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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
what does CA catalyse
reaction between CO2 + H2O to form carbonic acid
23
CO2 in 1L arterial blood
-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
bohr and haldane effect in lungs
low CO2 increases affinity of Hb for O2 high O2 increases oxy Hb - displaces CO2 O2 = held by RBC , CO2 removed
24
bohr and haldane effect in tissues
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
why should H+ ions be buffered
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
what are the 3 key mechanisms for buffering H+ ions
reaction with Hb reverse formation of carbonic acid reaction with plasma proteins
27
what is HA
weak acid is an unionised form
28
what is A-
weak acid in ionised form
29
what is pH dependent on
conc of CO2 conc of bicarbonate/H+
30
conc of CO2 - pH dependency explain
determined by respiratory system compensates for metabolic disturbances
31
conc of bicarbonate/H+ - pH dependency explain
determined by kidneys compensate for respiratory disturbances
32
metabolic disturbances types
metabolic acidosis metabolic alkalosis
33
metabolic acidosis
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
metabolic alkalosis
too little H+ - respiration decreases to retain CO2 - drives forward reaction, producing H+ ions (INCREASE) - pH returns to normal
35
respiratory acidosis
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
respiratory alkalosis
too little CO2 - kidneys retain H+ - pH returns to normal
37
metabolic acidosis examples
diarrhoea (HCO3- loss) diabetic ketoacidosis renal failure lactic acidosis
38
metabolic alkalosis examples
vomiting (H+ loss0 diuretics hypokalemia
39
respiratory acidosis examples
hypoventilation (COPD, airway obstruction, sedative overdose, respiratory failure
40
respiratory alkalosis examples
hyperventilation (in response to hypoxia, anxiety)
41
chloride shift
- 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
chloride shift
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
H+ ions mopped up by deoxy Hbb - chloride shift
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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