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RiteshChandra
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The lungs are located in the upper thoracic cavity of the chest, one on each side of the median line, and are separated from each other by the heart, the greater blood vessels and the larger air tubes. The lungs are spongy, porous, and their tissues are very elastic, containing innumerable air-sacs or alveoli. Each lung consists of an apex and a base. The base is directed towards the diaphragm, the muscular septum, the dividing wall between chest and the abdomen.
The air passage consists of the interior of the nose, pharynx or throat, larynx or voice box, trachea or windpipe, right and left bronchi and the smaller bronchial tubes. When we breathe, we draw in the air through the nose and after it has passed through the pharynx and larynx, it passes into the windpipe, thence into the right and left bronchial tubes, which in turn, subdivide into innumerable smaller tubes called bronchioles, which terminate in minute subdivisions in the millions of small air-sacs of the lungs. When spread out over an unbroken surface, these air-sacs of the lungs would cover an area of 1,40,000 square feet.
The air is drawn into the lungs by the action of the diaphragm. When it expands, the size of the chest and the lungs is increased and the outside air rushes into the vacuum thus created. The chest and lungs contract when the diaphragm relaxes and the air is expelled from the lungs.