Sodium and Water Balance COPY Flashcards

1
Q

what hormone controls water balance and where is it secreted from?

A

ADH (aka vasopressin)

secreted from posterior pituitary

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2
Q

what does ADH do?

A

makes you pee less by causing water to be reabsorbed from the renal tubules
increased ADH = small volume of concentrated urine
decreased ADH = large volume of dilute urine

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3
Q

what injury can cause a decrease in ADH secretion?

A

transection of pituitary stalk in head injury

diabetes insipidus

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4
Q

how is urine concentration measured?

A

urine osmolality
high osmolality = concentrated urine
low osmolality = dilute urine

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5
Q

A

sodium and (potassium?) pumped out of the loop of henle?

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6
Q

what controls sodium balance?

A

steroids

  • aldosterone (mainly)
  • other steroids (e.g cortisol)
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7
Q

what do steroids do to control sodium balance?

A

mineralocorticoid activity
- refers to Na+ reabsorption in renal tubules in exchange for K+/H+
too much mineralocorticoid activity = sodium gain
too little = sodium loss

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8
Q

how do you calculate sodium concentration?

A

mmol Na+ / 1 L water

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9
Q

how do intra and extracellular fluid differ/

A
intra = contains more fluid
intra = lower Na+ concentration
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10
Q

can water move between all body compartments?

A

yes

means that if you lose water you loose it from everywhere

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11
Q

can sodium move between all body compartment?

A

no
confined to the extracellular fluid
- Na+/K+ pump in plasma membrane keeps sodium in ECF
- if sodium is lost its only lost from ECF

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12
Q

how does water balance relate to sodium balance?

A

water follows solute (sodium is the most abundant solute so water basically follows sodium)
so if you loose or gain sodium, you loose or gain water with it

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13
Q

what are the two possible causes for reduced concentration of sodium?

A
loss of sodium from the ECF (dangerous)
fluid retention (too much water dilutes sodium)
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14
Q

what can cause increase in sodium concentration?

A

loss of water

increase in ECF sodium

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15
Q

why is loss of sodium from ECF dangerous?

A

little fluid in ECF anyway
if sodium lost then water will follow causing reduction in fluid volume
will have severe symptoms

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16
Q

what can cause sodium loss?

A

adrenal/kidney (adrenals not making steroid hormones so not reabsorbing sodium and water)
gut (diarrhoea and vomiting, fistulae)
skin (burns)

17
Q

what can cause fluid overload (too much water)?

A
reduced water excretion (SIADH)
increased intake (compulsive water drinking)
18
Q

what can cause increased sodium?

A

some IV medications
near drowning (consumption of high amount of sea salt water)
malicious (child been given salt by parent)

19
Q

what can cause loss of water?

A
diabetes insipidus (increased water loss)
reduced water intake
20
Q

how do you manage low sodium concentration?

A

if too little sodium - give sodium

if too much water - fluid restriction

21
Q

how do you manage increased sodium concentration?

A

too much sodium - remove sodium (i.e loop diuretic)

too little water - give water (as dextrose)

22
Q

what 3 fluids can be given and where does each affect?

A
dextrose = plasma, interstitial fluid and intracellular fluid compertment
saline = plasma and interstitial fluid
plasma/blood = plasma
23
Q

when is sodium inbalance serious?

A

if concentration <120 or >160
if high or low enough to cause symptoms (confusion, vomiting, nausea etc)
if sodium level has fallen or risen rapidly to its current level

24
Q

what are the 2 kinds of stimuli for ADH release?

A

osmotic (in health)

non-osmotic (in disease)

25
Q

give 3 examples of non-osmotic stimuli?

A

hypovolaemia/hypotension
pain
nausea/vomiting

26
Q

what is SIADH?

A

syndrome of inappropriate ADH

27
Q

2 opposing forces in capillary which control balance of water?

A
hydrostatic force (push water out)
oncotic force (pull water in)
28
Q

what can cause reduced oncotic force/increased hydrostatic force?

A

low proteins in the capillary (e.g low albumin)

29
Q

what is the impact of low blood volume on sodium?

A

causes ADH and aldosterone secretion which causes sodium and water retention leading to hyponatraemia
much of water reabsorbed ends up being pushed out into interstitial fluid and causing oedema

30
Q

what does oedema signift?

A

effective circulating volume depletion

low blood volume

31
Q

how is oedema managed?

A

loop diuretics

cause loss of sodium and water

32
Q

what is pseudohyponatraemia?

A

if tests show low serum sodium
but concentration of sodium in serum water is normal
total serum volume is made up of serum water component which contains sodium, and proteins/lipoprotein component which doesn’t contain sodium
if total serum volume is made of more proteins/lipoproteins and less serum water then sodium may look low for total serum volume but normal for serum water volume

33
Q

signs of pseudohyponatraemia?

A

if tests show very low sodium but patient has no symptoms

34
Q

what is the pathophysiology of addisons disease?

A

adrenal insufficiency > cant make enough steroids > not enough mineralocorticoid activity > cant retain enough sodium in kidneys > loss of sodium and water from ECF > reduced ECF = patient is clinically dehydrated

35
Q

what are the features of addisons disease and what causes these?

A

reduced ECF volume and hypotension cause dizziness
excess pigmentation in mouth and hand creases - from excess ACTH from pituitary
tanned skin - ACTH molecule contains sequence for MSH within it so when its degraded by proteases, the MSH is exposed

36
Q

how does water overload present?

A
patient often already in hospital
reduced [Na+]
unremarkable volume status
addisons test negative
often don't have symptoms of hyponatraemia
37
Q

why can volume status be clinically unremarkable in water overload?

A

as water retention is distributed all over body compartments

38
Q

how is ADH deficiency (e.g transection of pituitary stalk) treated?

A

desmopressin (exogenous ADH)