Transcript Chapter 22
Chapter 22: Circulation Copyright 2005 McGraw-Hill Australia Pty Ltd PPTs t/a Biology: An Australian focus 3e by Knox, Ladiges, Evans and Saint 22-1 Circulatory systems • Circulatory systems have a variety of functions – transport gases, nutrients, wastes, hormones and other substances in the body – redistribute heat in the body – immune response • Circulatory systems may be – open circulated fluid is indistinguishable from interstitial fluid – closed circulated fluid is separated from interstitial fluid Copyright 2005 McGraw-Hill Australia Pty Ltd PPTs t/a Biology: An Australian focus 3e by Knox, Ladiges, Evans and Saint 22-2 Open and closed systems • Open systems occur in invertebrates such as crustaceans (crabs, prawns) and most molluscs (snails, oysters) – blood or haemolymph passes from heart through vessels that open into interstitial spaces between cells – drains into sinuses and moves back to heart • Closed systems occur in vertebrates, cephalopod molluscs (squid, octopus) and annelid worms – blood or haemolymph passes through body in a system of vessels in a defined circuit Copyright 2005 McGraw-Hill Australia Pty Ltd PPTs t/a Biology: An Australian focus 3e by Knox, Ladiges, Evans and Saint 22-3 Vertebrate circulatory system • • Pattern of evolution of circulatory systems in vertebrates Reduction in number of major arteries – loss of arteries associated with gills in terrestrial vertebrates • Change in pattern of blood flow through heart – single circuit in fish – double circuit in vertebrates with lungs Copyright 2005 McGraw-Hill Australia Pty Ltd PPTs t/a Biology: An Australian focus 3e by Knox, Ladiges, Evans and Saint 22-4 Fig. 22.4a: Patterns of circulation Copyright 2005 McGraw-Hill Australia Pty Ltd PPTs t/a Biology: An Australian focus 3e by Knox, Ladiges, Evans and Saint 22-5 Fig. 22.4b: Patterns of circulation Copyright 2005 McGraw-Hill Australia Pty Ltd PPTs t/a Biology: An Australian focus 3e by Knox, Ladiges, Evans and Saint 22-6 Fig. 22.4c: Patterns of circulation Copyright 2005 McGraw-Hill Australia Pty Ltd PPTs t/a Biology: An Australian focus 3e by Knox, Ladiges, Evans and Saint 22-7 Fig. 22.4d: Patterns of circulation Copyright 2005 McGraw-Hill Australia Pty Ltd PPTs t/a Biology: An Australian focus 3e by Knox, Ladiges, Evans and Saint 22-8 Fig. 22.4e: Patterns of circulation Copyright 2005 McGraw-Hill Australia Pty Ltd PPTs t/a Biology: An Australian focus 3e by Knox, Ladiges, Evans and Saint 22-9 Fish • Heart with four chambers in line blood from body sinus venosus atrium ventricle conus arteriosus gills body • • Blood passes through the heart once in each circuit Blood pressure is highest in the gills Copyright 2005 McGraw-Hill Australia Pty Ltd PPTs t/a Biology: An Australian focus 3e by Knox, Ladiges, Evans and Saint 22-10 Amphibians • Heart with two atria and one ventricle – ventricle receives oxygenated and deoxygenated blood from left and right atria respectively – mixing minimised by folds of tissue in ventricle and conus arteriosus • Blood passes through the heart twice in each circuit – pulmonary (lung) circuit includes skin, which is also used as a respiratory surface – systemic circuit passes through rest of body Copyright 2005 McGraw-Hill Australia Pty Ltd PPTs t/a Biology: An Australian focus 3e by Knox, Ladiges, Evans and Saint 22-11 Reptiles • In most reptiles, the heart has two atria and one ventricle – ventricle partly divided into three chambers by folds of tissue – during systole (contraction) folds press against ventricle wall, preventing cross-flow • Crocodiles have completely divided ventricles – left and right aorta arise from different chambers, potentially allowing deoxygenated blood to recirculate – valves between the two arteries operate under certain conditions Copyright 2005 McGraw-Hill Australia Pty Ltd PPTs t/a Biology: An Australian focus 3e by Knox, Ladiges, Evans and Saint 22-12 Birds and mammals • Heart with four chambers • Complete separation of pulmonary and systemic circulations – blood passes through heart twice in one circuit through the body – oxygenated blood from lungs and deoxygenated blood do not mix in heart or blood vessels • Coronary circulation supplies heart with blood Copyright 2005 McGraw-Hill Australia Pty Ltd PPTs t/a Biology: An Australian focus 3e by Knox, Ladiges, Evans and Saint 22-13 Pulmonary circuit • Deoxygenated blood enters right atrium and passes into right ventricle – tricuspid valve prevents backflow • From right ventricle, blood enters pulmonary artery – semilunar valve prevents backflow • • Blood