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ZA - Renal System > Acid-Base Balance > Flashcards

Acid-Base Balance Flashcards

1
Q

Normal pH of arterial blood? What is the acceptable ranges?

A
  1. 4 is normal ideal value

7. 37-7.43 is the ideal range

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2
Q

Free [H+] in normal pH of blood?

A

40 x10^-9 moles/l
or
40x10^-6 mmoles/l

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3
Q

What sort of hydrogen ions contribute to pH?

A

Free

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4
Q

Does body make hydrogen ions? Where from?

A

Yes

Respiratory Acid - CO2

Metabolic Acid - inorganic (Phosphoric acid) /organic acids (lactric, fatty etc)

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5
Q

Major source of alkali?

A

Oxidation of organic anions - citrate

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6
Q

Difference between anion and cation?

A 
Anion = -ve
cation = +ve
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7
Q

What is a buffer?

A

Minimises changes in pH when H+ ions are added or removed

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8
Q

What is the HH equation measuring?

A

the pH in terms of the ratio of [A-]/[HA] NOT the absolute amounts

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9
Q

So what is the most important extracellular buffer in the body?

A

Bicarbonate

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10
Q

What is the ratio in the body between Bicarbonate:Carbonic acid.

A

20:1

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11
Q

Normal pCO2 level?

A

5.3 kPa / 40 mmHG

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12
Q

Normal HCO3 - conc

A

24 mmoles/L

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13
Q

What is the chemical reaction for the bodies buffer system?

A

(H+) + HCO3- H2CO3 H2O + CO2

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14
Q

What is the basic mechanism by which this buffer works?

A

Increase in ECF H+ ions drives reaction to the right to use up excess H ions and balance pH

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15
Q

What would normally happen in a normal buffer system in H+ was increased? Why is this ineffective in the body?

A

Reaction would drive to right but eventually right side would drive back and an
equilibrium will be reached

Ineffective as a buffer system in body as won’t last long

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16
Q

What does the body do to prevent this equilibrium occuring?

A

Expels the CO2 on the right side of the equation via increased ventilation

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17
Q

What is an important point to remember about the H ions when buffering occurs?

A

H ions aren’t removed - just buffered and stopped from contributing to pH changes

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18
Q

What happens if there is a decrease in H ions?

A

Reaction moves left

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19
Q

Where are H ions eliminated from the body?

A

Kidney’s

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20
Q

What is renal excretion of H ions coupled with?

A

The regulation of plasma HCO3- conc.

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21
Q

What are some intracellular buffers?

A

Organic and inorganic phospahtes

Proteins

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22
Q

What does buffering of H+ ions intracellularly cause and why?

A

Changes in plasma electrolytes since movement of H+ ions must be accompanied by Cl- or exchanged for a cation like
K+ to keep charges neutral

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23
Q

What causes hyperkalaemia in acidosis?

A

The movement if K+ out of cells by Intracellular buffering

Leads to depolarisation of excitable tissue = ventricular fibrillation and death

24
Q

Why does chronic renal failure lead to wasting of bones?

A

Bone carbonate provides an additional store of buffer

25
Q

How much more bicarbonate is needed that carbonic acid to maintain a pH of 7.4?

A

20x more

26
Q

How does the kidney regulate bicarbonate conc.?

A

Reabsorbs filtered bicarbonate and generates new bicarbonate

Both of which depend on active H+ ion secretion from the tubule cells into the tubule lumen

27
Q

How does the mechanism for reabsorption of bicarbonate work?

A

Active H+ ion secretion from tubule cells is coupled to passive Na+ reabsorption

The filtered bicarbonate reacts with secreted H+ ions to form carbonic acid

Carbonic acid then reacts in the in the presence of carbonic anhydrase to become CO2 and H2O

CO2 and H2O get absorbed into the proximal tubule cell and react with carbonic anhydrase again to form carbonic acid

Carbonic acid breaks down into H+ and Bicarbonate

Bicarbonate gets reabsorbed into peritubular capillary and the H+ ions used again and secreted out of cell actively in conjunction with passive Na+ reabsorption t

28
Q

What is the minimun and maximum urine pH values in humans?

A

4.5

8

29
Q

What acts as a buffer for urine to stop pH dropping too low?

A

Several weak acids and bases act as buffers. Most is done by dibasic phosphate, hydrogen phospahte also uric acid and creatinine

30
Q

What is this process of buffering urine called and why is it important?

A

Titratable acidity

Generates bicarbonate and removes hydrogen ions

31
Q

Where does titratable acidity happen?

A

In distal tubule

32
Q

Explain titratable acidity?

A

Sodium hydrogen phosphate exchanges a Na+ ion with a H+ ion (Na goes into cell H+ comes out)

This new molecule is excreted from body

New bicarbonate is made in the cell by combining CO2 and H2O to make carbonic acid then into bicarbonate and 1 hydrogen ion via carbonic anhydrase

The bicarbonate enters blood with the Na+ ion given off by sodium hydrogen phosphate and the excess hydrogen ion is used in the cycle again at step 1

33
Q

What is resp. acidosis?

A

Fall in pH due to a reduced ventilation and therefore retention of CO2

Causes pCO2 to increase

34
Q

Causes of resp. acidosis?

