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Chambers - Chambers The heart consists of two pumps the...

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Unformatted text preview: Chambers The heart consists of two pumps; the left side of the heart pumps into the systemic circulation while the right side of the heart pumps to the lungs. To control the entry and exit of blood into the two pumps, each side is divided into two chambers: the atria and the ventricles. The atria receive blood returning to the heart via the vena cavae or the pulmonary veins. The ventricles are the pumping chambers and pump blood out of the heart into the aorta or pulmonary arteries. Valves Valves ensure that blood flows one-way through the heart and vessels. There are four valves in the heart, two on each side. The atrioventricular valves control the movement of blood from the atria to the ventricles. The right AV valve has three cusps and is therefore often called the tricuspid valve. The left AV valve has only two cusps and is known as the bicuspid valve. Chordae tendineae stretch from the cusps of the AV valves to papillary muscles on the wall of the ventricles to prevent the cusps from swinging into the atria during ventricular contraction. The semilunar valves, so named because when closed they resemble half moons, control the flow of blood out of the ventricles and into the arteries. The pulmonary semilunar valve is between the right ventricle and the pulmonary artery while the aortic semilunar valve is between the left ventricle and the aorta. The familiar heart sounds heard through a stethoscope are the sounds of the valves closing during each cardiac cycle. (See Figure 4). Figure 4 Cardiac Muscle Cardiac muscle is unique in structure. The cardiomyocytes are short, thick and branched. Internally, they contain few sarcoplasmic reticula and very large T-tubules. This arrangement results in the majority of intracellular calcium needed for muscle contraction coming from the outside of the cell, rather than from the SR (as in skeletal muscle). Furthermore, individual cardiomyocytes are joined end to end through junctions known as intercalated discs. These intercalated discs are formed by desmosomes and gap junctions. ...
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