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Nutrition > Water and Electrolyte Balance > Flashcards

Water and Electrolyte Balance Flashcards

1
Q

How much water is required daily to balance insensible losses?

A

1 Litre

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2
Q

What is the daily RNI for sodium?

A

70mmol / 1.6g

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3
Q

Despite the RNI for sodium what is the usually intake range?

A

90-440mmol / 2-10g

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4
Q

What do high intakes of sodium lead to?

A

Hypertension

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5
Q

The WHO also recommends how much potassium to reduce blood pressure and cardiovascular risk of stroke and CHD?

A

90mmol / 3.5g

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6
Q

In healthy people the total body water constitutes what % of lean body weight in men and women?

A

Men 50-60% Women 45-50%

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7
Q

In a healthy 70kg male what would his approximate body water content be in litres?

A

42L

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8
Q

Body water is contained in what three major compartments?

A

Intracellular fluid, extracellular fluid and plasma

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9
Q

What % of lean body weight is ICF?

A

35% / 28L

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10
Q

What % of lean body weight is ECF?

A

12% / 9.4L

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11
Q

What % of lean body weight is plasma?

A

4-5% / 4.6L

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12
Q

What other areas of the body contain water?

A

Bones, dense connective tissue and epithelial secretions such as digestive secretions and cerebrospinal fluid

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13
Q

Intracellular fluid and interstitial fluid is separated by what?

A

The cell membrane

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14
Q

The interstitial fluid and plasma are separated by what?

A

The capillary wall

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15
Q

In the absence of solute, how do water molecules move across the semi-permeable membrane?

A

Randomly and in equal numbers

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16
Q

If solute is added what happens to the water?

A

It stays in the high-solute compartment

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17
Q

The ability to hold water in a compartment can be measured as?

A

Osmotic pressure

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18
Q

Osmotic pressure is defined as?

A

The primary determinant of the distribution of water between the three major compartments

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19
Q

The concentrations of major solutes in the compartments is different each having one solute that is primarily?

A

Limited to the compartment to determine its osmotic pressure

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20
Q

Intracellular fluid contains mainly which solute?

A

Potassium K+

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21
Q

Most of the cell’s magnesium Mg2+ is bound and therefore osmotically?

A

Inactive

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22
Q

In the extracellular compartment what solute predominates in the interstitial fluid?

A

Sodium Na+

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23
Q

Proteins are found in which compartment of extracellular fluid?

A

Plasma

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24
Q

The capillary wall is relatively impermeable to?

A

Plasma proteins

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25
Q

The cell membrane is relatively impermeable to?

A

Na+ and K+

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26
Q

Which pump restricts Na+ to ECF and K+ to ICF?

A

Sodium Potassium Pump

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27
Q

Na+ moves freely across ? to achieve similar concentrations in interstitium and plasma

A

Capillary Walls

28
Q

What crosses the cell membrane and capillary wall and is osmotically inactive?

A

Urea - therefore retention of urea in renal failure does not alter the distribution of total body water

29
Q

What stores are the primary determinant of ECF volume?

A

Na+ stores

30
Q

ECF volume and tissue perfusion are maintained by appropriate alterations in ? secretion

A

Na+ secretion

31
Q

If Na+ intake is increased, where will the extra Na+ be initially added to?

A

ECF

32
Q

When the increased Na+ intake is initially added to ECF what happens next?

A

Increased ECF osmolality causes H2O to move out of cells, leading to ECF volume expansion

33
Q

How is balance restored in the ECF when Na+ is too high?

A

Excess Na+ is excreted in the urine

34
Q

1 litre of water given intravenously as 5% glucose is distributed how between the compartments?

A

Equally

35
Q

1 litre Saline (0.9% salt/99.1% H2O) given intravenously, remains in which compartment?

A

Extracellular

36
Q

Which is the correct treatment for extracellular water depletion?

A

0.9% Saline - as the Na+ keeps the water in this compartment

37
Q

The extracellular volume is determined by the concentration of sodium balance exerted by?

A

Kidneys

38
Q

Renal Na+ secretion varies directly with?

A

The effective circulating volume

39
Q

In a 70kg man what fraction of ECF is plasma?

