Question

Explain how oxygen and carbon dioxide are transported and released at the lungs and tissues.

Answer 1

Transport of carbon dioxide:

- The partial pressure of carbon dioxide in the tissue is about 45 mm Hg. Whereas partial pressure of carbon dioxide in the arterial blood is 40 mmHg. Hence at tissue level carbon dioxide diffuses from tissue to the blood.

1) Carbon dioxide is more soluble in blood than oxygen. About 5 to 7 percent of all carbon dioxide is dissolved in the plasma.
2) carbon dioxide can bind to plasma proteins or can enter red blood cells and bind to hemoglobin. This form transports about 10 percent of the carbon dioxide.

3) the majority of carbon dioxide molecules near about 85% are carried as part of the bicarbonate buffer system. In this system, carbon dioxide diffuses into the red blood cells. Carbonic anhydrase (CA) within the red blood cells quickly converts the carbon dioxide into carbonic acid (H2CO3). Carbonic acid is an unstable intermediate molecule that immediately dissociates into bicarbonate ions
and hydrogen (H+) ions.
When the blood reaches the lungs, The H+ ion binds to the bicarbonate ion. This produces the carbonic acid intermediate, which is converted back into carbon dioxide through the enzymatic action of CA. The carbon dioxide produced is expelled through the lungs during exhalation.

Transport of oxygen: Partial pressure of oxygen in the atmosphere is 160 mmHg while in the lung capillaries, it is 70-100 mmHg hence oxygen diffuses from atmosphere into the lung capillaries.

- most of the oxygen is transported by binding to the hemoglobin.

Some amount s transported via dissolved form.