A

Acute - drugs like barbiturates and opiates which suppress the medullary reps. centres

Chronic - lung diseases like bronchitis, asthma, emphysema

35
Q

Bodies response to resp. acidosis?

A

Increased levels of bicarbonate to stabilize pH

Also increased reabsorption of bicarbonate

But this doesn’t treat the underlying cause - so blood gas values may still be abnormal but since renal system is compensating then pH is at a safe level

36
Q

What is resp. alkalosis?

A

Increased pH due to hyperventilation and increased CO2 blow off

37
Q

Causes of resp. alkalosis?

A

Acute - volunatry hyperventilation, aspirin or 1st ascent to altitude

Chronic - long term resistance at altitude or a decrease is pO2 below 60 mmHg stimulates peripheral chemoreceptors to increase ventilation

38
Q

Bodies response to resp. alkalosis?

A

Bicarbonate should be lowered

Less H+ is available for secretion into tubule therefore less filtered bicarbonate is reabsorbed

39
Q

What is metabolic acidosis?

A

A decrease of bicarbonate due to metabolic issues - either due to an increase buffering of H+ or a direct loss of bicarbonate

40
Q

causes of metabolic acidosis?

A

Increase production of H+ ions - either due to DKA or lactic acid increase

Failure to excrete normal dietary load of H+ due to renal failure

Loss of bicarb via diarrhoea - failure to reabsob dietary bicarb

41
Q

Bodies response to metabolic acidosis?

A

Stimulates ventilation into a kussmaul pattern to expel CO2 and increase pH

Kidneys also can help correct disturbances by restoring bicarbonate levels and excreting more H+ ions - but only if healthy

42
Q

What is a problem with the way the body responds to metabolic acidosis?

A

The increase resp rate to expel CO2 gets rid of the bodies source for H+ ions - carbonic acid

This basically means that the resp. compensation delays renal compensation to protect the pH - but pH more important in short term

43
Q

What is metabolic alkalosis?

A

Increase in bicarb

44
Q

Bodies response to increased bicarb/metabolic alkalosis?

A

Increase PCO2

45
Q

Causes of metabolic acidosis?

A
  1. increased loss of H+ ions via vomiting and losing gastric secretions
  2. Increased renal H+ ion loss due to aldosterone excess, or excess liquorice ingestion
  3. Excess administration of bicarbonate in a renal impaired patient (can’t compensate)
  4. Massive blood transfusions - blood banks contain citrate to prevent coagulation which is converted to bicarbonate in body (at least 8 units to have an effect)
46
Q

What is a unwanted affect of increased PCO2?

A

increase of CO2 helps reabsorb bicarb

This response helps stabilize pH in short term but again delays the renal excretion of excess bicarbs

47
Q

Why does liquorice cause metabolic acidosis?

A

contains glycyrrhizic acid which has a similar effect to aldosterone

48
Q

What is the anion gap?

A

A measure of the difference between the principle cations (Na+/K+) and anions (Cl-/HCO3-).
Usually about 14-18mmoles/l more cations than anions.

49
Q

Why is anion gap useful?

A

In acidosis
It increases when bicarbonate is used up by lactic acidosis/DKA

It stays the same when HCO3- is lost in the gut as its compensated by extra Cl-

50
Q

Patient with pH = 7.32, [HCO-3] = 15 mM, PCO2 = 30mmHg (4kPa)

What Acid/base disturbance is this? Why?

A

Metabolic acidosis

HCO3 and pCO2 are both low

51
Q

Patient with pH = 7.32, [HCO-3]= 33 mM, PCO2 = 60mmHg (8kPa)

What acid/base disturbance is this?

A

Chronic resp. acidosis

Chronic as more H+ means more HCO3 production and reabsorption - but this takes time to occur and bicarbonate would be normal in an acute attack

52
Q

Patient with pH = 7.45, [HCO-3] = 42 mM, PCO2 = 50mmHg (6.7kPa)

What is wrong?

A

Metabolic alkalosis - both are high

53
Q

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

What is wrong?

A

Acute resp. alkalosis

pCO2 is low and bicarb is normal so not chronic

In chronic the bicarb would be low too

54
Q

Patient with pH = 7.31, PCO2 = 7.7.kPa, (58mmHg), [HCO3-] =36mmoles/l.

Which of the following is true:

  1. It is likely that he has renal disease.
  2. He may have an acute respiratory infection.
  3. It is possible that he may have chronic bronchitis.
  4. There will be a decrease in his excretion of ammonium ions.
  5. His plasma potassium will be reduced.
A

3 is true as his high bicarb indicates chronic resp. acidosis

1 - can’t be renal as HCO3 is raised in an acidotic condition

2 - Can’t be acute

4 - False as ammonium extretion would increase

5 - Plasma K+ would increase due to increased H+ entering cells and K+ exiting

55
Q

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

Which of the following are true?

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

A

4 is true - metabolic acidosis

1 - Low pCO2 indicates a metabolic cause of acidosis

2 - acidosis causes hyperventilation

3 - Bicarb levels are low

5 - vomiting would cause loss of H+ ions via gastric secretions leading to alkalosis

ZA - Renal System (27 decks)

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