Sodium and Water Balance Flashcards
In the cell does water folow sodium or does sodium follow water?
Water follows sodium
Na+ loss means H2O loss
What controls the level of sodium?
Mineralocorticoid activity (sodium retention in exchange for K+ and/or H+ ions)
Which steroids have mineralocorticoid activity?
Aldosterone and cortisol
If you had too much mineralocorticoid activity what would happen?
Na+ retention
What controls the level of water?
Anti-diuretic hormone
Where from and when is ADH released?
From the posterior pituitary in response to osmotic (in health) and non-osmotic (in disease) stimuli
If there is increased levels of ADH, will the urine by dilute or concentrated?
Concentrated
How is the concentration of urine assessed?
As urine osmolality
Conc urine – high urine osmolality
dilute urine – low urine osmolality
What method occurs in the kidneys that leads to the fluid in the descending limb becoming more hypertonic?
Countercurrent multiplication
What 2 methods can cause a patient to have decreased Na+ and how would you treat each one?
too much water - fluid restrict
too little sodium - give sodium
What 2 methods can cause a patient to have increased Na+ and how would you treat each one?
too much sodium - diuretics and then replace water only
too little water - give water
What can cause a patient to have too much water?
SIADH
copulsive water drinking
patient is not dry
Give causes of a patient having too little sodium.
increased Na+ loss (Addisons)
decreased Na+ intake (rare)
pateint is clinically dry
What could cause a patinet to have too little water?
Increaased water loss (DI)
Decreased water intake
What can cause a patient to have too much sodium?
rare
some IV meds
near drowing in sea
infants given hig salt feeds
What is the normal value range for sodium?
135- 145
Give examples of non-osmotic stimuli that trigger the release of ADH.
Hypovolaemia/ hypotension
Pain
Nausea/ vomiting
Do the non-osmotic stimuli override the osmotic stimuli?
Yes - ADH continues to be released so blood becomes very dilute
What happens when hypovolaemia occurs in hyponatraemia?
Even bigger Na+ deficit - too little sodium
How is Na/H2O balance assessed?
In the context of hyponatraemia or hypernatraemia
What symptoms can occur if the patients Na+ is very low (155mmol/l)?
May develop: altered consciousness, confusion, nausea
