Loop of Henle

Question 1

what does the loop of Henle include? where is it located?

Answer 1

begins at the end of PT (outre medulla) and descends to the inner medulla as the thin descending limb. ascends as the thin ascending limb and then becomes the thick ascending limb

Question 2

what are the tALH and TAL (thin and thick ascending limbs) impermeable to? what does the TAL resorb 25% of?

Answer 2

water

sodium- effectively dilutes the urine below 100 mosm/L

Question 3

what happens to tubular osmolarity in the ascending limb of the loop of henle? why?

Answer 3

it is decreased because sodium and chloride are reabsorbed but water is not

Question 4

what does the active Na and Cl reabsorption in the TAL do?

Answer 4

maintains the solute concentration gradient surrounding the LH and collecting duct

Question 5

what odes the TAL do to defend against plassma volume depletion?

Answer 5

recycles urea back into the inner medulla to contribute to the solute gradient (to make concentrated urine)

Question 6

what happens to the osmolarity between the cortex and the inner medulla? does this go away with plasma osmolarity and ADH?

Answer 6

it progressively increases to 2-4 fold the plasma osmolarity

does not go away with osmolarity or ADH

Question 7

what are the functions of reabsorptive solute transport in the TAL?

Answer 7

excreting dilute urine with expanded plasma volume or concentrating osmolarity in collecting duct

Question 8

how does the TAL affect the resorption of the collecting duct?

Answer 8

maintains a gradient of interstitial osmolarity that drives resorption of water when plasma volume is contracted

Question 9

where is ADH secreted? in response to what?

Answer 9

posterior pituitary

in response to increase of plasma osmolarity

Question 10

what does ADH do in the kidney?

Answer 10

increases the water permeability of the collecting duct

allows osmotic equilibrium, meaning water resorption into the interstitium

Question 11

in the absence of ADH what is the collecting duct’s permeability to water?

Answer 11

it is impermeable- causes excretion of dilute urine

Question 12

what is the diluting segment of the nephron? how does the osmolarity here compare to plasma?

Answer 12

tALH, TAL and the distal convoluted tubule (thin and thick ascending limbs)
always less of the plasma regardless of its osmolarity

Question 13

what is the effect of ADH on the diluting segment of the nephron?

Answer 13

it has no affect- still impermeable to water

Question 14

what is diuresis? antidiuresis?

Answer 14

D- volume expanded and/or decreased plasma osmolarity

antiD- volume contracted and/or increased osmolarity

Question 15

what occurs to the concentration gradient between the cortex and the inner medulla with changing osmolarity of the plasma?

Answer 15

diuresis- gradient is less steep

antidiuresis- gradient is more steep

Question 16

describe the permeability of the thin descending limb of the loop of henle. what occurs to osmolarity?

Answer 16

low permeability to solutes and high permeability to water

osmolarity equilibrates with interstitium and concentrates the fluid as it descends

Question 17

describe solute movement of the thin ascending limb of the loop of henle.

Answer 17

passive NaCl resorption, impermeable to water, passive urea secretion

Question 18

describe transport in the thick ascending limb of the loop of henle. what does this do to osmolarity gradient?

Answer 18

active NaCl resorption, water impermeable

generates 200 mOsm/L gradient between fluid and interstitium

Question 19

how is the TAL function described as creating?

Answer 19

“counter current multiplication” of interstitial solute concentration

Question 20

what transporters exist on the TAL luminal membrane? the basolateral membrane?

Answer 20

luminal-Na/K/2Cl symporter, K channel and Na/H antiport

basolateral-Cl, K and Na/K pump

Question 21

what generates the lumen positive potential difference across the TAL tubular epithelium? what does this drive?

Answer 21

efflux of K back into the tubular fluid and Cl efflux at basolateral membrane
drives Na resorption across tubular epithelium

Question 22

what do loop diuretics do?

Answer 22

inhibit the Na/K/Cl cotransporter. decrease resorption of these three solutes

Question 23

what is the maximum ability of the TAL to pump solute in the outer medulla? how does the TAL surpass this?

Answer 23

able to pump against a gradient of 200 mOsm/L

countercurrent multiplication amplilifies the transport capacity up to 6 fold (1200 mOsm/L)

Question 24

how is countercurrent multiplication achieved?

Answer 24

5 cycles of 2 steps (pump- equilibrate- shift- equilibrate)

1) pump solute out of ascending limb to gradient of 200 mOsm/L with osmotic equilibrium with descending limb
2) axial shift of fluid forward in tubule and equilibrium of descending limb and interstitium

Question 25

once countercurrent exchange is complete, what does the interstitial osmolarity equilibrate outside of the loop of henle?

Answer 25

the collecting duct when ADH is present

Question 26

what causes the difference in inner medulla osmolarity during times of diuresis and antidiuresis?

Answer 26

amount of urea present in interstitum increases during diuresis to double the preexisting osmolarity difference

Question 27

what is the difference in osmolarity in the outer medulla is caused by what solutes? the inner medulla?

Answer 27

outer- mostly NaCl | inner- antidiuresis 1/2 is NaCl and 1/2 is urea

Question 28

what contributes to recycling of urea in the inner medulla?

Answer 28

resorption of urea from inner medullary collecting duct (end), secretion of urea into the ascending loop of henle and delivery of urea from the loop of henly to the inner medullary CD where it is again reabsorbed

Question 29

what does ADH do to urea recycling? how is the urea gradient maintained?

Answer 29

increases the urea permeability of the inner medullary collecting duct maintained by secretion into the loop of henle

Question 30

without ADH, what is the urea permeability of the collecting duct? the interstitial urea concentration?

Answer 30

it is very low along with water permeability | interstitial urea concentration in inner medulla falls below 100 mOsm/L

Question 31

during antidiuresis what is the inner medullary interstital osmolarity? how is this changed in diuresis?

Answer 31

1200 mOsm/L | lack of urea decreases to around 600 mOsm/L

Question 32

how does blood supply in the renal cortex and renal medulla organize?

Answer 32

they are segregated | allows solutes from proximal tubule to rapidly reenter circulation and exit the kidney

Question 33

what is the blood supply surrounding the loop of henle called?

Answer 33

the vasa recta

Question 34

what prevents washout of solutes from the medulla?

Answer 34

countercurrent exchange of solutes between the vasa recta and the interstitium facilitated by slower rate of blood flow and proximity to the loop of henle

Question 35

what is the main purpose of the vasa recta?

Answer 35

to provide oxygen and nutrients and to eliminate CO2 and waste from the loop of henle epithelia

Question 36

what type of solute transport is exhibited in the vasa recta?

Answer 36

passive exchange

Question 37

what happens to the osmolarity of the vasa recta as it moves around the loop of henle?

Answer 37

blood osmolarity increases as it descends towards the inner medulla and decreases as it moves back up to the cortex

Question 38

what is the purpose of solute and water exchange of the vasa recta around the loop of henle?

Answer 38

to prevent washout of medulla and to ensure the same osmolarity blood reenters circulation

Question 39

what washes out the interstitium of urea during diuresis?

Answer 39

the inner medullary Collecting duct secretes urea and causes excretion