What are the five primary functions of the respiratory system?

The five primary functions of the respiratory system, in order of significance, are:

1. The inhalation and exhalation of air or Breathing. This involves the nasal and oral cavities, the pharynx, the larynx, the trachea and the lungs. Also involved are the diaphragm, the intercostal muscles, and the rib cage to pull in air for inhalation and push it out for exhalation.

2. Gas exchange between the lungs and the bloodstream (External Respiration). This involves the passage of oxygen from the air in the alveoli (tiny sacs at the end of the bronchioles in the lungs) through the alveolar and capillary walls to the blood in the capillaries, as well as the passage of carbon dioxide from the bloodstream to the alveoli.

3. Gas exchange between the bloodstream and the body tissues (Internal Respiration). This involves the transport of oxygenated blood from the heart to all parts of the body, where the oxygen is delivered to tissues and cells for energy and metabolism, while carbon dioxide, as a waste product, is absorbed by the blood.

4. Vibration of the vocal cords in the larynx to produce Sound. This is a more specialised function in which air passing over the vocal cords is modulated by laryngeal muscles pushing the vocal cords together so that they vibrate when air passes over them, creating sound.

5. The sense of Smell. Olfaction, or the sense of smell, occurs when air passes over olfactory fibres in the nasal cavities that sense certain chemicals in the inhaled air that bind to them and transmit a signal to the brain which is then identified.