Figure 1.
Role of the circulatory system in transporting the respiratory gases and metabolic substrates around the body. The diagram is based on the situation in mammals. As well as transporting the respiratory gases, oxygen and carbon dioxide, to and from the metabolizing cells, the circulatory system also transports carbohydrates (diamonds, CHO) and fatty acids (circles, FAT), both directly from the gut and from stores in the liver and fat cells. The transported carbohydrates and fatty acids go either directly into the glycolysis (GS) or β-oxidation (βOX) pathways, respectively, and then to the Krebs cycle (KC) or to replenish the intracellular stores (CHOic and FATic). (Adapted from Hoppeler & Weibel [2].)