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LSS 2- Respiration > Gas Transport and Exchange ****** > Flashcards

Gas Transport and Exchange ****** Flashcards

1
Q 
What do the following stand for:
P
F
S
C
Hb
A
a
A 
P= Partial pressure (kPa or mmHg)
F= Fraction (% or decimal)
S= Hb saturation
C= content (mL)
Hb= Volume bound to Hb (mL)
A= Alveolar
a= arterial
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2
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.

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3
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.

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4
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.

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5
Q

State Boyle’s Law.

A

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

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6
Q

State Charles’ Law.

A

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

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7
Q

what happens as the altitude increases?

A

As you get higher the pressure of the atmosphere decreases but the proportions of the gases remains the same.

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8
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 (this is 100% saturation)

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9
Q

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

A

The air gets warmed, humidified, mixed and slowed.

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10
Q

How much oxygen can be dissolved in out bodies?

A

16 mL/minute

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11
Q

What is the normal oxygen consumption at rest?

A

250 mL/min

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12
Q

what does the amount of oxygen we can dissolve and the amount that we need mean?

A

it means that we can’t solely rely on dissolved oxygen to keep us alive.

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13
Q

What is the binding capacity of oxygen to haemoglobin?

A

1.34 mL/g

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14
Q

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

A

0.024

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15
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.

–

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16
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.

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17
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:2,3-Diphosphoglycerate (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)

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18
Q

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

A

Cooperativity

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19
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.

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20
Q

What are the benefits of having a sigmoid ODC?

A

100% haemoglobin saturation can occur at a broad range of partial pressures
Large range and scope for unloading oxygen in the tissues.

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21
Q

what would happen if the ODC was linear?

A

-We’d get a large variation in oxygenation in the lungs.

22
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.

23
Q

how can you figure out P50?

A

You figure this out by simply drawing a line across at 50% saturation

24
Q

What conditions can shift the ODC to the right?

A

Conditions brought about by exercise - hypercapnia (abnormal levels of CO2), increased temperature, acidosis, increased 2,3-DPG
Uncontrolled type 1 diabetes

25
Q

What conditions can shift the ODC to the left?

A

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

26
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)

27
Q

What conditions can shift the ODC downwards?

A

Anaemia - decreased oxygen carrying capacity of the blood

28
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.

29
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.

30
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. Fetal haemoglobin also has a high affinity because it needs to be able to steal oxygen from the mother’s blood.

31
Q

what do we all have in a small portion in our blood?

A

Methaemoglobin which is where the ferrous Fe2+ ion becomes ferric Fe3+, cannot bind to oxygen

32
Q

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

A

5.3 kPa

33
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.
  • (Post-alveolar venules converge into pulmonary veins)
  • Some deoxygenated blood enters the pulmonary circulation from the bronchial venous drainage.
  • This deoxygenated blood dilutes the PaO2 to 12.7 kPa (95 mmHg) and SaO2 from 100% to 97%.
34
Q

how many systems does the pulmonary system have?

A

2- it has it’s own blood supply to keep it alive and it has the pulmonary blood supply for oxygenation of blood. The circulation keeping the lung tissue alive drains back into he pulmonary circulation before returning to the left atrium.

35
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%

36
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

37
Q

How many mL in 1 dL

A

1 decilitre= 100 mL

38
Q

Describe the reaction of carbon dioxide with water. What is the consequence of this reaction?

A
  • CO2 is much more soluble than O2 and diffuses into plasma very quickly
  • It reacts with water to produce carbonic acid (H2CO3)
  • H2CO3 is a weak acid that dissociates into H+ and bicarbonate (HCO3-)
  • Reaction happens very slowly but can cause pH to fall significantly below tightly regulated set point of 7.4
39
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.

40
Q

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

A

AE1 transporter

41
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

42
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.

43
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 CARBAMINOH

44
Q

What is the net CO2 flux?

A

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

45
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.

46
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

47
Q

what is respiratory membrane?

A

Areas where the alveolar cells and endothelial cells of the capillaries are close enough for exchange to take place.

48
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.

49
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.

50
Q

why does the ventilation perfusion exist?

A

Less blood perfuses the apex of the lung because of the resistance of gravity.

At top = wasted ventilation
At bottom = wasted perfusion

51
Q

what are the zones in the lungs?

A

Zone 1: Alveolar pressure > arterial pressure> venous pressure
Zone 2: Arterial pressure> alveolar pressure> venous pressure
Zone 3: Arterial pressure> venous pressure> alveolar pressure

Arterial pressure will always be greater than venous pressure or the blood would flow backwards.

52
Q

How is blood oxygenated and returned back to the heart?

A
  • Arriving blood is not deoxygenated (it is about 75% oxygen bound), instead it is mixed venous blood
  • PvO2=5.3kPa and PAO2=13.5kPa so oxygen passively diffuses down a concentration gradient (Fick’s Law)
  • During oxygenation, it passes from the alveolar space, into the pulmonary epithelial cells, into the interstitial space, into vascular endothelial cells, into the plasma, into red blood cells, and then it binds to molecules of Hb that are not fully saturated.
  • After equilibration, post-alveolar PaO2 is equal to PAO2 (which is 13.5 kPa) and SaO2 will be 100%.

LSS 2- Respiration (17 decks)

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