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Cardiac chambers, cardiac muscles, cardiac excitation, and factors control the heart.

Abstract:

The heart acts as two separate pumps, right and left sides. Each side of the heart is equipped with two valves. Both ventricles pump the same volume of blood to systemic and pulmonary circulation. The right ventricle pumps blood to pulmonary circulation at low pressure. The left ventricle pumps blood through the systemic circulation at high pressure. Contraction of both atriums is followed by contraction of both ventricles during systole. All four chambers are relaxed during diastole. The heart is supplied by two coronary arteries that arise from the right and left coronary sinuses distal to the aortic valve. The venous system mainly follows the coronary arteries. It drains to the coronary sinus then to the right atrium. The heart is innervated by both sympathetic and parasympathetic fibers. Adrenergic nerves from central sympathetic chain, supply muscle fibers in the atriums and ventricles and the electrical conducting system to produce inotropic and chronotropic effects mediated by ?1-adrenergic receptors. The cardiac muscle cells are striated, branching and interdigitating, contain large number of elongated mitochondria. Cardiac muscle cells are approximately 15µm in diameter and 100 µm in length. It contains intercalated disk which is area where one muscle fiber obits another. The SA node is the normal cardiac pace maker. Impulses generated in the SA node pass through atrial pathway to AV node, through this node to the bundle of His, and through branches of it via the purkinje system to the ventricular muscle. The contraction of the cardiac muscle can not occur unless there is an increase in the cytoplasmic Ca ion concentration. As concentration of Ca ions rise, calcium binds in troponin precipitating contraction. Most important function of the heart is to push blood to different parts of the body by its contraction, this contraction follow the action potential of cardiac cells. In single muscle fiber contraction start just after depolarization and last until about 50 ms after repolarization is completed. Atrial systole starts after the P wave of ECG. Ventricular systole starts near the end of the R wave and ends just after the T wave.