PowerPoint PresentationSlide 2Slide 3Slide 4Slide 5Slide 6Slide 7Slide 8Slide 9Slide 10Slide 11Slide 12Slide 13Slide 14Slide 15Slide 16Slide 17Slide 18Slide 19Slide 20Slide 21Slide 22Slide 23Slide 24Slide 25Slide 26Slide 27Slide 28Slide 29Chapter 42: CIRCULATION AND GAS EXCHANGEThe circulatory system solves this problem by rapidly transporting fluid in bulk throughout the body, connecting the aqueous environment of the body cells {interstitial fluid or plasma} to the organs that exchange gases, absorb nutrients, and dispose of wastes. Diffusion alone is not adequate for transporting substances over long distances. The time it takes for a substance to diffuse from one place to another is proportional to the square of the distance. A body wall of cnidarians like hydrahydra is only two cells thick & encloses a central gastrovascular cavity, which serves for both digestion and for distribution of substances. Thin branches of the gastrovascular cavity extend into the tentacles.There is some bulk flow (mixing) in the cavity.Nutrients {and wastes} have only a short distance to diffuse to {and from} the cells of the outer layer.Most invertebrates have a gastrovascular cavitygastrovascular cavity {branching gut}or a circulatory systemcirculatory system {in mesodermal body cavity}for internal transport.Flatworms like planariaplanaria have a branching gastrovascular cavity, ensuring that all cells are bathed by a suitable medium and diffusion distances are short.For animals with many cell layers, gastrovascular cavities are insufficient.Two types of {mesodermal}{mesodermal} circulatory systems circulatory systems have evolved to overcome the limitations of diffusion: open circulatory systems and closed circulatory systems. 3 basic components: a fluid (blood), tubes (blood vessels), a muscular pump (heart). In insects, other arthropodsarthropods & most mollusksmost mollusks {except cephalopods}, blood bathes the organs directly in an openopen circulatory systemcirculatory system. There is no distinction between blood and interstitial fluidThere is no distinction between blood and interstitial fluid, and the general body fluid is more correctly termed hemolymphhemolymph. In insects and other arthropods, the heart is an elongated dorsal tube; it pumps hemolymph through vessels out into sinuses. When the heart relaxes, it draws in hemolymph through pores (ostia). Body movements squeeze the sinuses & help circulate the hemolymph.Instead of lungs, insects have trachea insects have trachea that take air directly to cells.Earthworms, squids, octopuses, and vertebratesEarthworms, squids, octopuses, and vertebrates have closedclosed circulatory systemscirculatory systems: blood is confined to vessels and is distinct from the interstitial fluid. One or more hearts pump blood into large vessels that branch into smaller ones coursing through the organs, where materials are exchanged by diffusion between the blood and the interstitial fluid bathing the cells. Note: earthworm ‘lungs’ are just skin capillaries. earthworm ‘lungs’ are just skin capillaries. {amphibians & turtles have some gas exchange through skin}A fish heartfish heart has two main chambers, one atrium and one ventricle. Blood pumped from the ventricle travels to the gills, where it picks up oxygen and disposes of carbon dioxide across capillary walls. The gill capillaries converge into a vessel that carries oxygen-rich blood to capillary beds in all other parts of the body (the systemic circulation ). Blood then returns in veins to the atrium of the heart. In fish, blood must pass through two capillary beds during each circuit {like hepatic circulation in mammals} w/ a big drop in pressure across each capillary bed; systemic circulation is quite slow, constraining the delivery of oxygen to body tissues, and hence the maximum aerobic metabolic rate of fishes.234Frogs and other amphibiansamphibians have a three-chambered heart, with two atria and one ventricle. The ventricle pumps blood into a forked artery that splits the ventricle’s output. The pulmocutaneous circulation leads to capillaries in the gas-exchange organs (the lungs and skin in a frog). Most of the oxygen-rich blood that returns to the ventricle is diverted into the systemic circulation by a ridge in the ventricle. Systemic circulation supplies all body organs and then returns oxygen-poor blood to the right atrium via the veins. This double circulation provides a vigorous flow of blood to the brain, muscles, and other organs because the blood is pumped a second time after it loses pressure in the capillary beds of the lungs or skin. Plethodontid (lungless) salamanders are long & thin;pulmocutaneous circulation is all cutaneous.234234Turtles, snakes & lizards Turtles, snakes & lizards {formerly known as Reptiles Reptiles } also have double circulation with pulmonary (lung) and systemic circuits.Although the ‘reptilian’ heart is three-chambered, the ventricle is partially divided and there is even less mixing of oxygen-rich and oxygen-poor blood than in amphibians. In the crocodilianscrocodilians (crocodiles and alligators), the ventricle is completely divided into separate right and left chambers. In birds & mammalsbirds & mammals, the ventricle is completely divided: the left side of the heart receives and pumps only oxygen-rich blood, while the right side handles only oxygen-poor blood. The evolution of double circulation w/ a powerful four-chambered heart was an essential to support the endothermy of birds and mammals. Endotherms use ten times as much energy per gram as ectotherms; their circulatory systems need to deliver about ten times as much fuel and oxygen to their tissues (and remove ten times as much CO2 and other wastes). Birds and mammals descended from different reptilian ancestors; their powerful four-chambered hearts evolved independently, an example of convergent evolutionconvergent evolution.Fetal heartFetal heart is functionally 3 chambered, bypassing the lungs {like a salamander!}In the fetus the lungs are nonfunctional In the fetus the lungs are nonfunctional and the blood largely bypasses them. and the blood largely bypasses them. As the blood from the inferior vena cava enters the right atrium, a large proportion of it is shunted directly into the left atrium through an opening called