Vascular System - portal systems in the body where blood...

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Vascular System Circulatory Routes The right side of the heart pumps blood through the pulmonary trunk and arteries to the lungs where gas exchange occurs. This is known as the pulmonary circuit. In contrast, the left side of the heart pumps blood through the aorta to the head, arms, organs and legs of the body. This is the systemic circuit. (See Figure 1). While the amount of blood flowing through the pulmonary circuit remains fairly constant, blood flow through the organs, muscles and brain can vary dependent upon use. The systemic circuits are actually parallel pathways; blood can "choose" a particular branch, flow through that organ, and then head back to the heart. Blood flow through the various pathways is dynamic and may change to accommodate metabolic changes. For instance, during exercise the amount of blood directed to the digestive organs decreases while the amount of blood to the skeletal muscles increases. While the usual systemic pathway of blood is artery --> capillary bed --> vein, there are several
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Unformatted text preview: portal systems in the body where blood flows from an artery --> capillary bed (where it picks up nutrients or hormones ) --> portal vein --> capillary bed (where it drops off nutrients or hormones) --> vein. (See Figure 2). The Vessel Wall As with most internal organs, the blood vessels have an outer connective tissue layer, the tunica externa, a middle smooth muscle layer, the tunica media, and an internal endothelial layer, the tunica intima . The tunica intima is very smooth to keep blood flowing without turbulence and coated with prostacyclins to repel platelets. The relative thickness of these layers in the arteries and veins varies dependent upon their distance from the heart; generally, the layers are thinner at greater distances from the heart. The thinnest blood vessels, containing only a single layer of endothelial tissue and a basement membrane , are the capillaries. It is at the level of the capillaries that all solute exchange takes place....
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