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

filtrate passes through DCT, water gets reabsorbed into surrounding hypertonic medullary interstitial causing high osmolarity

filtrate produced is concentrated as it passes through medulla

Question 3

countercurrent multiplier system - ascending limb

Answer 3

• thick ascending limb
  impermeable to water
• thick ascending limb is permeable to solutes by active transport
• na/k/cl- cotransporters from filtrate -> TAL
• na-k/ATPase pump reabsorbs na+ from interstitial forming concentration gradient

filtrate produced is diluted as nacl has been removed

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

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

concentrated urine formed + high urine osmolarity

Question 5

overhydration

Answer 5

• 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

aldosterone acts on DCT to increase sodium reabsorption

= dilute urine produced
= low osmolarity of urine