Lecture 21 11-18-10

Lecture 21 11-18-10 - Lecture 21 Lecture 18 November 2010...

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Unformatted text preview: Lecture 21 Lecture 18 November 2010 Respiration Respiration Atmosphere: Atmosphere: O2 source The Oxygen Cascade Mitochondria: Mitochondria: O2 sink The Air We Breathe The DRY AIR Pair = 760 mm Hg ≈ PN2 + PO2 PN2 = 0.78 x 760 mm Hg = 593 mm Hg PO2 = 0.21 x 760 mm Hg = 159 mm Hg Air is only 0.04% carbon dioxide PCO2 = 0.0004 x 760 mm Hg = 0.30 mm Hg Oxygen and Carbon Dioxide in Water Oxygen The partial pressure of oxygen or carbon dioxide in water or any other aqueous solution (e.g., blood plasma) is equal to the partial pressure of oxygen or carbon dioxide in a gas phase with which the solution is in equilibrium. DRY AIR Pair = 760 mm Hg ≈ PN2 + PO2 PN2 = 0.78 x 760 mm Hg = 593 mm Hg PO2 = 0.21 x 760 mm Hg = 159 mm Hg Air is only 0.04% carbon dioxide PCO2 = 0.0004 x 760 mm Hg = 0.30 mm Hg Oxygen and Carbon Dioxide in Water Oxygen Diffusion of gases follows partial pressure gradients. Gases diffuse from high to low partial pressure. Diffusion does not follow concentration gradients – it always follows partial pressure gradients. DRY AIR Pair = 760 mm Hg ≈ PN2 + PO2 PN2 = 0.78 x 760 mm Hg = 593 mm Hg PO2 = 0.21 x 760 mm Hg = 159 mm Hg Air is only 0.04% carbon dioxide PCO2 = 0.0004 x 760 mm Hg = 0.30 mm Hg Oxygen and Carbon Dioxide in Water Oxygen The bubble carried by this water beetle (Peltodytes) has a higher concentration but a lower partial pressure of oxygen than the surrounding water. Oxygen diffuses from the water into the bubble and can then be utilized by the beetle. DRY AIR Pair = 760 mm Hg ≈ PN2 + PO2 PN2 = 0.78 x 760 mm Hg = 593 mm Hg PO2 = 0.21 x 760 mm Hg = 159 mm Hg Air is only 0.04% carbon dioxide PCO2 = 0.0004 x 760 mm Hg = 0.30 mm Hg Oxygen and Carbon Dioxide in Water Oxygen Same story with this larval water beetle. At 20 C, a bubble of fresh air has a PO2 of 0.21 atm and a [O2] of 8.6 mmol/L. If the surrounding water is well­mixed and in equilibrium with the atmosphere, it has a PO2 of 0.21 atm and a [O2] of only 0.3 mmol/L. After the insect consumes half of the O2, the bubble has a PO2 of 0.1 atm and an [O2] of 8.6 mmol/ L. Under these conditions, O2 diffuses from the water into the bubble. The bubble effectively serves as a “gill”. Oxygen and Carbon Dioxide in Water Oxygen Water solubilities of O2 and CO2 are very different. At 760 mm Hg (1 Atm), the solubility of CO2 in distilled water at 0 °C is 77 mmol/L, compared to 2.2 mmol/L for O2. As a result of these physical properties, the partial pressures of O2 and CO2 in blood leaving the breathing organ differs dramatically between air breathers and water breathers. DRY AIR Pair = 760 mm Hg ≈ PN2 + PO2 PN2 = 0.78 x 760 mm Hg = 593 mm Hg PO2 = 0.21 x 760 mm Hg = 159 mm Hg Air is only 0.04% carbon dioxide PCO2 = 0.0004 x 760 mm Hg = 0.30 mm Hg Capacitance Coefficient (β) Capacitance Capacitance coefficient is the change in total gas concentration per unit change in gas partial pressure. In air, because of the universal gas law, O2 and CO2 have the same β. In water, βC02 = 23 ● βO2. Relationships between PO2 and PCO2 in exhaled air or water, assuming that CO2 is consumed at the same rate that O2 is CO2 is produced. The blue dot in the lower right represents fresh air or aerated water. Oxygen and Carbon Dioxide in Water Oxygen Gas solubility in water decreases as temperature increases. Gas solubility in water decreases as salinity increases. DRY AIR Pair = 760 mm Hg ≈ PN2 + PO2 PN2 = 0.78 x 760 mm Hg = 593 mm Hg PO2 = 0.21 x 760 mm Hg = 159 mm Hg Air is only 0.04% carbon dioxide PCO2 = 0.0004 x 760 mm Hg = 0.30 mm Hg Oxygen and Carbon Dioxide in Water Oxygen Gas solubility in water