Describe the gas exchange in lungs?

The exchange of oxygen and carbon dioxide between the lungs' air sacs and the bloodstream during breathing is known as gas exchange, also referred to as respiration or inspiration and expiration.

Here is an in-depth look at the process of gas exchange in the lungs:

Inspiration (Breathing In)

1. Diaphragm and Intercostal Muscles Contract: When you inhale, the diaphragm (the dome-shaped muscle separating the lungs and abdomen) contracts and moves downwards. Simultaneously, the intercostal muscles between the ribs also contract, elevating the rib cage.

2. Lung Expansion: As a result of these muscular contractions, the chest cavity increases in volume, causing a drop in intrathoracic pressure (inside the chest). This creates a pressure difference between the atmosphere and the lungs, enabling air to flow into the lungs.

3. Air Enters the Lungs: The pressure gradient causes air from the atmosphere, rich in oxygen, to flow through the trachea (windpipe), then through the bronchial tubes, and finally into the tiny air sacs of the lungs called alveoli.

Gas Exchange in the Alveoli

1. Alveolar Structure: The alveoli are thin-walled, grape-like structures with an extensive network of capillaries (tiny blood vessels) surrounding them. This provides a large surface area for efficient gas exchange.

2. Diffusion: Due to the difference in gas concentrations, oxygen from the alveoli moves down its concentration gradient into the bloodstream. Simultaneously, carbon dioxide, a waste product from cells, diffuses from the blood into the alveoli.

Expiration (Breathing Out)

1. Relaxation of Muscles: After inspiration, the diaphragm and intercostal muscles relax. The forces that kept the chest cavity expanded reduce, causing the chest and lungs to recoil to their resting positions.

2. Reduction in Lung Volume: As the chest cavity volume decreases, the pressure inside the lungs increases above atmospheric pressure. This causes the air in the lungs, which is now rich in carbon dioxide and depleted in oxygen, to be expelled.

3. Air Exits the Lungs: The exhaled air, containing a higher concentration of carbon dioxide and a lower concentration of oxygen compared to the inhaled air, exits the body through the bronchial tubes, trachea, and mouth or nose.

This cycle of inspiration and expiration ensures a continous exchange of oxygen and carbon dioxide between the lungs and bloodstream, supplying oxygen to the body's cells and removing waste carbon dioxide. It is facilitated by the structural and physiological adaptations of the respiratory system to maximise gas exchange efficiency.