sodium and potassium balance Flashcards
what is osmolarity
measure of solute concentration in solution (osmoles/litre)
*depends on number of dissolved particles
what is our normal plasma osmolarity
285-295 mosmol/L
sum of all particles
what is the most prevalent and important solute in ecf
sodium
how does increased dietary sodium lead to increased bp and vol
increased total body sodium
increased osmolarity
increased water intake and retention
increased ecf vol
what happens to sodium during euvolemia
supress na+ intake via lateral parabrachial nucleus
supressed by serotonin and glutamate
what happens during na+ deprivation
increased appetite for sodium driven by gaba and opioids
what is the peripheral mechanism for sodium reg
taste
salt is appetitive at low conc
how do macula densa cells respond to high tubular sodium
increased sodium and chloride uptake via triple transporter
adenosine is released from macula densa
this is detected by extraglomerular mesangial cells
reduces renin production
promotes afferent smc contraction
reduces perfusion pressure and so gfr
what happens if you need to retain/reabsorb sodium or water
reduce filtration rate
increase sympathetic activity which constricts efferent arteriole and sodium uptake by cells or pct
slso stimulates jca to secrete renin which leads to production of angiotensin 2 which further stimulates cells of pct to take up sodium
ag2 anlso stimulates production of aldosterone which stimulates uotake of na+ in dct and cd
what mechanisms take place to decrease sodium reabsorption
atrial naturietic peptide acts as vasodilator
reduces na+ uptake in pct,dct and ct
suppresses prod of renin by jca
what happens in cases of low sodium
low bp
decreased fluid vol
simulation of b1 sympathetic pathway which causes constriction of afferent arteriole and reduce pressure
increased production of renin (raas) stimulates zona glomerulosa producing aldosterone
angiotensin 2 also causes vasoconstriction
and increases nacl/h2o reabsorption
what happens in case of high sodium
higher blood pressure
increased fluid vol
decreased b1 sympathetic activity and decreased anp
reduces renin - downreg of raas, decreased aldosterone
decreased nacl/h20 reabsorption
decreased vasoconstriction/promote vasodilation
what is aldosterone
steroid hormone
synthesised and released from adrenal cortex
released in response to angioten2
stimulated by decrease in bp via baroreceptors
what is role of angiotensin 2
causes production of aldosterone synthase which is required in last 2 steps of aldosterone syn
what is the function of aldosterone
increased sodium reabsorption
controls at 35gna/day
increased potassium secretion
increased h+ secretion
what can aldosterone excess lead to
hypokalaemic alkalosis
how does aldosterone work
is a steroid hormone so lipid soluble
binds to mineralcorticoid receptor which is bound to hsp90
once aldosterone binds mineralocorticoid receptor dimerises and translocates into nucleus binds to dna
increased active sodium channels
what happens in hypoaldosteronism
reabsorption of sodium in distal nephron is reduced
increased urinary loss of sodium
ecf vol falls - causes diziness, low bp, salt cravings and palpitations
increased renin,ang2 and adh
what happens in hyperaldosteronism
reabsorption of sodium in distal nephron is increased
reduced urinary loss of sodium
ecf vol increases - causes high bp, muscle weakness,polyuria and thirst
reduced renin,ang2 and adh
increased anp and bnp
what is liddles syndrome
inherited disease of high bp
mutation in aldosterone activated sodium channel
channel is always on/activated
results in sodium retention, leads to hypertension
(low/normal aldosterone)
on the low pressure side where do we find baroreceptors
atria
right ventricle
pulmonary vasculature
on the high pressure side where do we find baroreceptors
carotid sinus
aortic arch
juxtaglomerular apparatus
on the low pressure side what happens when low pressure
reduced baroreceptor firing
signal through afferent fibres to brainstem increased sympathetic activity and adh release
what happens on the low pressure side when there is high pressure
atrial stretch
anp and bnp released
what happens on high pressure side when there is low pressure
reduced baroreceptor firing
- signal through afferent fibres to brainstem causes increased sympathetic activity and adh released
- renin released from jca cells
what is atrial natriuretic peptide
small peptide made in atria
released in response to atrial stretch(ie high bp)
what are the actions of anp
binds to guanylyl cyclase receptor which causes conversion of gtp to cyclic gmp and protein kinase g is activated
Causing:
- vasodilation of renal + other blood vessels
- inhibition of sodium reabsorption in pct and ct
- inhibits release of renin and aldosterone
- reduces bp
what does volume expansion cause
reduced sympathetic activity
reduced renin and angiotensin
increased anp and bnp
increased na+h2o excretion
what is the role of ace inhibitors
reduce production of ang2
also causes vasodilation which increases vasc vol will lead to low bp
direct renal effects: reduces na+ reuptake in pct
increased na+ in distal nephron
indirect effects: reduced na+ uptake in cct
increased na+ in distal nephron
reduces water reabsorption
where do other diuretics work
osmotic diuretics - less water reabsorp in pct carbonic anhydrase inhibitors - pct loop diuretics - thin ascending limb thiazide diuretics - dct k+ sparing diuretics - cd
how to carbonic anhydrase inhibitors work
block carbonic anhydrase
reduced na+ reuptake in pct
increased na+ in distal nephron
reduced water reabsorption
how do loop diuretics work
furosemide
triple transporter (na,cl,k) inhibitors
reduced na+ reuptake in loh
increased na+ in distal nephron (lose less water)
reduced water reabsorption
what is the role of thiazides
reduce na+ reuptake in dct
increased na+ in distal nephron
reduced water reabsorption
increased calcium reabsorption
what are potassium sparing diuretics
inhibitors of aldosterone function
e.g spironolactone
what is the main intracellular ion
potassium
what does high potassium cause
depolarises membranes
action potentials
heart arrhythmias
what does low potassium cause
heart arrhythmias
asystole
what is increased k+secretion in collecting duct stimulated by
increase in plasma k+
increase in aldosterone
increase in tubular flow rate
increase plasma ph
what can cause hypokalaemia
inadequate dietary intake diuretics diarrhoea surreptitious vomiting genetics e.g gitelmans syndrome
what can cause hyperkalaemia
seen in response to k+ sparing diuretics ace inhibitors elderly severe diabetes kidney disease
