HRR: electrolyte homeostasis Flashcards
What is a normal serum potassium?
3.5-5
Where is potassium usually found?
Intracellularly
Why is potassium tightly regulated?
Unregulated potassium leads to issues with action potentials, resting membrane potentials, and causes issues in pretty much every system
Potassium is mostly excreted via…
The urine
What is the long-term control of potassium?
Renal regulation
What happens to potassium after we eat?
It rapidly moves into cells until the kidney eliminates it
What happens with potassium between meals?
The plasma potassium can remain constant as it is released from the cells to balance what is excreted by the kidney
How does acidosis impact serum potassium?
Causes hyperkalemia; high H+ in the blood causes cells to take up H+, resulting in pushing K+ out
How does alkalosis impact serum potassium?
Causes hypokalemia; low H+ in the blood causes cells to shift H+ into the plasma which causes K+ to enter the cell
What 3 things impact potassium balance?
- Rate of filtration aka GFR
- Rate of reabsorption in the tubules
- Rate of secretion by the tubules
How is most K+ reabsorbed?
Paracellularly
Where do we find ROMK channels? What do they do?
Thick ascending limb, DCT, CCD; they secrete K+ into the tubular lumen
What are the primary sites of potassium secretion?
DCT/ CCD in principal cells
What causes K+ secretion in the CCD?
Sodium reabsorption via ENaC! Sodium is taken into the cell, creating a negative potential within the lumen. Potassium moves into the lumen via ROMK to balance out the charge
In alpha-intercalated cells during acidosis, what happens to K+?
It gets reabsorbed! These cells push H+ into the lumen, so K+ gets reabsorbed to balance the charge via a proton-K+ antiporter
What factors impact the functioning of ENaC?
- Na delivery to the distal nephron
- Urine flow
- Aldosterone
What happens to K+ in a low aldosterone state?
When aldosterone is low, we end up with hyperkalemia
What are classic causes of hypokalemia?
Diarrhea, vomiting and alkalosis, increased aldosterone, insulin, albuterol and epinephrine, renal tubular acidosis, diuretics
What are classic causes of hyperkalemia?
CKD/renal failure, urinary obstruction, insulin deficiency, HF, low aldosterone, acidosis, cell death/ischemia
How does HF cause hyperkalemia?
A decreased delivery of sodium to the distal nephron leads to less reabsorption of sodium and thus less potassium secretion
What is seen on EKG with hyperkalemia?
Peaked T wave followed by wide PR and wide QRS and eventual loss of p wave
How do we treat hyperkalemia?
Shifting therapies, increasing removal via kidneys
What are examples of shifting therapies for hyperkalemia?
Calcium, insulin, albuterol, bicarb
What does calcium do in the setting of hyperkalemia?
Stabilize the membrane in cardiac myocytes to help prevent arrhythmia. Does NOT change K+ concentration
What can we give to increase K+ removal?
Loop diuretics and potassium binders
What is convection?
Diffusion but with force; glomerulus does this!
Does hemodialysis use diffusion or convection?
Diffusion; one reason why people on dialysis don’t live as long since the kidney is really supposed to do convection
What are the 5 indications for hemodialysis?
- A- refractory acidosis
- E- electrolytes
- I- ingestions
- O- overload
- U- uremia
How is calcium reabsorbed?
Paracellularly
How much calcium is secreted into the tubule?
None
What is the important regulator of Ca?
PTH
Describe what happens to rebalance calcium when it is low.
Low calcium in the ECF triggers the parathyroid gland to release PTH that causes reabsorption of calcium from the bones to return serum calcium to normal
Thiazides and gitelman can cause what electrolyte imbalance? How?
Hypercalcemia
What is absorbed in the proximal tubule?
Everything but magnesium
How is phosphorus reabsorbed?
Transcellularly via Na-phosphate cotransporter
Where is magnesium reabsorbed?
Loop of henle
How is magnesium reabsorbed?
Paracellular transport
How does decreased extracellular calcium impact magnesium?
Causes less to be excreted!
