Alimentary Tract Motility
نویسنده
چکیده
Alimentary/Tract/Motility/ 1 SMOOTH MUSCLE Smooth muscle lines the walls of hollow organs (eg. intestine, uterus), the circulatory system (arteries and veins), and ducts of secretory glands. The primary role of smooth muscle is to regulate the diameter of the organ lumen which it surrounds. Although "smooth muscle" is used to categorize muscle components of these various tissues, there is a large degree of heterogeneity with respect to specific physiological responses and pharmacological sensitivities. On the other hand, smooth muscle is characterized by a slow speed of contraction, and an ability to maintain tension for long periods at low energy cost. These functional properties of smooth muscle suit its physiological responsibilities: maintenance of "organ" volume for extended periods (arteries) and slow rhythmic propulsion (intestine, uterus). Most smooth muscles exhibit strong electrical coupling through gap junctions, and only few areas of innervation. Smooth muscle of the cardiovascular system rarely show spontaneous electrical activity, and are primarily activated by agonist gated mechanisms, whereas "visceral" smooth muscles of the gut and uterus demonstrate pontaneous spike discharges which provide regulated propulsive contractions. s
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تاریخ انتشار 2006