Use the following answer code to compare the relative magnitudes of the pair of

Question

Use the following answer code to compare the relative magnitudes of the pair of items in the question. Write the letter (A,B, or C) in the space provided.

A. item A is greater than item B

B. item B is greater than item A

C. item A and item B are approximately equal

1. A. PO2 in blood entering the pulmonary capillaries

B. PO2 in the alveoli

2. A, PCO2 in blood entering the pulmonary capillaries

B. PCO2 in the alveoli

3. A. PO2 in the alveoli

B. PO2 in blood leaving the pulmonary capillaries

4. A. PCO2 in blood leaving the pulmonary capillaries

B. PCO2 in blood entering the systemic capillaries

5. A. PO2 in blood entering the systemic capillaries

B. PO2 in the tissue cells

Explanation / Answer

Ans.

1. Answer is Option B. ( Item B is greater than item A).

2. Answer is Option A (Item A is greater than item B).

3. Answer is Option C ( A and B are approximately equal).

4. Answer is Option C (A and B are approximately equal)

5. Answer is Option A (Item A is greater than item B).

The exchange of gases ( oxygen and carbon dioxide) between the alveoli and the blood occurs by diffusion. Diffusion requires a concentration gradient. (Molecules move from High concentrations to low concentration).

PO2 in blood entering the pulmonary capillaries =40mmHg

PO2 in alveoli =100mmHg

PCO2 in blood entering the pulmonary capillaries =45mmHg

PCO2 in alveoli =40mmHg

Thus due to pressure gradient, oxygen diffuses from alveoli into blood and carbon dioxide from blood into the alveoli.

PO2 in blood entering the systemic capillaries = 100 mm Hg.

PO2 in tissue cells = 40mm Hg.

PCO2 in blood entering the systemic capillaries =40mmHg

PCO2 in tissue cells = 45mmHg

Because of the differences in partial pressures of oxygen and carbon dioxide in systemic capillaries and body cells, oxygen diffuses from blood into tissue cells and carbon dioxide diffuses from cells into the blood.

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