Respiratory gases, nutrients, and metabolic waste products move between the capillaries and interstitial fluid by the process of __.
A endocytosis
B active transport
C diffusion
D bulk flow
The correct answer and explanation is:
Correct Answer: C) Diffusion
Explanation:
The movement of respiratory gases like oxygen and carbon dioxide, nutrients such as glucose and amino acids, and metabolic waste products such as urea between the capillaries and the interstitial fluid mainly occurs through the process of diffusion.
Diffusion is the passive movement of molecules from an area of higher concentration to an area of lower concentration. This means that molecules naturally spread out to evenly occupy a space, without the need for cellular energy or transport proteins. In the context of capillaries and interstitial fluid, diffusion plays a central role in exchange because capillary walls are thin and permeable to small, nonpolar molecules.
Oxygen, for example, is more concentrated in the blood within capillaries than in the surrounding interstitial fluid. As a result, oxygen diffuses from the blood into the tissues. On the other hand, carbon dioxide is more concentrated in the tissues and will diffuse into the blood to be carried away and expelled by the lungs. Similarly, nutrients like glucose diffuse from areas of high concentration in the blood into cells where they are used for energy. Waste products produced by cells move into the blood for removal from the body.
This process is vital for maintaining cellular respiration and homeostasis. Although other mechanisms like bulk flow and active transport do occur in certain contexts, they are not the primary means for moving respiratory gases and most small molecules. Endocytosis involves the engulfing of large molecules or particles by cells, and active transport requires energy to move substances against a concentration gradient, which is not typical for gases and small soluble substances in capillary exchange.
Therefore, diffusion is the primary and most efficient process responsible for the exchange of gases, nutrients, and waste products between the blood in capillaries and the surrounding tissues.