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CVR > gas transport and acid base balance > Flashcards

gas transport and acid base balance Flashcards

1
Q

what is oxygen transported by

A

haemoglobin

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2
Q

what chains is haemoglobin made from

A

alpha and beta

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3
Q

why is the relationship sigmoidal
-between % of Hb saturation & po2

A

affinity for oxygen increases as haem sites become occupied
in opposite direction, dissociation of O2 accelerates as haem sites freed

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4
Q

which was the does the bohr effect shift

A

right

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5
Q

O2 dissociation in tissues increases with metabolism - explain

A

rightward shift - bohr effect
O2 affinity of Hb decreases
O2 given up by blood more easily

results from increased PCOS, H+, temp, 2,3-DPG

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6
Q

describe Hb

A

2 x alpha chains
2 x beta chains
1 atom or iron per haem binds 1 x O2
4 x O2 per Hb

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7
Q

how much O2 binds to Hb in 1L of arterial blood

A

98.5% - 197mL

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8
Q

in 1L of arterial blood what % of O2 dissolves directly into blood

A

1.5% - 3mL

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9
Q

what is the total O2 content in 1L of arterial blood

A

200mL

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10
Q

what does O2 binding capacity depend on

A

Hb concentration

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11
Q

how is the saturation of O2 calculated by

A

O2 bound to Hb/ O2 binding capacity x100

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12
Q

where is there high PO2

A

lungs

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13
Q

what is dissociation like for O2 in tissues

A

easy

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13
Q

foetal haemoglobin

A

2 x alpha chains
2 x y chains
higher affinity for oxygen
low PO2 in placenta

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14
Q

where is there low PO2

A

tissues

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15
Q

what is the leftward shift caused by

A

decreases in the same factors in the lungs
O2 affinity of Hb decreases

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16
Q

why does foetal Hb have a high affinity for oxygen

A

oxygen has to pass from the mother to the foetus

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17
Q

myoglobin

A

oxygen store in muscles
high affinity for O2 at low PO2
50% saturated at 0.6kPa O2
90% saturated at 2.6kPa O2

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18
Q

carbon monoxide poisoning

A
  • CO has ~240x greater affinity for Hb compared with O2
  • 50% of haem occupied by CO at only 0.1% CO in the env

-huge decrease in oxygen content of blood

  • increased affinity of remaining Hb for O2

-difficult to dissociate

  • PaO2 normal as gaseous makeup of inspired air remain broadly normal (CO ONLY 0.1%)
18
Q

transport of CO2 via Hb

A

CO2 reacts with amino groups of proteins, especially Hb
formation of carbamino compounds
free H+ ion released

19
Q

first step of transport of CO2 via bicarbonate

A

CO2 recats with H2O to form carbonic acid
primarily in RBC
CA catalyses reaction
13,000 quicker than in plasma
CO2 + H2O -> H2CO3

20
Q

2nd step of CO2 transport via bicarbonate

A

carbonic acid dissociates into bicarbonate + free H+ ion
H2CO3 -> H+ + HCO3-

20
Q

chloride shift

A

HCO3- exchanged for Cl- ions
bicarbonate now in blood

prevents acidification of RBC
swapped -ve for -ve

bicarbonate reacts with Na in blood = NaHCO3

21
Q

what is CA stand for

A

carbonic anhydrase

22
Q

what does CA catalyse

A

reaction between CO2 + H2O to form carbonic acid

23
Q

CO2 in 1L arterial blood

A

-30% of CO2 is bound to Hb and other proteins = 147mL

-10% of CO2 is dissolved in blood = 49mL

-60% of CO2 forms bicarbonate (HCO3-) = 294mL

-TOTAL CONTENT OF ARTERIAL BLOOD = 490mL

  • TOTAL CO2 CONTENT OF VENOUS BLOOD INCREASES TO 540mL
24
Q

bohr and haldane effect in lungs

A

low CO2 increases affinity of Hb for O2
high O2 increases oxy Hb - displaces CO2
O2 = held by RBC , CO2 removed

