Capillaries - somewhat larger molecules, including some...

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Capillaries Capillaries are actually large multi-channeled structures that perfuse the tissues. Regulation of blood flow through the beds is controlled via thoroughfare channels and precapillary sphincters . (See Figure 9). These structures increase the flexibility of blood flow and perfusion of tissues to accommodate metabolic changes. Figure 9 Types of Capillaries Capillary beds are the only site of solute exchange, but what solutes are exchanged at the level of the tissues and organs varies. Reflecting this difference in function, capillaries have several structures. Continuous capillaries occur in most tissues and the endothelial cells of the walls have tight junctions with small intercellular clefts to allow the passage of most small solutes. Fenestrated capillaries are found primarily in the kidneys and small intestines where absorption of nutrients and filtration of the blood takes place. These fenestrations allow the passage of
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Unformatted text preview: somewhat larger molecules, including some small hormones, drugs and cellular breakdown products. A third type of capillary is a sinusoid capillary, found primarily in the liver, red bone marrow and spleen. These capillaries have extra large fenestrations and allow proteins and blood cells to enter the blood. Mechanisms of Venous Return The pressure in the veins is significantly lower than the arterial pressure that drives blood flow through the vascular system. However, there is a small pressure gradient driving blood towards the heart. Additionally, gravity drains blood from the head and neck and contraction of skeletal muscles (during use) and the diaphragm puts pressure on the veins and moves blood towards the heart. Venous valves prevent backflow of the blood....
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This note was uploaded on 01/30/2012 for the course BSC BSC1085 taught by Professor Sharonsimpson during the Fall '10 term at Broward College.

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