How does air enter the lungs?

The lungs are a pair of essential organs in the human respiratory system responsible for gas exchange - taking in oxygen and expelling carbon dioxide. The process of air entering the lungs involves several coordinated mechanisms:

1. Inhalation (Inspiration):

- When you inhale, the diaphragm, a large muscle located below the lungs, contracts, and the external intercostal muscles between the ribs also contract.

- These contractions cause the thoracic cavity (chest) to expand, increasing its volume.

- As the thoracic cavity expands, the lungs follow suit, creating a decrease in air pressure inside them.

- This pressure difference establishes a gradient between the higher atmospheric pressure and the lower intrapulmonary pressure.

2. Airflow into Lungs:

- The lower pressure in the lungs during inhalation creates a suction effect.

- As a result, air rushes in through the nose or mouth, passing through the pharynx, larynx, and trachea.

- The trachea branches into two bronchi, one leading to each lung.

- Inside the lungs, the bronchi further divide into smaller branches called bronchioles.

- The bronchioles end in tiny sacs called alveoli, which are the main sites of gas exchange.

3. Expansion of Alveoli:

- As air enters the alveoli during inhalation, they expand.

- The thin-walled alveoli are surrounded by capillaries (tiny blood vessels) that carry blood.

- The increase in lung volume allows for a greater surface area for gas exchange between the air in the alveoli and the blood in the capillaries.

4. Exchange of Gases:

- Oxygen (O2) from the inhaled air diffuses across the thin walls of the alveoli and into the blood capillaries.

- Simultaneously, carbon dioxide (CO2), a waste product of cellular metabolism, diffuses from the blood into the alveoli.

5. Exhalation (Expiration):

- When you exhale, the diaphragm and external intercostal muscles relax.

- The thoracic cavity and the lungs recoil to their resting positions, reducing the lung volume.

- The recoil creates a slight increase in intrapulmonary pressure compared to atmospheric pressure.

- This pressure difference forces the air, now containing higher levels of carbon dioxide, out of the lungs through the same pathway it entered during inhalation.

The cycle of inhalation and exhalation continues at a regular rate, allowing for continuous gas exchange vital for maintaining the body's oxygen supply and removing waste carbon dioxide.