(a) Tidal Volume (TV) is the volume of air inspired or expired during normal breath. This is about 500 mL , i.e., a healthy man inspire or expire about 6000 to 8000 mL of air per minute.

(b) Residual Volume (RV) is the volume of air remaining in the lungs even after a forcible expiration. It is about 1100 mL to 1200 mL .

(c) Asthma It is a disease caused due to an allergic reaction to foreign substances. The major symptoms are difficulty in breathing causing wheezing and coughing. Due to the inflammation of bronchi.

A fluid filled double membranous layer that surrounds the lungs is called pleura, and fluid is pleural fluid in between them. The outer pleural membrane is in close contact with the thoracic lining whereas, the inner pleural membrane is in contact with the lung surface. These collectively reduce friction on lung's surface.

The primary site for the exchange of gases in our body is alveoli. There are 300 millions of alveoli collectively in both the lungs. These alveoli have very thin wall consisting of squamous epithelium. With extensive network of blood capillaries. The presence of blood capillaries in the alveoli, result in easy exchange of gases. Each alveolus is also called as miniature lung.