4.5 Gas Exchange and Transport

Question 1

What is typical tidal volume?

Answer 1

500mL

Question 2

What is typical respiratory rate?

Answer 2

12-20/min

Question 3

How do you calculate total ventilation?

Answer 3

Tidal volume * respiratory rate

Question 4

Does the total ventilation represent the amount of air entering and leaving the alveoli in the lung? Why, or why not?

Answer 4

• No
• This does not account for the dead space, where no gas exchange occurs

Question 5

How is alveolar ventilation calculated?

Answer 5

(tidal volume-dead space) * respiratory rate

Question 6

What gases are present in the air that we breathe in?

Answer 6

• Nitrogen
• Oxygen
• Carbon Dioxide
• Argon

Question 7

What proportion of the air we breathe in is argon?

Answer 7

0.1%

Question 8

What proportion of the air we breathe in is nitrogen?

Answer 8

78%

Question 9

What proportion of the air we breathe in is carbon dioxide?

Answer 9

~0.04%

Question 10

What proportion of the air we breathe in is oxygen?

Answer 10

21%

Question 11

What is Dalton’s law?

Answer 11

The proportion of gases in terms of volume is equal to their proportions in terms of pressure (e.g. since O2 is 21% of air, the partial pressure of oxygen is 21% of total air pressure).

Question 12

What is partial pressure?

Answer 12

The proportion of total pressure of a gas supplied by a particular component, calculated using Dalton’s Law

Question 13

Why is PO2 lower in the alveoli than in air?

Answer 13

• In the alveoli, there are greater amounts of carbon dioxide which are being exchanged from the bloodstream
• This means that carbon dioxide takes up a greater proportion of the air in the alveoli, thus decreasing the proportion of oxygen
• By Dalton’s law, this results in an increased partial pressure of oxygen

Question 14

Consider the partial pressures of oxygen and carbon dioxide in oxygenated and deoxygenated blood

Answer 14

Deoxygenated:
- CO2 increased
- O2 decreased

Oxygenated
- CO2 decreased
- O2 increased

Question 15

Describe the differences between PA and Pa

Answer 15

• PA: Alveolar partial pressure
• Pa: arterial partial pressure

Question 16

Is more oxygen transported in dissolved form or bound to haemoglobin?

Answer 16

Bound to haemoglobin

Question 17

What is meant when it is said that oxygen shows cooperative binding to haemoglobin?

Answer 17

Oxygen will readily bind to haemoglobin, and when one oxygen molecules does, it is easier for others to follow it (kind of like humans)

Question 18

How many molecules of oxygen can bind to one molecule of haemoglobin?

Answer 18

Four

Question 19

What are the three ways in which carbon dioxide can be transported through the bloodstream?

Answer 19

• Dissolved
• Attached to proteins in erythrocytes
• Converted to bicarbonate

Question 20

How is nitrogen transported through the blood?

Answer 20

It readily dissolves in high amounts

Question 21

Describe the Haldane Effect

Answer 21

Unloading O2 from capillaries of the body makes it easier to load CO2 into the capillaries (and vice versa)

Question 22

Which enzyme catalyses the conversion of CO2 to bicarbonate? Where does it exist?

Answer 22

• Carbonic anhydrase
• Exists in erythrocytes

Question 23

Briefly explain how CO2 uptake can make it easier for erythrocytes to unload O2

Answer 23

• CO2 is converted to carbonic acid
• Carbonic acid ionises to form H+ and bicarbonate
• H+ binds to haemoglobin, which makes it easier for oxygen to be released from haemoglobin