# Gas Transport and Exchange Flashcards Preview

## LSS 1 - Resp > Gas Transport and Exchange > Flashcards

Flashcards in Gas Transport and Exchange Deck (40)
1
Q

State Dalton’s Law.

A

The partial pressure of a mixture of gases is equal to the sum of the partial pressures of the gases that make up the mixture.

2
Q

State Fick’s Law.

A

Rate of diffusion is directly proportional to diffusion capacity, concentration gradient and surface area and inversely proportional to the thickness of the exchange surface.

3
Q

State Henry’s Law.

A

At a constant temperature, the amount of a given gas that dissolves in a give type and amount of liquid is directly proportional to the partial pressure of the gas in equilibrium with the liquid.

4
Q

State Boyle’s Law.

A

At a constant temperature, volume is inversely proportional to pressure.

5
Q

State Charles’ Law.

A

At a constant pressure, volume is directly proportional to temperature.

6
Q

Describe how partial pressure of oxygen changes as it passes down the airways.

A

The partial pressure decreases from 21.3 kPa to 20 kPa to 13.5 kPa in the alveoli.

7
Q

What happens to the air as it passes down the airways?

A

The air gets warmed, humidified, mixed and slowed.

8
Q

How much oxygen can be dissolved in out bodies?

A

17 mL at 0.34 mL/dL

9
Q

What is the normal oxygen consumption at rest?

A

250 mL/min

10
Q

What is the binding capacity of oxygen to haemoglobin?

A

1.34 mL/g

11
Q

What is the solubility coefficient of oxygen in blood using mm Hg?

A

0.003 mL

12
Q

Describe the structure of a normal variant of haemoglobin and of foetal haemoglobin.

A

HbA2 is a normal variant that consists of two alpha chains and two delta chains (2% of adult haemoglobin)
HbF is present in foetus’ and consists of two alpha chains and two gamma chains.

13
Q

Explain why haemoglobin is considered an ‘allosteric’ molecule.

A

When oxygen binds, there is a conformational change which changes the structure and affinity of haemoglobin for oxygen meaning that oxygen is more likely to bind.

14
Q

What change occurs in the middle of the haemoglobin tetramer when oxygen binds?

A

Oxygen binding changes the structure of the middle of the haemoglobin creating a binding site for 2,3-DPG (a glycolytic by-product) - 2,3-DPG production is reflective of metabolism and it binds to the haemoglobin and squeezes out the oxygen (lowers the affinity of haemoglobin for oxygen)

15
Q

What is the name given to the phenomenon where oxygen binding to haemoglobin increases the affinity making more oxygen bind?

A

Cooperativity

16
Q

What would the consequences be if the oxygen dissociation curve was linear?

A

A lower haemoglobin saturation would be achieved in the lungs when the partial pressure of oxygen in the lungs is at the lower end of normal. There is also reduced potential to unload oxygen at respiring tissues.

17
Q

What are the benefits of having a sigmoid ODC?

A

100% haemoglobin saturation can occur at a broad range of partial pressures

18
Q

What is P50?

A

The partial pressure of oxygen at which haemoglobin is 50% saturated - gives an indication of the shape of the ODC

19
Q

What conditions can shift the ODC to the right?

A

Conditions brought about by exercise - hypercapnia, increased temperature, acidosis, increased 2,3-DPG

20
Q

What conditions can shift the ODC to the left?

A

The opposite conditions - hypocapnia, decreased temperature, alkalosis and decreased 2,3-DPG

21
Q

What conditions can shift the ODC upwards?

A

Polycythaemia - increase in the haematocrit (could be caused by an increase in the number of red blood cells)

22
Q

What conditions can shift the ODC downwards?

A

Anaemia - decreased oxygen carrying capacity of the blood

23
Q

How does haemoglobin saturation change in the previous two shifts of the ODC?

A

It doesn’t change because the haemoglobin is still fully saturated but the amount of oxygen carried by the blood increases.

