A bronchus is one of the large tubes that lead from the human trachea to the lungs. There is one large bronchus in each lung that branches out into smaller bronchi within the lungs. Bronchi carry air into and out of the lungs.
The respiratory system begins at the nose and mouth, which meet at the pharynx. At the bottom of the pharynx are the esophagus, for food, and the trachea, for air. The epiglottis is a flap of tissue that covers the trachea when swallowing, to prevent food from passing into the airway as it enters the esophagus.
At the top of the trachea is the larynx. This is the home of the vocal cords, which vibrate to create speech and sounds. The trachea continues beyond the neck and into the chest cavity, where it divides into the bronchi. The bronchi extend into the lungs.
The right main bronchus is larger than the left. It divides into three lobar bronchi. The left main bronchus splits off into two lobar bronchi. The lobar bronchi then branch into what are called tertiary bronchi, and then into smaller bronchioles.
The bronchioles eventually branch into alveolar ducts and sacs. The alveoli, or air sacs, are the primary units for the exchange of oxygen and carbon dioxide in the lungs. A human has approximately 480 million alveoli.
The muscle that separates the chest from the abdomen is the diaphragm. This is the main muscle used in respiration. Inhalation occurs when the diaphragm contracts and moves downward. The air pressure within the chest cavity is reduced, causing air to flow into the lungs. In exhalation, the diaphragm is relaxed and pushes air out of the chest.
Asthma is a disorder in which the bronchi are obstructed, often causing wheezing and difficult or painful breathing. Treatment may include inhaled corticosteroids to decrease inflammation, as well as bronchodilators to keep airways open. There is no cure for asthma and treatment is based on controlling symptoms.
Bronchospasm is the contraction of the smooth muscle in a bronchus or bronchiole. This condition may be caused by irritation or injury to the mucosa in the airway, by infection, or due to allergy. Symptoms include a severe cough and wheezing. Treatment is similar to that for asthma.
Bronchitis is an inflammation of the bronchial airways related to infection, allergies, or other causes. When the lining of the bronchi become inflamed, they swell and create excessive secretions. Antibiotics, cool-mist vaporizers, and fluids can all be included in its treatment.