Vivek Bhalla, MDDivision of Nephrology

Stanford University School of MedicineSeptember 14th, 2015

Regulation of Water Balance

Learning Objectives (3)1. A rise in tonicity does what?

– Stimulates ADH, thirst

2. How is the kidney primed to concentrate urine?– Countercurrent multiplication– Countercurrent exchange

3. How that concentrating mechanism is utilized to maintain water balance?– What does ADH do to the kidney?

“Big Picture”

Hypothalamus

“Big Picture”

Hypothalamus

Hypothalamus

• Paraventricular Neurons

• Supraoptic Nuclei

ADH Release

Kidney Anatomy

Hyperosmotic Medulla• Tubular Lumen• Tubular epithelial Cells• Interstitium

• Endothelial cells – vasa recta• Blood within the vasa recta

Kidney Anatomy• Tubular Lumen• Tubular epithelial Cells• Interstitium

• Endothelial cells – vasa recta• Blood within the vasa recta

Kidney Anatomy

Hyperosmotic Medulla

How is this gradient established?

Hyperosmotic Medulla

Counter Current Multiplication

Counter Current Multiplication

Countercurrent Multiplication

Countercurrent Exchange

A- ArteryB- VeinC- Collecting Duct

Countercurrent Exchange

Too Much or Too Little ADH

% ofwaterremainingIn the lumenRelative to the original glomerularfiltrate

Aquaporins – Water Channels

Aquaporins – Water Channels

Urinary Concentration

Take Home Points (3)1. ADH release and thirst are regulated by tonicity

2. Countercurrent multiplication and exchange ready the medulla for ADH-dependent water reabsorption

3. ADH stimulates Aquaporin 2 insertion in the luminal (apical) membrane along the collecting duct