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Cardiovascular Systems Distributing gases (O2 & CO2), Food nutrients, Hormones, Immune cells Overview • • • • Types of vascular systems Distribution of types among Animals Structures of closed vs. open systems Structure & function of hearts and vascular tissues – Innervation – Nutrient delivery – Tissue types Gastrovascular Cavities • No specialized exchange area • No distribution system – Diffusion is adequate • Why? • Td ∝ d2 Circulatory Systems • Blood, pumps (hearts) with chambers & valves, vessels • Closed: High BP, blood separate from interstitial fluid • Open: Low BP, blood & interstitial fluid are same Arthropods Molluscs Annelids Cephalopods Vertebrates Single circulation • • • • • Fishes, sharks Atria collects Ventricle pumps Valves prevent backflow Exchange @ gill capillaries & body tissues Double Circulation systems • Amphibians allow mixing. Why is this OK? • Lepidosaurs & Testudinates allow minimal mixing • Mammals & Archosaurs allow none! Why not? Archosaurs Mammalian Circulatory System • Four chambered heart with pacemakers • Thick arteries (away!) • Thin veins (towards!) • Capillary beds at lungs, head, forelimbs, abdomen, hindlimbs Anatomy • Pacemakers: autorhythmic cells in R atrium • Chambers – Atria: Right & Left; blood collector – Ventricles: Right & Left; blood pump • Vessels: Transport – Arteries: Pulmonary (lungs), Aorta (body) – Veins: Vena cava, pulmonary • Valves: Prevent backflow – Atrioventricular (AV): tri- & bicuspid – Semilunar: Pulmonary & aortic Anatomy & Blood Flow Valves prevent backflow • Pressure changes produce flow • Backflow is stifled by semi-lunar valve collapse • During systole, where is blood pressure highest?: – Atria – ventricles – arteries Cardiac cycle produces heart sounds • Cause = forceful closure of valves by high pressure blood • 1st heart sound: lubb – Beginning of systole; results from closure of AV valve • 2nd heart sound: dupp – Beginning of diastole; results from closure of semilunar valves Cardiac cycle • • • • Aorta Left Ventricle Left Atria What is happening when the traces cross? How does coordinated contraction occur? • Nodes: pacemakers – Innervated by neurons of MO • Purkinje fibers: signal propagators • Intercallated discs of cardiac muscle Pacemakers • Sinoatrial (SA) – Depolarize atria; coordinated contraction follows • Atrioventricular (AV) – Depolarize ventricles; purkinje fibers propagate AP; coordinated contraction of ventricles How is tetanus prevented? The Plateau phase deafens myocardia AP differences • Plateau phase: “long”, slow repolarization phase allows complete relaxation of myocardium – Caused by opening of Ca2+ channels in plasma membrane • What does Ca2+ do when those channels open? • Prevents tetanus – Safety mechanism • Without it, what would happen if AP’s arrived too frequently? Blood pressure and Velocity • C.S. Area & Distance from heart • As area increases, velocity & pressure decrease; as area decreases again, velocity increases • As distance increases, pressure decreases Structure reveals function • Arteries – Thick muscle & elastin to constrict arteries & allow stretch & recoil – Thick, elastic CT to allow stretch & recoil and withstand pressure • Veins – Large diameter, thinner-walled, less elastic Structure reveals function Artery layers Structure reveals function • Capillaries – Small diameter – Single endothelial cell layer is smooth, flat & permeable – Allows smooth flow, rapid exchange Mechanism of venous return • If pressure is low in veins, how does blood return to the heart? What is the driving force? • Skeletal muscles • Valves Capillary bed function • Blood flow controlled by sphincter muscles (smooth) that bind hormones – NO causes dilation – Endothelin causes constriction • Regulates: – Heat exchange – Gas exchange (O2 & CO2) – Nutrient delivery & waste removal (glucose & lactate) Multiple effects • Hormones can have multiple, often antagonistic effects – bind to different receptors – Different signal transduction pathways Mechanisms of Capillary Exchange 1. Diffusion – Concentration gradient – Avenues of exchange: between endothelial cells, protein channels, cell membranes, major sinuses – What factors affect diffusion rates?: short _______, steep _______, small _______. 2. Filtration – Hydrostatic pressure – Water and small solutes forced across capillary wall, leaving large solutes & proteins in blood Fluid exchange in capillaries • Blood pressure forces fluid, small solutes & gases out of capillaries • Osmotic pressure (large solutes) draw fluid back into capillaries