Respiratory Gas Exchange

Question 1

What are the three dietary “fuels” required for gas transport

Answer 1

Fat, carbohydrate and protein

Question 2

What are the three dietary fuels oxidised to form

Answer 2

Carbon Dioxide

Question 3

What is reduced in the process of oxidation of dietary fuels to form carbon dioxide

Answer 3

Coenzymes

Question 4

What is the role of the mitochondrial electron transport chain in the synthesis of ATP

Answer 4

It reduces oxygen (and re-oxidises the coenzymes) to water and the energy released it used to synthesise ATP.

Question 5

What is the terminal electron acceptor

Answer 5

Oxygen

Question 6

In which direction are oxygen and carbon dioxide transported

Answer 6

Oxygen is transported from the lungs to the tissues and carbon dioxide is transported from the tissues to the lungs.

Question 7

What is the standard unit of pressure

Answer 7

Atmospheres

Question 8

What is one atmosphere in mmHg

Answer 8

1 atmosphere = 760 mmHg

Question 9

What is 1 atmosphere in kPa

Answer 9

1 atmosphere = 101 kPa

Question 10

What is 1kPa in mmHg

Answer 10

7.5 mmHg.

Question 11

What is Daltons Law

Answer 11

Each gas in a mixture exerts a pressure independently of the others.

Question 12

What is atmospheric pressure a sum of

Answer 12

The partial pressures of all the gases in the atmosphere.

Question 13

What is Henry’s Law

Answer 13

The concentration of a gas dissolved in a liquid is directly proportional to its partial pressure.

Question 14

What is the formula for the solution concentration of a gas

Answer 14

Solution concentration = kH Pgas
wehre kH is the solubility constant. Since kH is a constant the concentration of a dissolved gas may be expressed as its partial pressure.

Question 15

Why do different gases have different concentrations in solution even if they have the same partial pressure

Answer 15

Because different gases have different solubility constants.

Question 16

What is gas exchange in the lungs driven by

Answer 16

Differences in partial pressure across the alveolar membrane.

Question 17

What will the concentrations of oxygen and carbon dioxide of inspired air be compared to that in plasma

Answer 17

Inspired air will have a higher concentration of oxygen and a lower concentration of carbon dioxide compared to plasma.

Question 18

Why is equilibrium usually attained in the alveoli

Answer 18

Because gas exchange is so rapid

Question 19

In what situation may equilibrium in the alveoli not be attained

Answer 19

If there is a ventilation perfusion mismatch (V/Q mismatch)

Question 20

Is the rate of diffusion of carbon dioxide or oxygen faster across alveolar membranes

Answer 20

Carbon dioxide - by about 20 times.

Question 21

What happens if gas exchange is slowed, for example if the functional exchange area is reduced

Answer 21

Hypoxia (low oxygen) will occur. This is more likely than hypercapnia (high carbon dioxide) because the rate pf diffusion for carbon dioxide is a lot faster than that for oxygen.

Question 22

What is the function of nitrogen in human metabolism

Answer 22

Nitrogen has no function in human metabolism

Question 23

What is the solubility of nitrogen in the blood

Answer 23

Low

Question 24

When may nitrogen narcosis develop

Answer 24

At high pressure nitrogen dissolves in blood and tissues and produces nitrogen narcosis.

Question 25

What happens after nitrogen narcosis when pressure returns to normal

Answer 25

Nitrogen emboli may form in capillaries which can cause local ischaemia.

Question 26

Why is such a high percentage of oxygen bound to haemoglobin in the blood

Answer 26

Because the solubility of oxygen in the blood is low

Question 27

Around what percentage of oxygen is bound to haemoglobin

Answer 27

Around 98.5%

Question 28

What is the oxygen carrying capacity of the blood dependent on

Answer 28

The haemoglobin content of the blood.

Question 29

What type of protein is haemoglobin

Answer 29

Tetrameric

Question 30

What two subunits is adult haemoglobin composed of

Answer 30

2 alpha 2 subunits and 2 beta 2 subunits

Question 31

What two subunits is foetal haemoglobin composed of

Answer 31

2 alpha 2 subunits and 2 gamma 2 subunits

Question 32

How many oxygen molecules does one haemoglobin molecule bind

Answer 32

Four

Question 33

What happens when oxygen binds to one subunit of haemoglobin

Answer 33

There is a conformational change in the protein

Question 34

What are the two conformations of haemoglobin

Answer 34

"Oxy" and "deoxy".

