renal - lecture 5 Flashcards
what is potassium
most abundant intracellular ion
where is potassium
98% in intracellular fluid
2% in extracellular fluid
why is potassium concentration important
k concentration in extracellular fluid v important for function of excitable tissues = nerve and muscle
bc resting membrane potentials of these tissues are directly related to relative intra and extracellular k concentrations
what is hyperkalemia and hypokalemia
hyperkalemia = high conc k in ecf >5meq/l
hypokalemia = low conc of k in extracellular fluid <3.5meq/l
both cause abnormal rhythms of heart and abnormalities of skeletal muscle
describe effect of hyperkalemia on ecg
6.0 = tall t wave
8.0 = qrs wide
k>8.0 = looks like sinusoidal wave = v tach to use aed *ventricular tachycardia
how is potassium balance maintained by kidney
tropical fuits, like oranges, bananas, papaya, nuts, tomatoes
Dietary intake = 90% excreted in urine and 10% excreted into feces/sweat
describe renal regulation of potassium
k freely filtered at glomerulus
normally tubules reabs most of filtered k so very little in urine
but k can be secreted at ccd
changes in k excretion due mainly to changes in k secretion in ccd some in dct toos
describe net reabs of k
15-99% - normally 86 = if eating normal
describe potassium regulation in ccd
secretion of k in ccd is coupled with na reabsorption
k pumped into cell and put back in lumen by channels
how is potassium secretion regulated
Dietary intake of potassium - can stimulate secretion
aldosterone - since coupled to sodium reabs
describe regulation of potassium by dietary intake and aldosterone
increase potassium intake = increase plasma k (directly stimulates ccd upregulate transport proteins in ccd) = increase aldosterone = increase plasma aldosterone = increase k secretion in ccd = increase potassium excretion
describe what happens when renin aldosterone system activated by other causes
k+ secretion can occur
decreased plasma = amount of na delivered to ccd lower = so mitigates aldosterone
doesnt cause hypokelemia tho
Decrease plasma vol = increase plasma angotensin 2 = stimulate adrenal cortex to increase aldosterone secretion
increase plasma k = stimulate adrenal cortex to increase aldosterone secretion
more aldosterone secretion = increase plasma aldosterone = increase ccd sodium reasb and potassium secretion = decreased sodium excretion and increase potassium excretion
what is hyperaldosteronism
adrenal hormone aldosterone released in excess = usually bc adrenal tumor - adenoma of adrenal gland that produced aldosterone autonomously
so na reasb stimulated in ccd = higher bp
increased fluid vol, hypertension, hypokelemia, renin suppressed - how its diagnosed, metabolic alkalosis seen = h+ secretion also controlled by aldosterone
describe hydrogen ion regulation
metabolic reactions highly sensitive to h+ concentration of environment
h+ conc of extracellular fluid tightly regulated
ph ~7.4 [H+] = 40nmol/l
describe important mass reaction
co2 + h2o <–> h2co3 <-> hco3 - + h+
via carbonic anhydrase
what happens when bicarb ion lost or gained in body
bicarb ion lost = same as if body gains hydrogen ion = shift to right
when body gains bicarb ion = same as if body lost hydrogen ion = shift to left
inversely impact each other
describe gain and loss - counteracting
generation of h+ from co2 (volatile) vs hyperventilation (loss of co2)
production of nonvolatile acids from metabolism of protein and other organic molecules vs utilization of hydrogen ions in metabolism of various organic anions
gain of hydrogen ions due to loss of bicarb in diahrrea or other nongastric gi fluids vs loss of hydrogen in vomitus
gain of hydrogen ions due to loss of bicarb in urine vs loss of hydrogen ions in urine
what are non volatile acids
phosphoric acid
sulfuric acid
lactic acid
= made by body and contributes to acid load
average net production = 40-80mmol of h+ per day
describe buffer of hydrogen ion
any substance that can reversibly bind h+ = buffer
most buffered by extracellular and intracellular buffers
ph = -log [h+] - normal ecf ph = 7.4 corresponds to 40nmol/l of hydrogen ions, without buffering = h+ conc changes a lot
what are buffers for body
major extracellular = co2/hco3- system
major intracellular = phosphates and proteins
what does buffering NOT DO
doesnt eliminate h+ from body
only keeps them locked up = sequestered to will not affect body
what is ultimate balance of hydrogen ions controlled by
respiratory system = by controlled co2
kidneys = by controlling bicarb
both systems work together to minimized change of ph - h+ conc
describe renal mechanisms of h+ control
via control of hco3-
low h+ conc (high ph = alkalosis)–> kidneys excrete hco3- = try to increase h+
high h+ conc (low ph = acidosis)–> produce new hco3- and add to the plasma = decrease h+
describe henderson hasselbalch equation
main important part = body ph determine by [bicarb]/[co2]
describe renal handling of bicarb
normally kidneys reabs all filtered bicarb
exception = alkalosis
in pct =
reaction happen vigorously- follows gradient hco3- to isf and h+ to tubular lumen - hco3- filtered = created h20 and co2 = reaction reversed
also h+ mediated by h+/k+ atpase and na+/h+ antiporter
describe bicarb reabsorption
majority in proximal tubule
some in tal
some in ccd
not excreted
name and describe 2 ways bicarb added to plasma
by h+ secretion and excretion on nonbicarb buffers like phosphate
by glutamine metabolism with nh4+ excretion - need this second mechanism if huge amount
both processes can be viewed as h+ excretion by kidney
kidneys normally contribute enough new bicarb to plasma to compensate for hydrogen ions from nonvolatile acids generated in body= 40-80mmol/day
describe addition of new bicarb by h+ secretion
happens only after all hco3- has be reabs and is no longer available in lumen
dct to ccd
bicarb produced and sent to isf = new bicarb ion added to body
h+ produced = goes to lumen and binds phosphorus and is excreted as h2po4-
describe addition of new bicarb by glutamine
mainly in proximal tubule
process also called h+
excretion bound to nh3
what is bicarb excretion equal to
hco3- excretion = hco3- filtered (+ hco3- secreted but not often) - hco3- reabs
glutamine enters from blood side - in case of acidosis and from lumen side bc 100% reabs
glutamine makes nh4 and bicarb (secreted into isf)
nh4 = eliminated by excretion
