What causes your lungs to pull in air from the atmosphere?

The primary factor that causes your lungs to pull in air from the atmosphere is the difference in air pressure between the inside of your lungs and the outside environment. This pressure difference is created by the contraction and relaxation of the diaphragm and the intercostal muscles, which are the muscles between the ribs.

Inspiration (breathing in):

1. Diaphragm Contraction: The diaphragm, the primary muscle of respiration, contracts and moves downwards, increasing the volume of the thoracic cavity (the space within the chest).

2. Intercostal Muscles Contraction: The external intercostal muscles between the ribs also contract, pulling the ribcage upwards and outwards.

3. Lung Expansion: As the thoracic cavity expands, the lungs expand along with it. The pressure inside the lungs decreases, creating a negative pressure compared to atmospheric pressure.

4. Air Inflow: Due to this negative pressure, air is drawn into the lungs through the nose or mouth. The air flows through the trachea (windpipe) and bronchi, eventually reaching the alveoli, the tiny air sacs within the lungs where gas exchange occurs.

Expiration (breathing out):

1. Diaphragm Relaxation: The diaphragm relaxes and moves upwards, decreasing the volume of the thoracic cavity.

2. Intercostal Muscles Relaxation: The external intercostal muscles relax, allowing the ribcage to return to its normal position.

3. Lung Recoil: The elastic nature of the lungs causes them to recoil passively, reducing their volume.

4. Air Expulsion: As the thoracic cavity decreases in volume, the pressure within the lungs increases, exceeding atmospheric pressure. This causes air to be pushed out of the lungs through the trachea, bronchi, and nose or mouth.

The coordinated contraction and relaxation of these muscles regulate the volume of the thoracic cavity and create pressure changes that facilitate the movement of air into and out of the lungs.