is oxygenated in capillaries of lung alveoli Oxygenated blood returns to heart (left atrium) via pulmonary vein Copyright 2005 McGraw-Hill Australia Pty Ltd PPTs t/a Biology: An Australian focus 3e by Knox, Ladiges, Evans and Saint 22-14 Systemic circuit • Oxygenated blood enters left atrium and passes into left ventricle – mitral valve prevents backflow • From left ventricle, blood enters aorta – aortic semilunar valve prevents backflow • • Blood is deoxygenated in capillary beds of body Deoxygenated blood returns to heart (right atrium) via vena cavae Copyright 2005 McGraw-Hill Australia Pty Ltd PPTs t/a Biology: An Australian focus 3e by Knox, Ladiges, Evans and Saint 22-15 Fig. 22.9a: Circulation through mammal heart during ventricular diastole Copyright 2005 McGraw-Hill Australia Pty Ltd PPTs t/a Biology: An Australian focus 3e by Knox, Ladiges, Evans and Saint 22-16 Fig. 22.9b: Circulation through mammal heart during ventricular systole Copyright 2005 McGraw-Hill Australia Pty Ltd PPTs t/a Biology: An Australian focus 3e by Knox, Ladiges, Evans and Saint 22-17 Electrical activity • Vertebrate heartbeat is myogenic – originates in heart muscle • Muscle fibres contract independently – must be coordinated to provide a functional heartbeat • Heartbeat cycle initiated by sinoatrial node (pacemaker) – non-contractile cells with rhythmic electrical activity (cont.) Copyright 2005 McGraw-Hill Australia Pty Ltd PPTs t/a Biology: An Australian focus 3e by Knox, Ladiges, Evans and Saint 22-18 Electrical activity (cont.) • Action potential from sinoatrial node transmitted through heart at c. 30 cms-1 – atria contract and shunt blood into ventricles • Ventricles are insulated from the action potential by non-conducting tissue layer – only atrioventricular node (AV) is uninsulated • Action potential passes from AV node through atrioventricular bundle (bundle of His) at c. 1500 cms-1 – Purkinje fibres throughout ventricles ensure contraction is coordinated Copyright 2005 McGraw-Hill Australia Pty Ltd PPTs t/a Biology: An Australian focus 3e by Knox, Ladiges, Evans and Saint 22-19 Blood vessels: arteries • • • A network of tubular vessels carries blood in one direction around the body Thick-walled arteries carry blood from the heart Elastin in artery wall maintains a more even blood pressure – when heart contracts (systole), pressure expands walls of arteries – expansion limited by outer layer of collagen – when heart relaxes (diastole), artery walls return to normal state, assisting in maintaining blood pressure Copyright 2005 McGraw-Hill Australia Pty Ltd PPTs t/a Biology: An Australian focus 3e by Knox, Ladiges, Evans and Saint 22-20 Blood vessels: veins • Veins return blood to the heart • Walls of veins are thinner than those of arteries – pressure lower once blood has passed across capillary beds • Blood circulates in veins through local muscular compression – valves prevent backflow Copyright 2005 McGraw-Hill Australia Pty Ltd PPTs t/a Biology: An Australian focus 3e by Knox, Ladiges, Evans and Saint 22-21 Fig. 22.13: Arteries and veins Copyright 2005 McGraw-Hill Australia Pty Ltd PPTs t/a Biology: An Australian focus 3e by Knox, Ladiges, Evans and Saint 22-22 Microcirculation • • • Smallest blood vessels connecting arterial and venous system Arterioles and metarterioles have smooth muscle in vessel wall Capillaries are composed of a single layer of endothelial cells – precapillary sphincters control blood flow into capillaries • Venules are composed of a single layer of endothelial cells surrounded by collagen Copyright 2005 McGraw-Hill Australia Pty Ltd PPTs t/a Biology: An Australian focus 3e by Knox, Ladiges, Evans and Saint 22-23 Capillary exchange • Material is exchanged across capillary walls principally by diffusion – O2, CO2, glucose, urea • Larger molecules and lipid-insoluble materials pass across capillary walls by pinocytosis – materials enclosed in vesicles, which transport them through the cell • Pressurised fluid is forced through discontinuities and fenestrae between the cells in the process of filtration Copyright 2005 McGraw-Hill Australia Pty Ltd PPTs t/a Biology: An Australian focus 3e by Knox, Ladiges, Evans and Saint 22-24 Filtration • Fenestrated and discontinuous capillary walls occur in regions that require rapid transport of fluid – kidney glomerulus, endocrine glands etc. • • Molecules up to 4 nm pass through Materials in filtrate taken up by other cells – most of remaining fluid reabsorbed into capillaries by osmosis – removed by lymphatic system Copyright 2005 McGraw-Hill Australia Pty Ltd