sodium and potassium balance

Question 1

what is osmolarity

Answer 1

measure of solute concentration in solution (osmoles/litre)

*depends on number of dissolved particles

Question 2

what is our normal plasma osmolarity

Answer 2

285-295 mosmol/L

sum of all particles

Question 3

what is the most prevalent and important solute in ecf

Answer 3

sodium

Question 4

how does increased dietary sodium lead to increased bp and vol

Answer 4

increased total body sodium
increased osmolarity
increased water intake and retention
increased ecf vol

Question 5

what happens to sodium during euvolemia

Answer 5

supress na+ intake via lateral parabrachial nucleus

supressed by serotonin and glutamate

Question 6

what happens during na+ deprivation

Answer 6

increased appetite for sodium driven by gaba and opioids

Question 7

what is the peripheral mechanism for sodium reg

Answer 7

taste

salt is appetitive at low conc

Question 8

how do macula densa cells respond to high tubular sodium

Answer 8

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

Question 9

what happens if you need to retain/reabsorb sodium or water

Answer 9

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

Question 10

what mechanisms take place to decrease sodium reabsorption

Answer 10

atrial naturietic peptide acts as vasodilator
reduces na+ uptake in pct,dct and ct
suppresses prod of renin by jca

Question 11

what happens in cases of low sodium

Answer 11

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

Question 12

what happens in case of high sodium

Answer 12

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

Question 13

what is aldosterone

Answer 13

steroid hormone
synthesised and released from adrenal cortex
released in response to angioten2
stimulated by decrease in bp via baroreceptors

Question 14

what is role of angiotensin 2

Answer 14

causes production of aldosterone synthase which is required in last 2 steps of aldosterone syn

Question 15

what is the function of aldosterone

Answer 15

increased sodium reabsorption
controls at 35gna/day
increased potassium secretion
increased h+ secretion

Question 16

what can aldosterone excess lead to

Answer 16

hypokalaemic alkalosis

Question 17

how does aldosterone work

Answer 17

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

Question 18

what happens in hypoaldosteronism

Answer 18

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

Question 19

what happens in hyperaldosteronism

Answer 19

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

Question 20

what is liddles syndrome

Answer 20

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)

Question 21

on the low pressure side where do we find baroreceptors

Answer 21

atria
right ventricle
pulmonary vasculature

Question 22

on the high pressure side where do we find baroreceptors

Answer 22

carotid sinus
aortic arch
juxtaglomerular apparatus

Question 23

on the low pressure side what happens when low pressure

Answer 23

reduced baroreceptor firing

signal through afferent fibres to brainstem increased sympathetic activity and adh release

Question 24

what happens on the low pressure side when there is high pressure

Answer 24

atrial stretch

anp and bnp released

Question 25

what happens on high pressure side when there is low pressure

Answer 25

reduced baroreceptor firing 1. signal through afferent fibres to brainstem causes increased sympathetic activity and adh released 2. renin released from jca cells

Question 26

what is atrial natriuretic peptide

Answer 26

small peptide made in atria | released in response to atrial stretch(ie high bp)

Question 27

what are the actions of anp

Answer 27

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

Question 28

what does volume expansion cause

Answer 28

reduced sympathetic activity reduced renin and angiotensin increased anp and bnp increased na+h2o excretion

Question 29

what is the role of ace inhibitors

Answer 29

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

Question 30

where do other diuretics work

Answer 30

``` osmotic diuretics - less water reabsorp in pct carbonic anhydrase inhibitors - pct loop diuretics - thin ascending limb thiazide diuretics - dct k+ sparing diuretics - cd ```

Question 31

how to carbonic anhydrase inhibitors work

Answer 31

block carbonic anhydrase reduced na+ reuptake in pct increased na+ in distal nephron reduced water reabsorption

Question 32

how do loop diuretics work | furosemide

Answer 32

triple transporter (na,cl,k) inhibitors reduced na+ reuptake in loh increased na+ in distal nephron (lose less water) reduced water reabsorption

Question 33

what is the role of thiazides

Answer 33

reduce na+ reuptake in dct increased na+ in distal nephron reduced water reabsorption increased calcium reabsorption

Question 34

what are potassium sparing diuretics

Answer 34

inhibitors of aldosterone function | e.g spironolactone

Question 35

what is the main intracellular ion

Answer 35

potassium

Question 36

what does high potassium cause

Answer 36

depolarises membranes action potentials heart arrhythmias

Question 37

what does low potassium cause

Answer 37

heart arrhythmias | asystole

Question 38

what is increased k+secretion in collecting duct stimulated by

Answer 38

increase in plasma k+ increase in aldosterone increase in tubular flow rate increase plasma ph

Question 39

what can cause hypokalaemia

Answer 39

``` inadequate dietary intake diuretics diarrhoea surreptitious vomiting genetics e.g gitelmans syndrome ```

Question 40

what can cause hyperkalaemia

Answer 40

``` seen in response to k+ sparing diuretics ace inhibitors elderly severe diabetes kidney disease ```