Sodium and Water Balance Flashcards
what hormone controls water balance
anti-diuretic hormone
what releases ADH
posterior pituitary
how does ADH work
causes water to be re absorbed from the renal tubules
stimulate the insertion of aquaporins into the membranes of kidney tubules
what happens to urine when there is increased ADH
small volume of concentrated urine is produced
what happen to the urine when there is decreased ADH
large volume of dilute urine is produced
what is urine osmolality
measure of urine concentration/ dilution
high osmolality= concentrated urine
dilute urine= low osmolality
what is AVP
arginine vasopressin- another name for ADH
how can trauma affect ADH secretion
if trauma transects pituitary stalk
what hormones affect sodium balance
steroids released from the adrenals- aldosterone (main one) + others e.g. cortisol
what is mineralocorticoid activity
the effect steroids have in Na+ activity
what does too much mineralocorticoid activity result in
sodium gain
how does aldosterone affect sodium
usually released in response to low BP, causes sodium reabsorption, increases the osmolarity in the extracellular fluid
what is the reference interval for sodium concentration
135-145 mmol/L
what are the two reasons behind decreased sodium concentration
decreased sodium or increased water
what are the two reasons behind increased sodium concentration
increased sodium, decreased water
where is there more sodium- intra or extra cellular fluid
more sodium in extracellular fluid
where is there more potassium- intra or extra cellular fluid
more potassium in intracellular fluid
where is pure water lost from
as water can move between all body compartments it is lost from the whole body
where is sodium confined to
extracellular fluid
what keeps sodium in the extracellular fluid
sodium and potassium ATPase pump
where is sodium lost from
the extracellular fluid
what does water follow
sodium
what happens to water if you lose/ gain sodium from the ECF
lose/ gain water with it
what happens when the body senses its ECF to be too high
excretes sodium which also causes loss of water and ECF
what causes too much water
water retention- ADH
which changes in sodium and water balance are most serious
when it is loss or gain of sodium causing the problem (not too mch or too little water as this is distributed across all body and cell compartments)
what are the features of fluid overload (and cause)
(increased sodium)
oedema, pleural effusion, raised JVP
what must you always think when you see signs of dehydration or fluid overload
problem with sodium concentration
what can cause decreased sodium concentrations
increased sodium loss- adrenal/ kidney (not producing steroids), gut (D and V, fistula), skin (burns)
decreased H2O secretion, increased intake (compulsive water drinking)
what can cause increased sodium
increased sodium intake- some IV meds, near drowning, malicious
increased water loss (diabetes insipidus), decreased H2O intake (elderly, young)
what sodium concentration problem can be fatal if you miss it
increased sodium loss causing dehydration (adrenal failure, kidney, gut, skin losses)
what is the treatment for sodium loss or excess
give sodium- sodium in saline
excess- loop diuretic
what sodium concentration problem can be fatal if you miss it
increased sodium loss causing dehydration (adrenal failure, kidney, gut, skin losses)
what is the treatment for too much water
fluid restriction
how do you replace water
give dextrose as will reach into all extra and intra cellular areas
where does saline get to
confined to extracellular fluid
what is dextrose
solution with dame tonicity of concentration as blood
when is sodium serious
if very low or very high (<120mmol/L or >160 mmol/L)
how do you tell if sodium is serious
if patients have symptoms from it: altered consciousness, confusion, nausea, vomiting, fitting, etc.
when is sodium in normal range serious
if it has suddenly fallen or risen to that level
what is SIADH
syndrome of inappropriate ADH
inappropriate for the osmolal state
what are the non osmotic stimuli for ADH release
hypovolaemia/ hypertension
pain
nausea/ vomiting
what are the non osmotic stimuli for ADH release
hypovolaemia/ hypertension
pain
nausea/ vomiting
does sodium affect ADH secretion
high serum sodium (high osmolality) can stimulate posterior pituitary to cause re-absorbtion water (by secretion of ADH)
what is capillary hydrostatic pressure
when water is pushed out
what is capillary oncotic pressure
water back in
what causes loss of water from the capillaries into the ECF
increased hydrostatic pressure/ too much protein in the blood
what does oedema do to circulating volume
is depleted, due to altered balance of starling forces at capillary level
what hormones are secreted in oedema in attempt to restore circulating volume- why does this create a viscous circle
ADH and aldosterone
these cause water retention in an attempt to increase volume but much of this fluid is retained in interstitial fluid
what do loop diuretics do
cause loss of sodium and water
what does an oedematous patient have too much off
water and sodium
what is the main treatment for oedema
loop diuretics
what is this disease:
A 24 year-old student presents with a six month history of malaise, tiredness, poor appetite and one stone weight loss. She has developed a craving for salty foods – crisps in particular. She has had a number of dizzy spells particularly while in warm places.
She is thin. She has low BP which falls further on standing. You have the impression that she is tanned, and you find increased pigmentation in her mouth and hand creases.
Her bloods show low sodium [122 mmol/L] and high potassium [5.8 mmol/L].
addisons
what causes addisons disease
adrenal insufficiency- cant make enough steroids, don’t have mineralocorticoid activity meaning you cant retain sodium in the kidneys - results in a loss of sodium (and water) from the ECF
why do you get symptoms of dizziness in addisons
hypotension due to decreased ECF
why do you get excess pigmentation in addisons
ACTH from pituitary- ACTH contains MSH within it and this is exposed when proteases degrade ACTH
why do you get increase K in addisons
as it is retained
what is the treatment for addisons
sodium replacement (saline) + can give hydrocortisone shot to replace steroids they are not making
what test is used to exclude addisons
synacthen test
what causes diabetes insipidus
disruption of hormone axis where patients cant secrete ADH or there is renal resistance to it
what are sodium levels like in diabetes insipidus
high- lack of water
what do you give when the pituitary gland cant produce ADJ
exogenous ADH (desmopressin)
