Lec 44 Loop of Henle Function

Question 1

What is main function of loop of henle?

Answer 1

1. generate hypotonic tubular fluid to deliver to distal by reabsorbing salt and leave fluid behind
2. create longitudinal gradient so that downstream segments of nephron can concentrate or dilute the urine

Question 2

What is the longitudinal [cortico-medullary] gradient?

Answer 2

• cortex is isotonic
• outer medulla isotonic
• near papilla migh be as high as 1200 mmol
• get increasing osmolarity from cortex to papilla –> creates driving force for water reabsorption out of collecting duct

Question 3

What type of transport is most of thin limbs – transcellular or paracelluar?

Answer 3

paracellular since squamous you don’t get much transcellular

Question 4

What is transported in thin descending?

Answer 4

• a little Na transport into descending limb
• cortico-medullary gradient means as you go down descending limb you have increasing osmotic drive for H2O to leave
• very little permeably to Na, high permeability to H2O2

Question 5

How does descending limb concentration change?

Answer 5

• increasing conc of fluid within descending limb

Question 6

What is water permeability in thin descending vs thin ascending vs thick ascending?

Answer 6

• thin descending is very water permeably

- thin and thick ascending are totally water impermeable

Question 7

What makes ascending limb impermeable?

Answer 7

• very tight junctions

- no aquaporins

Question 8

What is transported in thin ascending?

Answer 8

• a little salt diffusing out [because of decreassing Na conc outside in gadient]

Question 9

How does concentration of fluid change along thin ascending limb?

Answer 9

• some decrease in concentration along thin ascending

Question 10

What is transported in thick ascending limb?

Answer 10

• lots of Na/Cl/K into interstitium via Na/K/2Cl pump that uses Na gradient
• impermeable to H2O
• NH4
• paracellular reabsorption of cations
• Reabsorption NH4
• HCO3 reabsorption

Question 11

What happens to fluid conc along TAL?

Answer 11

• reduced fluid conc to become hypotonic

Question 12

What is mech of NaCl tranposrt in TAL?

Answer 12

lumen:
- Na/K/2Cl comes in via pump using Na gradient
[secondary active transport]
- some K back out to lumen via channel
Basolateral:
- Na-K ATPase [Na out, K comes into cell]
- Cl channel out
- K channel out

Question 13

What happens if defect in K channel in luminal membrane of TAL?

Answer 13

• K channel is backleak so brings K back into lumen
• recycles K back into lumen to be used for Na/K/2Cl transporter
• if defect you won’t have enough K in lumen so you won’t be able to bring Na/Cl into interstitium to create osmotic gradient
• means you won’t need to be able to concentrate urine

Question 14

What is significant function of Na/K/2Cl transporter?

Answer 14

• creates the osmotic gradient that is needed to concentrate urine

Question 15

What is unique bout tight junctions in TAL?

Answer 15

• impermeable to water

- permeable to small ions

Question 16

How is NH4 transported in TAL?

Answer 16

NH4+ gets reabsorbed by substituting for K in Na/K/2Cl transporter

Question 17

What are two functions of K back-leak channel in TAL?

Answer 17

• recycle K to be used for Na-K-2Cl transporter [main source of cortico-medullary gradient]
• create positive electrochemical potential in lumen [driving force for paracellular cation reabsorption]

Question 18

What happens to HCO3 in TAL?

Answer 18

reabsorbed via same mech as in PT

Question 19

What are 3 main functtions of TAL?

Answer 19

• diluting luminal fluid
• generating longitudinal gradient
• reclaiming HCO3

Question 20

What are the two things that regulate the longitudinal gradient?

Answer 20

• length of loop of henle: longer = bigger gradient

- activity of Na/K/2Cl transporter: more activity = bigger gradient

Question 21

What does ADH do in TAL?

Answer 21

• upregulates activity of Na/K/2Cl transporter

Question 22

What is role of vasa recta in loop function?

Answer 22

• exchange with surrounding interstitium
• does not impact the gradient
• as it follows descending: picks up salt and gives off water
• as it follows ascending: picks up water and gives off salt

Question 23

What are 3 effects on kidney of ADH?

Answer 23

• increase Na/K/2Cl activity –> bigger gradient
• increase urea permeability in inner medullary collecting duct –> bigger gradient
• increase water permeability of principal cells in late distal tubule and collecting duct –> reabsorb more H2O

Question 24

What happens to principal cells in presence of ADH?

Answer 24

• open water pores so H2O reabsorbed

Question 25

What is free water?

Answer 25

• water in our body that is not associated with a particle

- any water present out of the range of 300 mosm/L [you can artificially break into isotonic solution and distilled H2O]

Question 26

Where is free water generated in the kidney?

Answer 26

• its generated in the thick ascending limb = the diluting segment

Question 27

What is the equation for clearance of free H2O?

Answer 27

C[H2O] = V. - Cosm
V. = urine flow
Cosm = clearance of osmotic particles

Question 28

What does positive C[H2O] mean? Is urine hyper or hypo?

Answer 28

• positive free water clearance means vol of urine > clearance of osmotic particles
• means you are excreting free water
• hypotonic urine

Question 29

What does negative C[H2O] mean? Is urine hyper or hypo?

Answer 29

• negative free water clearance means vol of urine < clearance of osmotic particles
• means you are retaining free water in the body
• hypertonic urine

Question 30

What is equation for Cosm [clearance of osmotic particles]?

Answer 30

Cosm = Uosm * V. / Posm
Uosm = osmolality of urine
V = volume or urine
Posm = osmolality of plasma

this is from all osmotic particles

Question 31

Does concentrated urine necessarily have high Na concentration?

Answer 31

No!

• concentrated urine –> has lots of urea
• dilule urine –> has more Na and lots of H2O