[6.8] exchange of gases in the lungs

Question 1

what is needed for efficient gas exchange? (5)

Answer 1

• constant supply of oxygen to the body
• thin exchange surface
• partially permeable exchange surface
• exchange surface must have large surface area
• diffusion gradient must be maintained by movement of environmental medium (eg. air) and internal medium (eg. blood)

Question 2

how is a constant supply of oxygen to the body maintained?

Answer 2

red blood cells are slowed as they pass through pulmonary capillaries allowing more time for diffusion

Question 3

how does is the gas exchange have a short diffusion distance?

Answer 3

• distance between alveolar air and red blood cells is reduced as the red blood cells are flattened against the capillary walls
• walls of both alveoli and capillaries are very thin so diffusion distance is very short

Question 4

how does the gas exchange surface have a large surface area?

Answer 4

alveoli and pulmonary capillaries have a large total surface area as there are many of each of them

Question 5

how is the diffusion gradient maintained?

Answer 5

• a steep concentration gradient of gases to be exchanged is maintained by breathing movements constantly ventilate the lungs and the action of the heart constantly circulates blood around the alveoli
• blood flowing through the pulmonary capillaries maintains a concentration gradient

Question 6

what is emphysema?

Answer 6

• when alveolar tissue is destroyed and there are fewer blood vessels
• lower cumulative surface area for gas exchange
• effects on exercise because oxygen -> aerobic respiration -> ATP (hydrolysed) -> contraction of muscle

Question 7

what is the effect of emphysema?

Answer 7

1. alveoli tissue is directly damaged. therefore, cumulative SA decreases
2. blood vessel network becomes less extensive. therefore, less steep concentration gradient
3. remaining alveoli tissue thickens. therefore, diffusion pathway increases
4. remaining alveoli tissues becomes less elastic. therefore it is harder to expire, takes longer to breath in so longer before you can replenish air; concentration gradient becomes less steep

• all this means slower rate of gas exchange by diffuson