lecture 25 bio

lecture 25 bio - Lecture 25 Circulation and Gas Exchange...

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Lecture 25: Circulation and Gas Exchange Trading Places -exchange: resources/waste cross plasma membrane -unicellular: directly with environment…multi-cellular: specialized systems exchange with environment and transport -internal transport and gas exchange are functionally related in most animals 42.1 C IRCULATORY S YSTEMS L INK E XCHANGE S URFACES WITH C ELLS T HROUGHOUT THE B ODY -molecular trade involves every cell in the body…but diffusion is slow for large distances -time for one substance to diffuse is proportional to square of the distance -1 second diffuse 100 um…100 seconds 1 mm…3 hours 1 cm -many or all cells in direct contact with environment (only sponges, cnidarians, flatworms) -circulatory system (all other animals) moves fluid between each cell’s surroundings and tissues where exchange with the environment occurs Gastrovascular Cavities -lack distinct circulatory system…central gastrovascular cavity: digestion & distribution of substances -cnidarians (hydras, jellies) & flatworms (planarians) -single opening continuity between fluid inside the cavity and water outside inner & outer layers bathed by fluid but only inner layer has direct access to nutrients…nutrients diffuse from inner to outer (2 cells thick) -thin branches of gastrovascular cavity extend into animal’s tentacles -flat body optimizes diffusional exchange by increasing surface area and minimizing diffusion distances Open and Closed Circulatory Systems (mollusks (arthropods) and crustaceans) -circulatory system minimizes distances that substances must diffuse to enter or leave a cell (connects aqueous environment of body cells to organs that exchange gases, absorb nutrients, and dispose wastes) -3 components: circulatory fluid, set of interconnecting tubes, muscular pump ( heart ) -heart powers circulation-uses metabolic energy to elevate the hydrostatic pressure of the circulatory fluid which then flows through a circuit of vessels and then back to the heart - open circulatory system : circulatory fluid ( hemolymph) bathes the organs directly… hemolymph=interstitial fluid - contraction of 1 or more hearts pumps hemolymph through circulatory vessels into interconnected sinuses (spaces surrounding organs and chemical exchange occurs between hemolymph and body cells) - relaxation of heart draws hemolymph back in through pores -advantage: lower hydrostatic pressure less energy costly - closed circulatory system : blood is confined to vessels and is distinct from the interstitial fluid -1 or more hearts pump blood into large vessels which branch into smaller ones through organs - materials are exchanged between smallest vessels and interstitial fluid bathing the cells -advantage: high blood pressure enables effective delivery of nutrients and suited to regulate distributing of blood Organization of Vertebrate Circulatory Systems - cardiovascular system : closed circulatory system of humans and other vertebrates; blood circulates to and from the heart through an extensive network of
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lecture 25 bio - Lecture 25 Circulation and Gas Exchange...

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