Loop of Henle

Question 1

what type of epithelium lines the loop of Henle?

Answer 1

descending limb = squamous
thin ascending limb = squamous
thick ascending limb = cuboidal

Question 2

what occurs in the descending limb of the loop of Henle?

Answer 2

permeable to water so water flows out from the tubule
this increases the osmolarity within the tubule
membrane is impermeable to solutes such as Na

Question 3

what occurs in the ascending limb of the loop of henle?

Answer 3

membrane is impermeable to water
Na/K/Cl co transporter reabsorbsNa , K and Cl into the interstitium which increases the interstitial osmolarity
Na enters capillaries from the interstitium via Na/K ATPase which creates an electrochemical gradient for other ions to passively diffuse across into the capillaries
this reinforces the gradient for water to be reabsorbed from the descending limb

Question 4

what is the change in osmolarity through the loop of henle?

Answer 4

the fluid delivered from the proximal tubule is isotonic due to reabsorption of Na and water
the descending limb re-establishes tubular osmolarity increasing it to 1200
in the ascending limb, ions are reabsorbed so the osmolarity decreases again
this delivers a hypotonic fluid to the distal tubule

Question 5

how does loop diuretics act to induce diuresis?

Answer 5

the work on the ascending limb of the loop of henle
they block the Na/K/Cl co-transporter so these ions aren’t reabsorbed into the interstitium
therefore a gradient isn’t created for water to be reabsorbed from the descending limb so water remains in the tubule = diuresis

Question 6

what are the 2 main functions of the vasa recta?

Answer 6

deliver 02 to the medulla

removes volume from the interstitium

Question 7

is the flow rate in the vasa recta high or low and why?

Answer 7

low to allow adequate time for equilibrium

Question 8

how does vasa recta not interfere with the gradient?

Answer 8

they are arranged in specialised hair pin loops and so they don’t drain straight through the nephron
this allows the interstitium to have a concentration before all molecules are reabsorbed

Question 9

where does ADH work in the nephron and how?

Answer 9

ADH works on the collecting duct to increase the number of aquaporin 2 proteins on the apical membrane
this increases the permeability of the membrane to water so more water is reabsorbed from the collecting duct