What is the primary composition of deoxygenated blood?

Deoxygenated blood is primarily composed of low levels of oxygen and high levels of carbon dioxide. This occurs because, as blood travels through the body, it delivers oxygen to tissues and picks up carbon dioxide as a waste product of cellular respiration. The exchange takes place in the capillaries, where oxygen diffuses from the blood into the cells, while carbon dioxide moves from the cells into the blood. As a result, the blood that returns to the heart from the body is deoxygenated, meaning it has released its oxygen supply and absorbed carbon dioxide. This is crucial for maintaining the efficiency of gas exchange in the lungs, where deoxygenated blood is then re-oxygenated through the process of respiration.