Describe the mechanism of breathing in man.

Explanation

Breathing is a physical process involving inflow (inspiration) and outflow (expiration) of air between atmosphere and the alveoli of the ling.
During inspiration, the intercostal muscles contract and pull the rib cage upwards and outwards. At the same time, the diaphragm contracts and flattens. These movements increase the volume and therefore lowers the pressure in the thorax/chest cavity . As the pressure in the chest cavity falls below that of the atmosphere, air rushes in.
During expiration (breathing out), relaxation of intercostal muscles and diaphragm takes place. The ribs move downwards and inwards. The volume of the lungs decreases, squeezing the air inside them. Diaphragm comes back to its ogiginal C-shaped position. This increases the air pressure inside the lungs, forcing it out.