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Respiratory System > Gas Transport > Flashcards

Gas Transport Flashcards

1
Q

What are the prefixes in the nomenclature for respiratory gases

A 
P-Partial pressure (kPa or mmHg)
F- fraction (% or decimal)
S- Hb saturation (%)
C-content (mL)
Hb- Volume bound to Hb (mL)
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2
Q

What are the middle subscripts

A 
I- Inspired
E- Expired
A- Alveolar
a- arterial
v- mixed venous
P- peripheral 
D- Dissolved
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3
Q

Define Dalton’s law

A

Pressure of a gas mixture is equal to the sum (Σ) of the partial pressures (P) of gases in that mixture
Assume that gas occupies the whole volume of the other gases

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4
Q

Define Fick’s law

A

Molecules diffuse from regions of high concentration to low concentration at a rate proportional to the concentration gradient (P1-P2), the exchange surface area (A) and the diffusion capacity (D) of the gas, and inversely proportional to the thickness of the exchange surface (T)

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5
Q

Recall the equation for Fick’s law

A

V gas = A/T x D X (P1-P2)

To calculate this we need to know which gas the patient has been inhaling

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6
Q

Define Henry’s law

A

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

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7
Q

Define Boyle’s Law

A

At a constant temperature, the volume of a gas is inversely proportional to the pressure of that gas

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8
Q

Define Charle’s Law

A

At a constant pressure, the volume of a gas is proportional to the temperature of that gas

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9
Q

Recall the equation for Henry’s law

A

C d gas = a gas x p gas

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10
Q

Describe N2 at sea level

A

Percentage- 78.09
Partial pressure- 593mmHg
Solubility coefficient
(agas; mL gas/kPa/dL blood)- 1.1 x 10^-2

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11
Q

Describe O2 at sea level

A

20.95%
160mmHg
2.4^10-2

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12
Q

Describe CO2 at sea level

A
  1. 04%
  2. 30mmHg
  3. 57
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13
Q

Describe Ar at sea level

A
  1. 93%
  2. 1mmHg
  3. 6 x10^-2
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14
Q

Describe Ne, He, H2, Kr etc.at sea level

A

<0.01 %

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15
Q

Describe different situations with respiratory gases

A

 Oxygen therapy – more oxygen concentration (less N2) to give a steeper diffusion gradient.
 At altitude – the pressure of the atmosphere decreases but the proportions of gas remain the same so you just breathe in less of everything.
house fire- normal level of N2 but most oxygen replaced by CO2 and CO

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16
Q

Describe the changes in pressure in air as it passes through the respiratory airways

A

 As the air passes down the respiratory tract, it is:
o Warmed – cold air is an irritant.
o Humidified – dry air is an irritant.
o Slowed.
o Mixed.
 The PO2 decreases not because gas exchange has occurred by because it has become diluted by water vapour.

(PO2 decreases as PH2O increases in conducting airways; in respiratory airways, PO2 decreased as PCO2 increased

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17
Q

Quantify the pressure changes

A

Dry air at sea level:
PO2- 21.3kPa
PCO2 and PH20- 0

Conducting airways:
PO2- 20kPa
PCO2- 0Kpa
PH20- 6.3kPa

Respiratory airways:
PO2- 13.5kPa
PCO2- 5.3kPa
PH20- 6.3kPa

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18
Q

What happens at each generation

A

The cumulative cross-sectional area increases, slowing the air down.
No flow of air in the alveoli

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19
Q

How do we calculate the content of dissolved oxygen

A 
CD gas = αgas · Pgas
CDO2 = αO2 · PO2
CDO2 = 0.024 · 13.5
CDO2 = 0.32 mL·dL-1
CD O2 = 16 mL·min-1
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20
Q

Describe why we need Hb

A

 CD = Content of Dissolved Gas.
 Total O2 delivery at rest is about 16mLmin-1 BUT the oxygen consumption (VO2) of
the body is about 250mLmin-1 so we don’t rely solely on dissolved oxygen to keep
us alive – HAEMOGLOBIN!

