the infamous Loop of Henle Flashcards
Which segments are impermeable to water?
thin and thick ascending limb
What specifically is the driving force for the counter current multiplication system?
active reabsorption of NaCl in the thick ascending limb
- reabsorption of 25% of filtered Na
- mantains interstitium concentration gradient that inc from cortex to medulla
When plasma is hypoosmotic, what is the nature of the urine?
dilute
when plasma is hyperosmotic or contracted, what is the nature of the urine?
concentrated
ADH has what function in the nephron?
During INC plasma osmolarity:
- inc water permeability of the collecting duct
- inserts aquaporins into luminal and basolateral membranes
- drives water reabsorption in excess of solute reabsorption
When ADH is present, what is the nature of the urine?
concentrated stinky urine because you are one dehydrated prune
How does the osmolarity of the tubular fluid in the diluting segment (tALH, tAL, DCT) change when a person is dehydrated?
it DOESN’T
osmolarity is always less than plasma
no matter if ADH is present or not - insensitive
How does the gradient in the interstitium change during diuresis?
gradient is still present, but is less steep
In the thin descending limb describe:
- permeability to solute
- permeability to water
- what happens to tubular fluid
- permeability to solute - low
- permeability to water - high
- what happens to tubular fluid - concentrated
In the thin ascending limb describe:
- permeability to solute
- permeability to water
- permeability to solute - high to NaCl and urea passively
2. permeability to water - impermeable
In the thick ascending limb describe:
- method of solute reabsorption
- water permeability
- what gradient it mantains
- active - Na/K/2Cl symporter
- impermeable
- 200 mOsm/L
What percent of filtered sodium and potassium is reabsorbed in medullary and cortical thick ascending limb?
25% of sodium
20% of potassium
What do loop diuretics inhibit?
Na/K/2Cl symporter in luminal membrane of thick ascending limb
How do ions move across the basolateral thick ascending limb?
NaKATPase and ion specific channels for Cl and K+
What creates the lumenal positive voltage potential?
K+ efflux in lumen, Cl- efflux in basolateral membrane
What is the positive voltage potential in the thick ascending limb a driving force for?
paracellular Na reabsorption
What are the two basic steps of the countercurrent exchange mechanism?
- pumping of solute out ascending limb –> interstitium
- axial advance of fluid forward along tubule
pump- equilibrate - shift - equilibrate
How would the gradient in the interstitium be affected if the loop of henle was longer?
the gradient would be increased
the osmolarity of the inner medulla varies btwn what values in antidiuresis and diuresis?
antidiuresis - 1200 mOsm/L
diuresis - 500 mOsm/L
How does the concentration of urea vary btwn antidiuresis and diuresis?
antidiuresis – 600 mM
diuresis - <100 mM (usually at around 0)
In the outer medulla, the osmolarity of the interstitium is due mostly to what solute?
NaCl
In the inner medulla the osmolarity is due to what solute?
50% Nacl and 50% urea
What are the three steps of urea recycling?
- reabsorption at collecting duct
- secretion from medulla –> tDLH and tALH
- delivery of urea from tubular fluid to collecting duct
what are two factors of the vasa recta that allow it to mantain the countercurrent exchange process?
- slower rate of blood flow
2. hairpin anatomy
Is the diffusion of water and solutes through the vasa recta active or passive?
passive
In the descending part of the vasa recta describe what happens to solutes and water
solutes move into vasa recta
water moves out of vasa recta
blood osmolarity increases
in the ascending limb of the vasa recta describe what happens to solutes and water?
solutes move out
water moves into blood
blood osmolarity decreases
Describe the osmolarity of the blood as it enters the vasa recta in comparison to plasma? as it exits?
iso-osmotic for both
When is the collecting duct more permeable to urea?
during antidiuresis in the presence of ADH
during diuresis describe urea recycling?
does NOT occur, most of urea is excreted
