blood moving in one direction.
As the valves close, two at a time, the characteristic heart sound "lub-dupp" is
heard. Two valves are located between each atrium and the corresponding
ventricle, two valves are located between each ventricle and the artery exiting the
ventricle.
4. Blood flow circuit through the heart and lungs: Deoxygenated blood travels
towards the heart in larger and larger veins, until finally the blood reaches the
largest veins in the body called the Superior and Inferior Vena Cava. This blood
dumps into the Right Atrium, through a valve to the Right Ventricle, through a
valve to the Pulmonary Artery (also known as trunk). This artery takes
deoxygenated blood to the lungs to receive oxygen. Now, the oxygenated blood
returns to the heart from the lungs via the Pulmonary Vein. This vein dumps the
blood into the Left Atrium, through a valve to the Left Ventricle, through a valve,
to the largest artery in the body called the Aorta. The aorta leaves the heart
carrying oxygen to all tissues in the body from the head to the toes. The arteries
branch into smaller and smaller branches, ultimately to capillaries in which oxygen
diffuses out. The deoxygenated blood then flows through small veins back to the
Vena Cava.
5. Coronary arteries - These arteries carry oxygen and nutrients to the heart
muscle itself. Of course, if they get clogged, the heart muscle cannot get oxygen and
dies.
6. Heart Physiology:
a. Pacemaker - The heart beats on its own, because cells in the SA
Node, a region in the wall of the Right Atrium, spontaneously contract
60-80 times per minute at rest. All cardiac muscle cells are
interconnected, so that the SA node sets the pace for ALL muscle cells
of the heart to contract in unison.
b. Heart muscle contraction is electrical. Therefore, electrical
contractions can be monitored by placing electrodes on the skin and
running an ECG or EKG = Electrocardiogram. Normal and
abnormal heart rhythms can be detected from an ECG.
c. Cardiac cycle is one complete beat of the heart. It consists of a
contraction phase and a relaxation/refilling stage.
Systole - This is the contraction phase of the heart beat in which
the blood is being pumped. Systolic pressure is measured on an
arm artery and represents the force of the blood moving in the
artery when the heart is in systole. Normal systolic pressure is
about 120 mm Hg.
Diastole - This is the relaxation and refilling of the heart
chambers phase of the cardiac cycle. Diastole is important
because if the heart didn't relax, there would be no blood in the
heart chambers to pump. Diastolic pressure measured in your
arm artery represents the heart when it is in diastole and is
relaxing. Normal diastolic pressure is about 80 mm Hg. (120
mm Hg/80 mm Hg is normal blood pressure.)
D. Cardiovascular Pathology
1. Hypertension - Hypertension is continuously high blood pressure. It affects 20%
of the American population. Arterial pressures are above 160 mm Hg/95 mm Hg.
Causes include heredity, stress, obesity, smoking and diet. A healthy low-fat diet
and moderate exercise can reduce blood pressure. Additionally, hypertension is
treated with medications that can lower blood pressure.
a. Arteriosclerosis - A common complication of prolonged
hypertension is arteriosclerosis, or "hardening of the arteries". These
arteries cannot operate as normal arteries and are more susceptible to
blood clots forming within them.
b. Aneurysm - As blood bombards the walls of arteries with a high
pressure, another complication can be a weakening of the artery wall.
This can lead to a ballooning of the artery wall which could be weak
enough to burst.
2. Coronary Artery Disease is the leading cause of death in U.S. Remember that
the coronary arteries carry oxygen to the heart muscle itself.
a. Excessive cholesterol in the diet can build up in the walls of the
coronary arteries. Excessive amounts of fats in the diet, especially
saturated fatty acids (from animal sources such as butter and bacon)
can also build up in the coronary arteries. Atherosclerosis is the
condition in which fatty plaques are present in the walls of the
coronary arteries.
b. Heart attack - These clogged coronary arteries can block the blood
flow directly or result in the formation of a blood clot which also clogs
the coronary arteries. The heart muscle cells cannot receive their
oxygen and the cells die. Depending on the size of the blood vessel
blocked, a few cells to the entire side of the heart can die. Treatments
include "clot busting" drugs, angioplasty to open up clogged arteries,
or bypass surgery to graft arteries around the blockage.
c. Angina - Often the heart attack is preceded by chest pains as a
result of heart cells being deprived of oxygen, termed angina. It is
certainly a forewarning of worse things to come.
3. Varicose Veins & Hemorrhoids - While all of the above diseases are artery
diseases, veins can become abnormal as well. Veins that become overly distended
and damaged so that the valves breakdown are varicose veins. They appear as
bulging tortuous veins. Varicose veins near the anus, caused by excessive straining,
are hemorrhoids. Treatments include anti-inflammatory drugs, rest, vein injections
and surgery.