Chapter 19: Circulation and Short-Term Blood Pressure Regulation19.3: Structure and Function of Blood Vessels- Three primary types of blood vessels:o Arteries: Carries blood away from heart, branching into progressively smaller structureso Capillaries: Serves blood to organs and tissues of the body or lungs. Venules collect blood from capillary networkso Veins: Formed by convergence of venules; returns blood to the heart- Arteries distribute and veins collecto In systematic circulation: Arteries carry oxygenated blood and veins carry deoxygenated bloodo In pulmonary circulation:  Arteries carry deoxygenated blood and vein carry oxygenated blood- Blood Vessels have three layers called tunica:o Tunica intima: deepest layer; innermost portion is endothelium Endothelium creates smooth surface, limiting friction between blood vessel wall and blood flowing within Large arteries have membrane called internal elastic lamina; absent in veinso Tunica media: Circularly arranged smooth muscle fibers intertwined; middle layer Diameter of blood vessel is determined by contraction/relaxation of these smooth muscle fibers Has external elastic lamina Thickest tunico Tunica externa: connective tissue layer of loosely packed, irregularly arranged fibers Functions to stabilize blood vessel by securing it to neighboring tissue; mechanical support Externa of large arteries and veins possess vasa vasorum- System of smaller blood vessels that provide nutrients to larger blood vessels- Elastic arterieso Contains elastic tissue; includes aorta and its principal brancheso Have large lumens to collect large volumes of blood from the heart  Referred to as conducting arteries- Muscular arterieso Have largest tunica media of any blood vessel type; high smooth muscle contento Branch extensively to deliver blood to the arterioles serving organs and tissues Referred to as distributing arteries- Arterioles: Smallest artery typeo Largest arterioles contain all three tunicso Tiniest are simply endothelium surrounded by 1-2 layers of smooth muscle fiberso Often called resistance vessels Refers to arterioles ability to adjust local resistance of blood flowo Autoregulation processes  two categories: Metabolic responses: occur to adjust blood flow based on specific demands of local tissue  e.g. increased NO release during exercise Myogenic responses: occur reflexively within smooth muscle of the tunica mediao Capillaries: smallest blood vessel type; site of material exchange between blood and interstitial fluids Only tunica intima is present in capillaries  thin walls allow for easy diffusion Three types of capillaries:- Continuouso Least permeableo Most common; do not contain pores and are closely joined by tight junctionso Exchange via intercellular clefts of gases, ions, and hormones- Fenestratedo More permeable blood vesselso Endothelial cells are dotted with pores, more readily allowing passage of fluid and larger molecules- Sinusoido Most permeableo Allow movement of entire cells between blood and tissueso Larger fenestrations and has discontinuous basement membrane Typically organized as branching networks of vessels called capillary beds- Precapillary sphincters act as “valves” that allow or let blood bypass capillary beds depending on whether tissue is metabolically active or not- Structure and Function of Veinso Venules are smallest of the vessels carrying blood back towards the heart Have thin walls, but contain all three tunics  Converge to form larger vessels: Veins- Tunica externa is thickest layer- Have larger lumens and thinner walls- Veins hold largest volume of blood (64%)- Experience much lower pressures than arteries- Larger lumens offer less resistance to blood flow- Venous valves ensure unidirectional flow  Varicose Veins: Results from failure of venous valves, resulting in blood to back-up and pool in peripheral veins of legsMore complete lining/joining of endothelial cells19.4: Physiology of Circulation- Blood Flow (F): Volume of blood per unit of time moving through a vessel, tissue, or organ. F = cardiac output (CO)- Blood Pressure (BP or P): Form of hydrostatic pressure; force exerted onto given area of the vessel wall by the blood contained within- Resistance (R): the friction encountered by blood, impeding its flow- Increase blood flow = increase blood pressureo F = (delta P) / R- Three factors influence blood resistance:o Blood viscosityo Blood vessel lengtho Blood vessel radius o Key Points about blood vessel resistance Total peripheral resistance (TPR): Used to describe forces impeding blood flow throughout entire circulation Laminar flow is blood flow where blood moves within the vessel at the same relative velocity- Abrupt changes in diameter can cause turbulent flow, where blood moves with varying relative velocities  Increases resistance  Compliance is a measure of how easily a structure changes volume in response to a change in pressure  blood vessels are compliant- Pulse Pressure = Systolic Blood Pressure – Diastolic Blood Pressure- Mean Arterial Pressure (MAP) = Diastolic Blood Pressure + (Pulse Pressure/3)- Capillary Blood Pressure and Exchange:o Blood flow in capillaries have much slower velocities than in arteries or veins. This control of the amount of blood entering capillaries is a result of the total cross-sectional area- Velocity and cross-sectional area are inversely related Total cross-sectional area of the capillary network is much larger than that of arteries or veinso Filtration: At arterial ends of capillary beds, gradient forces fluid out of the blood and into the interstitial spaceo Reabsorption: At the venous end, gradient favors movement of fluids from the tissues back into the blood Capillary Hydrostatic pressure (CHP): pressure exerted by the blood onto the capillary wall  promotes filtration  declines as blood moves through capillary bed Interstitial fluid hydrostatic pressure (IFHP): acts to oppose filtration, impact is negligible Blood Colloid Osmotic Pressure (BCOP): Force created by particles in blood that cannot diffuse across the capillary wall  pull water towards them  opposes filtration and does not significantly change  Interstitial Fluid Colloid Osmotic Pressure (IFCOP): very low, does not vary across capillary bed Net Filtration Pressure (NFP):- NFP = (CHP + IFCOP) – (IFHP + BCOP)o If positive: filtration occurso If negative: