Structure of the respiratory organs
In breathing the body takes in oxygen and gives out carbon dioxide; in cells, substances are broken down with oxygen and energy is released. The air passages are the nasal cavity, pharynx, larynx, trachea and bronchi. In the nose air is cleaned of dust, moistened and warmed; when swallowing, the epiglottis closes the way so food does not enter the airway. The larynx holds the vocal cords: exhaled air makes them vibrate, and movements of lips, tongue and jaw turn sound into speech; shorter cords give a higher voice, and in adolescence the voice changes as the cords grow – this is normal. In the lungs bronchi branch and end in thin-walled alveoli; a network of capillaries surrounds the alveoli, where gas exchange happens. The lungs are covered by a double layer, the pleura. In inhalation the external intercostal muscles and diaphragm contract, the chest widens and air enters; in exhalation the muscles relax, the chest becomes smaller and air leaves. A calm adult breathes about 16–18 times a minute.
Place your hand on your ribs and breathe calmly and deeply: feel how the chest widens. Count breaths in a minute (lightly, without forcing).