Costanzo Renal Physiology: K+ regulation Flashcards
Where is most of the bodies K+ located?
In the ICF
What causes Hyperkalemia?
A shift of K+ out of cells
What causes Hypokalemia?
A shift of K+ in to cells
What is K+ balance?
K+ balance is the state in which the excretion of K+ exactly equals the intake of K+
What is the TF/P of K+ in Bowman’s space?
The TF/P ratio for K+ in Bowman’s space is 1 because it is freely filtered by the glomerulus.
What happens to K+ in the proximal tubule?
67% of K+ is reabsorbed in the proximal tubule along with Na+ and water.
What happens to K+ in the thick ascending loop of Henle?
20% of K+ is reabsorbed in the thick ascending loop via Na+, K+, 2Cl- cotransporter.
What happens to K+ in the distal tubule and collecting duct?
K+ is either reabsorbed or secreted in the distal loop and collecting tubule depending on intake.
How is K+ reabsorbed in the distal tubule and collecting duct?
K+ is reabsorbed by the H+, K+ ATPase which is stimulated only under conditions of a low K+ diet.
What cells are responsible for K= secretion in the distal tubule and collecting duct?
The principal cells.
How is K+ secreted in the distal tubule and collecting ducts?
Na+/K+ ATPase pumps K+ into tubule cells in the basolateral surface. K+ pores on the lumenal surface allow K+ to flow out of the cell and into the tubule.
How is K+ secretion by the distal tubule cells regulated?
(1) High K+ diet increases intracellular K+ thus increasing K+ secretion
(2) Low K+ diet leads to low intracellular K+ and less K+ secretion.
How does aldosterone increase K+ secretion?
Aldosterone stimulates the production of more Na+ transporters in the principal cells. This leads to more Na+/K+ activity, which leads to higher intracellular K+ and increased K+ secretion.
How does acid base balance effect K+ secretion?
(1) Acidosis leads to decreased intracellular K+ and increased H+ is exchanged across the basolateral surface for K+. The end result is decreased secretion of K+
(2) Alkylosis leads to high intracellular K+ because H+ shortage in the blood means that H+ moves out of cells sending K+ into cells. This leads to increased passive secretion of K+
What is the effect of Thiazide and loop diuretics on K+ secretion?
These drugs increase K+ secretion by increasing the distal tubule flow rate and diluting luminal K+. This drives more K+ into the lumen.