24
Q

bohr and haldane effect in tissues

A

high CO2 decreases affinity of Hb for O2 - BOHR
low O2 decreased oxy Hb , dexoy Hb reacts with CO2 - HALDANE
O2 removed by RBC - CO2 kept

25
Q

why should H+ ions be buffered

A

maintain acid - base balance
pH of aterial blood = 7.4 - opt for enzyme function
held within 0.15 pH units

pH determined by H+ ion conc
tight regulation of H+ ions required

3 key mechanisms

26
Q

what are the 3 key mechanisms for buffering H+ ions

A

reaction with Hb
reverse formation of carbonic acid
reaction with plasma proteins

27
Q

what is HA

A

weak acid is an unionised form

28
Q

what is A-

A

weak acid in ionised form

29
Q

what is pH dependent on

A

conc of CO2
conc of bicarbonate/H+

30
Q

conc of CO2 - pH dependency explain

A

determined by respiratory system
compensates for metabolic disturbances

31
Q

conc of bicarbonate/H+ - pH dependency explain

A

determined by kidneys
compensate for respiratory disturbances

32
Q

metabolic disturbances types

A

metabolic acidosis
metabolic alkalosis

33
Q

metabolic acidosis

A

too much H+
- reverse bicarbonate reaction uses up H+ ions - DECREASE
- respiration increases to remove excess CO2
- pH returns to normal
CO2 + H2O <- H2CO3 -> HCO3- + H+

34
Q

metabolic alkalosis

A

too little H+
- respiration decreases to retain CO2
- drives forward reaction, producing H+ ions (INCREASE)
- pH returns to normal

35
Q

respiratory acidosis

A

too much CO2
- forward bicarbonate reaction uses up CO2 (DECREASES)
- bicarbonate and H+ production INCREASES
- HCO3- reabsorbed by kidneys, H+ secreted by kidneys
- pH returns to normal
CO2 + H2O -> H2CO3 -> HCO3- + H+

36
Q

respiratory alkalosis

A

too little CO2
- kidneys retain H+
- pH returns to normal

37
Q

metabolic acidosis examples

A

diarrhoea (HCO3- loss)
diabetic ketoacidosis
renal failure
lactic acidosis

38
Q

metabolic alkalosis examples

A

vomiting (H+ loss0
diuretics
hypokalemia

39
Q

respiratory acidosis examples

A

hypoventilation (COPD, airway obstruction, sedative overdose, respiratory failure

40
Q

respiratory alkalosis examples

A

hyperventilation (in response to hypoxia, anxiety)

41
Q

chloride shift

A
  • bicarbonate (HCO3-) exchanged for chloride ions (Cl-)

-bicarbonate now in blood

  • prevents acidification of RBC

-swapped a negative for a negative

  • bicarbonate reacts with sodium in the blood to form sodium bicarbonate (NaHCO3)
  • H+ ions?? - mopped up by deoxy Hb
  • Hb reacts with H+ ions to form HHb

-favours formation of bicarbonate

-prevents the reverse reaction to CO2 + H2O

  • HHb favours oxygen dissocation

-can now react with CO2

-more carbamino compounds form

  • CO2 content of the blood increases
42
Q

chloride shift

A

bicarbonate (HCO3-) exchanged for
chloride ions (Cl-)
* Bicarbonate now in blood
* Prevents acidification of RBC
* Swapped a negative for a negative!
* Bicarbonate reacts with sodium in the
blood to form sodium bicarbonate (NaHCO3)
H+ ions???

43
Q

H+ ions mopped up by deoxy Hbb - chloride shift

A

Hb reacts with H+ ions to form HHb
* Favours formation of bicarbonate
* Prevents the reverse reaction to CO2 and H2O
* HHb favours oxygen dissociation
* Can now react with CO2
* More carbamino compounds formed
* CO2 content of the blood increases

CVR (3 decks)

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