QS Study

Respiration is a physiological process by which Oxygen is transported from the atmosphere to the cells for oxidation of the ingested food materials and Carbon dioxide is eliminated from cells to the atmosphere. It is the act of inhaling and exhaling air in order to exchange oxygen for carbon dioxide. In animals with lungs, physiological respiration involves respiratory cycles of inhaled and exhaled breaths. Inhalation (breathing in) is usually an active movement.

Respiration includes four processes:

  1. Pulmonary ventilation – This is a movement of air into and out of the lungs. Breathing supplies oxygen to the alveoli, and eliminates carbon dioxide.
  2. External respiration – This is the exchange of gases by diffusion between alveoli and blood in the alveolar capillaries, across respiratory membrane. Diffusion of oxygen and carbon dioxide depends on pressure differences, e.g. between atmospheric air and the blood, or blood and the tissues.
  3. Transport of respiratory gases (transport of oxygen and carbon dioxide)
  4. Internal respiration – It is an exchange of gases which takes places in tissue, so also known as cellular respiration. In tissue, oxygen carried in the form of Oxyhaemoglobin get dissociated to liberating free O2.

Fig: Respiration in human

Mechanism of respiration

The basic mechanism is expansion and contraction of lungs which can achieve by –

(a) Upward and downward movement of the diaphragm to lengthen and shorten the verticle diameter of the chest cavity.

(b) Elevation and depression of ribs to increase and decrease of the anterioposterior diameter of the chest cavity.