BIOLOGY Volume 2 - A Guide to General Biology - 2004

14. TRANSPORT IN ANIMALS

14.5. Blood vessels

14.5.3. Arterioles

Blood flows from the Arteries into smaller vessels known as arterioles. Their walls consist solely of an endothelium surrounded at regular intervals by rings of smooth Muscle Cells. Just before branching into capillaries, many arterioles are equipped with sphincters (Fig. 14.5). These are circular Muscles that contract to shut off blood flow into the capillary network. In certain Regions of the body, There are also arteriovenous anastomoses, which act as shunts between arterioles and venules, serving to regulate the volume of blood flowing through the capillary beds in accordance with the body's physiological needs.

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Fig. 14.5. Alternative pathways of blood flow between an arteriole, a capillary bed, and a venule.



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