24
Q

How does carbon monoxide shift the ODC and why?

A

Carbon monoxide shifts the curve downwards and leftwards. It moves downwards because it binds irreversibly to haemoglobin meaning that there is less haemoglobin available to bind to oxygen. It moves leftwards because if only a few of the 4 oxygen binding sites on the haemoglobin are occupied by oxygen, then the oxygen that is bound to haemoglobin will be less likely to dissociate, thus increasing the affinity of the haemoglobin for oxygen.

25
Q

Describe the shape of the ODC of myoglobin and foetal haemoglobin and why this shape is needed for their function.

A

Myoglobin is a store of oxygen in the muscles and it has a very high affinity for oxygen because it must be able to extract oxygen from the circulating blood. Foetal haemoglobin also has a high affinity because it needs to be able to steal oxygen from the mother’s blood.

26
Q

What is the PO2 of blood arriving at the respiratory exchange surface?

A

5.3 kPa

27
Q

Why does the Hb saturation of the blood decrease from 100% at the respiratory exchange surface to 97% in the systemic circulation?

A

This is because of the bronchial circulation joining the pulmonary circulation before returning to the left side of the heart. This also causes a decrease in partial pressure from 13.5 kPa to 13.3 kPa

28
Q

What are the changes in concentration of oxygen and saturation that take place at the tissues?

A

20.3 –> 15.1 mL/dL

97% –> 75%

29
Q

Define oxygen flux and state the usual oxygen flux at rest.

A

The overall amount of oxygen being deposited in the tissues.
Oxygen flux = 20.3 - 15.1 = around 5 mL/dL
Normal cardiac output = 5 L (50 dL) so oxygen flux is:
250 mL/min

30
Q

Describe the reaction of carbon dioxide with water.

A

Carbon dioxide reacts with water to produce carbonic acid (H2CO3)

31
Q

Why does this reaction take place faster in the red blood cells?

A

The red cells have carbonic anhydrase, which catalyses this reaction and allows it to occur at a rate 5000 times greater than in the cytoplasm.

32
Q

Which transporter moves the bicarbonate produced in the red blood cell into the plasma?

A

AE1 transporter

33
Q

This transporter also allows the influx of which ion? What is the term given the this movement of ions?

A

Chloride ions move in - this is called chloride shift

34
Q

What effect does the influx of chloride (antiport with bicarbonate via AE1) have on the red blood cell?

A

As an HCO3- is moving out, a chloride (also negatively charged) must move in to maintain the electrochemical neutrality. The chloride also draws water in with it, which is used to react with carbon dioxide.

35
Q

How does carbon dioxide binds to proteins and what does it form?

A

To prevent a decrease in intracellular pH, the excess H+ can be buffered by the globin chains of haemoglobin - certain residues within the globin chain are active proton acceptors.
Some of the intraerythrocytic carbon dioxide binds to haemoglobin - not at the oxygen binding site but at the AMINO group at the N terminus forming an NHCOOH end - this is called CARBAMINOHAEMOGLOBIN

36
Q

What is the net CO2 flux?

A

52-48 mL/dL (+4 mL/dL) - total of 200 mL of CO2 produced per minute

37
Q

Why are total oxygen consumption and total carbon dioxide production not equal?

A

Because some of the water is lost in metabolic water production.

38
Q

What is pulmonary transit time?

A

The time that blood is in contact with the exchange surface/respiratory membrane - usually around 0.75 s

39
Q

What is the Haldane effect?

A

The amount of carbon dioxide that binds to the amine end of proteins forming carbaminohaemoglobin depends on the amount of oxygen that is bound to the haemoglobin - this is another allosteric effect. Increasing oxygen binding means less carbaminohaemoglobin.

40
Q

What is the ventilation perfusion mismatching of the lungs?

A

The ventilation and perfusion is greater at the inferior parts of the lungs. V/Q at the base tends towards zero, V/Q at the apex tends towards infinity.