BSC 2086 1st Edition Lecture 12 Outline of Last Lecture I Introduction to Blood Vessels and Circulation II Structure of Blood Vessels III Arteries IV Capillaries Outline of Current Lecture I Capillaries Continued II Veins III Blood Distribution in Vessels IV Pressure and Resistance V Arterial Blood Pressure VI Venous Pressure and Return VII Capillary Pressures Current Lecture I Capillaries Continued a Thoroughfare Capillaries i Direct capillary connections between the arterioles and the venules ii Controlled by metarterioles smooth muscle segments b Collaterals i Multiple arteries contributing to one capillary bed ii Allows circulation if one artery is blocked prevents too much damage iii Arterial anastomosis 1 Union of 2 collateral arteries iv Arteriovenous anastomoses 1 Direct connectors of arterioles and venules which bypass the capillary bed II III IV c Angiogenesis i The making of new blood vessels ii VEGF vascular endothelial growth factor iii Location 1 Embryos as tissues and organs develop 2 In response to factors released by hypoxic oxygen starved cells a Very important in cardiac muscle d Vasomotion i Cycle of relaxation and contraction of capillary sphincters ii Allows the blood flow in the capillary beds to constantly change routes Veins a General facts i Collect blood from the capillaries found in tissues and organs ii Take blood back to the heart iii Larger in diameter than arteries but have thinner walls and lower blood pressure b Types of veins i Venules 1 Very small veins that get blood from capillaries ii Medium sized veins 1 Have a thin tunica media and few smooth muscle cells 2 Tunica externa has longitudinal bundles of elastic fibers iii Large veins 1 Have all 3 tunica layers 2 Thick tunica externa and thin tunica media c Venous valves i Folds of the tunica intima that prevent blood from flowing backwards ii Compression pushes the blood towards the heart Blood Distribution in Blood Vessels a 30 35 of blood volume found in heart arteries and capillaries b 60 65 of blood volume found in venous system i 1 3 of this blood is found in large venous networks of liver bone marrow and skin c Capacitance of a blood vessel i Relationship between blood volume in a vessel and blood pressure ii Capacitance vessels veins stretch more than arteries iii High capacitance expands easily at low pressure like a rubber balloon iv Low capacitance expands only with high pressure like a tire d Blood loss response of veins i Sympathetic nerves stimulated by vasomotor centers 1 Venoconstriction systemic veins contrict 2 Veins found in liver skin and lungs redistribute venous reserve a Venous reserve 20 of total blood volume Pressure and Resistance a Total capillary blood blow i Cardiac output ii Determined by pressure and resistance b Pressure P i Generated to overcome resistance R ii Pressure Gradient P difference between pressure at one end of vessel to another end 1 Circulatory pressure 2 More important than absolute pressure c Flow F i Proportional to the pressure gradient ii Divided by R d Measuring Pressure i Blood pressure BP 1 Pressure in arteries mm Hg ii Capillary hydrostatic pressure CHP 1 Pressure within capillary beds iii Venous pressure 1 Pressure in veins e Circulatory pressure i P across the systemic circuit 1 About 100 mmHg ii Must overcome total peripheral resistance R of entire cardiovascular system 1 Total peripheral resistance due to a Vascular resistance i Friction between blood and vessel walls ii Depends on length and diameter of vessel 1 Vessel length Is constant in adults angiogenesis does not normally occur in adults except in those with cancer 2 Diameter varies by vasodilation and vasoconstriction 3 R increases exponentially as diameter decreases because the greater the diameter the less blood coming into contact with the vessel walls therefore the less friction b Viscosity i R caused by molecules and materials suspended in liquid ii Blood viscosity is 4x that of water iii Can be affected by anemia polycythemia c Turbulence V VI i Swirling action that will disrupt the flow of liquids ii Occurs in the great vessels and the heart chambers iii Will hardly occur in small vessels unless their walls are damaged 1 Atherosclerotic plaques f Relationships of Blood Circulation i Flow is directly proportional to blood pressure BP and inversely proportional to peripheral resistance PR ii Resistance is inversely proportional to the 4th power of the vessel radius Arterial Blood Pressure a Systolic pressure vs Diastolic Pressure i Systolic peak arterial pressure during systole ii Diastolic minimum arterial pressure 1 Although there is no force pushing from the ventricles there is still pressure due to the vena cava and aorta being elastic arteries In order to return to original shape they squeeze remaining blood and use their pressure reservoir a This is the reason why the diastolic pressure doesn t drop to zero iii Pulse pressure difference between systolic and diastolic pressures iv Mean arterial pressure MAP 1 MAP diastolic pressure 1 3 pulse pressure a Example if BP is 120 90 then i MAP 90 1 3 120 90 100 mmHg b Abnormal BP i Normal 120 80 systolic pressure diastolic pressure ii Hypertension greater than 140 90 1 Abnormally high BP iii Hypotension is abnormally low BP 1 Usually caused by overly aggressive drug treatment of hypertension c Elastic rebound i Arterial walls stretch during systole and rebound during diastole ii Allows blood to keep flowing during diastole d Pressure in small arteries and arterioles i Pressure and distance relationship 1 MAP and pulse pressure decrease as the vessel gets farther from the heart 2 BP decreases with friction 3 Pulse pressure decreases due to elastic rebound Venous Pressure and Return a Indicator of how much blood will arrive at the atrium each minute b Low effective pressure in the venous system c Low resistance due to VII i Muscular compression of peripheral veins 1 Blood pushed towards heart by skeletal muscle compression a One way valves ii Respiratory pump 1 Action of the thoracic cavity 2 Inhaling decreases the thoracic pressure a Pulls air into lungs and the blood into the inferior vena cava 3 Exhaling increases thoracic pressure a Venous blood pushed into right atrium Capillary Pressures a Vital to homeostasis b Materials move across the capillary walls by i Diffusion movement of ions or particles from high concentration to low concentration along a concentration gradient 1 Extra energy not needed 2 Routes a Water ions
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