2. ►It is about 16 cycles per minute.
►It is composed of:
a)Inspiration.
b) Expiration.
c) Expiratory pause .

3. 1) Supply of O2 to tissues and
removal of CO 2 from them.
2) Regulation of PH of the blood.
3) Excretion of water vapour.
4) Regulation of body temperature.
5) Help voice production.

4. I)Peripheral mechanism.
II)Central mechanism.

5. A) Mechanics of inspiration:
1. The thoracic cavity increases in all
directions:
a) Vertically: by contraction of the diaphragm
and its descent 1.5 cm.
b) Transversely: by elevation of the ribs by
contraction of external intercostal muscles
c) Antero-posteriorly: by elevation of the ribs,

6. 2. Expansion of the thoracic cavity
leads to ⇒ increases the negativity of
the intrapleural pressure leading to
distension of the lungs ⇒cause rush
of 500 c.c. of atmospheric air into the

7. B) Mechanics of expiration:
Quiet expiration is a passive process, it is
done by:
1) Relaxation of inspiratory muscles
(diaphragm and external intercostal
muscles).
2) Drop of the thoracic cage by its weight .
3) Elastic recoil of the lung .
This pushes 500 c.c. of air out of the
lung.

8. Definition:
It is the pressure inside the pleural
sac.
►It is always negative (subatmospheric)
during normal resting respiratory cycle .

9. a) Over growth of the
thoracic cage than the lung.
b) Elastic recoil of the lung
against chest wall.

10. a) During normal expiration ⇒ I.P.P.
is -3 mmHg.
b) During normal inspiration ⇒ I.P.P.
is -6 mmHg.
c) During forced inspiration ⇒ I.P.P.
is -30 mmHg.
d) During forced expiration ⇒the
I.P.P. is + 40 mmHg.

11. 1) It helps the expansion of the lungs
during inspiration.
2) It helps the venous return from the
extrathoracic veins.
3) It helps flow of lymph from
extrathoracic lymph vessels.
4) It helps flow of blood through the
pulmonary vessels.
5) It is a measurement of elastic recoil of
the lung.