Lec46_Na_Handling Flashcards
Are salt and water regulated together or independently?
independently
What general thing regulates water balance?
ADH [which responds to plasma osmolarity and volume status]
What general thing regulates salt balance?
volume [by things that responds to changes in blood volume]
What 4 things regulated Na?
- aldosterone
- ANP
- sympathetics
- angiotensin II
What regulates K?
adrenal cortex –> aldosterone release which causes K secretion from principal cells
what regulates pCo2/pO2?
chemoreceptors –> changes in ventilation
What regulates Ca?
Ca-sensing receptor on parathyroid hormone [PTH]
What regulates cortisol?
pituitary feedback
What are 3 things that increase Na in body? What are they released in response to?
Aldosterone
Sympathetic nerves
Angiotensin II
- they are responding to changes in MAP or body volume not Na level
What percent of serum osmolality does Na and counter ion account for?
97% [280 of 300ish]
What will increasing plasma Na do to H2O in vasculature?
- increasing plasma Na moves H2O into vasculature
- leads to decreases H2O excretion
What is normal serum K?
4 mEq/L
What is normal serum Hgb?
15 g/dL
What is normal serum Na?
140 mEq/L
Does serum Na measure concentration or total Na level?
concentration
Does the body see serum Na?
No – it just sees serum osmolarity
What is normal Na handling after you ingest a lot of Na?
- ingest Na
- increase serum Na
- increase plasma osmolarity
- get compensatory mech to restore normal osmolarity
What are the 2 initial compensation mech for increased Na [increased osmolarity] in plasma?
- increased ADH –> increase water retention
- thirst –> increase water intake
What are 6 specific compensatory mech for increased blood volume?
- higher BP: increased RBF and same GFR –> causes lower FF
- Higher NaCl sensed at macula densa: causes decreased renin realse and thus decreased angiotensin II and aldosterone
- less Na reabsorbed in collecting duct
- decreased oncotic pressure in PTC so less favorable gradient for H2O reabsorption
- less Na reabsorbed in principal cells
- increased ANP
What is net result of compensatory mech responsible for increased blood volume?
- increase water and Na excretion to return to normal BV
What happens to plasma osmolarity, ADH, water balance, volume status, urinary salt excretion when excessive Na ingestion?
plasma osm: initial increase
ADH: initial increase
water balance: initial increased intake [thirst]
volume status: hypervolemia
urinary salt excretion: increased [to return normal V]
How much Na secretion when you are hypovolemic?
- excrete little Na because you are trying to retain volume of H2O that comes with it
- increased RAA, decreased ANP, increased sympathetics
What are ADH and RAA levels in hypovolemia?
- ADH and RAA both eleveated
What is treatment for hypovolemic hypernatremia?
- replace slat and water to fix hypovolemia and electrolyte imbalance
- ex. give normal saline
What does hypovolemic hypernatremia mean?
- salt deficit but even bigger H2O deficit
Do people with access to water become hypernatremic
very rarely
What is normal handling of water ingestion?
- ingest water
- get decrease in serum Na conc
- decrease plasma osmolality
- ADH release suppressed
dilute urine excreted
What is minimum urine osmolatiry?
50 mosm/L with no ADH
What is max amount of maximally dilute urine you can excrete per day?
16 L water/day
If you ingest more than 16 L/day of water without ingesting osmoles how much urine will you excrete?
- you will excrte 16 L of urine
- you will retain water beyond that
If you are hypervolemic will you retain or secrete Na?
secrete Na regardless of hyper vs hypo natremia
- because you sense high volume which causes you to want to get rid of salt/water
If you consume a bunch of water why aren’t you necessarily hypertensive or swollen?
- the increased water you consume doesn’t necessarily stay into the vasculature
How do you get mOsm from Na conc of blood?
mOsm is [Na]*2
ex. Na = 115 mEq/L, mosm = 2*115 = 230 mOsm/L
How much of water is in intercellular space?
60%
How much of water is in interstitial space?
32%
How much of water is in blood volume?
8%
What is source of side effect confusion in excess water intake?
- get extra water
- some of that water goes into cells to equalize osmolarity
- brain is in skull so brain starts to swell like everywhere else but there is no space for it to happen
- get cerebral edema
What is primary polydipsia?
- too much water intake in excess of consumed salt
- get hypervolemic, hyponatremic, secrete lots of Na in urine
What is treatment for primary polydipsia?
water restriction [maybe also hypertonic saline]
What is euvolemia?
too much water, normal salt
- primary polydipsia
What is hypovoluemia?
too little water but even lower salt
- GI/kidney loss
what is hypervolemia?
too much water and salt but more water than salt
- CHF, cirrhosis
