Breathing
Science: KS3, topic 1.1.23
Breathing (or Ventilation)
Breathing in and out, also known as ventilation, can be explained in a series of steps.
Breathing in (inspiration)
- The diaphragm contracts and moves downwards.
- The ribs move up and out.
- The volume of the chest increases.
- Pressure falls below that of the outside air.
- Air moves into the lungs from the outside air down the pressure gradient.
Breathing out (expiration)
- The diaphragm relaxes and moves upwards.
- The ribs move down and in.
- The volume of the chest decreases.
- Pressure now increases above that of the outside air.
- Air moves out of the lungs to the outside air down a pressure gradient.
Positive and negative factors
- There are some illnesses and lifestyle factors that can positively or negatively affect how well your lungs can exchange gases.
- Positive:
- Regular exercise.
- Negative:
- Asthma.
- Smoking.
Test yourself on Breathing
Inspiration
Expiration
Which are true of the following lifestyle factors and health conditions?
In inspiration, how does the diaphragm move?
During inspiration, the diaphragm contracts and moves downwards, so the volume of the chest increases. What would happen to the volume of the chest if the diaphragm did not contract?