AN 21 mechanism of respiration.pptx

THIS PRESENTATION HASDETAILED EXPLANATION ABOUT MECHNISM OF RESPIRATON

1. AN 21.9 – MECHANISM OF RESPIRATION Dheepika m 1 st 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

3. Principles of movements E ach 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

4. 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 .

5. 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.

6. 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.

7. Contd … Vertical diameter is increased by the ‘ piston movements ’ of the thoracoabdominal diaphragm.

8. 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

9. Respiratory Movements during Different Types of Breathing

10. 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.

11. 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 .

12. 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.

13. 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.

14. Deep and forced expiration Deep and forced expiration is brought about by strong contraction of the abdominal muscles and of the latissimus dorsi .

15. Clinical anatomy

16. 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.

17. 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.