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Question
Which of the following statements is not true for external respiration?
Which of the following statements is not true for external respiration?
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Solution
The correct option is A Alveolar pO2 is 159 mm Hg
External respiration is the process that describes the gaseous exchange between the lungs and the blood capillaries. The partial pressure of oxygen in the atmospheric air is 159 mm of Hg. Hence, oxygen easily diffuses into the alveoli which has a lower partial pressure of oxygen (104 mm of Hg) when compared to the atmospheric air. The blood capillaries surrounding the alveoli have a very low concentration of oxygen when compared to the alveoli. Hence, the oxygen moves from the alveoli into the surrounding deoxygenated blood which has a very low partial pressure of oxygen (40 mm of Hg). Movement of oxygen into the blood oxygenates the blood thereby increasing the partial pressure of oxygen in the blood. (partial pressure of oxygen in the now oxygenated blood is 95 mm of Hg). This oxygenated blood is circulated to the tissues where the oxygen is transferred to the tissues and carbon dioxide is taken from the tissues.
When the carbon dioxide is taken from the tissues by the blood, the blood becomes deoxygenated. This blood which surrounds the alveoli will now contain a higher partial pressure of CO2 (45 mm of Hg) when compared to oxygen. The alveoli has a lower partial pressure of CO2 (40 mm of Hg) when compared to this deoxygenated blood. Hence, the carbon dioxide easily diffuses from the blood to the alveoli. Since the concentration/partial pressure of carbon dioxide in the atmospheric air is very less (0.3 mm of Hg), the CO2 from the alveoli of the lungs easily diffuses out into the atmospheric air.
External respiration is the process that describes the gaseous exchange between the lungs and the blood capillaries. The partial pressure of oxygen in the atmospheric air is 159 mm of Hg. Hence, oxygen easily diffuses into the alveoli which has a lower partial pressure of oxygen (104 mm of Hg) when compared to the atmospheric air. The blood capillaries surrounding the alveoli have a very low concentration of oxygen when compared to the alveoli. Hence, the oxygen moves from the alveoli into the surrounding deoxygenated blood which has a very low partial pressure of oxygen (40 mm of Hg). Movement of oxygen into the blood oxygenates the blood thereby increasing the partial pressure of oxygen in the blood. (partial pressure of oxygen in the now oxygenated blood is 95 mm of Hg). This oxygenated blood is circulated to the tissues where the oxygen is transferred to the tissues and carbon dioxide is taken from the tissues.
When the carbon dioxide is taken from the tissues by the blood, the blood becomes deoxygenated. This blood which surrounds the alveoli will now contain a higher partial pressure of CO2 (45 mm of Hg) when compared to oxygen. The alveoli has a lower partial pressure of CO2 (40 mm of Hg) when compared to this deoxygenated blood. Hence, the carbon dioxide easily diffuses from the blood to the alveoli. Since the concentration/partial pressure of carbon dioxide in the atmospheric air is very less (0.3 mm of Hg), the CO2 from the alveoli of the lungs easily diffuses out into the atmospheric air.
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