Ch 14 Part 4 -- Urinary System -- VTPP 435

Ch 14 Part 4 -- Urinary System -- VTPP 435

Tubular Secretion

-always involves transepithelial transport but in reverse
-usually H+, K+, organic anions, and cations transferred from peritubular capillaries to tubular lumen

Hydrogen Ion Regulation

-secreted by proximal, distal, & collecting tubules into tubular fluid
-secreted when body fluids are too acidic

Potassium Ion Regulation

-plasma K+ tightly controlled by kidneys
-actively reabsorbed in proximal tubule and actively secreted by principal cells
-K+ reabsorption is unregulated
-K+ secretion is varied

Potassium Ion Secretion

-coupled with Na+ reabsorption by basolateral Na+-K+ pump
-takes K+ from lateral space into tubular cells
-aldosterone causes secretion
-high ECF K+ --> high aldosterone
-high K+ = low H+ in the intercalated cells

Potassium Ion Movement

1) Peritubular Capillary --> Interstitial Fluid
2) Interstitial Fluid --> Principal Cell (Active step)
3) Principal Cell --> Lumen (thru leak channel)

3 important functions of the organic secretory systems

1) adding more of some organic ion causes organic secretory pathways to help excrete it (like hormones)
2) excretion of ion not bound to plasma protein helps off load more that is bound thru tubular secretion
3) proximal tubule can easily remove foreign organic ions quickly