Aspartame is the most controversial food additive in history, and its approval for use in food was the most contested in FDA history. In the end, the artificial sweetener was approved, not on scientific grounds, but rather because of strong political and financial pressure.
The arterioles then divide further into capillaries. Capillaries are the smallest blood vessels and their walls are only one cell thick which allows diffusion between the blood and cells to occur. Nutrients and oxygen from the blood diffuses through the capillary walls into the tissues that need it. This is aided by the relatively high blood pressure that also squeezes the oxygen and nutrients through the capillary wall and into the cells of the tissue.
These molecules combine with oxygen at the respiratory membrane, where oxygen concentrations are relatively high and easily release the oxygen in deeper tissues, which are low in oxygen. 1  Filaments of a salmon's gills. In fish, water is pumped across gills to enable gas exchange.