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blood vessels and circulation.docx

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Biological Sciences
Kenneth Welch

Blood Vessels and Circulation The Anatomy of Blood Vessels Structure of vessel walls •Walls of arteries and veins contain three distinct layers •Tunic intima •Tunica media •Tunica externa Differences between arteries and veins •Compared to veins, arteries •Have thicker walls •Have more smooth muscle and elastic fibers •Are more resilient Arteries •Undergo changes in diameter •Vasoconstriction – decreases the size of the lumen •Vasodilation – increases the size of the lumen •Classified as either elastic (conducting) or muscular (distribution) •Small arteries (internal diameter of 30 um or less) are called arterioles Capillaries •An endothelial tube inside a basal lamina •These vessels •Form networks •Surround muscle fibers •Radiate through connective tissue •Weave throughout active tissues •Capillaries have two basic structures •Continuous •Fenestrated •Flattened fenestrated capillaries = sinusoids Capillary Beds •An interconnected network of vessels consisting of •Collateral arteries feeding an arteriole •Metarterioles •Arteriovenous anastomoses •Capillaries •Venules Veins •Collect blood from all tissues and organs and return it to the heart •Are classified according to size •Venules •Medium-sized veins •Large veins Venous Valves •Venules and medium-sized veins contain valves •Prevent backflow of blood Distribution of blood •Total blood volume is unevenly distributed •Venoconstriction maintains blood volume •Veins are capacitance vessels •Capacitance = relationship between blood volume and pressure Cardiovascular Physiology Circulatory Pressure •Circulatory pressure is divided into three components •Blood pressure (BP) •Capillary hydrostatic pressure (CHP) •Venous pressure Resistance (R) •Resistance of the cardiovascular system opposes the movement of blood •For blood to flow, the pressure gradient must overcome total peripheral resistance •Peripheral resistance (PR) is the resistance of the arterial system Overview of Cardiovascular Pressures •Factors involved in cardiovascular pressures include •Vessel diameter •Cross-sectional area of vessels •Blood pressure •Blood viscosity Arterial blood pressure •Arterial blood pressure •Maintains blood flow through capillary beds •Rises during ventricular systole and falls during ventricular diastole •Pulse is a rhythmic pressure oscillation that accompanies each heartbeat •Pulse pressure = difference between systolic and diastolic pressures Mean arterial pressure (MAP) Capillary Exchange •Flow of water and solutes from capillaries to interstitial space •Plasma and interstitial fluid are in constant communication •Assists in the transport of lipids and tissue proteins •Accelerates the distribution of nutrients •Carries toxins and other chemical stimuli to lymphoid tissues Processes that move fluids across capillary walls •Diffusion •Filtration •Hydrostatic pressure (CHP) •Reabsorption Forces acting across capillary walls •Capillary hydrostatic pressure (CHP) •Blood colloid osmotic pressure (BCOP) •Interstitial fluid colloid osmotic pressure (ICOP) •Interstitial fluid hydrostatic pressure (IHP) Filtration and reabsorption •Processes involved in filtration and reabsorption include •Net hydrostatic pressure •CHP - IHP •Net colloid osmotic pressure •BCOP - ICOP Venous pressure and venous return •Assisted by two processes •Muscular compression •The respiratory pump Cardiovascular Regulation •Autoregulation •Neural mechanisms •Endocrine mechanisms Autoregulation of blood flow within tissues •Local vasodilators accelerate blood flow in response to: •Decreased tissue O levels or increased CO levels 2 2 •Generation of lactic acid •Release o+ nitr+c acid •Rising K or H concentrations in interstitial fluid •Local inflammation •Elevated temperature Neural Mechanisms •Adjust CO and PR to maintain vital organ blood flow •Medullary centers of regulatory act
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