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Year 2 - Renal > Acid base balance > Flashcards

Acid base balance Flashcards

1
Q

Normal blood pH + normal range

A
  1. 4

7. 37 - 7.43

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2
Q

What ions contribute to pH

A

FREE H+ ions

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3
Q

Sources of H+ in the body (2)

A

Respiratory acid (i.e. carbonic acid) - produced from CO2 + water

Metabolic acid - e.g. inorganic acids (phosphoric acid) and organic acids (fatty acid, lactic acid)

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4
Q

Function of buffers

A

Minimise changes in pH when H+ ions are added or removed/ aqueous solution that resists changes in pH when acids or bases are added to it

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5
Q

Henderson-Hasselbalch equation relates to the fact that arterial pH depends on the ratio of

A

[bicarbonate ion] to pCO2

or in simpler terms base to acid

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6
Q

Henderson-hasselback equation:

pH =

A

pKa + log10 (base conc. / acid conc.)

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7
Q

Most important extracellular buffer

A

bicarbonate

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8
Q

Normal blood bicarbonate conc. + normal range

A

24mmol/l

22-26

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9
Q

Normal blood bicarbonate conc.

A

24mmol/l

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10
Q

Ratio of bicarbonate ions to carbonic acid in blood (this ratio is needed to maintain blood pH of 7.4)

A

20:1

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11
Q

What enzyme catalyses the reaction fo CO2 with water to form carbonic acid

A

carbonic anhydrase

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12
Q

What does carbonic acid immediately do once formed

A

dissociate into hydrogen and bicarbonate ions

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13
Q

Three major buffer systems that are responsible for regulating blood pH:

A

the bicarbonate buffer system, the phosphate buffer system, and the plasma protein buffer system.

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14
Q

Chemical reaction describing the equilibrium between carbonic acid and bicarbonate is:

A

CO2 + H2O H2CO3 HCO3- + H+

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15
Q

Chemical reaction describing the equilibrium between carbonic acid and bicarbonate is:

CO2 + H2O H2CO3 HCO3- + H+

An increase in ECF H+ conc. would drive the equilibrium to the

A

left - so that the additional H+ are removed from solution

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16
Q

Chemical reaction describing the equilibrium between carbonic acid and bicarbonate is:

CO2 + H2O H2CO3 HCO3- + H+

A decrease in ECF H+ conc. would drive the equilibrium to the

A

right - more carbon dioxide will combine with water and more carbonic acid will be produced so it can dissociate into more hydrogen ions

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17
Q

If blood becomes more acidic, how does resp function compensate

A

increased ventilation to decrease CO2 conc.

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18
Q

If blood becomes more alkaline, how does resp function compensate

A

decreased ventilation to retain CO2

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19
Q

Elimination of H+ by the kidneys is coupled to the regulation of plasma

A

bicarbonate conc.

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20
Q

Intracellular buffers include

A

proteins
phosphates
haemoglobin (in RBCs only)

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21
Q

Buffering of H+ ions by intracellular buffers is a bit different to extracellular buffers as it causes changes in conc. of

A

plasma electrolytes - as movement of H+ is accompanied by movement of other ions

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22
Q

In acidosis where ECF H+ increases, to maintain electrochemical neutrality, movement of H+ into cells causes a consequent increase of what ion in the plasma

A

K+ –> hyperkalaemia

- as H+ enters cell in EXCHANGE for K+ leaving cell

23
Q

Hyperkalaemia has what effect on the heart

A

excess depolarisation of cardiac muscle –> ventricular fibrillation

24
Q

2 ways the kidney maintains [HCO3-] + what do both of these depend on

A

Reabsorbing filtered bicarbonate ions

Generating new bicarbonate ions

Active H+ secretion from tubule cells into tubule lumen

25
Q

How does the kidney reabsorb bicarbonate ions to maintain plasma pH

  • what does it require the active secretion of
  • filtered bicarbonate reacts with what to form what
  • the above produced product then dissociates into CO2 + H2O, this CO2 then diffuses into tubule cell from lumen and gets converted back to … … which then dissociates into … and …
  • the bicarbonate ions then get reabsorbed into the … … with …
A

