Renal part 3 for final Flashcards
Changes in extracellular K+ can impact what?
resting membrane potential
What percent of total body K+ is intracellular?
98%
Increase in extracellular K+ does what?
decrease resting membrane potential–>increase excitability
What is the total extracellular fluid K+ content?
What does this mean?
~56mEq (14L X 4mEq/L)
Ingestion of small amounts of K+ from the GI tract could have significant effects on plasma conc. if retained within the ECF
How are dietary induced changes in [plasma K+] prevented?
RAPID cellular uptake of K+
(epinephrine, insulin, aldosterone->increase Na+K+ATPase)
SLOWER renal excretion
‘obligatory’ reabsorption of ~90% of the filtered load of K+ occurs where?
proximal tubule
thick ascending limb
If only 10% of filtered load K+ if delivered to the distal nephron, why is there higher filtered load percentages excreted in the urine?
Because K+ is SECRETED into the late distal and collecting tubule
How is K+ typically secreted into the distal and collecting tubule?
Uptake across basolateral membrane via Na+K+ATPase
Efflux across luminal membrane via: K+ channels and K+Cl- cotransp.
Na+ reabsorption creates lumen-negative potential which also promotes K+ secretion
What occurs in K+ depletion?
K+ secretion ceases and K+ reabsorption increases
Mechanism for K+ reabsorption during a state of K+ depletion.
Uptake across luminal membrane via energy-depend. K+H+ anti-porter
Efflux across basolateral membrane via K+selective channels
Hypertonic ECF causing the cell to shrink results in what?
regarding [K+]
Increases intracellular [K+] causing increase K+ efflux resulting
in hyperkalemia
What is the result of cell lysis releasing K+ into the ECF?
Whats an example that causes this phenomenon?
local hyperkalemia
Exercise-induced muscle breakdown
Metabolic alkalosis (decrease ECF H+) = ___plasma K+
decrease
Metabolic acidosis (increase ECF H+) = ___plasma K+
increase
How is plasma K+ effected from metabolic acidosis due to inorganic acids VS organic acids
Metabolic acidosis due to inorganic acids (HCl,H2SO4) increases plasma K+ to a much greater extent than organic acids (lactic acid, keto acids)
Do respiratory acid-base disorders have effect on plasma K+?
no
Increases in ECF [K+] increases K+ secretion and thus increases urine K+ excretion by what methods?
Directly increase Na+K+ATPase activity on the DISTAL nephron cells
Directly increase aldosterone secretion: Inc. Na+K+ATPase activity
Inc. luminal memb. K+ permeability
Increase in tubular flow does what to K+ secretion?
Increases
Extended use of loop diuretics does what?
increases K+ excretion and can lead to hypokalemia
Maintenance of normal plasma Ca2+ is dependent on what hormone?
parathyroid hormone
Where does PTH stimulate Ca2+ reabsorption in the kidney? And whats being stimulated there?
distal tubule
Ca2+ ATPase
Na+Ca2+ exchanger on the basolateral membrane
Maintenance of normal plasma Ca2+ is dependent on parathyroid hormone-mediated effects on what?
kidney
GI tract
bone
Resorption of bone releases what?
What could this potentially cause?
HPO4 2-
hyperphosphatemia
how is hyperphosphatemia prevented?
inhibitory effects of PTH on renal HPO4 2- reabsorption
An increase in PTH does what to HPO4 2- in the PROXIMAL tubule?
Decrease HPO4 2- reabsorption in the proximal tubule due to the inhibition of Na+-HPO4 2- co-transporter on the LUMINAL membrane
What are the 3 “lines of defense” that help prevent fixed acid-induced acidification of body fluids?
Physicochemical buffering Respiratory compensation (CO2 elimination) Renal compensation (H+ excretion; generation of HCO3-)
What is the “isohydric” principle?
The combined effect of ALL buffers in a given compartment determine the free [H+] (pH)
What is the most important extracellular buffer system? Why?
HCO3/CO2
lungs regulate CO2 levels
kidneys regulate plasma [HCO3-]
Where do red blood cells transport CO2?
from tissues to lungs (for elimination)
what is “chloride shift”
HCO3- diffuses out of the rbc in exchange for Cl-
what is H+ buffered by?
de-oxygenated hemoglobin
Where is the chloride shift process reversed?
at the lungs
Under normal conditions, what controls arterial pCO2?
alveolar ventilation
What is alveolar ventilation regulated by?
arterial pCO2
plasma [H+]
Where is more than 99% of filtered HCO3- reabsorbed?
proximal tubule
In the proximal tubule, is the reabsorptive process of HCO3- direct or indirect? Why?
indirect since HCO3- transport proteins are not present on the luminal membrane
an increase in pCO2 arterial blood does what to HCO3- reabsorption?
increases
an increase in Na+ reabsorption does what to HCO3- reabsorption?
increases
Where does renal generation of new bicarbonate predominantly occur?
DISTAL nephron…intercalated collecting tubule cells
What is the generation of NEW HCO3- dependent upon?
the availability of urinary buffers to accept secreted H+
“titratable acid” (HPO4 2-/H2PO4-)
Where can HCO3- be generated from?
glutamine metabolism in the proximal tubule
What hormone regulates HCO3 synthesis?
Aldosterone
What state increases glutamine metabolism and thus
HCO3 synthesis/NH3 availability?
metabolic acidosis
Acidemia has a blood pH of what?
<7.45
Respiratory disturbances involve renal compensatory responses at what type of pace?
relatively slow
What is the mechanism to restore plasma [HCO3] to normal?
24 mEq/L
Reabsorb ALL filtered HCO3
Generate NEW HCO3
What is normal plasma [HCO3]?
24 mEq/L
What is normal pCO2?
40 mmHg
If pCO2 < 40mmHg, what is the diagnosis? What compensates?
RESPIRATORY acidosis
Renal compensation
If [HCO3] is <24 mEq/L, what is the diagnosis? What compensates?
METABOLIC acidosis
Respiratory compensates
If arterial pH > 7.4 due to [HCO3]> mEq/L, what is the diagnosis? What compensates?
Metabolic alkalosis
Respiratory compensation
If arterial pH is >7.4 due to pCO2<40mmHg, what is the diagnosis? What compensates?
Respiratory alkalosis
Renal compensation
