Mammalian Gaseous Exchange System

Question 1

Mammalian Gaseous Exchange System

Answer 1

Lungs are pairs of inflatable sacs lying in the thorax (chest cavity). Gas exchange occurs at the alveoli.

Gaseous exchange – Oxygen passes from the air in the alveoli into the blood, carbon dioxide passes from the blood to the air in the alveoli. The lungs must maintain a steep concentration gradient for diffusion of gases to continue.

Question 2

Features of the lungs: large surface area

Answer 2

•Large surface area to provide space for molecules to pass through:
Alveoli are very small but there are many, so the total surface area is very large. The alveoli are also coated by a thin layer of moisture which evaporates when we breathe out, it is a surfactant that coats the internal surface of the alveoli to reduce to cohesive forces between water molecules, as these forces make the alveoli collapse.

Question 3

Features of the lungs: Barrier is permeable to oxygen and carbon dioxide:

Answer 3

•Barrier is permeable to oxygen and carbon dioxide:
The barrier to exchange is comprised of the alveolar epithelium and the capillary wall. The plasma membranes of these cells readily allow the diffusion of O2 and CO2, as the molecules are small & non-polar.

Question 4

Features of the lungs: Thin barrier to reduce diffusion distance:

Answer 4

•Thin barrier to reduce diffusion distance: Adaptations to reduce diffusion distance,
• Alveolus and capillary walls are 1 cell thick.
• Both walls consist of squamous cells – flattened or very thin.
• The capillaries are in close contact with the alveolus walls.
• The capillaries are so narrow that red blood cells are squeezed
against the capillary wall – making them closer to the air in the
alveoli and reducing their rate of flow.
The total barrier to diffusion is 2 flattened (squamous) cells.

Question 5

Good blood supply – large capillary network:

Answer 5

•Good blood supply – large capillary network:
Helps maintain steep concentration gradient, so gases continue to diffuse.
• The large capillary network transports CO2 from the tissues to the lungs, ensuring the concentration is higher than that in the air in the alveoli, so CO2 diffuses into the alveoli.
• The blood transports O2 away from the lungs, ensuring O2 concentration is higher in the alveoli.