Overview Every organism must exchange materials with its environment Exchanges ultimately occur at the cellular level In unicellular organisms these exchanges occur directly with the environment For most cells making up multicellular organisms direct exchange with the environment is not possible Gills are an example of a specialized exchange system in animals Internal transport and gas exchange are functionally related in most animals Copyright 2008 Pearson Education Inc publishing as Pearson Benjamin Cummings Concept 42 1 Circulatory systems Open and Closed In small and or thin animals cells can exchange materials directly with the surrounding medium Most complex animals have either open or closed circulatory systems that circulate fluid Both open and closed systems have three basic components 1 A circulatory fluid blood or hemolymph 2 A set of tubes blood vessels 3 A muscular pump the heart Copyright 2008 Pearson Education Inc publishing as Pearson Benjamin Cummings In insects other arthropods and most molluscs blood bathes the organs directly in an open circulatory system In an open circulatory system there is no distinction between blood and interstitial fluid tissue fluid and this general body fluid is more correctly called hemolymph In a closed circulatory system blood is confined to vessels and is distinct from the interstitial fluid Closed systems are more efficient at transporting circulatory fluids to tissues and cells Copyright 2008 Pearson Education Inc publishing as Pearson Benjamin Cummings Fig 42 3 Heart Hemolymph in sinuses surrounding organs Pores Heart Blood Interstitial fluid Small branch vessels In each organ Dorsal vessel main heart Tubular heart a An open circulatory system Auxiliary hearts Ventral vessels b A closed circulatory system Organization of Vertebrate Circulatory Systems Humans and other vertebrates have a closed circulatory system often called the cardiovascular system The 3 main types of blood vessels are arteries veins capillaries Arteries branch into arterioles and carry blood to capillaries Networks of capillaries called capillary beds are the sites of chemical exchange between the blood and interstitial fluid Venules converge into veins and return blood from capillaries to the heart Vertebrate hearts contain two or more chambers where blood enters through atrium is pumped out through ventricle Copyright 2008 Pearson Education Inc publishing as Pearson Benjamin Cummings Closed circulatory system is of 2 types Single Circulation and Double Circulation 1 Single Circulation Bony fishes rays and sharks have single circulation with a two chambered heart In single circulation blood leaving the heart passes through two capillary beds before returning Copyright 2008 Pearson Education Inc publishing as Pearson Benjamin Cummings Single Circulation Gill capillaries Artery Heart Gill circulation Ventricle Atrium Vein Systemic circulation Systemic capillaries 2 Double Circulation Amphibian reptiles and mammals have double circulation Oxygen poor and oxygen rich blood are pumped separately from the right and left sides of the heart In reptiles and mammals oxygen poor blood flows through the pulmonary circuit to pick up oxygen through the lungs Oxygen rich blood delivers oxygen through the systemic circuit Double circulation maintains higher blood pressure in the organs than does single circulation Copyright 2008 Pearson Education Inc publishing as Pearson Benjamin Cummings Fig 42 5 Double Circulation Amphibians Reptiles Except Birds Mammals and Birds Lung and skin capillaries Lung capillaries Lung capillaries Pulmocutaneous circuit Atrium A Right systemic aorta Atrium A Ventricle V Right Systemic circuit Left Systemic capillaries Pulmonary circuit A V Right Pulmonary circuit A A V Left Systemic capillaries Left systemic aorta A V V Right Left Systemic circuit Systemic capillaries Adaptations of Double Circulatory Systems Hearts vary in different vertebrate groups Mammals and birds have a four chambered heart with two atria and two ventricles The left side of the heart pumps and receives only oxygenrich blood while the right side receives and pumps only oxygen poor blood Mammals and birds are endotherms and require more O2 than ectotherms Copyright 2008 Pearson Education Inc publishing as Pearson Benjamin Cummings Concept 42 2 Coordinated cycles of heart contraction drive double circulation in mammals The mammalian cardiovascular system meets the body s continuous demand for O2 Blood begins its flow with the right ventricle pumping blood to the lungs In the lungs the blood loads O2 and unloads CO2 Oxygen rich blood from the lungs enters the heart at the left atrium and is pumped through the aorta to the body tissues by the left ventricle The aorta provides blood to the heart through the coronary arteries Copyright 2008 Pearson Education Inc publishing as Pearson Benjamin Cummings Blood returns to the heart through the superior vena cava blood from head neck and forelimbs and inferior vena cava blood from trunk and hind limbs The superior vena cava and inferior vena cava flow into the right atrium The heart contracts and relaxes in a rhythmic cycle called the cardiac cycle The contraction or pumping phase is called systole The relaxation or filling phase is called diastole Copyright 2008 Pearson Education Inc publishing as Pearson Benjamin Cummings Fig 42 6 Superior vena cava Capillaries of head and forelimbs 7 Pulmonary artery Pulmonary artery Capillaries of right lung Aorta 9 3 Capillaries of left lung 3 2 4 11 Pulmonary vein Right atrium 1 Pulmonary vein 5 Left atrium 10 Right ventricle Left ventricle Inferior vena cava Aorta 8 Capillaries of abdominal organs and hind limbs The heart rate also called the pulse is the number of beats per minute The stroke volume is the amount of blood pumped in a single contraction The cardiac output is the volume of blood pumped into the systemic circulation per minute and depends on both the heart rate and stroke volume Four valves prevent backflow of blood in the heart Copyright 2008 Pearson Education Inc publishing as Pearson Benjamin Cummings Fig 42 7 Pulmonary artery Aorta Pulmonary artery Right atrium Left atrium Semilunar valve Semilunar valve Atrioventricular valve Atrioventricular valve Right ventricle Left ventricle The 2 atrioventricular AV valves separate each atrium and ventricle The 2 semilunar valves control blood flow to the aorta and the pulmonary artery The lub dup sound of a heart beat is caused by