THIS PRESENTATION HASDETAILED EXPLANATION ABOUT MECHNISM OF RESPIRATON

1. AN 21.9 – MECHANISM OF
RESPIRATION
DHEEPIKA M
1ST YEAR MBBS
KILPAUK MEDICAL COLLEGE

2. The lungs expand during inspiration and retract during
expiration. These movements are governed by the
following two factors.
• Alterations in the capacity of the thorax are brought
about by movements of the thoracic wall. Movements of
the thoracic wall occur chiefly at the costovertebral and
manubriosternal joints.
• Elastic recoil of the pulmonary alveoli and of the
thoracic wall expels air from the lungs during expiration

4. PRINCIPLES OF
MOVEMENTS
Each rib may be regarded as
a lever, the fulcrum of which
lies just lateral to the
tubercle. because of the
disproportion in the length of
the two arms of the lever, the
slight movements at the
vertebral end of the rib are
greatly magnified at the
anterior end

5. CONTD…
The anterior end of the rib is lower than
the posterior end. Therefore, during
elevation of the rib, the anterior end also
moves forwards. This occurs mostly in
the vertebrosternal ribs. Along with the
up and down movements of the second
to sixth ribs, the body of the sternum
also moves up and down called pump-
handle movements. In this way, the
anteroposterior diameter of the thorax is
increased.

6. CONTD…
• The middle of the shaft of the rib lies at a
lower level than the plane passing through
the two ends. Therefore, during elevation
of the rib, the shaft also moves outwards.
This causes increase in the transverse
diameter of the thorax.
• Such movements occur in the
vertebrochondral ribs, and are called
bucket-handle movements.

7. CONTD…
The thorax resembles a cone, tapering
upwards. As a result, each rib is longer
than the next higher rib. On elevation, the
larger lower rib comes to occupy the
position of the smaller upper rib which
pushes sternum forwards. This also
increases the transverse diameter of the
thorax.

8. CONTD…
Vertical diameter is increased by the ‘piston
movements’ of the thoracoabdominal
diaphragm.

9. RESPIRATORY MUSCLES
• For inspiration—diaphragm, external intercostal muscle and
interchondral part of internal intercostal of contralateral side.
• Deep inspiration—erector spinae, scalene muscles, pectoral muscles.
• For expiration—passive process.
• Forced expiration—muscles of anterior abdominal wall

10. RESPIRATORY MOVEMENTS DURING
DIFFERENT TYPES OF BREATHING

11. QUIET INSPIRATION
• The anteroposterior diameter of the thorax is increased by elevation of
the second to sixth ribs. The first rib remains fixed.
• The transverse diameter is increased by elevation of the seventh to
tenth ribs.
• The vertical diameter is increased by descent of the diaphragm.

12. DEEP INSPIRATION
• Movements during quiet inspiration are increased.
• The first rib is elevated directly by the scaleni, and indirectly by the
sternocleidomastoid.
• The concavity of the thoracic spine is reduced by the erector spinae.

13. FORCED INSPIRATION
• All the movements described are exaggerated.
• The scapulae are elevated and fixed by the trapezius, the levator
scapulae and the rhomboids, so that the serratus anterior and the
pectoralis minor muscles may act on the ribs.
• The action of the erector spinae is appreciably increased.

14. QUIET EXPIRATION
The air is expelled mainly by the elastic recoil of the chest wall and
pulmonary alveoli, and partly by the tone of the abdominal muscles.

15. DEEP AND FORCED EXPIRATION
Deep and forced expiration is brought about by strong contraction of the
abdominal muscles and of the latissimus dorsi.

16. CLINICAL ANATOMY

17. DYSPNOEA
In dyspnoea or difficulty in breathing, the
patients are most comfortable on sitting
up, leaning forwards and fixing the arms.
in the sitting posture, the position of
diaphragm is the lowest allowing
maximum ventilation. fixation of the arms
fixes the scapulae, so that the serratus
anterior and pectoralis minor may act on
the ribs to good advantage.

18. • In young children (up to 2 years of age), the thoracic cavity is almost circular in
cross-section so the scope for anteroposterior or side-to-side expansion is
limited. The type of respiration in children is abdominal.
• In women of advanced stage of pregnancy, descent of diaphragm is limited, so
the type of respiration in them is mainly thoracic.