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Biochemistry > Acid-Base Regulation > Flashcards

Acid-Base Regulation Flashcards

1
Q

Define acid

A

A substance that can release a hydrogen ion when dissolved in water

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2
Q

Define base

A

A substance that can accept a hydrogen ion

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3
Q

Define buffer and give an example of one in the human body

A

A chemical that minimises the change in pH when an acid or base is added to a solution. Carbonic acid

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4
Q

Define anion

A

Atoms or groups of atoms that carry a negative charge

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5
Q

Define cation

A

Atoms or groups of atoms that carry a positive charge.

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6
Q

Features of PaCO2

A

Partial pressure of CO2 in arterial blood
Normal 38-42 mmHg
PaCO2 arterial blood = PaCO2 in alveolar air

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7
Q

Features of PaO2

A

Partial pressure of oxygen in arterial blood
Normal is 75-100mmHg

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8
Q

Features of bicarbonate and how its measured

A

Anion
Measured indirectly on an arterial blood gas
22-26mEq/L(mmol/L)

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9
Q

Role of lungs in Acid-base homeostasis

A

Regulate arterial PCo2 and thus the conc. of dissolved CO2 in blood via changes in alveolar ventilation

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10
Q

Role of kidneys Acid-Base homeostasis

A

Regulate HCO3- via changes in renal H+ excretion

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11
Q

What are the three components in response to Acid-Base perturbation?

A

1st defence: buffering
2nd defence: respiratory - alteration in arterial pCO2
3rd defence: renal - alteration in HCO3

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12
Q

Features of the immediate response: buffering

A

Rapid physico-chemical phenomenon
Buffering of fixed acids by bicarbonate

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13
Q

Features of the respiratory response: alteration in ventilation

A

Adjustment of the denominator pCO2 by alterations in ventilation is relatively rapid
Increased CO2 excretion due to hyperventilation
Useful physiologically because of its effect on intracellular pH as well as extracellular pH
CO2 crosses cell membrane easily so changes in pCO2 affect pH rapidly
Respond quickly because of the huge amounts of respiratory coif to be excreted

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14
Q

Three outcomes of increased CO2 excretion due to hyperventilation

A

1️⃣ Correction of respiratory acidosis
2️⃣ Production of a respiratory alkalosis
3️⃣ Compensation for a metabolic acidosis

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15
Q

Features of the renal response: alteration in bicarbonate excretion

A

Much slower process (several days) involves adjustment of bicarbonate excretion by the kidney
Responsible for the excretion of the fixed acids and for compensator changes in plasma [HCO3-] in the presence of respiratory acid-base disorders

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16
Q

__________ acid-base disorders change in bicarbonate concentration.

A

Metabolic

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17
Q

Explain the association metabolic acid-base disorders and diabetes mellitus

A

Altered intermediary metabolism in the absence of insulin causes a build-up of H+

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18
Q

____________ acid-base disorders change in pCO2

A

Respiratory

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19
Q

If the primary acid-base disorder is from a _____________ cause, then the kidneys will
compensate (renal compensation), renal mechanisms can bring about metabolic compensation.

A

Respiratory

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20
Q

If the primary disorder is from a ________ cause, then the lungs will compensate (respiratory
compensation), hyperventilation or hypoventilation can help: respiratory compensation.

A

Metabolic

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21
Q

How long does does respiratory compensation take?

A

12-24 hours

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22
Q

How long does renal compensation take?

A

2-5 days

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23
Q

Kidneys compensate for respiratory acid-base disturbances by _____________________

A

Adjusting bicarbonate

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24
Q

Lungs compensate for metabolic acid-base disturbances by ________________.

A

Adjusting carbonic acid

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25
Q

Compensatory response to respiratory disorders is two fold:

A

A fast response due to cell buffering
And a significantly slower response due to renal adaptation

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26
Q

Compensatory response to metabolic disorders involves only:

A

An alteration in alveolar ventilation

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27
Q

Metabolic acidosis

A

The primary disorder is a decrease in bicarbonate (HCO3-) concentration

28
Q

Metabolic alkalosis

A

The primary disorder is an increased bicarbonate (HCO3-).

29
Q

Respiratory acidosis

A

The primary disorder is an increased PCO2.

30
Q

Respiratory alkalosis

A

The primary disorder is a decreased PCO2.

31
Q

Metabolic acidosis

A

H+ elevated
Acidosis
⬇️HCO3-

32
Q

Metabolic alkalosis

A

H+ decreased
Alkalosis
HCO3- ⬆️

33
Q

Anion gap

A

The difference between the main cation and the main anions

34
Q

High anion gap acidosis

A

Renal failure

35
Q

Normal anion gap acidosis

A

Diarrhoea

36
Q

Two common causes of high anion gap metabolic acidosis

A

Diabetes ketoacidosis
Lactic acidosis

37
Q

Diabetic ketoacidosis

A

The lack of insulin causes the liver to excrete ketone bodies (beta-hydroxybutyric acid, acetoacetate) for cells to use as fuel. Ketone bodies add H+ to the blood.

