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Nutrition and Metabolism > Regulation of fluids > Flashcards

Regulation of fluids Flashcards

1
Q

What is the % of water neonates have compared to adults?

A

75-80% water with proportionately more extracellular fluid (ECF) than adults

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2
Q

How much larger is interstitial fluid proportion at birth as compared to an adult?

A

three times larger

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3
Q

What is the % of decrease in TBW (total body water) at 60 years of age in males?

A

50%

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4
Q

What is the reason for the decrease in TBW in males at 60yo mostly due to?

A

increase in adipose tissue

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5
Q

How many litres of fluids are in intracellular (ICF) and extracellular fluid (ECF)?

A 
intra = 23 L
extra = 19 L
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6
Q

Describe fluid balance in the ICF:

A
  • cytosol of cells

- makes up two-thirds of total body water

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7
Q

Describe fluid balance in the ECF:

A
  • major components includes interstitial fluid and plasma

- minor components include all other extracellular fluids

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8
Q

ICF and ECF are separated by?

A

cell membranes

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9
Q

What are the levels of ions in intracellular fluids?

A 
potassium/magnesium = high
sodium/chloride = low
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10
Q

Is there a single united compartment of intracellular fluid?

A

no. this concept is artificial

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11
Q

Is the ECF divided into several smaller compartments?

A

Yes

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12
Q

How are the compartments in ECF distinguished?

A

by different locations and kinetic characteristics

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13
Q

What are the levels of ions in extracellular fluids?

A 
potassium/magnesium = low
sodium/chloride = high
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14
Q

What does the interstitial fluid contain (ISF)?

A

all fluids which lie in the interstices of all body tissues

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15
Q

What are the ‘functions/purposes’ of the ISF?

A
  • bathes all cells in body
  • link between ICF and intravascular compartment
  • oxygen, nutrients, wastes, chemical messengers all pass through
  • has compositional characteristics of ECF
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16
Q

How is the ISF distinguished?

A

by its usually low protein concentration

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17
Q

Is the lymph considered part of ISF?

A

Yes

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18
Q

What is the relation of the lymphatic system with ISF?

A
  • lymphatic system returns protein and excess ISF to circulation
  • lymph more easily obtained for analysis than other ISF parts
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19
Q

What can we say about the plasma compartment?

A

the only major fluid compartment that exists as real fluid collection all in one location

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20
Q

What is the difference of plasma and ISF?

A

plasma much higher protein content and its high bulk flow (transport function)

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21
Q

What are the normal blood levels of sodium?

A

135-145 mEq/L

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22
Q

What are the normal blood levels of potassium?

A

3.5-5.5 mmoles/L

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23
Q

What are the normal blood levels of chloride?

A

96-106 mEq/L

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24
Q

What makes water move?

A

osmosis

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25
Q

Explain how the osmotic pressure works, making water move:

A
  • it’s the hydrostatic (hydraulic) pressure that opposes movement of water through semi-permeable membrane
  • in response to osmotic gradient
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26
Q

What is serum osmolality measured by?

A
  • use of an osmometer
    OR
  • calculated as sum of concentration of solutes present in solution
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27
Q

How many mL is the insensible loss of water from the body?

A

800mL

28
Q

How many mL is the minimal sweat loss of water from the body?

A

100mL

29
Q

How many mL is the faecal loss of water from the body?

A

200mL

30
Q

How many mL is minimal urine volume to excrete solute load, of water from the body?

A

500mL

31
Q

So, the daily obligatory water loss in mL is?

A

1,600mL

32
Q

What are the external fluid inputs?

A
  • oral intake of fluid and foods

- IV fluids

33
Q

What are the internal fluid inputs?

A

metabolic water production

34
Q

When is metabolic water produced?

A

during oxidation of food

- carbs are completely metabolised to carbon dioxide and water

35
Q

How much per day of metabolic water is produced?

A

350-400mls/day

36
Q

Give some examples of fluid loss:

A
  • pure gastric vomiting
  • bilious vomiting
  • panting
  • free water gain
  • diarrhea
37
Q

What happens in pure gastric vomiting?

