Gas Exchange (OCR GCSE Physical Education (PE)): Revision Note

Gas exchange in the alveoli

• The term gas exchange refers to the exchange of gases between the air and the blood

• Gas exchange occurs at the alveoli in the lungs

  • Oxygen enters the blood from the air

  • Carbon dioxide leaves the blood and enters the air

• Gas exchange occurs by the process of diffusion

  • There is a high concentration of oxygen in the alveoli and a low concentration of oxygen in the capillaries so oxygen diffuses from the alveoli into the blood

  • There is a high concentration of carbon dioxide in the capillaries and a low concentration in the alveoli, so carbon dioxide diffuses from the blood into the alveoli

• Both oxygen and carbon dioxide are capable of combining with haemoglobin

  • After diffusing into the blood oxygen binds to haemoglobin within red blood cells to form oxyhaemoglobin:

oxygen + haemoglobin → oxyhaemoglobin

Key features of the alveoli

• The structure of the alveoli is designed to assist with gaseous exchange:

  • They have moist, thin walls which are one cell thick, reducing the diffusion pathway for gases

  • An extensive capillary network surrounds each alveoli which means that the alveoli have an excellent blood supply

  • There are many alveoli within the lungs creating a large surface area across which diffusion can occur