Requires active H+ secretion from tubule cells into tubule lumen
-this is coupled to passive Na+ reabsorption as Na+ reabsorbed is exchanged for H+ exiting tubule cell

reacts with the secreted H+ to form carbonic acid which then dissociates into CO2 + H2O

Increased CO2 diffuses from the lumen into the tubule cell which then gets converted back to carbonic acid in the presence of carbonic anhydrase and dissociates into H+ and HCO3- again

The bicarbonate ions get reabsorbed into the peritubular capillaries with Na+

26
Q

Bulk of HCO3- reabsorption occurs in the

A

proximal tubule

27
Q

How does the kidney generate new bicarbonate ions to maintain plasma pH

  • based on a process called what
  • passive Na+ reabsorption from tubule lumen to tubule cell is exchanged for H+ exiting cell into lumen; this H+ combines with what
  • source of new bicarbonate comes from what compound
  • above compound enters tubule cell from lumen and combines with what to form what
  • this compound then dissociates in the presence of carbonic anhydrase to yield what
A

Based on a process called titratable acidity (generates bicarbonate ions and excretes H+)

Passive sodium reabsorption from lumen to distal tubule cell is exchanged for H+ exiting into lumen

The secreted H+ combines with dibasic phosphate ion and is excreted in urine

Source of new bicarbonate ions comes from CO2 in the blood, it enters tubule cells and combines with H2O to form carbonic acid then in the presence of carbonic anhydrase dissociates to form H+ (WHICH IS ACTIVELY SECRETED INTO TUBULE LUMEN) and NEW bicarbonate ions which pass with Na+ into the peritubular capillaries

28
Q

Name the 2 buffers the kidney uses to deal with acid loads by generating new bicarbonate ions and excreting H+

A

Dibasic phosphate

Ammonium

29
Q

Excretion of what ion is a mechanism the kidney uses to deal with acid loads

A

NH4+ (Ammonium)
-NH3 produced from amino acids inside tubule cell movies into tubule lumen and combines with the excess H+ to be excreted as NH4+

30
Q

Function of renal glutaminase

A

Removes amine group from amino acids, usually glutamine, to form ammonia

31
Q

Causes of respiratory acidosis

  • acute (2)
  • chronic (1)
A 
Acute
-Drugs which depress medullary respiratory centre
=barbiturates
=opiates
-Major airway obstruction

Chronic
-Chronic lung disease
=COPD
=asthma

32
Q

Define respiratory alkalosis

A

Increase in pH due to increased ventilation –> excess CO2 exhalation –> decreased PCO2

33
Q

Causes of respiratory alkalosis

  • acute (3)
  • chronic (1)
A

Acute

  • Voluntary hyperventilation
  • Aspirin
  • first time in high altitude

Chronic
- living in high altitude

34
Q

Normal PO2 value

A

100mmHg (13.5 kPa)

35
Q

Define metabolic acidosis

A

Decrease in pH due to decreased plasma bicarbonate conc.

36
Q

To protect pH in metabolic acidosis or alkalosis, what function has to compensate

A

lung function - PCO2 has to increase/decrease by changing ventilation

37
Q

Causes of metabolic acidosis (3)

A

Increased H+ production, e.g. in ketoacidosis or lactic acidosis

Failure to excrete normal dietary load of H+, e.g. in renal failure

Loss of bicarbonate, e.g. in diarrhoea - could be from malabsorption disorder

38
Q

Kidneys deal with acidosis by generating what ions and excreting what ions

A

bicarbonate

hydrogen

39
Q

Define metabolic alkalosis

A

Increased pH due to increased plasma bicarbonate

40
Q

Causes of metabolic alkalosis (4)

A

Increased hydrogen ion loss - e.g. vomiting

Increased renal H+ loss - e.g. aldosterone excess

Excess exogenous bicarbonate - unlikely to be the cause though if renal function normal

Massive blood transfusion - because bank blood contains citrate to prevent coagulation which is converted to bicarbonate

