By Chandan Sekhon - Medicine Student @ Peterhouse, Cambridge
Oxygen (O2) and carbon dioxide (CO2) are respiratory gases which must be exchanged between the external environment and tissues. Oxygen is taken into the bloodstream via diffusion from the lungs at alveoli, by crossing the alveolar epithelium and capillary endothelium into the bloodstream. The blood then transports this oxygen to tissues to allow aerobic respiration to occur. CO2 diffuses into the bloodstream after being produced as a waste product of respiration from cells. This CO2 is transported via the bloodstream into alveoli at the lungs, where it is expelled from the body. This system helps maintain a steep concentration gradient of these gases for efficient diffusion.