Respiratory system can be defined as system in which the oxygen is taken into the body and the waste part carbon dioxide is expelled from the body. It consists of the lungs, airways, windpipe, mouth, throat, diaphragm, respiratory muscles.

Gas exchange is the primary function of the Respiratory System. It is an mechanical cycle of inspiration and expiration.

When we take breath then oxygen enters through the mouth and nose in the respiratory system. After this the oxygen passes through the larynx and trachea ( is a tube that enters the chest cavity). Trachea then split into two smaller tubes that are called the bronchi which are again divided into bronchial tubes. The bronchial tubes lead directly into the lungs where they divides into many smaller tubes which directly connect to sacs called alveoli. The oxygen, which we take from the air, passes into the alveoli and then diffuses the capillaries into the arterial blood and the waste material (carbon dioxide) is released from the veins into the alveoli. When you exhale, the carbon dioxide fallows the same path out of the lungs.

There are several diseases that are related to Respiratory System. Asthama is very common disease of Respiratory system.
We categories these diseases of repository system into four general categories-

1) Obstructive Diseases
2) Restrictive Diseases
3) Vascular Diseases
4) Infectious, Environmental and Other Diseases

a-Obstructive Diseases

1) Asthma
2) Bronchitis
3) Emphysema
4) Bronchiectasis

b-Restrictive Diseases

1) Fibrosis
2) Sarcoidosis
3) Pleural Effusion

c-Vascular Diseases

1) Pulmonary Edema
2) Pulmonary Embolism
3) Pulmonary Hypertension
 
d-Infectious, Environmental and Other Diseases

1) Pneumonia
2) Tuberculosis