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Unformatted text preview: Chapter 44: Gas Exchange and Circulation All animals are involved in aerobic respiration. In this process that occurs mainly in the mitochondria, the carbons of organic compounds are oxidized by decarboxylation to yield carbon dioxide. The hydrogen atoms from organic compounds are accepted by molecular oxygen to form water. All animals need to gather molecular oxygen and expel carbon dioxide in the cellular respiration process In small flat organisms the surface area/volume ratio is large enough that molecular oxygen and carbon dioxide can diffuse through the body surface In larger animals, the surface area of the body is not large enough. Large animals have increased their surface areas to capture/release molecular oxygen and carbon dioxide by evolving gills, lungs, and insect trachea. These are called respiratory organs In order for molecular oxygen to be acquired and carbon dioxide expired in all of the animal’s tissues, a transport system moves molecular oxygen and carbon dioxide between the body surface and all tissues of the body. This transport system is called the circulatory system. Air and water as respiratory media o The atmosphere possesses 21% oxygen and .03% carbon dioxide at any altitude o The percentages of gases do not change so therefore the percentage is the same at all altitudes even though the amount changes. Thus to better reflect the amount of oxygen and carbon dioxide we speak in terms of partial pressures o Partial pressure of a gas = % of gas in total gas x total pressure of all gasses in mm Hg at a given altitude o For oxygen, P 02 = .21 x 760 mm Hg = 160 mm Hg o For carbon dioxide, P co2 = .0003 x 760 mm Hg = .228 mm Hg o The important point is that oxygen and carbon dioxide diffuse along their partial pressure gradients. At 29,000 ft, the partial pressure gradient is not large enough to transport enough oxygen into the lung tissue to sustain life. Oxygen and Carbon dioxide in water o Water contains much les oxygen than air o 1 liter of air = 209 mL of oxygen o 1 liter of water = 7 mL of oxygen o aquatic animals have to expend much more energy to capture the much needed oxygen for their tissues o because of several factors the amount of oxygen in the water is lower than the amount of oxygen in the air at the same partial pressure o the following factors are important: low solubility of oxygen in water solubility of oxygen decreases with increasing water temperature presence of solutes decreases solubility Respiratory organs o Water parameters are important in designing a respiratory organ. Remember that gases move by diffusion through tissues or membranes o Fick’s law of diffusion: k x A x ( p2-P1)/D o K=a constant depending on the solubility of the gas and on air temperature o A = area of exchange o (P2-P1) = difference in partial pressures of 2 gases on either side of a barrier to diffusion o D= distance or thickness of the barrier of diffusion o You can increase the rate of diffusion by...
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- Fall '11