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21
Q

How do we calculate VO2

A

cDO2 x cardiac output= 250mL/min which is not conducive for life

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22
Q

What is haemoglobin

A

Haemoglobin monomers consist of a ferrous iron ion (Fe2+; haem- ) at the centre of a tetrapyyrole porphyrin ring connected to a protein chain (-globin); covalently bonded at the proximal histamine residue
(Has two Hba subunits and two of Hb beta/sigma/gamma depending on type)

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23
Q

Describe the haem group of Hb

A

The haem group consists of a porphyrin ring containing iron and is responsible for the binding of oxygen; when it is in it’s ferrous state

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24
Q

Describe haemoglobin binding

A

Hb has four binding sites; the amount of oxygen carried in the blood depends on how many of these binding sites are occupied.
 As more oxygen binds, the affinity for oxygen increases and the molecule becomes ‘relaxed’.
o This is called ‘COOPERATIVITY’.

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25
Q

Describe the role of 2,3-DPG

A

2,3-DPG is a product of anaerobic metabolism. red blood cells possess no mitochondria and therefore carry out anaerobic respiration.
2,3-DPG binds more strongly to reduced Hb than to oxyhemoglobin
 2, 3-DPG binds to the relaxed central opening and aids the dissociation of oxygen to muscles (decreases affinity of haemoglobin for oxygen).
o 2, 3-DPG is produced in larger amounts in times of larger ATP production.

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26
Q

Why is Hb described as an allosteric protein

A

Hb is an ALLOSTERIC protein meaning it will change shape depending upon what is bound to it

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27
Q

Describe methaemoglobin

A

Ferrous iron oxidised to ferric from by various drugs and chemicals, including nitrites, sulfonamides, and acetanilide
There is a congenital cause in which the enzyme methaemoglobin reductase is deficient in the red blood cell
has Fe3+ not Fe2+; exists as <1% of total Hb in body - does not bind oxygen, constantly in equilibrium with Hb, switching between Hb and MetHb

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28
Q

Describe the intrinsic pathway for the production of MethHb

A

Fe3+ – Fe2+
Methaemoglobin reductase (reduced) – methaemoglobin reductase (oxidised)
Nad+ — NADH
Equilibrium

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29
Q

Describe the extrinsic pathway fro the production of MethHb

A

Methylene blue (oxidised) – methlyne blue (reduced)
This converts methylene blue reductase (reduced) to methylene blue reductase (oxidised)
which is converted back to methylene blue reductase (reduced)
NADPh- nadp
forming Fe2+
methylene blue increases Hb if met hB IS HIGH

30
Q

What are the consequences of MetHb

A

 MetHb does NOT bind oxygen so methaemoglobinaemia can cause a functional anaemia.

31
Q

Why is the oxygen dissociation curve not linear

A

not linear to ensure that high saturation occurs in lungs but that in systemic circuit a lot of oxygen can be unloaded when really needed, but at rest only remove ~25% of oxygen

32
Q

What is meant by the oxygen dissociation curve

A

How much oxygen binds to Hb depends on the partial pressure of oxygen in the blood. This relationship is represented by the oxygen dissociation curve; this is an equilibrium curve at specific conditions
150 g Hb/L
pH 7.4
37 degrees Celsius

33
Q

Describe the shape of the oxygen dissociation curve

A

Haemoglobin has a sigmoid dissociation curve.
 This gives us effectively a 100% saturation across a big range of alveolar PO2.
 In the tissues, you can go from 76% to 8% saturation so there is a very high unloading capacity.
you want to keep a large saturation for the systemic tissues- the tissues that need it

34
Q

What is P50

A

partial pressure of oxygen when HbO2 = 50%
We look at this to track changes
Not a static curve- looks different during different breathing patterns and in different parts of the body

35
Q

What is a consequence of a shift in the dissociation curve to the left

A

Makes oxygen binding easier (higher oxygen saturation at a particular PO2) and increases oxygen uptake by haemoglobin
Caused by hypothermia, alkalosis, hypocapnia, decreased 2,3-DPG

