Two tissues, A and B, are placed in a gas chamber and equilibrated with carbon m
ID: 1854212 • Letter: T
Question
Two tissues, A and B, are placed in a gas chamber and equilibrated with carbon monoxide gas at various partial pressures of CO. Equilibrium concentrations at five partial pressures are plotted for each tissue. (a) What is the solubility of CO in tissue B? (b) What is the partition coefficient of CO for tissue A relative to tissue B? (c) Steady-state diffusion of CO occurs through a tissue consisting of the same two tissues (A and B) in series. There is no resistance to CO transport at the interface. If we were to solve the diffusion equations in each tissue, what conditions must we specify at the interfaceExplanation / Answer
Carbon dioxide in the blood is transported as bicarbonate, since carbon dioxide combines with water to form carbonic acid: CO2 + H2O = H2CO3 which is in equilibrium with hydrogen ions and bicarbonate: H2CO3 = H+ + HCO3- The concentration of hydrogen ions (H+) determines the pH, a measure of the acidity, of the blood. The carbonic acid-bicarbonate equilibrium is an example of a buffer system and is involved in the maintenance of the acid-base balance in the body. The pH of the blood is related to the ratio of bicarbonate to carbonic acid, which is normally about 20:1. The carbonic acid-bicarbonate buffering system is extended by the body's ability to convert carbonic acid to carbon dioxide (catalyzed by the enzyme carbonic anhydrase) and the removal of CO2 in respired air. In addition, the body has the ability to eliminate hydrogen or bicarbonate ions via the kidneys to maintain pH. Since most body systems function best at a pH near7.4, the pH of the body must be maintained within a narrow range. When the blood pH is higher or lower than the normal level of 7.35 to 7.45, enzymes may function less effectively or not at all, nerve and muscle activity weakens, and finally all metabolic activity is undermined. Proteins also function as buffers; hemoglobin in particular is an important buffering agent in the blood. Oxygen-bound hemoglobin is a stronger acid than hemoglobin without oxygen, and tends to release hydrogen ions; when hemoglobin is exposed to the lower oxygen concentrations in the capillaries, oxygen is released, the hemoglobin becomes a weaker acid, and hydrogen ions are taken up. The relationship between pH and the ability of hemoglobin to bind oxygen, which is reflected in saturation levels of hemoglobin in arterial versus venous blood, is known as the Bohr effect.
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