Sodium and Water Balance Flashcards
what is the golden rule
Water FOLLOWS Sodium
Not the other way round
how is sodium levels controlled
by Mineralocorticoid activity
- aldosterone main one
- cortisol also contributes
what does too much mineralocorticoid activity mean
sodium retention
too little means sodium loss
what does sodium loss mean
water loss
what controls water level
ADH
how does ADH work
- released by posterior pituitary in response to osmotic or non-osmotic stimuli
- act on renal tubules
- causes water reabsorption
what does lots of ADH cause
concentrated urine
little ADH causes dilute urine
how do we assess ADH levels
urine osmolality
Concentrated urine - high urine osmolality
Dilute urine - low urine osmolality
how do we classify disorders of sodium/water balance
Decreased [Na]
- either too much water or too little sodium
Increased [Na]
- either too little water or too much sodium
what can cause decreased [Na] due to too much water
decreased excretion e.g. SIAD
increased intake e.g. compulsive water drinking
what can cause decreased [Na] due to too little sodium
increase sodium loss
- e.g. gut, skin
- kidneys (Addison’s)
decrease sodium intake
- rare
what can cause increased [Na] due to too little water
increase water loss
- diabetes insipidus
decrease water intake
- very young, elderly patients
what can cause increased [Na] due to too much sodium
Rare
- near drowning in sea
- some IV meds given as sodium salt
what is the problem in Addisons disease in regards to sodium
- can’t make enough steroids
- not enough mineralocorticoid activity
- can’t retain enough sodium in the kidneys
- loses sodium (and water) from ECF
- decreased ECF, means dehydration
why is there increase in potassium levels in Addisons
decreased Na causes potassium retention
