Describe how gas exchange occurs at the alveoli

Gas exchange at the alveoli occurs through the following steps:

1. Inhalation: When you inhale, air containing oxygen enters the lungs and travels down the bronchial tubes, eventually reaching the alveoli, which are tiny air sacs at the end of the respiratory tree.

2. Diffusion: The walls of the alveoli are extremely thin and are surrounded by a network of capillaries. Oxygen from the inhaled air diffuses across the alveolar walls and enters the blood in the capillaries.

3. Oxygen Transport: Once oxygen diffuses into the blood, it binds to hemoglobin molecules in red blood cells. This oxygen-rich blood is then transported through the pulmonary veins to the left side of the heart, which pumps it out to the rest of the body.

4. Carbon Dioxide Removal: At the same time, carbon dioxide, which is a waste product of cellular metabolism, diffuses from the blood in the capillaries into the alveoli. This occurs because the concentration of carbon dioxide is higher in the blood than in the alveolar air.

5. Exhalation: Finally, when you exhale, the carbon dioxide-rich air is expelled from the alveoli, travels back up the bronchial tubes, and is released from the body through the nose or mouth.

This process of gas exchange is continuous and ensures that oxygen is supplied to the body while carbon dioxide is removed efficiently.