Gas Exchange

This lesson covers: 

1. The structures involved in gas exchange
2. How gas exchange occurs in the lungs
3. Adaptations of the lungs for gas exchange

Structures involved in gas exchange

The gas exchange system is a needed for breathing to ensure oxygen is taken into the body and carbon dioxide is removed.

The main parts include:

• Lungs - These are sponge-like and are surrounded by the ribcage.
• Diaphragm - This is a large muscle. When it contracts it moves down and we breathe in. When it relaxes it moves up and we exhale.
• Trachea - This tube allows inhaled air to pass from the throat to the lungs. It divides into two smaller tubes called the bronchi.
• Bronchi - These lead to each lung, and further split into smaller tubes known as bronchioles.
• Bronchioles - They are numerous small air passages in the lungs that lead air directly to the alveoli.
• Alveoli - These are tiny, grape-like sacs at the ends of bronchioles that are the sites of gas exchange with the blood.

Gas exchange in the lungs

Gas exchange occurs in the alveoli, where oxygen (O₂) and carbon dioxide (CO₂) pass between the air and the blood. One alveoli is called an alveolus.

Breathing caused by the action of the diaphragm and ribcage drives gas exchange.

• Oxygen diffuses from an area of high concentration in the alveoli to an area of low concentration in the bloodstream.
• Carbon dioxide, a waste product of respiration, diffuses from the blood into the alveoli, from where it is exhaled.

Lung adaptations

To efficiently carry out gas exchange, the lungs have several adaptations:

1. Moist surface - The alveoli have a moist lining that helps the diffusion of gases.
2. Good blood supply - A network of capillaries surrounds the alveoli, ensuring a short distance for gas diffusion.
3. Large surface area - Due to the huge number of alveoli, the lungs have a large surface area for gas exchange.