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Chemical Pathology Wits > Water and Electrolytes > Flashcards

Water and Electrolytes Flashcards

1
Q

Name types of water intake

A

Food
Drinking
Metabolic water

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2
Q

What is the most important way of water intake and what is it regulated by?

A

Drinking, regulated by thirst

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3
Q

Name types of water loss

A

Skin
Lungs
Gut (stool)
Kidneys

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4
Q

What is the most important way of water intake and what is it regulated by?

A

Urine excretion, regulated by ADH

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5
Q

What is TBW?

A

Total body water

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6
Q

What is TBW in adult men?

A

60% of body weight

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7
Q

What is TBW in adult women?

A

55% of body weight

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8
Q

What is TBW in infants and children?

A

75-80% of body weight

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9
Q

What is the distribution of TBW in the body?

A

2/3 ICF
1/3 ECF

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10
Q

What is the distribution of ECF in the body?

A

3/4 interstitial fluid (ISF)
1/4 plasma

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11
Q

Which 2 semipermeable membranes are involved in the distribution balance of water?

A
  1. Cellular membrane
  2. Capillary membrane
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12
Q

Which membrane allows water distribution between ICC and ECC?

A

Cellular membrane

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13
Q

What determines the cellular membrane?

A

ECF osmolality/tonicity -> isotonicity has to be maintained

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14
Q

Which membrane allows water distribution between plasma and interstitial compartment?

A

Capillary membrane

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15
Q

What determines the capillary membrane?

A

Oncotic pressure
Hydrostatic pressure

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16
Q

What are substances dissolved in a solution called?

A

Ions

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17
Q

What is a cation?

A

Positively charged electrolyte

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18
Q

What is an anion?

A

Negatively charged electrolyte

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19
Q

What are the dominant cations in the intracellular compartment (ICC)?

A

K > Mg

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20
Q

What are the dominant anions in the intracellular compartment (ICC)?

A

Organic phosphate compounds > proteins > HCO3

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21
Q

What are the dominant cations in the extracellular compartment (ECC)?

A

Na

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22
Q

What are the dominant anions in the extracellular compartment (ECC)?

A

Cl > HCO3 > protein

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23
Q

What is the total body sodium?

A

40-50mmol/kg

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24
Q

How much sodium is freely exchangeable and where is the majority found?

A

70% freely exchangeable
Majority in extracellular compartment (ECC)

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25
Q

How much sodium is complexed in bone?

A

30%

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26
Q

How is freely exchangeable sodium distributed?

A

10% in ICF
60% ECF

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27
Q

What maintains the trans-cell membrane gradient?

A

Na-K-ATPase pump

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28
Q

Discuss sodium intake

A

Salt (NaCl) 100-200mmol/24h
Most absorbed via gut through active transport

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29
Q

How much sodium is secreted into the gut?

A

1000mmol/24h -> majority reabsorbed

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30
Q

Discuss sodium excretion

A

Urine (90%)
Sweat/stool (10%)

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31
Q

What is the major organ involved in sodium excretion?

A

Kidney

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32
Q

How much obligatory loss of sodium is there per 24h?

A

<20mmol

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33
Q

How much sodium is secreted into the gut per 24h?

A

1000mmol

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34
Q

How much sodium is filtered by the kidneys per 24h?

A

2500mmol

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35
Q

How much of the filtered sodium reaches the distal tubules?

A

<5%

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36
Q

Where does fine control of sodium balance occur?

A

Distal tubules

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37
Q

What are the major regulator hormones of sodium excretion?

A

Aldosterone
ANP

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38
Q

What are the functions of sodium?

A
  1. Nerve impulse transmission and conduction
  2. Vascular fluid osmolarity
  3. Body fluid level regulation
  4. Sodium pump
  5. Acid-base balance regulation
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39
Q

Which diuretics act on the PCT?

A

Osmotic diuretics

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40
Q

Which diuretics act on the loop of Henle?

A

Loop diuretics

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41
Q

Which diuretics act on the proximal DCT?

A

Thiazides

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42
Q

Which diuretics act on the distal DCT?

A

Osmotic diuretics
K-sparing diuretics

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43
Q

Which diuretics act on the collecting duct?

A

Osmotic diuretics

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44
Q

Which electrolytes are reabsorbed into blood at the PCT?

