Loop of Henle, Distule Tubule, and Collecting Duct Flashcards
(49 cards)
Where do most regulatory mechanisms target urine formation?
distal tubular segment
Is reabsorption in the proximal tubule iso-osmotic?
yes
Explain the osmolarity of the urine formation in the distal tubule?
it’s variable, which is why the regulatory mechanisms frequently target the distal tubule.
What are the functions of the distal tubules?
tubular fluid is converted into urine
spexialized and tightly regulated trasnport characteristics
what are the parts of the distal tubule?
loop of henle (thin descending limb, thin ascending limb, thick ascending limb)
distal convoluted tubule
collecting ducts (even though not part of nephron?)
in general, why does water leave the distal tubule for reabsorption?
the area outside is more concentrated, so water diffuses down it’s concentration gradient
where does the thin descending limb of loop of henle start?
at the end of the proximal straight tubule
where does the descending thin limb of the loop of henle run?
from the cortex to the outer medulla
describe he intersitial environment around the descending thin limb of loop of henle?
hypoosmotic to plasma
increases progressively between cortex and medulla
reaches maximum of 1200 mosm (half urea and half nacl)
what’s the function of the descending thin limb of the loop of henle?
concentrates tubular fluid no active epithelial transport highly permeable to water (aquaporins) minimal permeability to nacl and urea driving force is osmotic gradient: osmolarity increases from 280 to 1200
why is it important that nacl isn’t permeable in the decending thin limb of the loop of henle?
because urea and nacl cannot move through, water is the only way to modulate the osmolarity.
what is permeable vs impermeable in the thin ascending limb of the loop of henle?
water is completely impermeable (no aquaporins)
nacl is strongly reabsorbed
urea is impermeable
In the thin ascending limb of the loop of henle, does osmolarity rise or drop?
drop
why does the osmolarity of the thin ascending limb in the loop of henle drop?
nacl diffusion and tubular fluid impermeability
where is the thick ascnedling limb located?
between the medulla and the cortex
what are the transport properties of the thick ascneding limb?
serves in reabsorption of nacl
impermeable to water
strong nacl reabsorption (active transport mechanism)
how are the thin and thick ascending limbs different in terms of cell contents and filtration ability?
the cells in the thick ascending limb have more mitochondria
the thin ascending limb has some nacl reabsorption while the thick ascneding limb has strong nacl reabsorption
why does the thick ascending limb have strong nacl reabsorption ability? be specific
it has two active na transporters
nak2cl - transport down the electrochemical gradient
nak atpase - pumps na out and k in. creates electrochemical gradient.
where is the nak atpase located on the epithelial cell of the thick ascneding limb? why is it important
the nak atpase is located on the basolateral side of the epithelial cell. this is important because it pushes the na out of the epithelial cell, creating a low concentration within the cell. as such the nak2cl transport can help the elements move from the lumen into the cell for reabsorption.
where is the nak2cl transporter located?
on the apical membrane of the epithelial cell in the thick ascneding limb of loop of henle
what are two diuretics that target the nk2cl channel?
furosemide, bumetanide
what part of the nak2cl transporter do furosemide and bumetanide target
the chlorine site
explain the mechanism of furosemide and bumetanide
the drugs bind to the chlorine channel, blocking nacl reabsorption, this increases the nacl load delivery to the distal nephron, interfering with urine concentration, leads to diuresis (increased water loss in urine)
what two drugs stimulate nacl reabsorption?
ADH and AVP (arginine vasopressin)
