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Gas Transport Flashcards

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1
Q

What is P?

A

partial pressure (kPa or mmHg)

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2
Q

What is F?

A

fraction (% or decimal)

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3
Q

What is S?

A

Hb saturation (%)

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4
Q

What is Dalton’s Law?

A

pressure of a gas mixture is equal to the sum of the partial pressures of gases in that mixture
(N, O then other)
Pgas mixture = ΣPgas1 + Pgas2 + … + Pgasn

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5
Q

What is Ficks Law?

A

molecules diffuse from high [] region to low [] at rate proportional to [] gradient (P1-P2), the exchange SA (A), diffusion capacity of the gas (D) and inversely proportional to the thickness of the exchange surface (T)

e.g. movement from alveolar space to blood

Vgas = A X D X (P1-P2) / T

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6
Q

What is Henry’s Law?

A

at constant T, [] of gas that dissolves in given type/V of liquid is directly proportional to the partial pressure of that gas in equilibrium with that liquid and solubility of the gas

CDgas = agas x Pgas

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7
Q

What is Boyle’s Law?

A

at constant T, V of gas is inversely proportional to the pressure of the gas

P proportional to 1/Vgas

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8
Q

What is Charles’ Law?

A

at constant P, volume of gas proportional to T

Vgas proportional to Tgas

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9
Q

What is the composition of the air that we breathe in?

A

N - 78%
O - 21%
Ar - 0.9%
CO2 - 0.04%

oxygen therapy - increased O2
smoke (house fire) - increased CO2, CO
high altitude - lower barometric pressure, reduced oxygen intake (same proportion)

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10
Q

How do we modify inspiratory gases?

4 steps

A

warmed, humidified, slowed and mixed passing down the respiratory tree .

dry air at sea level
(PO2 = 21kPa, PCO2 = 0kPa)

conducting airways
(PO2 reduced slightly due to mixing - 20)
PH2O = 6.3 kPa

respiratory airways
PO2 = 13.5
PCO2 = 5.3
PH2O = 6.3
greater mixing effect - O2 diluted
CO2 higher as moving out of blood to be cleared
saturated with water to facilitate gas exchange

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11
Q

Why is gas slowed down by generation 23?

A

to facilitate gas exchange by increased cross sectional cumulative area at each generation

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12
Q

How to find total O2 delivery at rest hypothetically?

A

CDgas = agas x pgas
= 0.32mL/dL diffused across alveoli
CO is 5L/min therefore approx total oxygen delivery is 16mL/min (VO2) at rest

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13
Q

How is O2 delivered in reality?

A

but resting VO2 is 250mL/min so cannot rely on oxygen alone to deliver O2 to tissues

use haemoglobin

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14
Q

What haemoglobin?

A

monomers with ferrous iron (Fe2+ haem) at centre of tetrapyrole porphyrin ring that is connected to protein chain globin
covalently bonded at proximal histamine molecule

all haemoglobin has 2 alpha monomers

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15
Q

HbA?

A

Hb alpha and beta

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16
Q

HbA2?

A

Hb alpha and delta

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17
Q

HbF?

A

Hb alpha and gamma

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18
Q

How does haemoglobin work?

A
  1. Low O2 affinity initially when no O2 bound
  2. Binding of O2 increases oxygen affinity of Hb via COOPERATIVE BINDING
    4th subunit has increased affinity for O2 of x3000
  3. Increased affinity relaxed state opens extra binding site for 2,3-DPG
  4. 2,3-DPG binding pushes relaxed Hb into a tense state by causing O2 to be ejected
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19
Q

What behaviour does Hb exhibit?

A

allosteric behaviour
= binding of oxygen to one of the subunits is affected by its interactions with the other subunits causing structural changes

These cause increase affinity of Hb for O2 - COOPERATIVE BINDING

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20
Q

What is methaemoglobin?

A

MetHb is 0.5-1% of haemoglobin at one point
- constant flux between MetHb and Hb
Fe3+ instead
does not bind O2

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21
Q

What does Hb do to the skin?

A

provides us with colour

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22
Q

Describe foetal haemoglobin?

A

higher affinity for O2 than adult Hb

O2 dissociation curve it has a left shift

  • greater affinity for O2
  • lower partial pressure of O2 required to generate 50% Hb saturation
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23
Q

What is given in surgical scenario if MetHb too high

Study These Flashcards
A

Methylene blue -

24
Q

What is the intrinsic enzyme to reduce MetHb?

