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Ch15 Blood Vessels & Circulation

Ch15 Blood Vessels & Circulation - The Vascular...

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1 The Vascular System The Vascular System Aorta c3down Arteries c3down Arterioles c3down Capillaries c3down Venules c3down Veins c3down Venae Cavae Tunics of Blood Vessels Tunics of Blood Vessels 3 tunics/layers (except for capillaries) square6 Tunic intima : inner layer square6 endothelium square6 Tunic media : middle layer square6 smooth muscle square6 controlled by sympathetic NS square6 Tunic externa/Adventitia square6 outer layer square6 fibrous connective tissue square6 Elastic tissue between layers allow stretching of vessel when receiving blood Arteries and Arterioles square6 Arteries = carry blood away from the heart square6 large arteries are more elastic than smaller arteries to withstand stronger BP square6 medium arteries (distributing arteries ) have more smooth muscles than large arteries (which facilitate blood flow) square6 Arterioles = smaller arteries square6 have all 3 layers square6 get thinner as they divide square6 Metarterioles square6 branches of arterioles square6 form arteriovenous shunts Veins and Venules square6 Veins= carry blood to the heart square6 same 3 tunics as arteries square6 walls are thinner square6 lumen is wider square6 large veins have valves square6 Venules square6 smaller veins that join capillaries to veins
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2 Movement of Blood square6 Arterial blood is moved by pressure from the heart’s pumping action square6 Veins use the “milking” action of skeletal muscles to move blood upwards square6 One-way valves prevent blood backflow square6 Pressure changes during breathing aids in the venous return square6 flattening of the diaphragm during inhalation puts pressure on the abdominal veins square6 Arteries and Veins Capillaries square6 Very small thin vessels made of 1-layer of endothelial cells and a basement membrane square6 No smooth muscle middle tunic square6 Primary site of exchange of fluid, electrolytes & gases between the blood and tissue cells Capillary Beds square6 Interweaving networks capillaries square6 Microcirculation = flow of blood arteriole f4right capillary f4right venule square6 Arteriovenous/Vascular shunt square6 directly connects an arteriole to a venule at opposite ends square6 True capillaries square6 actual exchange vessels square6 Precapillary sphincters square6 control blood entry into true capillaries Types of Capillaries square6 Continuous capillaries square6 intercellular clefts f4right lowest permeability square6 only small molecules can pass through square6 found in muscle, skin, lung & CNS (with tight junctions) square6 Fenestrated capillaries square6 pores in the endothelium f4right medium permeability square6 medium molecules can pass though square6 found in endocrine glands, kidneys & intestines square6 Sinusoidal/ Discontinuous capillaries : square6 large intercellular gaps f4right highest permeability square6 large molecules, proteins & blood cells, can pass through square6 found in the liver, spleen & bone marrow Capillary Exchange Mechanisms square6 Direct diffusion: square6 for lipid-soluble
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