Loop of Henle, Distule Tubule, and Collecting Duct Flashcards
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)
what do ADH and AVP do to the interstitial fluid osmolarity?
they increase the ISF osmolarity (which then feeds back, blocking adh and avp mechanisms)
where does the distal convoluted tubule start
from the thick ascending limb
6-8 distal convoluted tubules join together to form what
collecting duct
the collecting duct starts in which part of the kidney, running to where?
cortex down to medulla
when several collecting ducts join together, what do they form?
ducts of bellini
Explain the factors of fluid processing in the distal convoluted tubule
receives 10% of filtered load of water
less than 10% of filtered load of nacl and kcl and 50% urea
Na is actively reabsorbed
K is secreted (allowing for regulation)
Na reabsorption is greater than K secretion; therefore Cl- is also reabsorbed
What is the fluid in the distal convoluted tubule diluted or concentrated before leaving?
diluted (b/c insoluble to water but ions can leave and do more than they come in)
Explain to the two Na transport mechanisms used in the DCT and CT
Electrically conductive Na channel (similar to proximal tubule), Na entry down it’s concentration gradient (due to NAKATPase pump on basal side), in both dct and ct
na-cl co-transporter (present only in dct, different from nk2cl) electroneutral transport
What are diuretics that target the dct and ct?
amiloride, triamterene - block na channels
thiazide - inhibit na-cl cotransporters
loop diuretices are 10 fold more efficient
What are the driving forces for potassium excretion?
high intracellular concentration due to nak activity
lumen-negative transepithlial voltage
Is K secreted from the epithelial cell into just the lumen?
no, some also goes to the renal interstitium
Does increased or decreased Na reabsorption result in higher lumen-negative transepithelial voltage?
Decreased (due to diuretics)
HAVE SOMEONE EXPLAIN THIS CARD
Effects of Diuretics On K Balance
- Loop diuretics increase flow and Na output (greater membrane depolarization) into distal tubule, and therefore, increase K secretion
- Thiazides block electro-neutral Na transport without affecting membrane depolarization
- Amilorides prevent membrane depolarization; no increase in K secretion
Where does aldosterone do it’s actions?
DCT and CD
What are the effects of aldosterone?
Increase Na reabsorption and increase K secretion
What changes occur in the cell upon aldosterone administration?
increased in open na channels and increase in nacl cotransporters, increased reabsorption of na
increased synth of nka and increased basolateral surface area
increased atp synthesis
increased activity of apical membrane K channel
What is addison’s disease?
complete absence of aldosterone, increased urinary excretion of nacl, leaving about 8% to be reabsorbed because not completely dependent on aldosterone
what is conn’s syndrome?
aldosterone secreting tumor, increased Na reabsorption and K secretion, leads to hypokalemia and hypernatremia and htn
what is liddle’s syndrome?
pseduo hyperaldosterinism
Where does final acidification of the urine occur?
in the dct and cd
How does acidification of the urine occur in the dct and cd?
bicarbonate is reabsorbed and h is secreted
what cell types are involved in proton secretion in the urine?
principal cells (na reabsorption and k secretion) intercalated cells (proton secretion)
what is required to pump protons into the lumen
atpase
under alkalosis, bicarbonate secretion is achieved by what two types of intercalated cells?
alpha-cells - proton channel in the luminal membrane
beta-cells -bicarbonate channel in the luminal membrane
what hormone is necessary for calcium reabsorption in the distal nephron?
parathyroid hormone
