What is the site of gas exchange in the circulatory system?

Gas exchange in the circulatory system primarily occurs in the capillaries. Capillaries are the smallest blood vessels in the body, and they create a network that facilitates the exchange of oxygen and carbon dioxide between the blood and surrounding tissues. Their thin walls, which are only one cell thick, allow for efficient diffusion of gases.

Oxygen from the blood passes through these thin walls into the tissues, while carbon dioxide produced by cellular metabolism moves from the tissues into the blood, where it can be transported back to the lungs for exhalation. This exchange process is essential for maintaining the body’s oxygen supply and removing waste gases.

In contrast, veins carry deoxygenated blood back to the heart but are not involved in gas exchange. Arteries transport oxygenated blood away from the heart to the tissues and also do not participate in gas exchange. The atria of the heart are chambers that receive blood but do not play a role in gas exchange either. The unique structure and function of capillaries make them the critical site for this essential physiological process.