Capillaries definitions Flashcards
Capillaries definitions
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Capillaries Smallest blood vessels, 5-10 micrometers in diameter, facilitating nutrient and gas exchange between blood and tissues. Tunica intima The only layer in capillary walls, consisting of endothelium and a basement membrane, allowing for efficient exchange. Erythrocytes Red blood cells, about 7.5 micrometers in diameter, often travel single file through capillaries. Capillary beds Networks of branched capillaries facilitating microcirculation, fed by arterioles and drained by venules. Continuous capillaries Most common type, least permeable, with tight junctions and small intercellular clefts. Fenestrated capillaries Capillaries with small pores, moderate permeability, found in kidneys and endocrine glands. Sinusoid capillaries Most permeable capillaries with large holes, found in liver and bone marrow, allowing large molecules to pass. Microcirculation Blood flow through capillary beds from terminal arterioles to postcapillary venules. Vascular shunt Structure in mesenteric capillary beds allowing blood to bypass capillaries, consisting of metarteriole and thoroughfare channel. Metarteriole Transitional vessel with precapillary sphincters, part of the vascular shunt controlling blood flow. Thoroughfare channel Continuation of metarteriole without smooth muscle, connecting to postcapillary venule. Precapillary sphincters Smooth muscle rings controlling blood flow into capillary beds, part of metarterioles. Arterioles Small arteries regulating blood flow to capillary beds through vasoconstriction. Postcapillary venules Smallest venules receiving blood from capillary beds, beginning the return to the heart. Endothelium Inner lining of capillaries, forming a barrier for exchange of substances between blood and tissues.
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