3.3.2 Gas exchange

Question 1

How are the lungs adapted as an exchange surface?

Answer 1

Large surface area
Thin permeable surface
Steep diffusion gradient

Question 2

How is a large surface area achieved in the lungs?

Answer 2

Has a large number of alveoli per lung
Each alveolus is folded to form a set of interconnected spaces

Question 3

How is a thin permeable surface achieved by walls found in the lungs?

Answer 3

Alveolus wall is a single layer of flattened epithelial cells
Capillary wall is a single layer of flattened endothelial cells

Question 4

How is a steep diffusion gradient maintained in the lungs

Answer 4

Blood in capillaries is circulated
Lungs are ventilated and air inside is replaced by breathing

Question 5

What happens during inspiration - breathing in?

Answer 5

1. External intercostal muscles and the diaphragm muscles contract, this uses energy from ATP - active process (internal intercostal muscles relaxes)
2. Ribs are pulled upwards, diaphragm is pulled flatter - volume of thorax increases
3. Volume of lungs increases, pressure inside becomes lower than atmospheric pressure
4. Air is forced into alveoli via the trachea, bronchi and bronchioles due to pressure difference

Question 6

What happens during expiration - breathing out?

Answer 6

1. External intercostal muscles and the diaphragm muscles relaxes, this does not use energy from ATP - passive process (internal intercostal muscles contracts)
2. Ribs are pulled downwards by the thorax walls due to elastic recoil of the lungs, diaphragm returns to its original domed position - volume of thorax decreases
3. Volume of lungs decreases, pressure inside becomes greater than atmospheric pressure
4. Air is forced out of the alveoli via the bronchioles, bronchi and trachea due to pressure difference

Question 7

Why does the movement of the ribs and the diaphragm influence the movement of the lungs - thus pressure is altered?

Answer 7

Lungs are attached to the inside of the rib cage by the pleural membranes - has a slightly sticky quality due to water’s surface tension (permeable)

Question 8

What happens during forced expiration - e.g. breathing out during exercise?

Answer 8

1. Internal intercostal muscles and muscles of abdominal wall contracts, this uses energy from ATP - active process