Renal mechanisms for excreting either dilute or concentrated urine

Question 1

countercurrent multiplier system - loop of henle

Answer 1

controls if urine produced is concentrated or diluted
interacts with descending vs ascending limbs of loop of henle
by creating a concentration gradient in renal medulla
allowing body to conserve/ excrete water depending on body needs

Question 2

countercurrent multiplier system - descending limb

Answer 2

permeable to water
impermeable to solutes

as filtrate moves through
- water is reabsorbed into surrounding medulla interstitium
- producing high osmolarity of medullaty interstitial fluid
- producing a concentrated filtrate

Question 3

countercurrent multiplier system - ascending limb

Answer 3

• impermeable to water
• permeable to solutes
  active transport of na/k/cl- out of filtrate into medullary interstitium

this increases osmolarity of interstitial fluid
forming a concentration gradient
helping water reabsorption

Question 4

dehydration - ADH

Answer 4

• body needs to conserve water
• ADH released from posterior pituitary gland
• ADH functions to activate aquaporins-2-channels onto collecting duct cell membrane
• ADH increases permeability of collecting duct to allow water to be reabsorbed from filtrate into bloodstream

aldosterone acts on DCT to increase sodium reabsorption

= concentrated urine formed
= high urine osmolarity

Question 5

dehydration - UREA

Answer 5

urea reabsorbed in PCT -> loop of henle -> recycled in medulla

Question 6

overhydration

Answer 6

• body needs to lose water
• ADH inhibited from posterior pituitary gland
• so ADH does not functions to activate aquaporins-2-channels onto collecting duct cell membrane
• so ADH does not permeability of collecting duct to allow water to be reabsorbed from filtrate into bloodstream

sodium reabsorption without water retention

= dilute urine produced
= low osmolarity of urine