Internal Fluids and RespirationChapter 31 Exchanging MaterialsEvery organism must exchange materials with its environment.This exchange ultimately occurs at the cellular level. Exchanging MaterialsIn unicellular organisms these exchanges occur directly with the environment.For most o! the cells ma"ing up multicellular organisms direct exchange with the environment is not possi#le. Circulatory $ystems Re!lect %hylogenyTransport systems !unctionally connect the organs o! exchange with the #ody cells. Inverte#rate CirculationThe wide range o! inverte#rate #ody si&e and !orm is paralleled #y a great diversity in circulatory systems.$imple animals such as cnidarians have a #ody wall only two cells thic" that encloses a gastrovascular cavity.The gastrovascular cavity !unctions in #oth digestion and distri#ution o! su#stances throughout the #ody. 'astrovascular Cavities$ome cnidarians such as (ellies have ela#orate gastrovascular cavities. )pen and Closed Circulatory $ystemsMore complex animals have one o! two types o! circulatory systems* open or closed. )pen and Closed Circulatory $ystems+oth o! these types o! systems have three #asic components*, circulatory !luid -#lood.., set o! tu#es -#lood vessels.., muscular pump -the heart.. )pen Circulatory $ystemIn insects other arthropods and most molluscs #lood -hemolymph. #athes the organs directly in an open circulatory system. Closed Circulatory $ystemIn a closed circulatory system #lood is con!ined to vessels and is distinct !rom the interstitial !luid.Closed systems are more e!!icient at transporting circulatory !luids to tissues and cells. $urvey o! /erte#rate Circulation0umans and other verte#rates have a closed circulatory system called the cardiovascular system.+lood !lows in a closed cardiovascular system consisting o! #lood vessels and a two1 to !our1cham#ered heart. $urvey o! /erte#rate CirculationArteries carry #lood to smaller vessels called arterioles then to the tiny capillaries 1 the sites o! chemical exchange #etween the #lood and interstitial !luid. +lood then !lows !rom capillaries into venules then to larger veins which return #lood to the heart. Fishes, !ish heart has two main cham#ers*)ne ventricle and one atrium.+lood pumped !rom the ventricle travels to the gills where it pic"s up )2 and disposes o! C)2 ,mphi#iansFrogs and other amphi#ians have a three1cham#ered heart with two atria and one ventricle.The ventricle pumps #lood into a !or"ed artery that splits the ventricle3s output into the pulmocutaneous circuit and the systemic circuit. Reptiles -Except +irds.Reptiles have double circulation with a pulmonary circuit -lungs. and a systemic circuit.Turtles sna"es and li&ards have a three1cham#ered heart.Crocodilians have a !our1cham#ered heart. Mammals and +irdsIn all mammals and #irds the ventricle is completely divided into separate right and le!t cham#ers.The le!t side o! the heart pumps and receives only oxygen1rich #lood while the right side receives and pumps only oxygen1poor #lood. Mammals and +irds, power!ul !our1cham#ered heart was an essential adaptation o! the endothermic way o! li!e characteristic o! mammals and #irds. Mammalian Circulation* The %athway0eart valves dictate a one1way !low o! #lood through the heart.+lood #egins its !low with the right ventricle pumping #lood to the lungs.In the lungs the #lood loads )2 and unloads C)2. Mammalian Circulation* The %athway)xygen1rich #lood !rom the lungs enters the heart at the le!t atrium and is pumped to the #ody tissues #y the le!t ventricle.+lood returns to the heart through the right atrium. The Mammalian 0eart* , Closer 4oo", closer loo" at the mammalian heart provides a #etter understanding o! how dou#le circulation wor"s. The Mammalian 0eart* , Closer 4oo"The heart contracts and relaxes in a rhythmic cycle called the cardiac cycle.The contraction or pumping phase o! the cycle is called systole.The relaxation or !illing phase o! the cycle is called diastole. The Mammalian 0eart* , Closer 4oo"The heart rate also called the pulse is the num#er o! #eats per minute.The cardiac output is the volume o! #lood pumped into the systemic circulation per minute. Maintaining the 0eart3s Rhythmic +eat$ome cardiac muscle cells are sel!1excita#le meaning they contract without any signal !rom the nervous system. Maintaining the 0eart3s Rhythmic +eat, region o! the heart called the sinoatrial (SA) node or pacemaker sets the rate and timing at which all cardiac muscle cells contract.Impulses !rom the $, node travel to the atrioventricular (AV) node.,t the ,/ node the impulses are conducted through the bundle of His and then travel to the Purkinje fibers that ma"e the ventricles contract. Maintaining the 0eart3s Rhythmic +eatThe impulses that travel during the cardiac cycle can #e recorded as an electrocardiogram -EC' or E5'.. Maintaining the 0eart3s Rhythmic +eatThe pacema"er is in!luenced #y nerves hormones #ody temperature and exercise. +lood /essel $tructure and FunctionThe 6in!rastructure7 o! the circulatory system is its networ" o! #lood vessels.,ll #lood vessels are #uilt o! similar tissues and have three similar layers. +lood /essel $tructure and Function$tructural di!!erences in arteries veins and capillaries correlate with their di!!erent !unctions. +lood /essel $tructure and FunctionArteries have thic"er walls to accommodate the high pressure o! #lood pumped !rom the heart. +lood /essel $tructure and FunctionIn the thinner1walled veins #lood !lows #ac" to the heart mainly as a result o! muscle action. +lood Flow /elocityThe velocity o! #lood !low varies in the circulatory system and is slowest in the capillary #eds as a result o! the high resistance and large total cross1sectional area. +lood %ressureBlood pressure is the hydrostatic pressure that #lood exerts against the wall o! a vessel. +lood %ressureSystolic pressure is the pressure in the arteries during ventricular systole.The highest pressure in the arteries.Diastolic pressure is the pressure in the arteries during diastole.4ower than systolic pressure. Capillary FunctionTwo mechanisms regulate the distri#ution o! #lood in capillary #eds.In one mechanism contraction o! the smooth muscle layer in the wall o! an arteriole constricts the vessel. Capillary FunctionIn a second mechanism precapillary sphincters control the !low o! #lood #etween arterioles and venules. Capillary FunctionThe critical exchange o! su#stances #etween the #lood and interstitial !luid ta"es place across the thin endothelial walls o! the capillaries. Capillary FunctionThe di!!erence #etween #lood pressure and osmotic pressure drives !luids out o! capillaries at the arteriole end and into capillaries at the venule end. Fluid Return #y the 4ymphatic $ystemThe lymphatic system returns !luid to the #ody !rom the capillary #eds.,ids in #ody de!ense. +lood is Connective TissueBlood in the circulatory systems o! verte#rates is a speciali&ed connective tissue. +lood Composition and Function+lood consists o! several "inds o! cells suspended in a li8uid matrix called plasma.The cellular elements occupy a#out 9:; o! the volume o! #lood. %lasma+lood plasma is a#out