Chapter 42 Circulation and Gas Exchange Circulatory systems link Exchange Surfaces with Cells Throughout the Body 2 solutions to exchange of nutrients and wastes o Body shape and size to keep many all cells in contact with the environment Cnidarians flatworms o Circulatory system that moves fluid between cells and area of exchange Gastrovascular cavities animals that lack circulatory system o Central gastrovascular cavity distributes substances and digests materials o Fluid bathes cells inside cavity and on outside of organism Organism only 2 cells thick so nutrients can easily diffuse Flatworms have a flat body and gastrovascular cavity Evolutionary variation in circulatory system o Organisms with many cell layers cannot rely on diffusion alone for nutrient waste exchange o General properties of a circulatory system Circulatory fluid Interconnecting vessels Heart muscular pump Connects body cells to organs that exchange gases absorb nutrients and dispose of wastes o Number of circuits in body varies o Differently structured organized pumps o Either open or closed Open circulatory system fluid bathes organs directly Hemolymph circulatory fluid interstitial fluid Heart pumps hemolymph through vessels into interconnected sinuses space between organs Chemical exchange occurs between cells and hemolymph Heart relaxation draws the hemolymph in through valved pores Body movements also squeeze sinuses Arthropods and most mollusks o Larger crustaceans have more extensive vessel system and an accessory Closed circulatory system circulatory fluid blood conferred to vessels and distinct from interstitial fluid Heart pump blood into large branched vessels Chemical exchange between blood and interstitial fluid then to cells Annelids cephalopods and all vertebrates pump Advantages Closed High hydrostatic pressure good for O2 and nutrient deliver to cells in large and active animals Help regulate distribution of blood to organs Open Low hydrostatic pressure Less energy expenditure Origin of Vertebrate circulatory Systems o Cardiovascular system closed circulatory system of vertebrates Blood circuits to and from heart in vessels o Arteries away from heart to organs Heart of vertebrates Branch into arterioles small blood vessels that carry blood to capillaries within organs Capillaries microscopic vessels with thin porous walls Capillary beds networks of capillaries that infiltrate every tissue Allows for exchange between blood and interstitial fluid Capillaries converge into venules which converge into veins o Veins carry blood back from capillaries to the heart o 2 or more chambers o Atria atrium chambers that receive blood entering the heart o Ventricles pump blood out of the heart o Single circulation heart made of 2 chambers atrium and ventricle blood passes through heart 1 time in each complete circuit Blood enters the heart and is pumped to gills co collect O2 and remove CO2 then to capillary beds then back to the heart Blood pressure drops significantly as blood passes through capillary beds Happens twice per line through heart Muscle contraction helps speed circulation Bony fishes rays and sharks o Double circulation 2 lines through heart per circuit Pulmonary circuit right side of heart pumps blood to gas exchange to get O2 and remove CO2 and back to heart Called pulmocutaneous circuit if capillaries are in lungs and skin Systemic circuit left side pumps blood to capillary beds in organs and Higher blood pressure because it only goes through capillary bets 1 time per amphibian Lungs in mammals reptiles tissues and back to heart pump Pressure higher in systemic circuit deoxygenated blood Amphibians have 2 atria and 1 ventricle so oxygenated blood mixes with Reptiles have incomplete septum divides ventricle into 2sort of chambers Has a right systemic aorta to shift blood away from lungs when swimming underwater Mammals and birds have a 4 chambered heart Result of convergent evolution Coordinated cycles of Heart Contraction drives double circulation in mammals The heart o Fist sized behind the sternum o Mostly cardiac muscle o Atria have thin walls o Blood enters when the heart muscles relax o Ventricles have thicker walls and contract more forcibly exp left ventricle sends to all body organs Both pump same volume of blood with each contraction Cardiac cycle 1 sequence of pumping and filling o Systole contraction phase o Cardiac output volume of blood each ventricle pumps per minute 5 L min o Heart rate rate of contraction bpm average resting 72 o Stroke volume amount of blood pumped by a ventricle in 1 contraction average o Diastole relaxation phase 70 mL 4 valves keep blood flowing unidirectional o Atrioventricular AV valve between atrium and ventricle Keep blood from flowing back to the atria o Semilunar valves at the exits of the heart Where the aorta leaves the left ventricle Where the pulmonary artery leaves the right ventricle o Pushed open by pressure of contraction o heart murmur if blood goes backward through a defective valve Maintaining heart beat o Originates in the heart itself o Some auto rhythmic contract and relax without any signal from nervous system o Sinoatrial SA node pacemaker collection of auto rhythmical cells near where superior vena cava enters heart that sets the rate and timing at which all cardiac muscle cells contract Generates impulse much like nerve cells Gap junctions connecting cardiac muscle cells SA pulses spread rapidly cause atria to contract in unison Also generate currents that go to the skin that can be recorded by an electrocardiogram EKG SA reach atrioventricular AV node in the wall between the right and left atria Signals delayed so atria can empty into ventricles Signals from AV node conducted to heart apex and throughout ventricular walls by bundle branches and Purkinje fibers specialized muscle fibers o Altering heart tempo by physiological cues Sympathetic nervous system speeds up pacemaker Parasympathetic slows down pacemaker Hormones can increase decrease Body temperature increases heart rate vessels Patterns of blood pressure and flow reflect the structure and arrangement of blood Blood vessel structure and function o Central cavity lumen lined with endothelium single layer of flattened epithelial cells Smooth to minimize resistance to blood flow Surrounded by different tissues based on the type of vessel o Capillaries smallest diameter barely bigger than a blood cell 7 micrometers 10 micrometers Thin walls of endothelium and its basal
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