Section 4 - Breathing In and Breathing Out

Question 1

Describe ventilation and its purpose

Answer 1

Ventilation (breathing) ensures that air with a high concentration of oxygen is taken into the lungs, and air with a high concentration of carbon dioxide is removed from the lungs. This maintains high concentration gradients between air (inside your alveoli) and blood, increasing the rate of diffusion of oxygen and carbon dioxide.

Question 2

What happens to the pressure if the volume of an enclosed space is increased?

Answer 2

Decreases

Question 3

The lungs are suspended in the airtight _______.

Answer 3

thorax

Question 4

What happens to the air pressure in the lungs when the volume of the thorax increases?

Answer 4

It decreases to below atmospheric pressure. Air flows into the lungs, inflating them until the pressure in the alveoli equals that of the atmosphere.

Question 5

What happens to the air pressure in the lungs when the volume of the thorax decreases

Answer 5

It increases and air flows out until the pressure in the alveoli drops to atmospheric pressure

Question 6

Describe what happens when breathing in (3)

Answer 6

1) Intercostal muscles and diaphragm (a muscular sheet) contract.
2) Thorax volume increases.
3) This decreases the pressure, so air flows in.

Question 7

Describe what happens when breathing out (3)

Answer 7

1) Intercostal muscles and diaphragm relax.
2) Thorax volume decreases.
3) This increases the pressure, so air flows out.