What process describes the exchange of substances in capillaries?

The exchange of substances in capillaries is a multifaceted process that encompasses diffusion, transcytosis, and filtration, making "all of the above" the correct choice.

Diffusion is a fundamental mechanism where molecules move from an area of higher concentration to an area of lower concentration. In the context of capillaries, oxygen and carbon dioxide exchange between blood and tissues occurs primarily through diffusion, allowing essential gases to meet the metabolic needs of tissues.

Transcytosis involves the transport of substances across a cell. In capillary endothelial cells, larger molecules that cannot pass through the endothelial cell membranes may be engulfed by these cells and moved across to the other side, a process critical for transporting proteins and certain nutrients.

Filtration refers to the movement of fluid and solutes through the capillary walls due to hydrostatic pressure differences. This is particularly important in the kidneys and in areas where fluids and solutes need to be filtered out of the bloodstream.

Understanding that all three processes—diffusion, transcytosis, and filtration—play integral roles in the capillaries allows for a comprehensive view of how substances are exchanged efficiently within the circulatory system. Each mechanism serves specific functions, contributing to the overall regulation of nutrient and gas