Respiratory System

The respiratory system supplies the blood with oxygen, which is then distributed throughout the body by the circulatory system through the action of breathing; oxygen is brought into the body when a person inhales.

The respiratory system also removes the poisonous gas carbon dioxide when a person exhales. Carbon dioxide and oxygen molecules are exchanged between the external environment and the blood by diffusion; this exchange happens in the lungs' alveolar region.

The respiratory system's primary organs and anatomical features include the lungs, the airways - including the mouth, nose, and trachea - and the diaphragm and other respiratory muscles.

The trachea is a tube which runs from the throat down into the chest cavity; within the chest, the trachea divides into two smaller tubes. These are the bronchi; these divide again, into the bronchial tubes.

The bronchial tubes lead down into the lungs, where they split into many very small tubes which connect to tiny, air-filled sacs of spongy tissue (the alveoli). Most adults have around 600 million alveoli, which are surrounded by capillaries. Inhaled oxygen moves into the alveoli and diffuses into arterial blood through the capillaries; at the same time, the veins release carbon dioxide directly into the alveoli, and the carbon dioxide is removed from the lungs upon exhaling. The diaphragm is the muscle which inflates and deflates the lungs, moving air into and out of them.