Describe what happens during inspiration.

The external intercostal muscles contract and swing the ribs upwards and outwards while the diaphragm contracts and flattens, so the volume of the thorax increases, the pressure inside falls below atmospheric pressure and air flows in.

Which muscles are used in forced expiration?

The internal intercostal muscles contract and pull the ribs down and in, and the abdominal muscles contract and push the organs of the abdomen up against the diaphragm.

Why is quiet expiration described as a passive process?

No muscle contracts to drive the air out, since the movement is produced by the relaxation of the inspiratory muscles and the elastic recoil of the stretched lung tissue.

What is the role of the pleural membranes and the fluid between them?

They enclose each lung in an airtight space, and the film of fluid allows the two membranes to slide over one another while holding the lung against the chest wall, so the lung follows every movement of the ribs and diaphragm.

Eduqas A-Level Biology A400QS

Biological Molecules

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Adaptations for Gas Exchange

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Adaptations for Gas Exchange

Ventilation and gas exchange in humans

3 things to know
Component 3

Overview

Ventilation of the lungs, what happens during inspiration and what happens during quiet expiration.

What you need to know

Answer each one before you reveal it.

Your recallNot started

Key term

Describe what happens during quiet expiration.

Key term

Compare the composition of inspired air with that of expired air.

Key term

What is meant by ventilation of the lungs?

Questions from this subtopic

Each one with the model answer underneath.

1
What is meant by ventilation of the lungs?
Model answer
Ventilation is the movement of air into and out of the lungs, which renews the air in the alveoli and keeps the diffusion gradients steep.
2
Describe what happens during inspiration.
Model answer
The external intercostal muscles contract and swing the ribs upwards and outwards while the diaphragm contracts and flattens, so the volume of the thorax increases, the pressure inside falls below atmospheric pressure and air flows in.
3
Describe what happens during quiet expiration.
Model answer
The external intercostal muscles and the diaphragm relax so the ribs fall and the diaphragm returns to its domed shape, the elastic tissue of the lungs recoils, the thorax becomes smaller and the raised pressure drives air out.
4
Which muscles are used in forced expiration?
Model answer
The internal intercostal muscles contract and pull the ribs down and in, and the abdominal muscles contract and push the organs of the abdomen up against the diaphragm.
5
Why is quiet expiration described as a passive process?
Model answer
No muscle contracts to drive the air out, since the movement is produced by the relaxation of the inspiratory muscles and the elastic recoil of the stretched lung tissue.
6
What is the role of the pleural membranes and the fluid between them?
Model answer
They enclose each lung in an airtight space, and the film of fluid allows the two membranes to slide over one another while holding the lung against the chest wall, so the lung follows every movement of the ribs and diaphragm.

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