The major function of the respiratory system is to bring air in contact with the blood so that oxygen may diffuse from the air into the blood and carbon dioxide may diffuse out from the blood. Respiratory system also clears the airway from the particles1.
Oxygen is required to sustain the human body. Oxygen reaches the human cell through the passage of respiratory tract. Coming from the nose, nasopharynx and larynx, the air enters the trachea which is the main windpipe of the respiratory tract. The trachea contains cilia which move back and forth carrying the mucus out and upwards. The mucus, sticky in nature, collects germs, dust and other components which are inhaled in the respiratory system. Thus, with mucus, cilia expels all the harmful substances out of the respiratory tract2.
Respiratory system also helps in phonation. Phonation is the creation of sound by the structures present in the upper part of the respiratory tract. During expiration, the air comes out from the lungs and pass through the larynx or "Voice Box". The muscles in larynx move the cartilage which in turn changes the shape of vocal cords helping in the production of sound3.
The respiratory system is also involved in the process of smelling. Smelling is a chemical process in which chemical particles in the air hit the smelling receptors in the nose which then stimulates the CNS and sensation of smelling is felt4.
The pH level of arterial blood is 7.40 and that of venous blood is lower. If the pH of arterial blood decreases below 7.4 then it is considered as acidosis. If that pH increases above 7.40 then it is regarded as alkalosis. There are two means for acidosis and alkalosis. One is respiratory e.g any short term change in pCO2 due to change in ventilation. Other mean is metabolic e.g addition of acid in the body. Similarly, the pH is compensated by two means. One of them is by respiratory system and other is by renal system.
The respiratory system does hyperventilation to expel CO2 in case of acidosis and does hypoventilation to retain CO2 in case of alkalosis. This compensatory function is more quick as compared to the renal mechanism5.
5. Ganong W. Review Of Medical Physiology. New York: Lange Medical Books; 2005:615-616