The Mechanism of Breathing

Question 1

How and why is air moved into the lungs when breathing in?

Answer 1

INSPIRATION (Breathing in)
-External intercostal muscles contract whilst the internal intercostal muscles relax
-Ribs pull upwards and outwards increasing the thorax volume
-Diaphragm muscles contract causing it to flatten increasing the thorax volume
-Reduction of pressure in the lungs
-Atmospheric pressure is greater than lung pressure causing air to be forced into the lungs

Question 2

How and why is air moved out of the lungs when breathing out?

Answer 2

EXPIRATION (Breathing out)
-Internal intercostal muscles contract and external intercostal muscles relax
-Ribs push downwards and inwards decreasing volume
-Diaphragm muscles relax causing it to be pushed upwards
-Increase of pressure in the lungs
-Atmospheric pressure is now lower than lung pressure causing air to be forced out of the lungs

Question 3

What is meant by ‘pulmonary ventilation’? How is it calculated?

Answer 3

-Pulmonary ventilation is the total volume of air that is moved into the lungs during 1 minute.
-Pulmonary ventilation (Decimetres cubed per min) = tidal volume (Decimetres cubed) x breathing rate (Number of breaths per minute)