2. Write a paragraph of 3-5 sentences answering the following question. Your res

Question

2. Write a paragraph of 3-5 sentences answering the following question. Your response should first answer the question and then go on to state physiological interpretation's behind your answer. Paragraphs that demonstrate complete and thorough reasoning will receive full points. As plasma moves through a capillary bed in the systemic circulation, the decrease in plasma Po2 is much greater than the increase in plasma Pco2 even though the amount of 02 that diffuses out of the plasma is approximately equal to the amount of CO2 that diffuses into the plasma. Why is this the case?

Explanation / Answer

The partial pressure of a gas is directly related to the amount or content of the gas in a mixture of gases. The gradient in partial pressures of two different gases is reflected in the relative content of gases present in the mixture. However, this is not always correct for the gases in a solution if the solubilities of the gases in the particular solvent are very different as is the case for oxygen and carbon dioxide dissolved in blood plasma. The solubility of oxygen in water (and plasma since 90% of blood plasma is water) is low. In contrast, the solubility of carbon dioxide in water is very high. Therefore, a unit change in oxygen content in plasma reflects a much greater change in partial pressure compared to a similar unit change in carbon dioxide content.

Further, carbon dioxide can be transported in the blood in three ways: as bicarbonate ion, soluble CO2 in plasma, and as bound to plasma proteins. Oxygen is transported in soluble form (2%) and as oxyhaemoglobin (98%), one haemoglobin can bind with four oxygen molecules. Blood leaving systemic capillaries have haemoglobin still 75% saturated meaning it releases only 1/4 of the oxygen at the cells. The oxygen that remains bound serves as a reservoir that cells can draw on if metabolism increases. Thus the amount of diffusion of O2 and CO2 might be same in the capillary bud during systemic circulation, but the available O2 and CO2 content in the blood make the difference in their partial pressures.

Related Questions

Navigate

• Browse (All)
• Browse 2
• Subjects

---

---

Integrity-first tutoring: explanations and feedback only — we do not complete graded work. Learn more.