Microcirculation, transport, continuous capillary, fenestrated capillary, discontinuous/sinusoidal capillary, factors affecting PO2

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Biomedical Science
BMS 420
Charles Miller

10 September Vasomotion – waxing and waning of tone of upstream vascular smooth muscle cells Anatomy of the Microcirculation Density of capillaries (vascularization) obviously important for exchange – lung has capillary area of 3,500 cm /g while muscle is about 100 cm /g; tendon – low density Degree of patency varies – 100% heart to 20 – 30% in skeletal muscle and intestines at rest Pericapillary sphincters controlled by local factors Vascular Bed Arterioles: 5 – 25 μm; continuous VSM; innervated (sympathetic); controls capillary Q Metarterioles: discontinuous VSM; short Precapillary sphincter: single band of VSM; usually not innervated; controls capillary Q True capillaries: 2 -5 μm; primarily endothelial cells; thin walled (200 – 300 nm); not innervated Exchange Occurs primarily in capillaries but also in metarterioles (oxygen) and venules (protein) Types of capillaries Continuous Fenestrated – largish pores between cells (kidney, e.g.) Discontinuous Pinocytotic vesicles allow higher weight molecules to move out of blood 4 types of transport: diffusion, bulk flow, vesicular transport, active transport Shared Characteristics Single layer of endothelial cells (.2 μm thick) Clefts or slits at junction of cells Basement membrane beneath EC cells Micro-pinocytotic vessels Continuous Capillary
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