The alveoli in the lungs are tiny sacs of air surrounded by an intricate web of blood vessels. Oxygen from inhaled air diffuses from this air sac across into the blood down its concentration gradient. Carbon dioxide diffuses from the blood into the air sac to be exhaled.
The process of diffusion is a passive process but it can be made more efficient by several factors. The first is surface area ~ the greater the surface area, the greater the rate of diffusion. The alveoli are shaped like groups of bubbles, and have an extremely large surface area. The presence of water is also important ~ the membranes in the lungs are always kept moist to make sure conditions are right for diffusion.
The walls of the alveoli and the walls of the capillaries that surround them are also very thin ~ the gases can diffuse more easily if they do not have to travel very far. Finally, the rich blood supply from the capillaries that surround the alveoli take away the oxygen very quickly, maintaining a large concentration gradient. This encourages the diffusion of more oxygen into the blood from inhaled air.
The process of diffusion is a passive process but it can be made more efficient by several factors. The first is surface area ~ the greater the surface area, the greater the rate of diffusion. The alveoli are shaped like groups of bubbles, and have an extremely large surface area. The presence of water is also important ~ the membranes in the lungs are always kept moist to make sure conditions are right for diffusion.
The walls of the alveoli and the walls of the capillaries that surround them are also very thin ~ the gases can diffuse more easily if they do not have to travel very far. Finally, the rich blood supply from the capillaries that surround the alveoli take away the oxygen very quickly, maintaining a large concentration gradient. This encourages the diffusion of more oxygen into the blood from inhaled air.
