Respiration provides our body with oxygen. But before the oxygen is extracted the air passes through the respiratory organs and is filtered and warmed.

The air enters our body through the mouth or the nose cavity . The nose cavity is separated from the mouth by the hard palate. It enables us to breathe and swallow at the same time. The soft palate closes the back of the nose cavity and the epiglottis closes the windpipe when we swallow food. If we try to speak and swallow at the same time, however, we 'swallow the wrong way'.

Air we breathe in is usually fairly dry, very dusty and often very cold. Before it gets to the lungs it must be warmed , cleaned and checked for dangerous substances before it reaches them. Therefore the nose cavity is lined with a tissue of ciliated cells, cells producing mucus and cells reacting to chemical substances.

Then the air passes through the larynx (voice box) (1) and enters the trachea (windpipe). (2). It is about 12 cm) long and 2-5 cm in diameter. The windpipe divides into two smaller tubes, bronchi (3) (singular: bronchus), which enter the lungs. Both tubes are kept open by rings of cartilage (4) and their inside is lined by a ciliated mucous membrane. In the windpipe and bronchi just as in the nose cavity dust particles and bacteria become trapped in the mucus and are transported upward by the movement of the cilia. When they reach the top of the windpipe, they pass down the gullet during normal swallowing.

The lungs are inside your chest cavity or thorax. They consist of a pink and spongy tissue and they are protected by the ribs with their intercostal muscles (5). Each lung is surrounded by a double pleural membrane (6)). There is pleural fluid in the space between the two membranes which allow the movement of the lungs against the ribs when they extend. The base of the lungs reaches the diaphragm (7), a sheet of muscle that separates your thorax from the abdomen.

The bronchi entering the lungs divide into smaller tubes or bronchioles which have air sacs at the ends. The air sacs consist of many tiny bags or alveoli (singular: alveolus) (8) . There are about 300 million alveoli in one set of human lungs. Alveoli are very delicate structures and for them to work properly their linings must be kept moist, free of dust and not exposed to extremes of temperature. If they could be spread out flat they would cover the area of a tennis court. The alveoli are covered by a network of capillary blood vessels (9). In the alveoli the exchange of gases takes place by diffusion.

l. 3 nose cavity - Nasenhöhle; l. 4 hard palate - harter Gaumen; l. 5 epiglottis - Kehlkopfdeckel; l. 10 tissue of ciliated cells - Schleimhaut mit Flimmerhärchen; l. 10 mucus - Schleim; l. 12 larynx (voice box) - Kehlkopf; l. 15 rings of cartilage - Knorpelspangen; l. 18 gullet - Speiseröhre; l. 20 intercostal muscles - Zwischenrippenmuskeln; l. 21 pleural membranes - Ripp- und Lungenfell; l. 24 abdomen - Bauch(raum); l. 26 alveoli - Lungenbläschen; l. 28 lining - here: Innenwand