PPTs t/a Biology: An Australian focus 3e by Knox, Ladiges, Evans and Saint 22-25 Lymphatics • • • Lymphatic capillaries are blind-ended channels that collect interstitial fluid Lymph passes through lymph nodes before entering venous system Lymphatic system – – – – removes ‘leaked’ proteins from extracellular fluid transports lipids transports liver products important in immunity Copyright 2005 McGraw-Hill Australia Pty Ltd PPTs t/a Biology: An Australian focus 3e by Knox, Ladiges, Evans and Saint 22-26 Regulation of blood flow • Rate of blood flow depends on blood pressure and resistance to blood flow through vessels – smaller vessels have higher resistance than larger vessels • • Cardiac output measured as volume of blood that passes through left ventricle every minute (in mammals and birds) Changes in cardiac output respond to changes in arteriole diameter to regulate blood flow Copyright 2005 McGraw-Hill Australia Pty Ltd PPTs t/a Biology: An Australian focus 3e by Knox, Ladiges, Evans and Saint 22-27 Cardiovascular regulation • • • Vertebrates regulate blood flow through a negative feedback system Receptors provide information on flow Baroreceptors – stretch receptors monitoring distension of vessels • Chemoreceptors – respond to changes in O2, CO2, pH (cont.) Copyright 2005 McGraw-Hill Australia Pty Ltd PPTs t/a Biology: An Australian focus 3e by Knox, Ladiges, Evans and Saint 22-28 Cardiovascular regulation (cont.) • Vasomotor and cardiac centres in the brain stem integrate information from baroreceptors – changes contraction of smooth muscle of arteriole walls – changes rate and force of heart beat • Respiratory and cardiovascular centres in the brain stem integrate information from chemoreceptors – changes in pattern of respiration (cont.) Copyright 2005 McGraw-Hill Australia Pty Ltd PPTs t/a Biology: An Australian focus 3e by Knox, Ladiges, Evans and Saint 22-29 Cardiovascular regulation (cont.) • Hormones also affect blood flow • Adrenaline – produced by adrenal glands – increases heart beat, constricts arterioles • Vasopressin – produced by anterior pituitary gland – causes vasoconstriction • Angiotensin – produced in blood in response to kidney hormone renin – causes vasoconstriction Copyright 2005 McGraw-Hill Australia Pty Ltd PPTs t/a Biology: An Australian focus 3e by Knox, Ladiges, Evans and Saint 22-30 Regulation of blood flow • • Precapillary sphincters regulate blood flow through capillaries Tone (degree of contraction) is controlled intrinsically (autoregulation) or extrinsically – intrinsic regulation stretched walls of capillary change in metabolite concentrations change in concentrations of other vasoactive substances – extrinsic control nerves hormones Copyright 2005 McGraw-Hill Australia Pty Ltd PPTs t/a Biology: An Australian focus 3e by Knox, Ladiges, Evans and Saint 22-31 Blood • Functions of blood – transports respiratory gases, nutrients, hormones, waste products – immunity – water balance – temperature regulation • Blood consists of plasma and cellular material (cells and fragments of cells) (cont.) Copyright 2005 McGraw-Hill Australia Pty Ltd PPTs t/a Biology: An Australian focus 3e by Knox, Ladiges, Evans and Saint 22-32 Blood (cont.) • Plasma – 55 to 60 per cent of blood volume – fluid containing albumins, globulins and other proteins • Cells – – – – 40 to 45 per cent of blood volume (haematocrit) erythrocytes (red blood cells) leucocytes (white blood cells) thrombocytes (platelets) Copyright 2005 McGraw-Hill Australia Pty Ltd PPTs t/a Biology: An Australian focus 3e by Knox, Ladiges, Evans and Saint 22-33 Erythrocytes • • Red blood cells are biconcave discs, 7 to 8 μm in diameter (in humans) Respiratory pigment haemoglobin carries O2 – O2-carrying capacity of blood depends on type of animal • Formation of erythrocytes in bone marrow is regulated by kidney hormone erythropoietin • Old cells broken down in liver, spleen and bone marrow – amino acids and iron recycled Copyright 2005 McGraw-Hill Australia Pty Ltd PPTs t/a Biology: An Australian focus 3e by Knox, Ladiges, Evans and Saint 22-34 Blood clotting • • Blood exposed to air rapidly forms a clot (thrombus) When blood is exposed, thrombin converts fibrinogen (soluble) to strands of fibrin (insoluble) – network of fibrin traps erythrocytes and platelets • Platelets are also affected by thrombin – become sticky – release ADP to promote linking with fibrinogen – form processes that mesh with other platelets Copyright 2005 McGraw-Hill Australia Pty Ltd PPTs t/a Biology: An Australian focus 3e by Knox, Ladiges, Evans and Saint 22-35