A

Water
Sodium
Potassium
Glucose
Amino acids
Chloride
HCO3
Urea
Ca2+
Mg2+

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45
Q

Which electrolytes are secreted into urine at the PCT?

A

H+
NH4+
Urea
Creat

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46
Q

How is water reabsorbed at the PCT?

A

Osmosis

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47
Q

How is sodium reabsorbed at the PCT?

A

Sodium pumps
Symporters
Antiporters

48
Q

How is glucose reabsorbed at the PCT?

A

Symporters
Facilitated diffusion

49
Q

How are amino acids reabsorbed at the PCT?

A

Symporters
Facilitated diffusion

50
Q

How is chloride reabsorbed at the PCT?

A

Diffusion

51
Q

How is HCO3 reabsorbed at the PCT?

A

Facilitated diffusion

52
Q

How is urea reabsorbed at the PCT?

A

Diffusion

53
Q

How is calcium reabsorbed at the PCT?

A

Diffusion

54
Q

How is magnesium reabsorbed at the PCT?

A

Diffusion

55
Q

Which electrolytes are reabsorbed at the Loop of Henle?

A

Water
Na
K
Cl
HCO3
Ca2+
Mg2+

56
Q

Which electrolytes are secreted at the Loop of Henle?

A

Urea

57
Q

How is water reabsorbed at the Loop of Henle?

A

Osmosis in descending limb

58
Q

How is sodium reabsorbed at the Loop of Henle?

A

Symporters in ascending limb

59
Q

How is potassium reabsorbed at the Loop of Henle?

A

Symporters in ascending limb

60
Q

How is chloride reabsorbed at the Loop of Henle?

A

Symporters in ascending limb

61
Q

How is HCO3 reabsorbed at the Loop of Henle?

A

Facilitated diffusion

62
Q

How is calcium reabsorbed at the Loop of Henle?

A

Diffusion

63
Q

How is magnesium reabsorbed at the Loop of Henle?

A

Diffusion

64
Q

At the end of PCT, what is the tonicity of tubular fluid?

A

Isotonic to blood (300 mOsm/L)

65
Q

At the end of Loop of Henle, what is the tonicity of tubular fluid?

A

Hypotonic (100-150 mOsm/L)

66
Q

Which solute present in blood is NOT considered a filtered substance?

A

Proteins

67
Q

Which electrolytes are reabsorbed at the DCT?

A

Water
Na
Cl
Ca2+

68
Q

How is water reabsorbed at DCT?

A

Osmosis

69
Q

How is sodium reabsorbed at DCT?

A

Symporters

70
Q

How is chloride reabsorbed at DCT?

A

Symporters

71
Q

How is calcium reabsorbed at DCT?

A

Stimulated by PTH

72
Q

Which electrolytes are reabsorbed in the principal cells of the DCT?

A

Water
Sodium
Urea

73
Q

How is water reabsorbed at the principal cells in DCT?

A

Insertion of water channels stimulated by ADH

74
Q

How is sodium reabsorbed at the principal cells in DCT?

A

Sodium pumps

75
Q

Which electrolyte is secreted at the principal cells in DCT?

A

Potassium

76
Q

How is potassium secreted at the principal cells in DCT?

A

Leakage channels

77
Q

Which electrolytes are reabsorbed at the intercalated cells in DCT?

A

HCO3
Urea

78
Q

Which electrolytes are secreted at the intercalated cells in DCT?

A

H+

79
Q

What is osmolality?

A

Total number of dissolved particles in 1kg solution

80
Q

What is osmolarity?

A

Total number of dissolved particles in 1L solution

81
Q

How is osmolality determined in the lab?

A

Using freezing point depression osmometer

82
Q

Which solutes contribute to ECG osmolality?

A
  1. Na
  2. Cl
  3. HCO3
    Glucose
    Urea
    Proteins
83
Q

What is the formula for calculated osmolarity?

A

2 [Na] + [urea] + [glucose]

84
Q

What does determined osmolality include?

A

Calculated osmolarity plus concentrations of other solutes present in plasma

85
Q

What should you expect if osmolarity > osmolality?

A

Laboratory error
Calculation error

86
Q

What is the definition of tonicity?

A

Indication of the effective osmolality of a fluid

87
Q

Why do urea and other small molecules not influence the distribution of H2O between intra and extracellular fluid?

