Final answer:
Low pressures in the pulmonary capillaries facilitate the diffusion of oxygen into the blood and removal of carbon dioxide from the blood due to pressure gradients. This exchange process is essential for cellular function and occurs through the systemic and pulmonary circulations of the cardiovascular system.
Step-by-step explanation:
The question is about the low pressures in the pulmonary capillaries which correspond to the body's tissue needs for gas exchange.
In the lungs, oxygen diffuses out of the alveoli and enters the pulmonary capillaries due to a pressure gradient—it is higher in the alveoli (PALVO₂ = 100 mm Hg) than in the blood (Po₂ = 40 mm Hg) in the capillaries.
Similarly, carbon dioxide (CO₂) diffuses from the blood where it has a higher pressure (45 mm Hg) into the alveoli with a lower pressure (40 mm Hg).
This diffusion process ensures both gases move down their respective pressure gradients, allowing oxygen to bind to hemoglobin in red blood cells and be carried to the tissues, while CO₂ is transported to the lungs to be exhaled.
Within the systemic circulation, oxygen is released from hemoglobin and diffuses into tissue cells where Po₂ is lower (40 mm Hg) compared to the blood in the capillaries (Po₂ = 100 mm Hg).
At the same time, CO₂ diffuses into the capillaries from the tissues where its pressure is higher (45 mm Hg) compared to the blood (40 mm Hg). This continuous exchange of gases is critical for maintaining the functioning of the body's cells.