Chapter 17
Cardiovascular System: The Heart
By Boundless
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The heart is an organ responsible for pumping blood through the blood vessels using rhythmic contractions of cardiac muscle.
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The pericardium is a thick, membranous, fluid-filled sac which encloses, protects, and nourishes the heart.
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The heart wall is comprised of three layers: the outer epicardium, the middle myocardium, and the inner endocardium.
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The heart has four chambers. The two atria receive blood into the heart and the two ventricles pump blood into circulation.
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Great vessels are the major vessels which directly carry blood into or out of the heart.
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The myocardium (cardiac muscle) is the thickest section of the heart wall and contains cardiomyocytes, the contractile cells of the heart.
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The cardiac skeleton, also known the heart's fibrous skeleton, consists of dense connective tissue in the heart that separates the atria from the ventricles.
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Coronary circulation is the circulation of blood in the blood vessels of the heart.
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The atrioventricular valves separate the atria from the ventricles and prevent backflow from the ventricles into the atria during systole.
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The semilunar valves allow blood to be pumped into the major arteries, but prevent backflow of blood from the arteries into the ventricles.
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The cardiovascular system has two distinct circulatory paths, pulmonary circulation and systemic circulation.
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Cardiac muscle appears striated due to the presence of sarcomeres, the highly-organized basic functional unit of muscle tissue.
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Cardiac muscle fibers undergo coordinated contraction via calcium-induced calcium release conducted through the intercalated discs.
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Cardiac cells contain numerous mitochondria, which enable continuous aerobic respiration and production of adenosine triphosphate (ATP) for cardiac function.
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Cardiac contraction is initiated in the excitable cells of the sinoatrial (SA) node by both spontaneous depolarization and sympathetic activity.
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An electrocardiogram, or ECG, is a recording of the heart's electrical activity as a graph over a period of time.
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The two major heart sounds are "lub" (from the closure of AV valves) and "dub: (from the closure of aortic and pulmonary valves).
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The cardiac cycle describes the heart's phases of contraction and relaxation that drive blood flow throughout the body.
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Cardiac output (Q or CO) is the volume of blood pumped by the heart, in particular by the left or right ventricle, in one minute.