Gaseous Exchange At The Lungs And At The Tissue

Exchange at the lungs 

Gaseous exchange at the lungs is concerned with the replenishing of oxygen in the blood and the removal of carbon dioxide. In the lungs, diffusion is aided by the structure of the alveoli:

• One cell thick, so there is a short diffusion distance
• Vast surface area, facilitates diffusion
• Surrounded by a dense network of capillaries
• Moist surface, eases diffusion

Oxygen makes up about 21% of the air, so it exerts a partial pressure. Gases flow from areas of high pressure to areas of low pressure. As oxygen moves from the alveoli to the blood and then to the muscles, its partial pressure in each has to be successively lower. The exchange of gases at the lungs take place between the alveolar air and the blood flowing through the lung (pulmonary) capillaries. Oxygen enters the blood from the alveoli because the partial pressure of oxygen in the alveoli (105 mmHg) is higher than the partial pressure of oxygen in the…