23.1 Arteries, - • since small arteries and arterioles are narrow they provide the greatest resistance to blood flow • arterioles are the main

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4/6/08 1:06 AM Biology141 (Physiology) Page 1 of 2 https://courses.bio.psu.edu/spring2008/biol141/Background%20to%20blood%20vessels2.htm Biology141 (Physiology) M. Whim BLOOD VESSELS . [1]. BACKGROUND. • after leaving the heart the blood flows through arteries arterioles capillaries. • capillaries are very small vessels that join the arterial flow to the venous return of blood to the heart. • blood returns to the heart through capillaries venules veins heart. • the walls of arteries and veins are composed of layers: middle layer is smooth muscle. • arteries and veins have a generally similar structure but some important differences do exist (see below). arteries ; vessels that carry blood from the heart. veins ; carry blood to the heart. capillaries ; connect the smallest arteries to the smallest veins. [2]. ARTERIES.
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Unformatted text preview: • since small arteries and arterioles are narrow they provide the greatest resistance to blood flow . • arterioles are the main site of variable resistance in the systemic circulation. [3]. CAPILLARIES. • the arterial system branches very extensively. • the branching is so great that each cell in the body is no more than 80 micrometers away from a capillary. • the walls of capillaries are only 1 cell thick. • so there is a rapid exchange of material between the blood and the tissues. [4]. VEINS. • the average pressure in veins is low compared to that in the arterial system • veins contain valves (these are not found in arteries). 4/6/08 1:06 AM Biology141 (Physiology) Page 2 of 2 https://courses.bio.psu.edu/spring2008/biol141/Background%20to%20blood%20vessels2.htm...
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This note was uploaded on 04/05/2008 for the course BIOL 141 taught by Professor Viti,janehartwel during the Spring '08 term at Pennsylvania State University, University Park.

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23.1 Arteries, - • since small arteries and arterioles are narrow they provide the greatest resistance to blood flow • arterioles are the main

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