36
Q

Describe hyper and hypo- capnia

A

Hypercapnia- a high partial pressure of carbon dioxide in the arteries (>45mmHg)
Hypocapnia- a low partial pressure of carbon dioxide in the arteries (<40mmHg)

37
Q

What is a consequence of a shift to the right

A

Allows easier dissociation of oxygen (lower saturation at a particular PO2) and increases oxygen release from oxyheamoglobin
less o2 bound to Hb

38
Q

What causes a right shift

A

hyperthermia, acidosis, hypercapnia, increased 2,3-DPG

in exercise, it is a metabolic activity, exothermic reaction, temp goes up

39
Q

Describe the vertical shifts

A

Upwards shift: polycythaemia
(Increased oxygen carrying capacity) - more total O2 in blood
Downwards shift: anaemia
(Impaired oxygen carrying capacity) - less total O2 in blood

SATURATION IS THE SAME

Down and leftwards: decreased capacity and increased affinity results from increased HbCO (carboxyhaemoglobin)

40
Q

Describe the downwards shift

A

 Anaemic people have a lower haemoglobin concentration so they have a reduced amount of oxygen in the blood but the same saturation.
 If you have less haemoglobin, you have a lower oxygen carrying capacity.

41
Q

Describe the upwards shift

A

 Polycythaemia = an increase in haematocrit in the blood possibly due to increase in red cell number.
 Blood flows slower due to more RBCs so slower O2 delivery.

42
Q

Describe the effects of carbon monoxide poisoning

A

Downwards and left shift.
 Hb has a much greater affinity for CO than O2.
 The overall affect of CO is to:
o Increase affinity for oxygen (so it won’t dissociate in the tissues).
o Decrease the capacity of the Hb for O2.

43
Q

What is key to remember about the vertical shifts

A

Hb saturation at a given PO2 does not change

P50 is same PO2

44
Q

Describe myoglobin

A

Much much greater affinity than adult HbA to ‘extract’ oxygen from circulating blood and store it.
Helps provide O2 for high-intensity, short duration exercises
Not a haemoglobin variant:
 A monomeric protein with a hyperbolic ODC.
 This is a protein that stores oxygen inside muscles in times of increased muscular activity.

45
Q

Describe foetal haemoglobin

A

Greater affinity than adult HbA to ‘extract’ oxygen from mothers blood in placenta
Helpful in the hypoxic environment of the foetus

46
Q

Describe why foetal haemoglobin has a higher affinity for oxygen

A

Has two gamma chains instead of 2 beta chains
Gamma chains bind to 2,3-DPG less avidly than the beta chains of adult Hb and can therefore bind O2 at lower partial pressures (venous PvO2 can be <40mmHg)
Release of carbon dioxide causes a shift to the left of the fetal Hb dissociation curve
This released co2 binds to maternal hB reducing its affnity for O2
O2 released by maternal and binds to fetal
Double Bohr shift

47
Q

Describe oxygen transport at the tissues

A

– At the alveoli:
 Blood arriving to the alveoli have about 75% oxygen bound – NOT depleted.
 Mixed venous blood returning has a PO2 of around 5.3kPa while alveolar PAO2 is 13.5kPa – pressure gradient.

48
Q

Describe the pre and post alveolar levels of molecules

A

Pre-alveolar
PvO2- 5.3kPa (40 mmHg)
SvO2- 75%

Post-alveolar
PO2- 13.5kPa (101mmHg)
SaO2- 100%
HbO2- 20.1mLdL-1
CdO2- 0.34 mL/dL
CaO2- 20.4mL/dL
49
Q

Describe oxygen transport at the tissues

A

At the tissues, the following takes place:
1. Concentration of O2: 20.3  15.1 mLdL-1.
2. Saturation of O2: 97%  75%.
PO2 decreases from 12.7kPa (101mmHg) to 3.5 kPa (40mmHg)
HbO2 decreases from 20mL/dL to 15 mL/dL
CdO2 decreases from 0.32 mL/dL to 0.14mL/dL

