renal - lecture 5

Question 1

what is potassium

Answer 1

most abundant intracellular ion

Question 2

where is potassium

Answer 2

98% in intracellular fluid
2% in extracellular fluid

Question 3

why is potassium concentration important

Answer 3

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

Question 4

what is hyperkalemia and hypokalemia

Answer 4

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

Question 5

describe effect of hyperkalemia on ecg

Answer 5

6.0 = tall t wave
8.0 = qrs wide
k>8.0 = looks like sinusoidal wave = v tach to use aed *ventricular tachycardia

Question 6

how is potassium balance maintained by kidney

Answer 6

tropical fuits, like oranges, bananas, papaya, nuts, tomatoes
Dietary intake = 90% excreted in urine and 10% excreted into feces/sweat

Question 7

describe renal regulation of potassium

Answer 7

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

Question 8

describe net reabs of k

Answer 8

15-99% - normally 86 = if eating normal

Question 9

describe potassium regulation in ccd

Answer 9

secretion of k in ccd is coupled with na reabsorption
k pumped into cell and put back in lumen by channels

Question 10

how is potassium secretion regulated

Answer 10

Dietary intake of potassium - can stimulate secretion
aldosterone - since coupled to sodium reabs

Question 11

describe regulation of potassium by dietary intake and aldosterone

Answer 11

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

Question 12

describe what happens when renin aldosterone system activated by other causes

Answer 12

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

Question 13

what is hyperaldosteronism

Answer 13

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

Question 14

describe hydrogen ion regulation

Answer 14

metabolic reactions highly sensitive to h+ concentration of environment
h+ conc of extracellular fluid tightly regulated
ph ~7.4 [H+] = 40nmol/l

Question 15

describe important mass reaction

Answer 15

co2 + h2o <–> h2co3 <-> hco3 - + h+
via carbonic anhydrase

Question 16

what happens when bicarb ion lost or gained in body

Answer 16

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

Question 17

describe gain and loss - counteracting

Answer 17

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

Question 18

what are non volatile acids

Answer 18

phosphoric acid
sulfuric acid
lactic acid
= made by body and contributes to acid load
average net production = 40-80mmol of h+ per day

Question 19

describe buffer of hydrogen ion

Answer 19

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

Question 20

what are buffers for body

Answer 20

major extracellular = co2/hco3- system
major intracellular = phosphates and proteins

Question 21

what does buffering NOT DO

Answer 21

doesnt eliminate h+ from body
only keeps them locked up = sequestered to will not affect body

Question 22

what is ultimate balance of hydrogen ions controlled by

Answer 22

respiratory system = by controlled co2
kidneys = by controlling bicarb
both systems work together to minimized change of ph - h+ conc

Question 23

describe renal mechanisms of h+ control

Answer 23

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+

Question 24

describe henderson hasselbalch equation

Answer 24

main important part = body ph determine by [bicarb]/[co2]

Question 25

describe renal handling of bicarb

Answer 25

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

Question 26

describe bicarb reabsorption

Answer 26

majority in proximal tubule
some in tal
some in ccd
not excreted

Question 27

name and describe 2 ways bicarb added to plasma

Answer 27

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

Question 28

describe addition of new bicarb by h+ secretion

Answer 28

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-

Question 29

describe addition of new bicarb by glutamine

Answer 29

mainly in proximal tubule
process also called h+
excretion bound to nh3

Question 30

what is bicarb excretion equal to

Answer 30

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