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Structure of the Heart__________________________________________________________
The obvious starting point of this system is the heart. The heart is a muscular pump about the size of a human fist. The heart
is made of a unique muscle tissue called cardiac muscle, which is found within the myocardium, which makes up the wall
of the heart. Like skeletal muscle, it is striated with strands of actin and myosin proteins. However, unlike skeletal muscle,
and like the smooth muscle found in the digestive system, it is involuntary (requiring no conscious control). It has a much
higher amount of mitochondria to allow for nearly continuous aerobic respiration, which permits the muscle to avoid fatigue
under normal circumstances. Like all muscles, this muscle requires a blood supply, which comes from the coronary arteries.
It was widely believed that cardiac muscle tissue was incapable of reproduction during a person’s lifetime, but testing with
radioactive isotopes has shown that this occurs very slowly over a lifetime.
The heart consists of four chambers. The bottom two chambers are called ventricles, which are the larger and more powerful
of the chambers, and are responsible for pumping blood out of the heart and into the arteries. The top chambers are called
atria (singular: atrium), which collect blood from the veins, and hold it before letting it into the ventricles.
The Path of Blood______________________________________________________________
Blood enters the right atrium from one of two large veins, collectively known as the venae cavae. The superior (top)
vena cava brings deoxygenated blood from parts of the body above the heart, and the inferior (bottom) vena cava brings
deoxygenated blood from the lower body. The blood passes through the tricuspid valve into the right ventricle, where it is
pumped through the semilunar valve into the pulmonary arteries, where it is taken to the lungs to exchange carbon dioxide
for oxygen. After that, the oxygenated blood returns to the heart through the pulmonary veins and enters the left atrium. The
blood passes through the biscupid valve (also known as the mitral valve) into the left ventricle. The blood is then pumped
through another semilunar valve (or the aortic valve) before entering the thick-walled, high pressure aorta, the largest
artery in the body.
Arteries take blood away from the heart (mnemonic: arteries away), and veins carry it to the heart. People often
think “arteries carry oxygenated (red) blood and veins carry deoxygenated (blue) blood”, but that is reversed in the
pulmonary blood vessels.
The blood passes through the arteries, which constantly branch into smaller and smaller vessels until the blood reaches the
arterioles. Arterioles lead directly to capillaries, which are small and thin enough to allow diffusion of materials into and out
of the blood stream. The blood then enters venules, followed by a series of veins that repeatedly join into larger and larger
veins before reaching the vena cava.
Notable Blood Vessels__________________________________________________________
superior & inferior venae cavae
pulmonary arteries & veins
aorta
carotid arteries
jugular vein
converse of the carotid arteries—take blood from the brain down the neck subclavian veins
one on each side; joined to all veins in each arm coronary arteries
superior & inferior mesenteric arteries
celiac artery
renal arteries & veins
iliac arteries & veins
supply reproductive organs, buttocks, inner thighs Composition of Blood__________________________________________________________
erythrocytes (red blood cells)
transport oxygen, which is bound to iron-containing hemoglobin
leukocytes (white blood cells)
part of the immune system—attack and destroy invading bacteria thrombocytes (platelets)
the liquid component of blood—mostly salty water antigens
bound to blood cells to identify them as non-foreigncause blood types in the ABO system and the Rh factor system, according to antibodies
attack cells not marked with antigens, destroying them Scholastic Community Outreach Program 2010-2011 Anatomy: Circulation
Version 1.2
Cardiovascular Disorders and Their Treatment_____________________________________
arteriosclerosis
hardening of the arteries by plaque, a fatty deposit atherosclerosis
arteriosclerosis in the coronary arteries myocardial infarction (heart attack)
caused by a blockage of arteries when arteriosclerosis becomes very severe
consists of the destruction of heart tissue, disrupting the electrical signals from
the sinoatrial node (pacemaker), which regulates heartbeat
ventricular fibrillation (V-fib)
the stopping of blood circulation when the heart twitches erratically instead ofbeatingoften the result of very severe myocardial infarctions defibrillation
the application of electrode paddles to the chest, disrupting the irregularsignals of V-fib and restoring normal electrical rhythm a fairly new drug, specific examples of which include Lipitor, Crestor, and Zocor, which lower cholesterol and may even reverse atherosclerosis the event of the brain being cut off from its blood supply, often because of carotid artery blockage, causing brain tissue to die cerebral hemorrhage
the most severe type of stroke, the actual rupture of a brain blood vessel the condition of a reduced capacity to carry oxygen in bloodoften caused by injury-induced blood loss, too little iron intake (causing low hemoglobin production), too little Vitamin B12 intake (also causing low hemoglobin production), radiation poisoning (damages blood marrow, which produces red blood erythrocytes) sickle-cell disease
a recessive genetic disease, most common in people of African descent, causing misshapen (sickle-shaped) erythrocytes that lead to anemiahomozygous persons generally die young; carriers have an immunity to malaria leukemia
a form of cancer in which leukocytes reproduce out of control hemophilia
a condition in which blood clotting is inhibited, causing the sufferer to be unable to stop bleedingoften caused by low Vitamin K intake, or an error in an X-linked factor that codes for clotting factor VIII (this type is very rare in females, but more common in males)carried by and suffered from by many European royal families due to intermarriage and inbreeding, originating with Queen Victoria phlebitis
the converse of hemophilia: clots form in unwanted places, causing capillaries to burst, blocking coronary arteries and leading to heart attacks, blocking cerebral arteries and leading to strokes, etc.
anticoagulants
hemotoxins
poisons, often administered by rattlesnakes, vipers, and some spiders, that destroy blood cells to prevent the movement of oxygen and carbon dioxide a blood clot that has become free in the circulatory system embolism
the event of an embolus becoming lodged in capillaries, causing a blockage and buildup of pressure followed by a vessel bursting aneurysm
the weakening of an artery’s wall, causing it to bulge out and often leading to a rupture Scholastic Community Outreach Program 2010-2011

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