Tissue PO2 = 5.3 kPa (40 mmHg)

50
Q

Describe oxygen flux

A

Oxygen Transport – At the tissues:
Oxygen Flux = The movement of oxygen.
 Here it is: -5 mLdL-1.
 As the body has 50dL, this equals -250mLO2min-1.
change is -5mL dL-1, and cardiac output is 5L min-1 so meet 250mL min-1 VO2

51
Q

Describe the 3 ways in which carbon dioxide is transported

A

Dissolved in plasma
As bicarbonate ions
As carboamino compounds

52
Q

Describe CO2 transport in the plasma

A

Obeys Henry’s law and is around 20 times more soluble than oxygen
10% is carried in solution
1. In the plasma, CO2 reacts with water to form carbonic acid.
a. The carbonic acid SLOWLY dissociates (no enzymes present) into a proton and bicarbonate.
2. In the red blood cell, the same reaction occurs 5000x quicker due to carbonic anhydrase enzyme!
RBCs do most of the CO2 shifting!

53
Q

Describe CO2 transport as bicarbonate ions

A

Approximately 60% of carbon dioxide is transported as bicarbonate ions
Dissolved carbon dioxide interacts with water to form carbonic acid (carbonic anhydrase)
Ionic dissociation of carbonic acid into H+ and HCO3-
When the conc of ions increases in the cell, HC03- moves out, but H+ cannot easily do this due to membrane impermeability to cations.
Thus, to maintain electrical neutrality, Cl- ions move into the cell from the plasma, chloride shift

54
Q

Describe the chloride shift

A

RBC CO2 Transport
 The bicarbonate ion diffuses out via the AE1 transporter and a chloride ion moves in.
a. CHLORIDE SHIFT maintains RMP.
 Movement of Cl- in, draws water in with it to react with the CO2 to maintain the osmolality.

55
Q

Describe the transport of CO2 as carboamino compounds

A

Also binds to Hb (amine end of the globin chains, 1 Hb = 4 O2 and 4 CO2)
 These proteins make a good buffer for any excess proteins inside the RBC.

56
Q

Describe the role of Hb as a buffer

A

If the ionic dissociation of carbonic acid continued, a large amount of H+ would be produced, shifting the equilibrium to the left and halting this reaction
H+ can bind to haemoglobin, allowing the reaction to continue rapidly
H+ + HbO2- — HHb + o2
H+ = HB- — HHb

Hb chains: have amino acids with negative chains that are proton acceptors i.e histadine

57
Q

Describe carbon dioxide in the tissues

A

Tissue PCO2 = 6.1 kPa (46 mmHg)

PaCO2 = 5.3kPa
CO2 as HCO3-= 43mL/dL
HbCO2 = 2.5 mL/dL
CDCO2 = 2.5ml/dL
CaCO2 = 48mL/dL
pH = 7.40 
PVCO2 = 6.1kPa (46mmHg)
CO2 as HCO3- =. 45.2
HbCO2 = 3
CDCO2 = 3.8
CVCO2 = 52
pH = 7.36
58
Q

Describe CO2 flux at the tissues

A

 CO2 flux goes from 52 (venous)  48 mLdL-1 (arterial).- change is +4
 CO2 is produced at 200mLmin-1.
 O2 is consumed at 250mLmin-1.
a. Note these are not equal – this is because some water is lost in metabolic water production.

