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Unformatted text preview: 1 The Vascular System The Vascular System The Vascular System The Vascular System Aorta c Arteries c Arterioles c Capillaries c Venules c Veins c Venae Cavae Tunics of Blood Vessels Tunics of Blood Vessels Tunics of Blood Vessels Tunics of Blood Vessels 3 tunics/layers (except for capillaries) s Tunic intima : inner layer s endothelium s Tunic media : middle layer s smooth muscle s controlled by sympathetic NS s Tunic externa/Adventitia s outer layer s fibrous connective tissue s Elastic tissue between layers allow stretching of vessel when receiving blood Arteries and Arteries and Arterioles Arterioles s Arteries = carry blood away from the heart s large arteries are more elastic than smaller arteries to withstand stronger BP s medium arteries (distributing arteries ) have more smooth muscles than large arteries (which facilitate blood flow) s Arterioles = smaller arteries s have all 3 layers s get thinner as they divide s Metarterioles s branches of arterioles s form arteriovenous shunts Veins and Venules Veins and Venules s Veins= carry blood to the heart s same 3 tunics as arteries s walls are thinner s lumen is wider s large veins have valves s Venules s smaller veins that join capillaries to veins 2 Movement of Blood Movement of Blood s Arterial blood is moved by pressure from the heart’s pumping action s Veins use the “milking” action of skeletal muscles to move blood upwards s One-way valves prevent blood backflow s Pressure changes during breathing aids in the venous return s flattening of the diaphragm during inhalation puts pressure on the abdominal veins s Arteries and Veins Capillaries Capillaries s Very small thin vessels made of 1-layer of endothelial cells and a basement membrane s No smooth muscle middle tunic s Primary site of exchange of fluid, electrolytes & gases between the blood and tissue cells Capillary Beds Capillary Beds s Interweaving networks capillaries s Microcirculation = flow of blood arteriole f capillary f venule s Arteriovenous/Vascular shunt s directly connects an arteriole to a venule at opposite ends s True capillaries s actual exchange vessels s Precapillary sphincters s control blood entry into true capillaries Types of Capillaries Types of Capillaries s Continuous capillaries s intercellular clefts f lowest permeability s only small molecules can pass through s found in muscle, skin, lung & CNS (with tight junctions) s Fenestrated capillaries s pores in the endothelium f medium permeability s medium molecules can pass though s found in endocrine glands, kidneys & intestines s Sinusoidal/ Discontinuous capillaries : s large intercellular gaps f highest permeability s large molecules, proteins & blood cells, can pass through s found in the liver, spleen & bone marrow Capillary Exchange Mechanisms Capillary Exchange Mechanisms s Direct diffusion: s for lipid-soluble substances s e.g. O 2 and CO 2 s Vesicular exchange: s endocytosis/exocytosis s for lipid-insoluble substances s Intercellular cleft s Fenestration...
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This note was uploaded on 05/04/2008 for the course HP 320 taught by Professor Islam during the Spring '08 term at USC.
- Spring '08