BIOL 2312 Chapter 49: The Circulatory System pt 2
14 Sep 2017
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5:02 pm: 49. 5- characteristics of blood vessels: Blood leave heart---> arteries--->arterioles---> capillaries---> venules ---> veins---> heart. Larger vessels have 4 tissue layers: inner to outer: Capillaries only have endothelium to allow gas exchange. Arteries and arterioles have evolved to withstand pressure: more elastic fibers, more smooth muscle. But s(cid:373)aller arteries have less of elasti(cid:272), they do(cid:374)"t (cid:271)urst (cid:271)e(cid:272)ause of s(cid:373)ooth muscle: less diameter= more frictional resistance. 1/2 the size and increase resistance 16x: vasoconstriction= contract smooth muscle. Capillaries form a vast network for gas exchange of materials. Every cell within in 100 micrometer of a capillary: diameter slighter larger than 1 rbc--- 1 mm long. Rbc flexible enough to squeeze through capillaries: greatest total cross sectional area of all vessels--- goes more slowly and thus more time for exchange. At end of capillary, blood released o2 and nutrients and gain co2 and waste. Blood loses velocity (thus pressure) in arterioles and capillaries, but picks back up in the venous side.
