Breathing in humans involves two main phases: inhalation (inspiration) and exhalation (expiration). Inhalation is the process of taking air into the lungs, while exhalation is the process of releasing air from the lungs. These two processes, coupled with the exchange of oxygen and carbon dioxide, are vital for life.
Inhalation:
1. Diaphragm Contraction:
The diaphragm, a large muscle sheet located below the lungs, contracts and moves downwards, increasing the space in the chest cavity.
2. Rib Cage Movement:
Muscles between the ribs contract, pulling the rib cage upwards and outwards, further expanding the chest cavity.
3. Increased Volume and Decreased Pressure:
The combined effect of the diaphragm and rib cage movement increases the volume of the chest cavity, which in turn reduces the pressure inside the lungs.
4. Air Inflow:
Since the air pressure inside the lungs is now lower than the surrounding atmosphere, air rushes into the lungs through the nostrils or mouth.
5. Air Pathway:
The air travels through the nasal passages, pharynx, larynx, trachea, bronchi, and bronchioles, eventually reaching the alveoli, tiny air sacs within the lungs where gas exchange takes place.
Exhalation:
1. Diaphragm Relaxation:
The diaphragm relaxes, moving upwards and returning to its dome shape.
2. Rib Cage Return:
Muscles between the ribs relax, causing the rib cage to return to its original position.
3. Decreased Volume and Increased Pressure:
The chest cavity volume decreases, resulting in increased pressure inside the lungs.
4. Air Outflow:
The increased pressure inside the lungs forces air out of the lungs through the same pathway as inhalation, eventually exiting through the nostrils or mouth.
Gas Exchange:
In the alveoli, oxygen from the inhaled air diffuses across the thin walls of the alveoli into the blood, while carbon dioxide, a waste product of cellular metabolism, diffuses from the blood into the alveoli to be exhaled.
This process, known as gas exchange, is essential for providing oxygen to the body’s tissues and removing carbon dioxide.