Chapter 28: ECF Osmolarity and Na+ Concentration Regulation (Discussion 3)

Question 1

Urine Osmolarity

Answer 1

• Average adult excretes ~600 mOsm of solutes/day
• Minimum concentration ability ~50 mOsm/L
  
  • Remove excess water through dilute urine
  • Formed when ADH secretion is reduced
• Maximum concentration ability ~1200 mOsm/L
  
  • Obligatory Urine Volume (OUV) = volume needed to remove the excreted solutes –> 0.5 L/day
  • Sea water dehydrates you because >1200 mOsm/L and creates extra solutes from metabolizing it
• Pretty much always around 100 mOsm/L after the loop
• ADH regulates distal tubule-collecting ducts action to produce dilate vs concentrated
  
  • H2O reabsorption –> concentrated
  • Solute reabsorption with H2O –> dilute

Question 2

Creating hyperosmotic medulla

Answer 2

• H2O reabsorption mostly occuring in cortical tubules –> prevents dilution of medullary interstitium
• Urea recycling from medullary collecting ducts –> increases osmolarity in medulla
• Counter-current exchange with vasa recta
  
  • Improve gradient for transport
  • Carry water up out of medulla
  • Carry solutes deeper into medulla

Question 3

Counter-current Exchange Diagram

Answer 3

Question 4

Central Diabetes Insipidus

Answer 4

Pituitary fails to secrete ADH –> Excrete large volumes of dilute urine –> Treat with desmopressin (synthetic analog of ADH) acts at V2 receptors

Question 5

Nephrogenic Diabetes Insipidus

Answer 5

Failure of renal tubules to adequately respond to ADH

Either can’t concentrate urine because of low osmolarity in medulla or tubules don’t respond to ADH (lithium or tetracyclines)

Question 6

Things that increase ADH secretion (and thirst)

Answer 6

Increase in plasma osmolarity

Decrease in blood volume

Decrease in blood pressure

Question 7

Things that decrease ADH secretion (and thirst)

Answer 7

Decrease in plasma osmolarity

Increase in blood volume

Increase in blood pressure

Alcohol