Sodium, Potassium, Phosphate, Calcium, Magnesium Balance - Bishop's Notes Flashcards
The thin descending limb…
- permeable to water and small solutes - water out, solutes in
The thin ascending limb…
- permeable to small solutes but NOT to water - solutes move out, water does NOT move
At the PCT, ______ of Na+ is reabsorbed
67%
At the thick ascending limb, ______ of Na+ is reabsorbed
25%
At the DCT, _______ of Na+ is reabsorbed
5%, then 3% at collecting duct
The early proximal tubule has a lumen charge of _____ and a blood charge of _____
-4 mV; 0 mV
What is absorbed/secreted at the early proximal tubule? It’s a real mess. (1)
What is absorbed/secreted at the late proximal tubule? This is where 67% Na+ has been reabsorbed. (2)
The thick ascending limb is… (3 things)
- Electrogenic
- Load dependent
- Impermeable to water
Why is the thick ascending limb electrogenic?
K+ leaks back into the lumen.
Since it is electrogenic, it helps drive other solutes via the paracellular route (Ca, Mg, etc.)
What does the water impermeability of the thick ascending limb contribute?
- Separation of water and solutes
- Establish corticopapillary osmotic gradient
What is reabsorbed/secreted in the thick ascending limb? (3)
What is absorbed/secreted at the early distal tubule? (4)
The early distal tubule is… (2 things)
- Load dependent
- Impermeable to water (“cortical diluting segment”)
What is absorbed/secreted at the late distal tubule and collecting duct, for a principal cell? (5)
Water permeability at the late distal tubule and collecting duct is controlled by:
ADH (vasopressin)
What is spironolactone?
Aldosterone antagonist; K+ sparing diuretic
Aldosterone causes the distal tubule and collecting duct to…
Reabsort Na+ and secrete K+ (alters transcription and translation in principal cells)
What is furosemide?
A powerful diuretic; inhibits the Na-K-2Cl symporter in the thick ascending limb
What factors keep K+ constant?
- Epinephrine
- Insulin
- Aldosterone
What factors displace plasma K+?
- Acid-base balance
- Plasma osmolality
- Cell lysis
- Exercise
____ K+ reabsorbed in PCT
____ K+ reabsorbed in thick ascending limb
____ K+ reabsorbed in laste distal tubule and collecting duct
67%; 20%; (only reabsorbed in low K+ diet)
There is variable secretion of K+ into the collecting duct as well.
What is absorbed/secreted at the late distal tubule and collecting duct, for an alpha-intercalated? (5)
Aldosterone causes H+ secretion here (pee out acid)
What are some causes of increased K+ secretion by the principal cells?
- High K+ diet
- Hyperaldosteronism
- Alkalosis
- Thiazide diuretics
- Loop diuretics
- Luminal anions
- High tubular flow
- High Na+ diet
____ phosphate is excreted in the PCT
____ phosphate is excreted in the late proximal tubule
____ phosphate is excreted in the urine (buffer for urinary H+)
70%; 15%; around 15%
Parathyroid hormone (PTH) inhibits…
Proximal tubule cotransporter, increasing PO4 excretion
Hyperparathyroidism causes…
Phosphaturia, along with cAMP
Ca2+ reabsorption parallels Na+, except for…
the distal tubule
The thick ascending limb drives paracellular transport of Ca2+ by…
+ luminal potential
Loop diuretics inhibit the Na+/K+/Cl- cotransporter (like spironolactone), which…
Disrupts the + potential
What does PTH do?
- Increase Ca2+ reabsorption in distal tubule
- Decrease Ca2+ reabsorption in proximal tubule, along with PO4
The net effect is reabsorption
____ Ca2+ is reabsorbed in the PCT
____ Ca2+ is reabsorbed in the thick ascending limb (decreased by furosemide)
____ Ca2+ is reabsorbed in the distal tubule/collecting duct (increased by PTH, thiazide diuretics)
67%; 25%; 8%
<1% excreted
____ Mg2+ is reabsorbed in the PCT
____ Mg2+ is reabsorbed in the thick ascending limb (decreaed by furosemide)
____ Mg2+ is reabsorbed in the distal tubule and collecting duct
30%; 60%; 5%
about 5% excreted
Loop diuretics inhibit Mg2+ reabsorption by ________ (in the thick ascending limb)
inhibiting the Na+/K+/Cl- transporter