decreases as temperature increases. Gas solubility in water decreases as salinity increases. Oxygen and Carbon Dioxide in Water Oxygen When a gas chemically combines with other molecules in solution, it does not contribute to partial pressure of that gas. For example, when O2 is combined with hemoglobin, it does not contribute to the partial pressure of O2 in blood. DRY AIR Pair = 760 mm Hg ≈ PN2 + PO2 PN2 = 0.78 x 760 mm Hg = 593 mm Hg PO2 = 0.21 x 760 mm Hg = 159 mm Hg Air is only 0.04% carbon dioxide PCO2 = 0.0004 x 760 mm Hg = 0.30 mm Hg Oxygen and Carbon Dioxide in Water Oxygen Gases diffuse more rapidly in air than in water. DRY AIR Pair = 760 mm Hg ≈ PN2 + PO2 PN2 = 0.78 x 760 mm Hg = 593 mm Hg PO2 = 0.21 x 760 mm Hg = 159 mm Hg Air is only 0.04% carbon dioxide PCO2 = 0.0004 x 760 mm Hg = 0.30 mm Hg Diffusion and Convection Diffusion Respiratory gases are transported by diffusion and convection. Diffusion and Convection Diffusion Convection (bulk flow) moves the respiratory medium (air or water) between the environment and the region of the respiratory exchange surface. Ventilation of Respiratory Surfaces Ventilation Ventilation can be tidal (bidirectional; in­out; mammals and other air­breathing vertebrates) or unidirectional (one­way; fish; airflow across avian respiratory exchange surface. Diffusion and Convection Diffusion Diffusion exchanges respiratory gases (O2 and CO2) across the respiratory exchange surface between the respiratory medium and the blood. Diffusion and Convection Diffusion Convection (bulk flow) moves the respiratory gases through the circulatory system from the respiratory exchange surface to the capillaries of the systemic circulation. Diffusion and Convection Diffusion Diffusion moves the respiratory gases between the sytemic capillaries and the cells where O2 is consumed and CO2 is produced. Oxygen Extraction Oxygen How effectively does the gas exchange system remove O2 from the respiratory medium? The answer depends on the spatial relation between the flow of blood and the flow of respiratory medium (air or water). Oxygen Extraction Oxygen In humans and other tidal ventilators (left), and in co­current ventilators (right), partial pressures of O2 and CO2 equilibrate between blood and respiratory medium (inhaled air). Oxygen Extraction Oxygen Note: numbers here are for illustrative purposes only. They are realistic but do not represent any particular respiratory system. Oxygen Extraction Oxygen In countercurrent gas exchangers (e.g., fish), blood leaves the respiratory system with a higher PO2 than that of the medium. Oxygen Extraction Oxygen In countercurrent gas exchangers (e.g., fish), blood leaves the respiratory system with a higher PO2 than that of the medium. Oxygen Extraction Oxygen In countercurrent gas exchangers (e.g., fish), blood leaves the respiratory system with a higher PO2 than that of the medium. Oxygen Extraction Oxygen In countercurrent gas exchangers (e.g., fish), blood leaves the respiratory system with a higher PO2 than that of the medium. Oxygen Extraction Oxygen In crosscurrent gas exchangers (e.g., birds), blood leaves the respiratory system with a higher PO2 than that of the medium. Oxygen Extraction Oxygen In crosscurrent gas exchangers (e.g., birds), blood leaves the respiratory system with a higher PO2 than that of the medium. Anterior Air Sacs Posterior Air Sacs Oxygen Extraction Oxygen In crosscurrent gas exchangers (e.g., birds), blood leaves the respiratory system with a higher PO2 than that of the medium. ...
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This note was uploaded on 04/03/2011 for the course BIO 704:360 taught by Professor John-alder during the Fall '11 term at Rutgers.

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