A

1/3rd (4.6L)

40
Q

The plasma in the ECF of a 70kg male has what % lying in the venous side and what % in the arterial circulation?

A

85% (3.9L) venous side and 15% (0.7L) arterial circulation

41
Q

The fullness of the arterial vascular compartment (effective arterial blood volume) is the primary determinant of?

A

Renal Na+ and H2O excretion - which is the effective circulatory volume for body fluid homeostasis

42
Q

The fullness of the arterial compartment depends on the relationship between?

A

cardiac output and peripheral arterial resistance

43
Q

A diminished effective arterial blood volume is initiated by?

A

a fall in cardiac output or a fall in peripheral arterial resistance

44
Q

Changes in what … contribute towards the main adaptive response to fluctuations in the effective circulating volume?

A

Tubular reabsorption

45
Q

Tubular reabsorption is X - dependant?

A

Flow-dependant

46
Q

Neurohormonal regulation of Na+ reabsorption occurs mainly in which areas of the kidney?

A

Proximal tubules and collecting ducts

47
Q

Neurohormonal regulation of ECF volume is mediated by?

A

Volume receptors rather than alterations in sodium concentration

48
Q

Which hormones control the day-to-day variations in Na+ excretion through their ability to diminish and augment Na+ reabsorption in the collecting ducts?

A

Aldosterone and Atrial Natriuretic Peptide (ANP)

49
Q

If there is a salt load, what is the chain of events that happens in the body to lead to an increase in Na+ excretion and homeostatic fluid rebalance?

A
  1. Salt load leads to increase in circulatory and extracellular volume
  2. Renal perfusion pressure and atrial and arterial filling pressure increases
  3. Increase in renal perfusion pressure reduces the secretion of Renin, subsequently angiotensin 2 and aldosterone
  4. Increase in atrial and arterial filling pressure increases release of ANP (atrial natriuretic peptide)
  5. These factors combine to reduce Na+ reabsorption in the collecting duct promoting excretion of excess Na+
50
Q

If there is salt depletion in those with low salt intake or diarrhoea/vomiting what is the series of events that happens in the body to try and achieve homeostatic fluid rebalance?

A
  1. Decrease in effective volume enhances the activity of the renin-angiotensin-aldosterone system
  2. Also decreases secretion of ANP
  3. Net effect is enhanced Na+ reabsorption in the collecting ducts
  4. Reduced Na+ excretion increasing ECFV towards norm
51
Q

Marked hypovolaemia causes a decrease in GFR and proximal and ascending limb Na+ reabsorption leading to?

A

Na+ retention

52
Q

Body water homeostasis is affected by?

A

Thirst and kidneys diluting and concentrating function

53
Q

Thirst and kidney function is controlled by what receptor initially and in which gland?

A

Osmoreceptors / Hypothalamus

54
Q

Which hormone plays a central role in urinary concentration?

A

ADH

55
Q

The presence of ADH promotes?

A

Water reabsorption in the collecting ducts down the favourable osmotic gradient between the tubular fluid and the more concentrated intersitium

56
Q

Hyponatraemia is defined by which mmol/L Na+?

A

<135mmol/L

57
Q

What could be the cause of hyponatraemia with hypovolaemia extrarenally?

A

Vomiting, diarrhoea, haemorrhage, burns, pancreatitis

58
Q

What could be the cause of hyponatraemia with hypovolaemia in the kidneys?

A

Osmotic diuresis (e.g hyperglycaemia), diuretics

59
Q

Most people have a dietary potassium intake of?

A

80-150mmol daily depending on fruit and veg intake

60
Q

Most of the body’s potassium is within which fluid compartment?

A

Intracellular

61
Q

A number of drugs affect K+ homeostasis by affecting the release of which hormone?

A

Aldosterone - these drugs include NSAIDs, heparin

62
Q

Diuretics affect K+ homeostasis by directly affecting?

A

Renal potassium handling

63
Q

What % of potassium intake is secreted in the GI tract?

A

10%

64
Q

How much K+ does vomit contain?

A

5-10mmol/L

65
Q

K+ is secreted by the colon and diarrhoea contains how much?

A

10-30mmol/L

66
Q

Hypokalaemia is defined at which mmol/l?

A

<3.5mmol/L

Nutrition (12 decks)

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