Describe the mechanism of gaseous exchange in man

Inhalation

• The external intercostal muscles contract while the internal intercostal muscles relax. The ribs and rib cage move upwards and outwards as a whole. The diaphragm muscle contracts to become flat. The volume of the thoracic cavity increase as pressure decrease compared to the atmospheric pressure. Air rich in oxygen enters the lungs through the nostrils, trachea, bronchi, and bronchioles into the numerous alveoli.

The Process of Gaseous Exchange

• Oxygen in the air within the alveolus dissolves in the moist film lining the inside of the alveolus wall. Oxygen which is in high concentration diffuses through the thin wall of the alveolus and the thin-walled blood capillaries into the blood within the capillaries. At the same time, Carbon (IV) oxide which is high in concentration in blood diffuses from the blood into the alveoli.

 Exhalation

• The external intercostal muscles relax while the internal intercostal muscles contract. The ribs and the rib cage moves downwards and inwards as a whole. The diaphragm relax to become dome-shaped. Volume of the thoracic cavity decrease as pressure increase compared to the atmospheric pressure. The air in the lungs is forced out through the bronchioles, bronchi, trachea and out through nostrils.