Loop of Henle, Distule Tubule, and Collecting Duct Flashcards Preview

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Flashcards in Loop of Henle, Distule Tubule, and Collecting Duct Deck (49)

Where do most regulatory mechanisms target urine formation?

distal tubular segment


Is reabsorption in the proximal tubule iso-osmotic?



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?



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)



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



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