A

Rapid, unobstructed passage through the membranes

88
Q

How is tonicity calculated?

A

2[Na] + [glucose]
OR
Osmolality - [urea]

89
Q

Name causes of hyperosmolality

A

Hypertonic dehydration
DM
Renal failure
Hepatic failure
Lactic acidosis
Sepsis
Intoxication
High protein intake

90
Q

Name indications for determining plasma osmolality

A
  1. Low plasma sodium interpretation
  2. Hydration status assessment
  3. Presence of toxins
  4. Assess water electrolyte balance
  5. Water deprivation test
91
Q

Which 2 factors affect urine osmolality?

A

Hydration state
Renal function

92
Q

How is urine plasma osmolality ratio affected in dehydration and over hydration?

A

Normal = 1
Dehydration >1
Overhydration <1

93
Q

What is the osmolal gap?

A

Difference between determined osmolality and calculated osmolarity

94
Q

When would osmolal gap increase?

A
  1. Increase in volatile substances
  2. Change in fractional water content
95
Q

Give examples of situations that increase osmolal gap

A
  1. Uremia
  2. DM
  3. Lactic acidosis
  4. Hyperlipoproteinaemias
  5. Hyperproteinaemia
  6. Ethanol/methanol/ethylene glycol intoxication
  7. Glycine
  8. Mannitol
96
Q

How is ECF osmolality an indicator of ECG volume?

A

Increase plasma osmolality = decreased ECF volume
Decreased plasma osmolality = increased ECF volume

97
Q

What is the mechanism of ECF osmolality homeostasis in water loss from ECF?

A
  1. Increased ECF osmolality -> water moves from ICF to ECF
  2. Thirst center stimulated -> incr water intake
  3. ADH release simulation -> renal water reabsorption
  4. RAAS stimulation
98
Q

What is the mechanism of ECF osmolality homeostasis in water excess in ECF?

A
  1. Decr ECF osmolality -> water movement from ECF to ICF
  2. Inhibition of thirst center -> decr water intake
  3. ADH release inhibition -> diuresis
  4. ANP release stimulation -> natriuresis and diuresis
99
Q

What is isotonic water depletion?

A

H2O loss = Na loss
s[Na] = s-Osmol

100
Q

What is hypertonic water depletion?

A

H2O loss > Na loss
s[Na] > s-Osmol

101
Q

What is hypotonic water depletion?

A

H2O loss < Na loss
s[Na] < sOsmol

102
Q

How do you calculate water deficit?

A

Current body water - new body water

103
Q

What is the formula for new body water?

A

CBW x s[Na]/140

104
Q

What is the only case where calculation of water deficit is useful?

A

Hypernatremia

105
Q

Name the causes of water depletion

A

Decreased intake
Increased loss

106
Q

Name the causes of decreased intake resulting in water depletion

A

Infancy
Old age
Unconscious
Dysphagia
Oral intake restriction

107
Q

Name the causes of increase loss resulting in water depletion

A
  1. Kidneys
    - renal tubular acidosis
    - diabetes insipidus
    - incr osmotic load
  2. Skin
    - sweating
    - burns
  3. Lungs
    - hyperventilation
  4. Gut
    - diarrhoea
    - vomiting
108
Q

Name symptoms of water depletion

A

Thirst
Dry mouth
Difficulty swallowing
Weakness
Confusion

109
Q

Name signs of water depletion

A

Weight loss
Dry mucous membranes
Decreased saliva secretion
Concentrated urine
Decreased urine volume
Tachycardia
Hypotension

110
Q

Name causes of water excess

A

Increased intake
Decreased excretion

111
Q

Name causes of increased intake resulting in water excess

A

Compulsive water drinking
Excessive IV fluids
Bladder irrigation

112
Q

Name causes of decreased excretion resulting in water excess

A

Renal failure
Cortisol deficiency
SIADH
Drugs

113
Q

Which drugs stimulate ADH release?

A

Carbamazepine

114
Q

Which drugs potentiate the action of ADH?

A

Chlorpropamide

115
Q

Which drugs are agonists of ADH?

A

Oxytocin

116
Q

Which drugs interfere with renal diluting capacity?

A

Diuretics

117
Q
A

Chemical Pathology Wits (4 decks)

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