Study These Flashcards
A

MetHb reductase -

25
Why are linear O2 dissociation curves no good?
too great variability in binding in lungs | small binding range systemically to offload (no sufficient access to reserve O2)
26
How to track changes in oxygen dissociation curves?
P50 Find partial pressure of O2 at 50% saturation This is assuming normal Hb [] of 150g/L
27
What causes right shift?
increased temp acidosis increase 2,3-DPG hypercapnia all lead to decrease affinity for O2 --> at given partial pressure less O2 bound to Hb
28
What causes left shit?
decreased T alkalosis decreased 2,3-DPG hypocapnia increased affinity (loading)
29
What causes upwards shift?
``` polycythaemia - tumour secreting erythropoietin - increase [] RBCs in blood increased O2 carrying capacity saturation same ```
30
What causes downwards shift?
anaemia impaired oxygen carrying capacity less O2 in blood saturation same!
31
What causes downwards and leftwards shift?
increase HbCO | decreased capacity for release, increased affinity (cannot release O2 already bound)
32
Describe myoglobin O2 dissociation curve?
steeper - provide O2 for early stages of exercise increased affinity to store O2 Myoglobin has an increased affinity than adult HbA to extract O2 from circulating blood and store it
33
Saturation of Hb in capillary after returning to lungs? What is the PO2 in capillary and alveolar space?
``` 75% PO2 capillary = 5.3kPa lung = 13.5kPa HbO2 = 15ml/dl dissolved O2 lower (0.14) ```
34
How is oxygen transported in the lungs?
O2 moved to capillary along [] gradient till plasma PO2 = 13.5kPa Some binds to Hb so SO2 (saturation) is 100% but some dissolved (0.34) HbO2 = 20.1 ml/dl
35
Why does blood arriving at tissues have lower PO2 than in lungs?
lung tissue has 2 circulations | - some bronchial drainage from bronchial circulation drains into pulmonary veins to provide haemodilution
36
How do values change at the tissues?
PO2 decreased - 12.7 SO2 slightly decreased HbO2 - 20 (down slightly) dissolved O2 content slightly decreased
37
What does sigmoidal curve mean?
despite large decrease in PO2 entering and leaving tissues | the saturation of O2 decreased by a much smaller %
38
What is oxygen flux?
difference between the total dissolved and Hb bound O2 entering and leaving the tissues (unloaded O2) = HbO2 leaving - HbO2 entering (negative _ mL/dL)
39
What are the standard values for oxygen flux?
delta = -5mL/dL multiplied by cardiac output (5L/min) (x50) gives -250ml O2/ min this is the resting VO2 as well as oxygen flux
40
What does [CO2] equal?
[H+]
41
What is tissue PCO2?
6.3 kPa
42
Where is CO2 converted to H2CO3?
in RBC | by carbonic anhydrase
43
How is HCO3- removed from RBC?
by AE1 transporter via chloride shift to maintain RMP of RBC
44
How is CO2 transported in the blood? What is major form?
1. solution 2. as bicarbonate 3. bound to Hb AS BICARBONATE
45
Where does CO2 bind on Hb?
to amine end of globin chains 4 CO2 / Hb to form carbaminohaemoglobin
46
How is increased in RBC H+ addressed?
negatively charged amino acids on globin chain of Hb (especially histadine) bind to protons to avoid lowering pH dramatically
47
What are the significant changes in PCO2 across tissue?
less significant increase in PCO2 compared to decrease in PO2 not sigmoidal shape as O2 dissociation curve
48
What is the CO2 flux?
difference between total dissolved/bicarbonate CO2 (leaving - entering) 52 - 48 = +4 mL/dL +200mL CO2 / min
49
Overall consumption of O2 and CO2?
200 ml of CO2 released for 250 ml of O2 used / min
50
What is the Haldane effect?
oxygenation of blood in the lungs displaces carbon dioxide from haemoglobin which increases the removal of carbon dioxide oxygenated blood has a reduced affinity for carbon dioxide when Hb bound 4 O2 (100% saturated) will not bind any CO2
51
What is the pulmonary transit time?
amount of time that blood is in contact with the respiratory exchange surface 0.75s / erythrocyte time for PO2 to equilibrate between alveolus and plasma gas exchange time (0.25s for PCO2 to equilibrate between tissue and plasma)
52
What happens if CO increases?
more pulmonary capillary beds recruited if very intense exercise, blood flows through capillary beds faster
53
Explain the regional differences in ventilation in the lung?
- Airways at top of lung more stretched, larger and less compliant due to reduced gravity effect - Ppl more negative (-8cmH2O) so greater transmural pressure gradient LESS VENTILATION - greater pressure required to inflate alveoli more -At bottom alveoli are smaller and more compliant - Smaller gradient (Ppl is less negative at -2cmH2O) MORE VENTILATION
54
Explain regional differences in perfusion of lung?
``` TOP Lower intravascular pressure (gravity effect) less recruitment more resistance lower flow ``` ``` BOTTOM Higher intravascular pressure more recruitment less resistance higher flow rate ```
55
Are the difference in ventilation and perfusion the same? Why?
No Greater impact on perfusion than ventilation Blood flow is denser and so more susceptible to effects of gravity
56
What is V/Q?
ventilation-perfusion ratio at base tends toward 0, at apex tends towards infinity at base there is wasted perfusion because there not as much ventilation, at apex there is wasted ventilation because there is not as much perfusion IDEAL - where lines cross

Respiratory (7 decks)

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