6.7 The mechanism of breathing

Question 1

What is ventilation?

Answer 1

breathing

Question 2

What is inspiration?

Answer 2

inhalation, when the air pressure of the atmosphere is greater than the air pressure inside the lungs, air is forced into the lungs.

Question 3

What is expiration?

Answer 3

exhalation, when the air pressure in the lungs is greater than that of the atmosphere, air is forced out of the lungs.

Question 4

What 3 sets of muscle causes pressure change in lungs and what are they?

Answer 4

1. diaphragm
   - sheet of muscle that separates the thorax from the abdomen
2. internal intercostal muscles
   - whose contractions leads to expiration
3. external intercostal muscles
   - whose contractions leads to inspiration

Question 5

Explain the process of inspiration.

Answer 5

• active process
• EXTERNAL intercostal muscles CONTRACT, while the internal intercostal muscles relax
• the ribs are pulled UPWARDS and OUTWARDS, increasing the volume of the thorax
• the DIAPHRAGM muscles CONTRACT, causing it to FLATTEN which also increases the volume of the thorax
• the increased volume of the thorax results in REDUCTION OF PRESSURE in the lungs
• atmospheric pressure is now greater than pulmonary pressure and so air is forced into the lungs.

Question 6

Explain the process of expiration.

Answer 6

• passive process
• the INTERNAL INTERCOSTAL muscles CONTRACT while the EXTERNAL INTERCOSTAL MUSCLES RELAX
• the ribs move DOWNWARDS AND INWARDS, DECREASING the volume of the thorax
• the diaphragm muscles relax and so it is pushed up again by the contents of the abdomen that were compressed during inspiration. The volume of the thorax is therefore further decreased
• the decreased volume of the thorax increases the pressure in the lungs.
• the pulmonary pressure is now greater than that of the atmosphere, and so air is forced out of the lungs.

Question 7

What is the main component responsible for air being forced out during breathing?

Answer 7

the recoil of the elastic tissue in the lungs