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Respiratory Systems: Physics & Strategies Respiratory Systems 1. 2. Purpose: Gas Exchange Receive oxygen from environment Remove carbon dioxide from blood Respiration Respiration = the entire sequence of events that results in the exchange of oxygen and carbon dioxide between the external environment of an animal and the mitochondria within its cells. Mitochondrial Respiration Mitochondria consume O2 and act as sinks. Mitochondria deplete local [oxygen]. An oxygen gradient is formed from the outside of the cell to the mitochondrion. Oxygen moves into the mitochondria and carbon dioxide moves out. The Pathway for Oxygen Respiratory Strategies 3 main respiratory strategies: 1. Circulate external medium though the body. 2. Diffusion of gases across all or most of the body surface, accompanied by transport of gases in an internal circulatory system. 3. Diffusion across specialized respiratory surface accompanied by circulatory transport. Circulating External Medium Sponges, cnidarians, terrestrial arthropods. Cutaneous Respiration Diffusion of gases through skin. Most aquatic inverts, terrestrial annelid worms, some vertebrates such as salamanders and frogs. Cutaneous Respiration Limitations: ◦ Very thin skin: minimize diffusion distance and maximize diffusion rate ◦ Thin barrier must remain moist: enables dissolved O2 to diffuse into the cell Usually confined to aquatic or very moist terrestrial habitats. Surface area of the skin is usually quite limited. Exception: Lake Titicaca Frog Exception: Adult Male Hairy Frog Respiratory Strategies As organisms get larger surface area to volume ratio decreases which: ◦ Limits the surface area available for diffusion. ◦ Increases the distances within the animal that oxygen must diffuse across ◦ Increasing the time needed for diffusion. Respiratory Strategies Larger animals: diffusion alone is insufficient. Many animals have specialized respiratory organs (ex. gills or lungs) with large surface areas which they use for external gas exchange Respiratory Strategies Animals with internal gills or lungs often move external medium by bulk flow across their respiratory surface. This process is called ventilation. Respiratory Strategies In animals which ventilate a respiratory surface, respiration is divided into 4 steps: 1. Bulk flow of medium across respiratory surface 2. Diffusion across this surface 3. Bulk flow (gas transport) in the circulatory system. 4. Diffusion into the tissues. Physics of Respiratory Systems The rate of diffusion will be greatest when: (1) the ability of substance to diffuse is high (2) the area of the membrane is large (3) the energy gradient is large (4) and the diffusion distance is small. Consequently … ◦ Gas exchange surfaces are typically thin, often fragile, and have large surface areas. Specialized Respiratory Surfaces Confine their gas exchange to a small region of the body. Increase the surface area of this region. Respiratory surface is moist and thin, with a large surface area. Body covered with thick protective layer. Specialized Respiratory Surfaces Major Classifications: ◦ Gills ◦ Lungs Often ventilated – move external medium across these surfaces by bulk flow. Gills Originate as out-pocketings (evaginations) of the body surface. Can be external or located within a respiratory cavity protected by a flap or other covering. Most common in water. Lungs Originate as infoldings (invaginations) of the body surface Forming an internal body cavity that contains an external medium. Most common in air Oxygen Content In Air v. In Water Oxygen Content In Air v. In Water Molar [oxygen] (sea level at 20C): ◦ in air = 9mM, ◦ in water = >0.3 mM. IMPORTANT IMPLICATIONS for the respiratory strategies of an organism! To obtain the same amount of oxygen, an animal that uses water as a respiratory medium must move 30x more fluid across its respiratory surface. Implications Solubility of oxygen in water decreases with increasing temperatures, resulting in large decreases in [oxygen]. For fish, body temperature and oxygen demand increase with increasing temperature = CHALLENGE! Implications Solubility of gases decreases with increasing ion concentration in a fluid. So solubility of O2 in seawater is 20% less than in freshwater at the same temp. CHALLENGE for marine species!
