Inhalation (Inspiration): When we inhale, the diaphragm and intercostal muscles contract. The diaphragm moves downward, and the rib cage expands, increasing the volume of the thoracic cavity. This expansion lowers the air pressure inside the lungs, causing air to rush in through the nose or mouth, down the trachea, and into the lungs. Oxygen from the inhaled air diffuses across the thin alveolar membrane into the bloodstream, where it is transported to body tissues.
Exhalation (Expiration): Exhalation is a passive process. When the diaphragm and intercostal muscles relax, the thoracic cavity decreases in volume, causing the air pressure inside the lungs to increase. This forces air out of the lungs, expelling carbon dioxide, a waste product of cellular respiration, from the body.
