Exchange of gases in the lungs

Question 1

What do the alveoli do?

Answer 1

It’s the site for gas exchange in mammals.

Question 2

How can a constant supply of oxygen be transferred?

Answer 2

• A diffusion gradient must be maintained at the alveolar surface.
• For an efficient transfer, exchange surface must be thin, partially permeable and have a large SA.
• To maintain a diffusion gradient, there have to be movements of both environmental medium - air and the internal medium - blood.

Question 3

How are the alveoli adapted for efficient gas exchange?

Answer 3

• The alveolar wall is made up of a single layer of cells.
• There’s a net of capillary wall wrapping around the alveoli so short diffusion of oxygen across to the blood capillary and the capillary is also one-cell thin.
• The alveoli are very tightly packed together so short diffusion pathway.

Question 4

Why are the alveoli inside the organism?

Answer 4

Being thin so it’s specialised for exchange surfaces but also it means that it can be easily damaged so it located inside of the organism for protection.

Question 5

What capillary is surrounding each alveolus?

Answer 5

Pulmonary capillary, it’s very narrow (7-10um), even RBC needs to be flattened against the thin capillary walls to squeeze through.
These capillaries have walls that are only one cell thick.

Question 6

How can the diffusion of gases between the alveoli and the blood be rapid?

Answer 6

• RBC are slowed down which allows more time for diffusion as lumen is tight.
• The distance between the alveolar air and RBC is shortened because RBCs are flattened against the capillary walls.
• The walls of both alveoli and the capillary are one cell thick so diffusion distance is shortened.
• Alveoli and pulmonary capillaries have very large total SA.
• Breathing allows constant ventilation in the lungs and the heart constantly circulates blood around the alveoli so a steep concentration gradient of the gases to be exchanged is maintained.
• Blood flow through the pulmonary capillaries maintains a concentration gradient.

Question 7

Why is the alveolar surface moist?

Answer 7

So oxygen can be dissolved in the moisture and this allows a faster diffusion from the alveoli into the pulmonary capillary.

Question 8

Why is the air sac in a lobed shape?

Answer 8

To increase the SA.

Question 9

What is the epithelial cell made up of?

Answer 9

Squamous, it is squashed to reduce the SA.