41
Q

In respiratory acidosis

  • is plasma H+ increased/decreased
  • is pH increased/decreased
  • is PCO2 (i.e. the cause) increased/decreased
  • what does the kidney do to compensate
A

increased

decreased

increased

increases plasma bicarbonate by reabsorbing/generating more bicarbonate

42
Q

In respiratory alkalosis

  • is plasma H+ increased/decreased
  • is pH increased/decreased
  • is PCO2 (i.e. the cause) increased/decreased
  • what does the kidney do to compensate
A

decreased

increased

decreased

decrease plasma bicarbonate by excreting more of it

43
Q

In metabolic acidosis

  • is plasma H+ increased/decreased
  • is pH increased/decreased
  • is plasma bicarbonate (i.e. the cause) increased/decreased
  • what do the lungs do to compensate
A

increased

decreased

decreased

hyperventilation to blow of CO2 and decrease PCO2

44
Q

In metabolic alkalosis

  • is plasma H+ increased/decreased
  • is pH increased/decreased
  • is plasma bicarbonate (i.e. the cause) increased/decreased
  • what do the lungs do to compensate
A

decreased

increased

increased

hypoventilation to increase PCO2 to retain more CO2

45
Q
  • Describe the mechanisms used for the secretion of organic acids such as PAH (Aminohippuric acid)
  • Describe the principles involved in renal replacement therapy and state the social, economic and psychological implications of dialysis and renal transplantation.
A

Excretion/clearance of para aminohippuric acid measures the RENAL PLASMA FLOW which measures renal function

PAH is avidly secreted by the renal tubules so that nearly all of the blood that enters the kidneys is “cleared” of PAH

46
Q

Severe vomiting leads to metabolic alkalosis which would trigger aldosterone as there’s loss of NaCl and H2O so Na+ reabsorption stimulated in distal tubule

The resp compensation for metabolic alkalosis is decreasing ventilation in order to retain CO2 and so increase PCO2, however what consequence does this have

A

increased CO2 retention means more CO2 available to form carbonic acid with water which will then dissociate to yield more H+ and HCO3- ions

Since Cl- will be decreased from losing it in the vomiting, Na+ reabsorption will be exchanged for H+ secretion which therefore means more H+ loss in urine so EXACERBATES THE ORIGINAL METABOLIC ALKALOSIS but volume correction more important than correction of metabolic alkalosis in this case

47
Q

Anion gap =

A

The difference between the sum of the principal cations ( Na+ and K+) and the principal anions in the plasma (Cl- and HCO3- )

48
Q

Which simple Acid/Base Disturbance has this person got?

pH = 7.32 (low)
[HCO3-] = 15 mM (low)
PCO2 = 30mmHg (4kPa) (low)

A

metabolic acidosis

49
Q

Which simple Acid/Base Disturbance has this person got?

pH = 7.32 (low)
[HCO3-] = 33 mM (high)
PCO2  = 60mmHg (8kPa) (high)
A

Chronic resp acidosis
- not acute because for an increase in PCO2 so big, the pH is fairly well maintained so likely to be the pH this person has adapted to living with, bicarbonate has changed indicating chronic, if acute bicarbonate won’t have changed yet

50
Q

Which simple Acid/Base Disturbance has this person got?

pH = 7.45 (high)
[HCO3-] = 42 mM (high)
PCO2  = 50mmHg (6.7kPa) (high)
A

metabolic alkalosis

51
Q

Which simple Acid/Base Disturbance has this person got?

pH = 7.45 (high)
[HCO-3] = 21 mM (low)
PCO2  = 30mmHg (4kPa) (low)
A

Respiratory alkalosis

52
Q 
pH = 7.25 (low)
[HCO3-] = 12mmoles/l (low)
PCO2 = 3.3kPa (25mmHg) (low)

a) They are indicative of a respiratory acidosis
b) The reduction in Pco2 is a result of under-breathing
c) The subject has probably been taking bicarbonate of soda
d) It could be related to impaired renal function
e) The subject may have been vomiting very badly

A

metabolic acidosis

d

53
Q

Reabsorption and generation of new bicarbonate ions requires the active secretion of what into the tubule

A

H+

54
Q

Does hyperventilation increase or decrease PCO2

A

decrease

Year 2 - Renal (21 decks)

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