Fluid and electrolytes- sodium and water Flashcards
is there a greater conc of K+ in ICF or ECF
ICF
is there a greater conc of Na+ in ICF or ECF
ECF
how can you check for ECF clinically
plasma- bp, HR, jvp. interstitial fluid- skin turgor, muscous membranes, oedema
how can you check for ICF clinically
neuro status- cerebral oedema or dehydration
what is osmolality
ionic concentration of a fluid mOsm/kg
what is osmolality important for
determining the vol of a fluid compartment
what is tonicity
decription of osmolality compared to another solution, dependent on osmotically active components that do not cross the cell membrane
how much of total body water is ICF and ECF
2/3 and 1/3
how much of ECF is plasma
1/4
where is ADH released from
post pituitary
where does the ADH originate from
hypothalamic, supraventricular and supra orbital nuclei
what triggers ADH release
plasma osmolality increasing (thirst reflex), low bp (baroreceptors)
what does ADH bind to and what is the sequence of events
vasopressin 2 receptors in collecting duct, opens aquaporin channels leads to reabsorption of water from the urine into the plasma
what is isotonic fluid
fluid with the same osmlolality as plasma
what happens in isotonic depletion
decrease in ECF but no change in osmolality so no fluid shift
what happens in sodium depletion
decrease Na+, affects ECF so osmolality is higher in ICF thus leading to fluid shift into the ICF
what triggers renin release
decrease BP or Na+
what are the actions of angiotensin 2
acts on adrenal cortex to secrete aldosterone, and release ADH
what does aldosterone act on
tubular- for the reabsorption of Na+ and water; and the excretion of K+
what is hypertonic (referring to plasma)
decrease in plasma Na+
what is hypotonic (referring to plasma)
increase in plasma Na+ - so losing more water than sodium
what happens in water excess
Na+ decreases
what happens in sodium excess
osmolality higher in ECF than ICF so water shifts from here to ECF. however if driven by low circulating blood volume or decrease in BP, ADH is released which may result in further water retention and hyponatraemia
what is most fluid loss in the body
hypotonic
what lab investigations can be done
plasma/serum sodium, osmolality, plasma glucose, serum urea and creatinine, urine osmolality and sodium, urine vol, serum cortisol, serum TFTs
