Write brief notes on pharyngitis, laryngitis, bronchitis, asthma.

Pharyngitis : It is an inflammation of pharynx often called sore throat. It may accompany the common cold and it usually involves the tonsils (tonsilitis).

Laryngitis : It is an inflammation of larynx that often accompanies pharyngitis. In laryngitis inflammation of larynx disturbs the vibration of vocal cords and the person has difficulty in speaking.

Bronchitis : It is an inflammation of the bronchi. The lining of bronchi swells and produces excess mucus.

Asthma : It is more correctly called bronchial asthma. It is  caused due to an allergic reaction to foreign substances that affect the respiratory tract. Allergens stimulate the release of histamine from the mast cells. Histamine has several effects, one of which is to cause bronchial smooth muscle to contract.