Question 35

What is meant by co-operativity

Answer 35

When oxygen binds at one haemoglobin subunit there is a conformational change which results in higher affinity for oxygen at other subunits.

Question 36

What is most often the cause of problems with oxygen delivery

Answer 36

Reduced deoxygenation (rather than incomplete oxygenation)

Question 37

What are the factors which favour the release of O2 from haemoglobin

Answer 37

- Increased pH - Increased pCO2 - Increased temperature

Question 38

How does carbon monoxide poisoning result in low oxygen delivery to tissues

Answer 38

Carbon monoxide is very similar structurally to oxygen and so can bind to haemoglobin. When it binds, it increases the affinity of haemoglobin for oxygen so release of oxygen is poor and oxygen is not delivered to tissues.

Question 39

How is haemoglobin converted to mathaemoglobin

Answer 39

By oxidation of the iron molecule to Fe3+.

Question 40

What is the problem with methaemoglobin

Answer 40

It does not bind oxygen

Question 41

Which enzyme converts methaemoglobin back to haemoglobin in erythrocytes

Answer 41

Methaemoglobin reductase.

Question 42

What can cause increased levels of mathaemoglobin

Answer 42

Genetic mutation favouring the oxidised state.

Question 43

What is the solubility of carbon dioxide in water compared to oxygen

Answer 43

Carbon dioxide is much more soluble in water than oxygen.

Question 44

What is produced on hydrating carbon dioxide

Answer 44

Carbonic acid

Question 45

How does carbon dioxide bind to haemoglobin

Answer 45

It does not bind to the haem groups but reacts with the N-termini amino groups.

Question 46

What is the Haldane effect

Answer 46

Deoxygenation of oxygen haemoglobin promotes the binding of CO2 to deoxy-haemoglobin and vice versa.

Question 47

What is most CO2 transported as in the plasma

Answer 47

Bicarbonate.

Question 48

What is the order of solubility in water of carbon dioxide, oxygen and nitrogen from lowest to highest

Answer 48

Nitrogen (least soluble), oxygen, carbon dioxide (most soluble).

Question 49

In which part of the body is haemoglobin most saturated

Answer 49

The lungs. As it travels to the tissues the oxygen gets used up and the haemoglobin becomes less saturated.

Question 50

In which direction does gas move along a pressure gradient

Answer 50

From a high partial pressure of that gas to a low partial pressure. This is why oxygen moves across alveolar membranes from the lungs into the plasma.

Question 51

Why does carbon dioxide diffuse faster across membranes compared to oxygen when oxygen is a smaller molecule

Answer 51

The diffusion constant of oxygen is greater than that for carbon dioxide because it is a smaller molecule. However, the partition coefficient of carbon dioxide is greater than that of oxygen so CO2 equilibrates faster

Question 52

How does altitude sickness occur

Answer 52

If there is an increase in altitude, there is a decrease in the pressure of the air. This means there is less oxygen in the blood and respiration becomes anaerobic to cause altitude sickness.

Question 53

Over what concentration range is haemoglobin released

Answer 53

A narrow concentration range.

Question 54

What is the Bohr effect

Answer 54

Oxyhaemoglobin becomes protonated so oxygen is released to create deoxyhaemoglobin.

Question 55

What does the binding of 2,3-bisphosphoglycerate do to oxyhaemoglobin

Answer 55

Causes it to release oxygen.

Question 56

Why does foetal haemoglobin have a higher affinity for oxygen

Answer 56

Because it has a lower 2,3-BPG affinity than adult haemoglobin. 2,3-BPG causes the release of oxygen from haemoglobin so improves delivery to tissues.

Question 57

What is the role of carbonic anhydrase

Answer 57

It catalyses the hydration of carbon dioxide to carbonic acid which then ionises to from bicarbonate.

Question 58

What did inhibition of carbonic anhydrase used to be used for

Answer 58

Diuretic drugs - particularly acetazolamide because it inhibits the reuptake of sodium and bicarbonate in the kidney.

Question 59

What is acetazolamide (the carbonic anhydrase inhibitor drug) now used most commonly for

Answer 59

Preventing altitude sickness by lowering the pH of the blood stimulating respiration and release of O2 from oxyhaemoglobin.