A
  • loss of HCl

- volume causes hypochloremic metabolic alkalosis

38
Q

What happens in bilious vomiting?

A
  • loss of K, HCO3, Na

- cause hypokalemia, acidosis (colour of vomit is important)

39
Q

In panting, what are the losses?

A
  • loss of free water

- but no electrolyte loss

40
Q

What can promote ion loss in the free water gain situation?

A

dilution and diuresis

41
Q

What is by far the most important indication for fluid and electrolyte replacement?

A

dirrhoea

42
Q

What enhances intestinal absorption of sodium and water?

A

by glucose (other carbs)

43
Q

What is the solution to replacement of fluid/electrolytes lost through diarrhea?

A

Oral rehydration therapy (ORT) - give solutions containing Na, K, and glucose (other carbs, starch)

44
Q

What is a result of the oral rehydration solution?

A
  • enhance absorption of water/electrolytes
  • replace electrolyte deficit
  • contain alkalinising agent to counter acidosis
  • be slightly hypo-osmolar (250mmol/L) to prevent possible induction of osmotic diarrhoea
  • simple to use in hospital/at home
  • palatable and acceptable to children esp.
  • readily available
45
Q

What is WHO’s rehydration salt formulation containing?

A

NaCl = 2.6g
KCl = 1.5g
Na citrate = 2.9g
anhydrous glucose = 13.5g

(But solutions are lower in sodium for UK since patients suffer less sodium loss)

46
Q

How long is the rehydration process?

A

3-4hrs

47
Q

What is the maximum rate of sweating?

A

50mls/min
2000mls/hr
8000mls/day??

48
Q

What is the % losses of TBW through sweating during stress?

A

25%

49
Q

What is lost through sweating?

A
  • fluid (hot environment, physically active)
  • solute (acclimatisation)
  • heat (high latent evaporisation of water)
50
Q

How much of sweat is solute in %?

A

0.2-1%

51
Q

Where is sweat loss from?

A

sweat glands, specialised skin appendages

52
Q

Where is insensible fluid loss from?

A
  • skin

- respiratory tract

53
Q

What is the role of sweat?

A

regulate body temperature

54
Q

Under extreme conditions, how much sodium can be lost in a day?

A

350mmols/day

55
Q

What is the central controller of water balance?

A

hypothalamus

56
Q

What are the key parts of the hypothalamus involved in water balance?

A
  • osmoreceptors
  • thirst center
  • OVLT and SFO (respond to angiotensin II)
  • supraoptic and paraventricular nuclei (ADH synthesis)
57
Q

What are the 2 types of thirst?

A

hypovolemic and osmotic

58
Q

What are the 4 major stimuli to thirst?

A
  1. Hypertonicity
  2. Hypovolaemia
  3. Hypotension
  4. Angiotensin II
59
Q

What is hypertonicity?

A

cellular dehydration, via osmoreceptor mechanism

60
Q

What is hypovolaemia?

A

low volume sensed via the low pressure baroreceptors in great veins and right atrium

61
Q

What is hypotension?

A

high pressure baroreceptors in carotid sinus and aorta provide the sensors for this input

62
Q

what is angiotensin II?

A

produced consequent to release of renin by kidney (response to renal hypotension)

63
Q

What is ADH?

A

antidiuretic hormone

  • nonapeptide synthesised in hypothalamus
  • vasopressin because vasopressor response to pharmacological doses
64
Q

What is ADH’s major role?

A

regulation of water balance by its effect on kidneys

65
Q

What is the half life of intravascular ADH?

A

15mins, being rapidly metabolised in liver/kidney to inactive products

66
Q

What properties do both caffeine and alcohol have?

A

diuretic properties

  • work by restricting ADH activity
  • inhibit pituitary secretion of anti-diuretic hormone
67
Q

At what levels of caffeine would there be diuretic effect?

A

excess of 300mg

Nutrition and Metabolism (14 decks)

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