Renal Handling of K

Question 1

Why do serum/plasma potassium levels NOT reflect the status of total body potassium?

Answer 1

Inside the cell 140
Outside 4
Muscle largest potassium store

Question 2

1. How does potassium move between cells and the extracellular fluid?

Answer 2

Na/K ATpas (2 into cell), H+ K+ antiporter, diffusion down gradient

Question 3

On a short-term basis, how does this movement protect the extracellular fluid from large changes in potassium concentration?

Answer 3

Insulin- direct upregulation of NAK ATP ase pump
Glucose and Na is co transporter in to the cell. Then to get out of cell the NaK ATPase is up regulated.

Epinephrine- Beta 2 receptor up regulates NaK ATPase pump

GI tract- peptides hormones are release, and result in increase potassium absorption

Question 4

What are the relative amounts of potassium reabsorbed by the proximal tubule and thick ascending limb of the loop of Henle? How is this affected by potassium intake (or supplementation)?

Answer 4

90% does not vary

Question 5

Describe how nephron segments beyond the thick ascending limb of the LoH can manifest net secretion or reabsorption. What is the role of the principal and intercalated cells in these processes?

Answer 5

Intercalated- ATP driven responsible for reabsorption
Principal – primary secretion

Collecting ducts have HK antiporter

Question 6

How is potassium secretion regulated in the distal tubule?

Answer 6

Principal cells, DCT cells,
Possible to excrete more K than can be filtered at the Bowman’s space (up to 150%)

Plasma level high, aldosterone primary
Flow rate and acid/base status

Question 7

There are two potassium channels located on the apical membrane of the principal cells in the distal tubule. What are they, what are their roles, and how are they regulated?

Answer 7

K channel; KCl co transporter

Secreted passively out of principle cells down its concentration gradient (electrochemical gradient)

Question 8

How do changes in plasma potassium concentration influence aldosterone secretion

Answer 8

Increased ECF potassium concentrations directly stimulate the adrenal cortices to synthesize and secrete aldosterone
Enhances principal cells to have potassium secretion; directly stimulates the basolateral NaKAtpase pump, promotes the placement of additional potassium channels into the luminal principal cell membrane, thus boosting its permeability for potassium secretion.
Represents the likely mechanism for proper maintenance of ECF K levels

Question 9

How (by what mechanism) do the common diuretics effect potassium secretion

Answer 9

Loop diuretics- Inhibits the NaK2CL co transporter which increases K secretion leading to hypoK

All but K sparing will increase K excretion
K sparing is the competitive aldosterone diruetics

Question 10

What are the major mechanisms for development of hyperkalemia

Answer 10

Obstruction; anuric/oliguric RF
Lack of aldosterone
iatrogenic

Question 11

How are acid-base status and potassium levels associated?

Answer 11

Potassium increase ECF as Hydrogen increases (acidity)
Potassium decreases in ECF as hydrogen decreases (alkalotic)
Clinically if alkalosis is persistenting need to correct hypokalemia
*** With low bicarb need to treat first prior to treatment for HyperK