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Air enters through the nostrils into the nasal cavity where hairs and mucus filter out harmful particles like bacteria and dirt. The air is then warmed and humidified before traveling through the pharynx and larynx into the trachea. The trachea bifurcates into two bronchi that lead to the left and right lungs, where air continues through progressively smaller bronchioles to reach the alveoli for gas exchange.

The bronchi and bronchioles are lined with cilia that beat upward to move mucus and trapped debris toward the throat for disposal through swallowing. This mucus traps foreign particles that pass through the nasal cavity defenses or enter via the mouth. Smoking damages cilia, making mucus removal difficult and increasing susceptibility to respiratory infections.

Alveoli are tiny sacs where gas exchange occurs between the lungs and the circulatory system. Each alveolar duct divides into approximately 100 alveolar sacs, each containing 20-30 alveoli. This grape-like structure maximizes surface area—the lungs contain 75 square meters of alveoli surface area, equivalent to a small apartment, enabling efficient oxygen uptake and carbon dioxide removal.

The trachea is a 10-12 centimeter tube located in front of the esophagus that allows air to enter and exit the lungs. Its C-shaped hyaline cartilage keeps the trachea open during breathing. When smooth muscle in the trachea contracts, the diameter decreases and exhaled air is pushed out forcefully, as occurs during coughing.

As the trachea enters the thoracic cavity, it bifurcates into two bronchi corresponding to the left and right lungs. Each bronchus then splits into increasingly smaller branches called bronchioles. This branching pattern creates a tree-like structure that distributes air throughout the lungs while maximizing surface area for gas exchange.

In cases of damage to the throat or mouth that blocks breathing, a tracheostomy—a surgically-created hole in the trachea—can allow air to enter and exit the lungs, bypassing the obstruction. This procedure provides an alternative airway when normal breathing passages are compromised.

The nasal cavity filters, warms, and humidifies incoming air. Hairs and mucus in the nasal cavity trap particulate matter such as bacteria and dirt that could be harmful if inhaled. This initial processing ensures that cleaner, conditioned air reaches the lower respiratory tract and lungs.