During gas exchange in tissue capillaries, what happens to oxygen and carbon dioxide?

During gas exchange in tissue capillaries, what happens to oxygen and carbon dioxide?

• A. Oxygen diffuses from tissue cells into blood; carbon dioxide diffuses from blood into tissue cells.
• B. Oxygen diffuses from blood to cells; carbon dioxide diffuses into blood.
• C. Oxygen binds to plasma proteins; carbon dioxide binds to hemoglobin.
• D. Oxygen remains in cells; carbon dioxide remains in plasma.

Answer: (B)

Gas exchange at tissue capillaries is driven by diffusion from areas of higher partial pressure to lower partial pressure. The blood arriving at tissues has more oxygen than the tissue cells and fluids around them, while the tissue cells generate carbon dioxide as a waste product, raising its local partial pressure. Because of these gradients, oxygen moves from the blood into the tissue cells, and carbon dioxide moves from the tissue cells into the blood. In the blood, oxygen is largely carried by hemoglobin in red blood cells and is released where it’s needed, while carbon dioxide is carried back to the lungs primarily as bicarbonate in plasma (with some carried by hemoglobin or dissolved in plasma). This directional flow of gases matches the normal physiology of gas exchange at systemic tissues.

Gas exchange at tissue capillaries is driven by diffusion from areas of higher partial pressure to lower partial pressure. The blood arriving at tissues has more oxygen than the tissue cells and fluids around them, while the tissue cells generate carbon dioxide as a waste product, raising its local partial pressure. Because of these gradients, oxygen moves from the blood into the tissue cells, and carbon dioxide moves from the tissue cells into the blood. In the blood, oxygen is largely carried by hemoglobin in red blood cells and is released where it’s needed, while carbon dioxide is carried back to the lungs primarily as bicarbonate in plasma (with some carried by hemoglobin or dissolved in plasma). This directional flow of gases matches the normal physiology of gas exchange at systemic tissues.