Diffusion alone governs direction of gas flow. Oxygen diffuses into the capillary because there is a higher concentration of it in the alveolus. High altitude planes pressurize cabins to maintain this gas pressure. Internal Respiration Cleanses Tissue Fluid a. Internal respiration is exchange of gases between blood in systemic capillaries and surrounding tissue fluid.
Blood entering systemic capillaries is bright red due to oxyhemoglobin.
The lower PO 2 of the tissues is due to tissues constantly using up oxygen in aerobic cellular respiration. HCO 3 - h. Enzyme carbonic anhydrase in RBCs speeds up the reaction. External and Internal Respiration Revisited a. PO 2 of air entering lungs is about 100 mm Hg, sufficient to cause hemoglobin to become saturated with oxygen. Respiration and Health Respiratory Tract Infections a.