Physiology : a manual for students and practitioners . Valves of the Heart. these is an elastic layer of fibrous tissue, which has interlaced inits structure muscle-cells. Each artery has its own vasa vasorum,or nutrient vessels, and is usually enmeshed in a plexus of sympa-thetic nerves, vaso-motor nerves. Describe the capillaries. The capillary blood-vessels are channels of very small butvariable size, but usually of about sufficient calibre to just permitthe passage of the red and white corpuscles. They are usuallycomposed of a single layer of endothelial cells joined at the edges,though ne
Physiology : a manual for students and practitioners . Valves of the Heart. these is an elastic layer of fibrous tissue, which has interlaced inits structure muscle-cells. Each artery has its own vasa vasorum,or nutrient vessels, and is usually enmeshed in a plexus of sympa-thetic nerves, vaso-motor nerves. Describe the capillaries. The capillary blood-vessels are channels of very small butvariable size, but usually of about sufficient calibre to just permitthe passage of the red and white corpuscles. They are usuallycomposed of a single layer of endothelial cells joined at the edges,though near the arteries and veins there is sometimes an elasticfibrous coat. A sympathetic nerve-plexus surrounds these capillaries form a complicated network in the tissues, and themesh of the net varies in shape and size greatly with the vascu-larity and function of the tissue. Describe the characteristics of the veins. In structure the veins are similar to the arteries, but much less CIRCULATION OF TlIK 5. 31. Capillary Plexus in a Portion of the Web of a Frogs Foot (magnified 110 diameters): 1,trunk of vein ; 2, 2, 2, its branches; 3, 3, pigmeut-cells. firm and elastic; veins collapse, while arteries remain open whennot distended by blood. Valves occur in most of the veins ; theseare so placed as to prevent the blood from tending to flow back-ward. The valves are so placed as to aid the onward progress ofthe blood in the veins, the pressure of neighboring muscles forcingforward the blood, which cannot regurgitate past the valves. What is the relative area of arteries, capillaries, and veins ? With the divisiuii of the arteries into branches the sectionalarea of the branches is greater than of the stem. Of the veinsthe same is true, while the total sectional area of the capillarysystem is much greater than of either. For of simile thecomparison may be made of two funnels placed base to base. Innumbers one may consider the sectional area of aorta as 1
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Keywords: ., bookcentury1800, bookdecade1890, booksubjectphysiology, bookyear1
