Question

8. Where does gas exchange occur in the lungs? 

9. What role do the diaphragm and rib muscle play in inhalation and exhalation?

Answer 1

8) Alveoli are the primary sites of exchange of gases in the lungs. Exchange of gases mainly occur in between the alveolar cavity of lungs and blood capillaries.

The diffusion membrane is made up of three layers namely, the thin squamous epithelium of the alveolar wall, the endothelium of the alveolar capillaries and basement material in between them. As it is very thin border, it is favourable for diffusion of gases.

9) Expansion of chest during inspiration occurs as a results of muscular activity, partly voluntary and partly involuntary.

The main muscles used in normal breathing are the intercostal muscles of ribs and the diaphragm.

The external intercostal muscles.

These extend downward and forwards from lower border of the rib above to the upper border of the ribs below. They are involved in inspiration.

The internal intercostal muscles :

These extend downwards and backwards from lower border of the rib above to the upper border of the ribs below, crossing the external intercostal muscle fibers at right angles. The internal intercostals are used when exhalation becomes active as in exercise.

The first rib is fixed. Therefore when the external intercostal muscles contract they pull all other ribs towards the first rib. Because of shape and sizes of the ribs they move outwards when pulled upwards enlarging the thoracic cavity.

Diaphragm :

The diaphragm is a come shaped muscular structure separating the thoracic and abdominal cavities. It forms the floor of the thoracic cavity and roof of the abdominal cavity and consists of a central tendon from which muscle fibers radiate to be attached to lower ribs and sternam and to vertibral column by two crura.

When the muscle of the diaphragm is relaxed the central tendon at the level of eight th (8 th) thoracic vertebra. When it contacts it's muscle fibers shorten and central tendon is pulled downwards to th level of 9 th thoracic vertebra lengthening the thoracic cavity. This decrease pressure in thoracic cavity and increase it in abdominal pelvic cavities.