Summary
Highlights
Air first enters the nasal cavity, then moves to the pharynx, which is divided into three parts: nasopharynx, oropharynx, and laryngopharynx. Air can also enter via the oral cavity. These structures, along with the larynx, constitute the upper respiratory tract, which is clinically relevant for upper respiratory tract infections.
The air then proceeds to the trachea, which bifurcates into the left and right main stem bronchi. These bronchi further branch about 23 times into smaller bronchioles, eventually leading to the alveoli. The lungs, comprising these branching structures and alveoli, along with the trachea and bronchi, form the lower respiratory tract.
The right lung has three lobes (superior, middle, inferior), while the left lung has two (superior, inferior). The difference in the number of lobes is due to the cardiac notch on the left lung, which accommodates the heart.
The right main stem bronchus is wider and more vertical, making it more likely for inhaled foreign objects to be lodged in it.
The nasal cavity contains turbinates, which are folds lined with mucus and blood vessels. These turbinates spin inhaled air, causing particulates (pathogens, pollutants) to stick to the mucus, preventing them from reaching the lungs. They also warm and humidify the air, optimizing it for gas exchange in the alveoli.
The larynx, also known as the voice box, contains the vocal cords. The laryngeal prominence, or Adam's apple, is cartilage present in both males and females. The soft portion below the laryngeal prominence can serve as an accessory airway if the primary airway is blocked.
The trachea is lined with cartilage to keep it open (patent) and prevent collapse due to negative pressure during inspiration, similar to how a straw collapses if blocked. As the airways branch into smaller bronchioles, the amount of cartilage diminishes while muscle increases.
The increased muscle in bronchioles allows them to open and close, playing a crucial role in airflow regulation. Clinically, asthma is a disease of the bronchioles where the smooth muscle constricts, affecting breathing.
The alveoli are tiny air sacs in the lungs where gas exchange occurs. Their vast surface area, approximately that of a tennis court, facilitates efficient exchange of oxygen into the bloodstream and carbon dioxide out of the bloodstream for exhalation.
Dr. Mike introduces a video series on the respiratory tract, focusing on the pathway of air from the atmosphere into the lungs and the major anatomical structures involved in this process.