Gaseous Exchange at the Alveoli

Gaseous Exchange at the Alveoli

Function of Alveoli

• Alveoli, tiny sac-like structures at the end of bronchioles, function as the site of gaseous exchange in the human body.
• They play a central role in the process of respiration, where oxygen taken from the air is diffused into the bloodstream and carbon dioxide is released out from the bloodstream.

Structure of Alveoli

• Each of these alveoli is surrounded by a network of tiny blood vessels, or capillaries.
• The walls of the alveoli are extremely thin (just one cell thick), allowing rapid diffusion of gases.
• The inner surface of the alveoli is coated with a thin layer of water known as surfactant. This reduces surface tension to prevent the alveoli from collapsing when air leaves during exhalation.

Oxygen Transport

• The oxygen in the air breathed in diffuses across the thin walls of the alveoli and capillaries into the red blood cells in the capillaries.
• Here, it binds to a molecule called haemoglobin, creating oxyhaemoglobin. This compound is transported throughout the body to supply oxygen to the body’s cells.

Carbon Dioxide Removal

• Carbon dioxide, a waste product of metabolism, enters the alveoli from the blood through diffusion across the thin alveolar and capillary walls.
• Once in the alveoli, it is removed from the body as we exhale.

Necessary Conditions for Efficient Gas Exchange

• This process of gaseous exchange relies on the partial pressure gradient, with each gas moving from an area of higher pressure to an area of lower pressure.
• Optimal gas exchange at alveoli also relies on the large surface area provided by the many alveoli in the lungs and their close proximity to the extensive network of capillaries.