6.7 The mechanism of breathing Flashcards
1
Q
How is diffusion across the alveolar epithelium maintained
A
Air is constantly moved in and out of the lungs. This is done by breathing (ventilation)
2
Q
What happens when the air pressure of the atmosphere is greater than the air pressure inside the lungs
A
Air is forced into the lungs (INSPIRATION)
3
Q
What happens when the air pressure of the atmosphere is lower than the air pressure inside the lungs
A
Air is forced out of the lungs (EXPIRATION)
4
Q
How are the pressure changes within the lungs brought about
A
By the movement of three sets of muscles:
- The diaphragm, which is a sheet of muscle that separates the thorax from the abdomen
- The intercostal muscles, which lie between the ribs. Two sets:
- Internal intercostal muscles, contraction leads to expiration
- External intercostal muscles, contraction leads to inspiration
5
Q
Describe the process of inspiration
A
- The external intercostal muscles contract, while the intercostal muscles relax.
- The ribs are pulled upwards and outwards, increasing the volume of the thorax
- The diaphragm muscle contract, causing it to flatten, which also increases the volume of the thorax
- The increased thorax volume results in a pressure reduction within the lungs
- Atmospheric pressure is now greater than pulmonary pressure, and so air is forced into the lungs
6
Q
Describe the process of expiration
A
- The internal intercostal muscles contract, while the external intercostal muscles relax
- The rips move downwards and inwards, decreasing thorax volume
- The diaphragm muscles relax and so it is pushed up again by the contents of the abdomen. The thorax volume is decreased
- The decreased thorax volume 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
7
Q
What happens when the external intercostal muscles contract
A
Inspiration
8
Q
What happens when the internal intercostal muscles contract
A
Expiration
