Ch. 42 notes

Ch. 42 notes - 17:42 Diffusion is very slow for distances...

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17:42 Diffusion is very slow for distances of more than a few millimeters puts constraint on the body plan of an animal How does each cell participate in exchange? Body size and shape that keep many or all cells in direct contact with the environment exchange materials directly with the surrounding medium Certain invertebrates (cnidarians, flatworms) Circulatory system that moves fluid between each cell’s immediate surroundings and the tissues where exchange with the environment occurs Animals that lack a distinct circulatory system Hydras, jellies, and other cnidarians Central gastrovascular cavities – distribution of substances throughout the body and in digestion An opening at one end connects the cavity to the surrounding water In a hydra, thin branches of the gastrovascular cavity extends into its tentacles In jellies, it has a more elaborate branching pattern In animals with gastrovascular cavity: fluid baths both the inner and outer tissue layers, facilitating exchange of gases and cellular waste Only the cells lining the cavity have direct access to nutrients released by digestion. ..but since the body wall is only 2 cells thick, nutrients only have to diffuse a short distance to reach the cells of the outer tissue layer Planarians, most other flatowrms: no circulatory system as well Gastrovascular cavity + flat body = good for exchange with environment Flat body optimizes diffusional exchange by increasing surface area and minimizing diffusion distances Circulatory system 3 parts Circulatory fluid Set of interconnecting vessels
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Muscular pump (heart) Powers circulation by using metabolic energy to elevate the hydrostatic pressure of the circulatory fluid, which flows through the vessels and back to the heart Transport fluid throughout body connects the aqueous environment of the body cells to the organs that exchange gases, absorb nutrients, and dispose of wastes O 2 only has to travel a distance of 2 cells before reaching the blood through diffusion Either open or closed, vary with regard to the number of circuits in the body, and rely on pumps that differ in structure and organization Open and closed Open circulatory system – circulatory fluid bathes the organs directly Circulatory fluid = hemolymph = interstitial fluid that bathes body cells Contraction of one or more hearts pumps the hemolymph through the circulatory vessels into interconnected sinuses (spaces surrounding the organs) Within the sinuses, chemical exchange occurs between the hemolymph and body cells Relaxation of the heart draws hemolymph back in through powers, which are equipped with valves that close when the heart contracts Body movements help circulate the hemolymph by periodically squeezing the sinuses Closed circulatory system – circulatory fluid called 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 that infiltrate the organs Chemical exchange occurs between the blood and the interstitial fluid, and also between the
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Ch. 42 notes - 17:42 Diffusion is very slow for distances...

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