59
Q

Describe the Haldane effect

A

carriage of carbon dioxide is increased in deoxygenated blood

  1. Reduced Hb has a greater affinity for carbon dioxide than does oxyhaemoglobin- when 100% saturated, globing chains do not bind to CO2
  2. Reduced Hb is less acidic ( a better proton acceptor) than oxyhemoglobin

The haldan effect minimises changes in pH when gaseous exchange occurs
The decrease in pH due to oxygenation of Hb is offset by the increase that results from the loss of CO2. The reverse occurs in tissues

60
Q

Why is minimising pH changes an important effect

A

In the peripheral capillaries, unloading of O2 aids the binding of CO2
In the pulmonary capillaries, the loading of oxygen reduces the binding of carbon dioxide
this allows the efficient gas exchange of CO2 in the tissues and lungs

61
Q

Summarise the CO2 dissociation curve

A

the carriage of CO2 is dependent on the partial pressure of CO2 in the blood
The curve is more linear
much steeper
varies according to oxygen saturation of Hb

62
Q

Describe how and why the CO2 dissociation curve varies with the O2 conc of Hb

A

The lower the saturation of Hb with O2, the larger the co2 conc for a given PCO2- Haldane effect

63
Q

Describe pulmonary transit time

A

time each red blood cell can participate in gas exchange (0.75s)
 The gas exchange occurs within 0.75s at the respiratory membrane location.
 By 0.25s, all of the gas exchange is complete.
 During exercise, increased blood flow rate means the lines stretch right but gas exchange still has ample room and time.
 CO2 is much quicker at exchanging as it’s more water soluble than O2.

64
Q

Describe regional differences in ventilation

A

Base of lungs ventilate more
Intrapleural pressure is less negative at the bottom- due to weight of lung (anything that is supported above it requires a larger pressure below it than above it)
The lung is easier to inflate at smaller volumes than larger volumes, where it becomes stiffer
because the expanding pressure at the base of the lungs is small, the region has a small resting volume, vbut as its situated on a steep part of the pressure-volume curve- it expands a lot in inspiration
Apex has a large expanding pressure, a big resting volume, and a small change in volume in inspiration
Thus the base has better ventilation

65
Q

Describe the regional differences in perfusion

A

Lower intravascular pressure at top of lung leads to less recruitment, greater resistance and lower flow rates compared to base; blood flow more susceptible to change
Diffusion follows the path of least resistance

66
Q

Summarise V/Q matching

A

 The blood flow to the lungs is not homogenous as gravity exerts an influence on blood flow.
a. This means less blood perfuses the apex.
b. This is also true of individual alveoli.
 Differences in V/Q:
a. Base – tends towards ZERO.
b. Apex – tends towards INFINITY.
 Due to the effect of gravity, look at the PZones.

67
Q

Why are the effects of gravity greater on perfusion than ventilation

A

Because blood is more dense than air

68
Q

What determines the amount of oxygen transferred to blood

A

PaO2
Which is dependent on ventilation and perfusion
V/Q determines CaO2

69
Q

Describe the relative Pa cones in different regions

A

Apex
lOWER THAN PA but greater than PV

Middle
Greater than PA and PV (PA> PV)

Lower
Greater than both (PV greater than PV)

70
Q

Why does Hb saturation decrease slightly initially

A

 Blood arriving to tissues have about 97% saturation.
The pulmonary system has 2 circulations:
 The pulmonary blood supply for oxygenation of blood for the heart.
 It’s own blood supply which drains into the above pulmonary arteries.
o This means the blood is diluted by this mixed venous blood return.

71
Q

What is key to remember about the CO2 dissociation curve

A

Haldane Effect = amount of CO2 that binds to the amine end of the haemoglobin protein chains changes depending on how much oxygen is bound.
 This only describes the grey part of the graph – CO2 binded as carbaminohaemoglobin.
 A = arterial blood.
 B = mixed venous blood.
 Post-alveoli – oxygen saturation is 100% and we we don’t need CO2 binding so CO2 does not bind to the amine ends of the proteins.
 Post-tissue – after unloading oxygen, proteins become more susceptible to binding of CO2.

72
Q

What are the different types of Hb

A 
o	HbA (2 Hbα &amp; 2 Hbβ)		Adult Hb; 98% 				Alpha, Beta.
o	HbA2 (2 Hbα &amp; 2 Hbδ)		Adult Hb normal variant; ~2%		Alpha, Delta.
o	HbF (2 Hbα &amp; 2 Hbγ)		Foetal Hb; trace amount.			Alpha, Gamma.

Respiratory System (23 decks)

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