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Circulation and Gas Exchange 1 Gastrovascular cavity allows exchange of nutrients etc. in animals with simple body plans (cnidarians, planarians) Land-dwellers and aquatic animals with multiple layers of cells require an internal transport system Open circulatory system Body fluid= hemolymph 1+ heart(s) pump this fluid throughout the body through spaces between organs (sinuses) Material exchange directly between cells and hemolymph ex: arthropods, mollusks Closed circulatory system Blood contained within specialized vessels; distinct from interstitial fluid Material exchange between blood and interstitial fluid Ex: earthworms, cephalopods (squid and octopus), vertebrates Heart Atria: receiving chambers (like an atrium in a large building) Ventricles: large, muscular chambers that pump blood out of heart Blood and blood vessels Arteries: carry blood out of heart; branch into arterioles and capillaries Beauchemin 2007 Circulation and Gas Exchange 2 Veins: carry blood towards heart; capillaries branch into venules, then veins Circulation patterns (Fig 42.3) Fish: heart with one atrium and one ventricle; gas exchange at gills Amphibians heart with 2 atria and one ventricle double circulation: pulmocutaneous circuit leads to gas exchange in tissues and systemic circuit gets oxygen from capillaries some mixing of O2-rich and O2-poor blood in ventricle Reptiles: also 3-chambered heart, but ventricle is partially divided—this reduces mixing of blood (except— crocodilians have completely divided ventricle) Birds and mammals 2 atria, 2 ventricles double circulation: left side of heart contains O2-rich blood; right side contains O2-poor blood complete separation of blood makes O2 delivery more efficient—advantage to endotherms Atria are small with thin walls; ventricles are much larger with thick, muscular walls Valves maintain unidirectional blood flow Atrioventricular (AV) valves: betw atrium and ventricle; closed when ventricle contracts Beauchemin 2007 Circulation and Gas Exchange 3 Semilunar valves: located at exit points—betw aorta/left ventricle and pulmonary artery/right ventricle; opened when ventricle contracts Heart rate: # of times your heart beats per minute; can be measured by taking your pulse—which is the stretching of the arteries as the heart pumps blood through them Cardiac cycle: consists of contraction phase (systole) and relaxation phase (diastole) Sinoatrial (SA) node: aka. Pacemaker—sets the pace of heartbeat; is able to contract independently of nerve stimulation Heart rate is influenced by several factors, including sympathetic/parasympathetic n.s., exercise, body temperature Three basic tissue layers Outside: elastic connective tissue Middle: smooth muscle and more connective tissue Inside: endothelium—single layer of flattened cells allowing smooth blood flow Capillaries faciliate gas exchange, made of endothelium and basement membrane only Arteries have thicker middle and outer layers to provide strength and elasticity as blood is pumped vigorously through Veins are passageways where blood flows with less speed and pressure; they contain one-way valves directing blood back to heart Beauchemin 2007 Circulation and Gas Exchange 4 Blood flow is far faster in the arteries than in the capillaries because the total diameter of all the capillary vessiles is much smaller than the diameters of the largest arteries (the reverse happens as blood flows from capillariesvenulesveins Blood pressure is the force exerted by blood against vessel walls Blood pressure in veins is not affected by heart; instead, blood is propelled forward by contraction of smooth and skeletal muscles Plasma Liquid solution consisting of 90% water Solutes include electrolytes and plasma proteins Also contains substances being transported within blood, i.e. metabolic wastes, hormones, CO2, O2 Cell components Erythrocytes (red blood cells) Biconcave disc shape No mitochondria (undergoes anaerobic resp. instead) or nuclei Contains hemoglobin, which functions to bind to O2 Leukocytes (white blood cells) Function to fight infection Usually found outside circulatory system in interstitial fluid Platelets Beauchemin 2007 Circulation and Gas Exchange 5 Bits of cells Function in blood clotting Stem cells RBC’s, WBC’s and platelets are formed from stem cells in red bone marrow Negative feedback system triggers RBC production If tissues are not getting enough O2, the hormone erythropoietin is released, stimulating RBC production If tissues are getting more than enough, erythropoietin production is reduced, thus slowing production of RBCs Blood clotting Platelets release clotting factor that converts (inactive) fibrinogen into (active) fibrin Hemophiliacs suffer from an inability to naturally heal wounds and even minor cuts can result in severe bleeding When platelets clump up within a blood vessel they create a thrombus which forms a dangerous barrier to bloodflow. Beauchemin 2007 Circulation and Gas Exchange 6 Beauchemin 2007