Function of the Alveoli

The functional unit of lungs is tiny air sacs that arise from bronchioles called alveoli. These terminal air sacs is the area where exchange of gases takes place within the lungs. This air exchange consists of absorption of oxygen and removal of carbon dioxide. In the following paragraphs, you shall learn more about the function and structure of this air sac.

Before moving on to the function of alveoli, let us understand their structure. This is because the function and structure of this unit go hand in hand. So, let us highlight a few facts about the respiratory system. There are about 300 to 400 million alveoli in an adult lung.

The average diameter of an alveolus is about 200 to 300 microns. The alveoli contain collagen and elastic fibers. These are lined with epithelial cells and the pores between them are called Kohn. During exhalation, the elastic connective tissues that make up the space between alveoli of the lungs come into function.

An alveolus is made up of three different major cells like squamous alveolar cells, squamous epithelial cells, and great alveolar cells. The squamous epithelial cells are also called Type I cells and great alveolar cells are also known as Type II cells. The structure of an alveolar wall is made up by squamous alveolar cells.

The squamous epithelial cells make up the capillaries that cover about 70% of the area. The function of these capillaries is diffusion of gases. Finally, the great alveolar cells secrete a surfactant that helps in the reduction of surface tension of water. It also helps in separation of membranes and increasing the exchange of gases.

If the endothelium of the alveolus gets damaged, the great alveolar cells help in repairing them. The alveolus also consists of macrophage cells. These cells help in destroying any foreign matter like bacteria, etc. and has functions related to the immune system.

So, basically the function and structure is specifically designed to help in the exchange of gases efficiently with the help of:

• Extremely thin walls
• Large surface area in relation to the volume
• Fluid lining that helps in exchange of dissolved gases
• Number of capillaries surrounding each alveolus.

The basic function of alveoli is exchange of gases. Its structure is the site where the gaseous exchange during respiration takes place. These structures are surrounded by capillaries carrying blood. The exchange of carbon dioxide in the blood from these capillaries occurs through the walls of alveolus.

The alveoli begins to function when we breathe in air through our nostrils. The air passes through a long route consisting of various organs of the respiratory system. These organs include the nasal passages, pharynx, larynx, trachea, main bronchi, small bronchial tubes, bronchioles, and finally reaching the alveolus through tiny air sacs.

The air contains oxygen that is absorbed by the blood flowing through the capillaries. This oxygen is then passed on to the circulatory system, thus completing the gaseous exchange cycle.

It diffuses into the blood that is in the low oxygen concentration gradient. This is because of the continuous oxygen consumption in the body. The same thing happens in case of carbon dioxide.

Blood contains high concentration of carbon dioxide and alveoli contains low concentration. Thus, the gaseous exchange takes place through passive diffusion as a part of the function of respiratory system.

Gas exchange is the main function of alveoli. They are the terminal branches of the respiratory system.