Figure 2.

Overview of normal K⁺ homeostasis. Absorption of K⁺ from the gastrointestinal tract is faster than kidney excretion, necessitating a shift of K⁺ into the cell to guard against pathologic rises in extracellular K⁺ concentration. Insulin, catecholamines, and aldosterone all act to shift K⁺ into the intracellular space through effects that increase the activity of the Na⁺-K⁺-ATPase pump. Kidney K⁺ excretion eventually matches dietary intake such that total body K⁺ content is maintained within a narrow range. A brief summary of kidney K⁺ handling is depicted. There is evidence that kidney K⁺ excretion is initiated through a gastric-kidney signaling pathway as early as entry of dietary K⁺ into the stomach. Approximately 10% of dietary K⁺ is excreted in the colon. This component of K⁺ handling increases as CKD progresses. PT, proximal tubule; TAL, thick ascending limb.