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CH%2044%20Gas%20Exchange%20and%20Circ[1] - BLY 122 Chapter...

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Chapter 44 Gas Exchange and Circulation 1 BLY 122 A. Hunter from C. S. Major Chapter 44 Gas Exchange and Circulation I. Gas exchange between the mitochondria and the environment relies on diffusion. A. Gas exchange in all animals involves a three-part sequence. 1. Ventilation—air or water moving through the gas-exchange organ 2. Circulation—the transportation of dissolved gases to the animal’s cells 3. Respiration—the exchange of gases between the blood or interstitial fluid and the mitochondria B. The exchange of O 2 and CO 2 differs depending on whether air or water is the respiratory medium. 1. How do oxygen and carbon dioxide behave in the air? a. Oxygen content is 21% no matter what the altitude. b. However, the air at higher altitudes is less dense, so less O 2 is available. c. The partial pressure of oxygen indicates how much oxygen is present, taking into account the density of the air at any given altitude. d. In both air and water, gases move from a region of high partial pressure to one of lower partial pressure. 2 How do oxygen and carbon dioxide behave in water? a. Water contains far less oxygen than air does. b. Water is far denser than air, so more energy is required to ventilate a gas exchange surface with water than with air. c. The diffusion of gases in aquatic habitats is dependent on several factors: II. Organs for Gas Exchange A. Fick’s Law of Diffusion 1. Fick’s law states that the rate of diffusion depends on five parameters: 2. This law states that oxygen and carbon dioxide diffuse in the largest amounts when three conditions are met: a. The surface area of the gas exchange surface is large. b. The respiratory surface is very thin. c. The partial pressure gradient is large. B. Most aquatic animals rely on gills for gas exchange. 1. The gill structure allows for a large surface area for gas exchange. 2. Invertebrate gills vary in structure. a. Some invertebrates have gills that project from the body surface and contact surrounding water directly. b. In other invertebrates, gills are internal, so water must be driven over them. 3. The gills of all bony fishes are similar. 4. The flow of blood through the gill runs countercurrent to the flow of water, maintaining a partial pressure gradient for gas exchange across the entire surface. C. The insect tracheal system transports air directly to respiring cells. 1. Openings, called spiracles, regulate the rate of gas exchange to minimize water loss.
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