The windpipe, also known as the trachea, is a part of the respiratory tract through which air passes from the nose or mouth to the lungs. It is membranous and flexible, but its walls contain a number of rings of cartilage that protect it from injury and collapse. The trachea is connected to the larynx above it, and below it are the primary bronchi, which branch from the windpipe to the lungs. The rear of the trachea can change shape to allow for the passage of food through the esophagus, which is situated directly behind it. Surgery is sometimes performed on the trachea in operations to allow airflow into the lungs.
The walls of the trachea are composed of connective tissue and smooth muscle. A number of C-shaped rings of cartilage, usually between 15 and 20, are contained in the tracheal wall. The C shape is open to the rear of the windpipe due to its nearness to the esophagus. This allows the esophagus to expand toward the front of the throat when food passes through it. The rings of cartilage also keep the trachea from collapsing due changes in air pressure that normally occur during respiration.
At their rear, the rings contain smooth muscle fibers instead of cartilage. These band of muscle are collectively called the trachealis muscle, and they can contract to narrow the windpipe's diameter. This response helps to expel irritants in the airway through coughing and is also partially responsible for the force of sneezes.
The trachea and its rings of cartilage can be felt at the front of the throat, directly below the laryngeal prominence or Adam's apple. The windpipe is located below the larynx, which contains the human vocal cords. From there, it descends into the thorax and is connected to the lungs by the primary bronchi, which go on to form extensive networks in the lungs. Different anatomical divisions place the trachea either at the bottom of the upper respiratory tract or at the top of the lower respiratory tract. With the bronchi, it is sometimes collectively called the tracheobronchial tree.
Medical procedures that are required to establish or maintain airflow to the lungs can involve the windpipe. A tracheostomy is a procedure performed on the trachea, usually between the second and third cartilage rings, that allows for the insertion of a tube for breathing. While this operation is sometimes called a tracheotomy, the word tracheotomy more strictly refers to the cutting or incision of the trachea.