38
Q

Lactic acidosis

A

Hypoxia causes cells to undergo anaerobic metabolism, and excessive lactate is produced. Lactate adds H+ to the blood.

39
Q

Two common causes of normal anion gap metabolic acidosis

A

Diarrhea (intestinal loss of HCO3-)
Renal tubular acidosis (renal loss of HCO3-)

40
Q

How is electroneutrality maintained in normal anion gap metabolic acidosis?

A

Cl- levels rise to replace the lost HCO3-

41
Q

In ___________________, the normal response of the kidneys is to excrete acid as ammonium.

A

Metabolic acidosis

42
Q

How do we distinguish RTA from other forms of acidosis?

A

In RTA, NH4+ excretion is impaired so we can distinguish by measuring the amount of NH4+ present in the urine. Usually done indirectly with the urinary anion gap or urinary osmolal gap.

43
Q

In what conditions is the urinary Osmolal gap preferred?

A

Urinary pH> 6.5
Polyuria
Ketoacidosis
Acetaminophen overdose

44
Q

The urinary gap should be _______ in metabolic acidosis because NH4+ is excreted with chloride (NH4+Cl-). A positive gap is a sign of ___ and/or ______________.

A

Negative
RTA
Kidney failure

45
Q

The most common cause of ___________________ is vomiting and dehydration.

A

Metabolic alkalosis

46
Q

_____of H+ and Cl- in gastric fluid raises plasma HCO3-.

A

Loss

47
Q

Dehydration and potassium loss lead to renal ______ retention which further exacerbates the alkalosis.

A

HCO3-

48
Q

Metabolic alkalosis is typically driven by 3 processes:

A

Chloride loss/malabsorption
Increased mineralcorticoid activity
Low potassium

49
Q

In metabolic alkalosis, the lungs ________ ventilation in order to retain CO2, but the effect is limited by the respiratory stimulatory effects of ________ PaCO2 and ________ PaO2.

A

Decrease
Increased
Decreased

50
Q

How is Cl- lost?

A

Vomitting
Nasogastric suction
Diuretic use

51
Q

Decreased Cl- absorption occurs in:

A

Bartter and Gitelman syndrome

52
Q

Decreased Na+ transport through the Na+-Cl- and Na+-K+Cl-Cl- cotransporters promotes…

A

…promotes Na+-H+ exchange, and HCO3- is retained

53
Q

What causes increased mineralcorticoid activity?

A

Hypovolemia
Cushing’s syndrome
Conns syndrome
Exogenous steroids
Bartters syndrome
Licorice ingestion

54
Q

Effects of increased mineralcorticoid activity

A

Stimulate the H+ pump causing HCO3- to be retained
Na+-K+ exchange is also increased and K+ loss is enhanced

55
Q

How is K+ lost?

A

Vomiting
Increased mineralcorticoid activity
Diuretic use
Chloride deficiency stimulates movement of intracellular K+ into plasma via K+-H+ exchange
Increases in intracellular H+ stimulate HCO3- retention

56
Q

How do we distinguish between chloride loss from syndromes associated with excessive mineralcorticoid activity and impaired chloride re absorption?

A

Check urinary chloride

57
Q

Low spot urinary chloride

A

Chloride depletion is likely present e.g. vomiting

58
Q

High spot urinary chloride

A

Excessive mineralcorticoid activity e.g. Conn’s syndrome or impaired chloride absoprtion e.g. Bartter and Gitelman syndromes may be the primary disorder

59
Q

Respiratory acidosis

A

H+ elevated
Acidosis
PCO2⬆️

60
Q

Respiratory alkalosis

A

H+ decreased
Alkalosis
PCO2⬇️

61
Q

In acute respiratory acidosis why is there no renal compensation?

A

It takes 48-72 hours for renal compensation to become fully effective

62
Q

The problem in acute respiratory acidosis is…

A

Alveolar hyperventilation

63
Q

An example of acute uncompensated respiratory acidosis

A

Choking

64
Q

Example of chronic respiratory acidosis

A

COAD accompanied with maximal renal compensation

65
Q

In many patients with ______ respiratory conditions, extensive renal compensation will keep the blood [H+] near normal, despite grossly impaired ventilation.

A

Chronic

66
Q

Features of respiratory alkalosis

A

Les common
No renal compensation
Remove cause of hyperventilation
Hysterical over breathing
Mechanical over-ventilation

67
Q

What happens in a patient with chronic bronchitis who develops renal impairment?

A

Raised H+
PCO2 will be increased and HCO3- conc will be low, both expected findings in primary respiratory and primary metabolic acidosis

Biochemistry (19 decks)

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