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MD4001 WEEK 10 > Fluid and electrolyte balance > Flashcards

Fluid and electrolyte balance Flashcards

1
Q

What are the major divisions of fluid compartments?

A

Intracellular

```
Extracellular:
Subdivided into:
- Plasma
- Interstitial
- Synovial
(- Intra-ocular)
~~~

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2
Q

Describe the major compartments and volumes for a 70kg man.

A

Total body fluid : 42L

28L intracellular fluid (including ~2L blood cells)

11L interstitial fluid: between membrane and capillary wall

3L plasma: bound by capillary wall

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3
Q

Describe the barrier between the plasma and interstitial fluid.

A

Capillary wall:

  • Leaky
  • Protein stays inside vessels (in health) to produce oncotic pressure
  • When not healthy… oedema occurs
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4
Q

Describe the barrier between extracellular fluid and intracellular fluid.

A

Plasma membrane:

  • channels/ membranes
  • water follows freely as ions take channels into/out of cells
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5
Q

What are the intracellular, interstitial and plasma levels of K+?

A

Intracellular: 150 mM

Interstitial: 4.5 mM

Plasma: 4.5 mM

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6
Q

What are the intracellular, interstitial and plasma levels of Na+?

A

Intracellular: 10 mM

Interstitial: 130mM

Plasma: 130mM

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7
Q

What are the intracellular, interstitial and plasma levels of Mg2+?

A

Intracellular: 2.5 mM

Interstitial: 0.85 mM

Plasma: 0.85 mM

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8
Q

What are the intracellular, interstitial and plasma levels of Cl-?

A

Intracellular: 10 mM

Interstitial: 110mM

Plasma: 110 mM

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9
Q

What are the intracellular, interstitial and plasma pHs?

A

Intracellular: ~7.0

Interstitial: 7.4

Plasma: 7.4

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10
Q

What are the gains of body fluid?

A

Food and water intake;

Oxidation of food

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11
Q

What are the losses of body fluid?

A

Urine (average 1500 ml)
Faeces (average 100 ml)
Swear (average 50 ml)
Insensible losses (average 900 mL)

TOTAL LOSSES: (average): 2550 mL

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12
Q

What is insensible water loss?

A
  • Insensible losses are solute free
  • Trans-epidermal diffusion: water that passes through the skin and is lost by evaporation
  • Evaporative loss from respiratory tract
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13
Q

Describe the source, solute loss and role of sweat.

A

Source: from specialized skin appendages called sweat gland

Solute loss: yes, variable

Role: body temperature regulation

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14
Q

Describe the source, solute loss and role of insensible fluid.

A

Source: from skin (trans-epithelial)

Solute loss: none

Role: cannot be prevented; evaporation of insensible fluid is a major source of heat loss from the body each day but is not under regulatory control

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15
Q

Where are the sensors for body fluid found?

A
  • Osmoreceptors: in hypothalamus
  • Low pressure baroreceptors: in right atria and great veins
  • High pressure sensory: in carotid sinus and aorta
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16
Q

What is the key driver if total volume?

A

Total sodium

17
Q

What occurs in total sodium drops and osmolality stays the same?

A

The total volume falls (including plasma volume)

18
Q

What occurs in total sodium rises and osmolality stays the same?

A

The total volume will rise

19
Q

What occurs if osmolality rises?

A
  • Increase in thirst
  • Increase in release of ADH
  • Increase in water intake/retention
    = increase in volume
20
Q

What occurs if osmolality falls?

A
  • Decrease in thirst
  • Decrease in release of ADH
  • Decrease in water intake/retention
    = Decrease in volume
21
Q

What occurs in an increase in volume?

A

Increase in stretch of vascular system:
- Baroreceptors (high pressure areas; low pressure areas)
- Decrease in renin release
- Decrease in aldosterone release
- Increased release of ANP (cardiac myocytes)
= Decreased sodium and water retention

22
Q

What occurs in an decrease in volume?

A 
Decrease in stretch of vascular system:
- Baroreceptors (high pressure areas; low pressure areas)
- If pressure (from decreased volume) falls, also influences ADH release and thirst centres
- Increase in renin release
- Increased levels of AII
- Increase in aldosterone release
- Decreased release of ANP
= Increased sodium and water retention
23
Q

Describe the control of plasma Na+.

A
  • Hormones controlling sodium balance must act on the kidney
  • DCT is the area of control in the nephron
  • Noreceptors detecting Na+
  • Controlled indirectly via volume sensors
  • Changes in Na+ lead to changes in blood volume
  • Net sodium excretion = Na+ filtered – Na+ reabsorbed
24
Q

Describe the control ok K+.

A
  • K+ is freely filtered
  • Predominantly reabsorbed again in the PCT with controlled secretion at the DCT
  • Secretion is linked to Na+ reabsorption (sodium pump)
  • K+ is tightly regulated
  • 98% of K+ is inside cells
  • Significant & variable intake of potassium from diet - Intracellular potassium acts as a reservoir (attenuates change)
25
Q

What occurs with increased K+ plasma?

A
  • Increases activity of basolateral sodium pump
  • More K+ enters the cell
  • Increased secretion across simple diffusion channels on apical membrane
  • Increased secretion of aldosterone
  • NOT driven by AII, but by direct detection of raised K+ levels by the aldosterone-secreting cells of the adrenal cortex
26
Q

What is the effect of aldosterone on the DCT?

A
  • Increases activity of sodium pump (basolateral)
  • Increases the number of sodium pumps (basolateral)
  • Increases the number of sodium and potassium channels in apical membrane
    Result: increased reabsorption of sodium and increased secretion of potassium
27
Q

What is Conn’s syndrome?

A

Hyperaldosteronism leading to:

  • hypertension from increased fluid volume
  • hypokalaemia
28
Q

Describe IV fluid - crystalloids and where they distribute.

A
  • 5% dextrose (glucose)
    Initially distributes through ISF and plasma; glucose
    metabolised so effectively adding just water. Further distributes into cells as well as ISF and plasma.
  • 0.18% NaCl 4% dextrose
  • 0.9% NaCl (isotonic saline)
  • Plasmalyte
    Distributes through ISF and plasma; does not enter cells
29
Q

Describe IV fluid - colloids and where they distribute.

A
  • 4.5% albumin
    Supplied in 0.9% NaCl
    Tends to stay in plasma; does not enter cells
    Blood product
  • Hydrolysedgelatin
    Supplied in 0.9% NaCl
    Initially tends to stay in plasma; does not enter cells
    Protein metabolised over time so then equivalent to 0.9% NaCl
  • Blood
    Stays in the vasculature and increases blood volume
30
Q

What are the clinical features of diabetic keto-acidosis?

A

Hyperglycaemia

  • Dehydration
  • Tachycardia
  • Hypotension
  • Clouding of consciousness

Acidosis

  • Air hunger (Kussmaul’s respiration)
  • Acetone on breath
  • Abdominal pain
  • Vomiting
31
Q

What can cause dehydration in DKA?

A

Hyperglycaemia
Vomiting
Kaussmaul respiration
Altered conscious level - reduced intake

MD4001 WEEK 10 (12 decks)

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