Man faces the same general problems of obtaining oxygen and getting rid of carbon dioxide, as do all other large and complex animals. He must have moist and thin respiratory surface across which gaseous exchange with the environment can occur. In addition, he must have some means of transporting oxygen and carbon dioxide to and from the cells. We breathe in air to get oxygen and breathe out carbon dioxide. This is called gas exchange.
3.1.1 Air Passageway and Lungs
The organs responsible for gas exchange in man are the two lungs and the air passages which lead to the lungs.
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The air passageway consists of nose, pharynx, larynx, trachea, bronchi, and bronchioles.
Nose: The nose is an elevated structure. It is divided into two parts. The external openings of the nose are nostrils having hairs. The nostrils lead into a nasal cavity. The top of the nasal cavity has lining of nerve cells, which are responsible for sense of smell. The walls and the base of the nasal passage are lined with cilia. Between the ciliated epithelial cells are goblet cells, which produce sticky fluid, called mucus.
The nasal cavity performs important functions. The air entering the respiratory system must be warmed, moistened and filtered to keep the lung tissue healthy. The hairs lining the entrance to the nasal cavity trap large dust particles. The thin layer of mucus moistens the air and also traps particles of dust or smoke. The cilia sweep the trapped particles and mucus towards the pharynx. These are either swallowed or spit out. By the time air
Do You Know?
All the cilia in the respiratory system beat toward the back of the throat, up from the lungs and down from the nose. Cilia may beat 1,000 times a minute.
the lungs it is relatively dust free, germ free, warm and moist. These protective measures keep the lungs clean, so that the lungs can perform the important work of gas exchange.
Pharynx: Air is drawn out of the nasal passages into a channel called pharynx, at the back of the mouth. There are several openings in the pharynx. The air is channelized from the pharynx into the larynx. Larynx or voice box is a cartilaginous structure. It surrounds the upper end of the trachea. The cavity of the larynx is called glottis. Epiglottis is a cartilaginous structure.