Like other tissues, a series of systemic vascular flows can be recognized in the biopsy specimens of peritoneal tissue. Specifically, the series is composed of a small artery, arteriole, precapillary arteriole, capillary, postcapillary venule, venule, and small vein.
The small artery has a triple-layered structure including intima that is covered with endothelial cells, media constituting a layer composed of smooth muscle cells, and adven-titia that is composed mainly of collagen and a few fibroblasts. The first two layers are distinguished by the formation of internal elastic lamina; the adventitia, however, is an aggregate of collagen fibers that does not form a membranous structure like an internal elastic lamina. The arteriole is composed of two layers—one of endothelial cells and the other of the media. The latter is made up of one or two layers of smooth muscle cells, but the growth of the elastic lamina is not well developed. The inner vascular diameter is less than 15 mm. The morphological characteristics of the capillary are low muscular volume and composition of only endothelial cells, basement membrane, and a few pericytes that form a reticular periphery; they also lack an intima and media. The inner diameter is less than 10 mm for the capillary. More peripherally located postcapillary venules are of diameter 10 to 30 mm and have a richer loose media component composed of reticular frame lamella and smooth muscle cells. The larger venule and small vein are composed of endothelial, intima that is made up of cells, and smooth muscle cell-based media. The inner diameter is less than 50 mm for venules and 100 mm for small veins.
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This ebook provides an introductory explanation of the workings of the human body, with an effort to draw connections between the body systems and explain their interdependencies. A framework for the book is homeostasis and how the body maintains balance within each system. This is intended as a first introduction to physiology for a college-level course.