The Respiratory System consists of the rib cage (ribs, intercostal muscles), diaphragm, lungs, mouth, nose and a series of tubes connecting the nose and mouth to the lungs
The lungs are roughly shaped like a cone. They are formed by an elastic tissue and each lung is surrounded by a membrane, the pleura. This consists of two leaflets, one glued to the rib cage the other glued to the lungs. The virtual space between the two membranes is the pleural cavity. This space contains a thin layer of liquid (pleural fluid), which makes possible the movement of the lungs during breathing (inspiratory phase).
In inspiration , air enters through the nasas and through the mouth, through the pharynx, which is a short tube of soft tissues, common to the airways and digestive. The pharynx is divided into two tubes: the trachea and the oesophagus. The epiglottis is a cartilage located in this bifurcation, which selects the food for the esophagus and the air for the trachea. Before reaching the trachea, the air circulates through the larynx, where the vocal cords are inserted.
The trachea is formed by a series of semicircular cartilaginous rings. When it penetrates the thoracic cavity it forks into the left and right bronchi, which branch into the left and right lungs respectively.
Inside the lungs, the bronchi divide into smaller and smaller tubes, such as the trunk of a tree. These small branches of the respiratory tree, the bronchiolos , have a cartilaginous reinforcement.
The alveolos are situated at the end of the bronchiolos. They have very thin walls and are covered by a network of capillary vessels. It is usually said that the pulmonary alveolos look like bunches of grapes (the word alveolo derives from the Latin – alveus – meaning cavity).
In both lungs there are thousands of alveolos that together occupy about 300m2, area equivalent to a tennis court.
The barrier between gas and blood is called an alveolo-capillary membrane. If this membrane ruptures or deteriorates, pulmonary barotrauma may occur.