Explain the mechanism of breathing in human beings.

In human beings, as in most vertebrates and mammals, gaseous exchange occurs in a pair of lungs. They are enclosed in an air-tight compartment called thorax (or chest). This region is bound by the ribs and the diaphragm. Several organs participate in the process of respiration in human beings. They are the nasal cavity, larynx, trachea, bronchi, alveoli and lungs. Air is inhaled or exhaled by the body as lungs are expanded or contracted by the simultaneous contraction and expansion of muscles attached to the ribs and diaphragm. The air containing oxygen is taken in through the nose where it is filtered and cleaned from dust particles, bacteria and other foreign substances by the mucus (stick liquid) and hair present in the nostrils. This air then passes through the larynx, the voice-box chamber situated in the neck region, to reach the tracheal tube or the windpipe. The trachea is a tube that runs from the larynx down the neck region into the thorax. From the thorax air reach the alveoli through bronchioles.