Loop of Henle, DT, and CD (Rao) Flashcards Preview

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Flashcards in Loop of Henle, DT, and CD (Rao) Deck (40):

What is the function of the DT?

to form urine w/ variable osmolarity


According to physiologist, where does the DT start?

at loop of henle, contains distal convoluted tubule, and collecting duct


What maintains the pH of urine from 4.5-8?

PO4 and H+


What is the loop of Henle thin?

lack of mitochondria or few of them since no active transport occurs here


What happens to the ISF environment of the thin descending LOH?

1. hyperosomotic to plasma
2. increases progressively b/w cortex and medulla
3. reaches max of 1200 mOsm


What is the function of the thin descending LOH?

1. concentrates tubular fluid
2. no active transepithelial transport
3.highly permeable to water - due to lots of AQP
4. minimal permeability to NaCl and Urea
5. osmotic gradient is the driving forces


What are the transport properties of the thin ascending LOH?

1. extremely water IMPERMEABLE
2. Impermeable to urea
3.permeable to NaCl -- strong NaCl reabsorption


What happens to the osmolarity in the thin ascending LOH?

it drops b/c of NaCl diffusion and impermeable to tubular fluid


What is the structure of the Thick Ascending LOH?

1. b/w medulla and cortex
2. thick epithelial cells w/ many mitochondria


What are the transport properties of the thick ascending LOH?

1. serves in STRONG reabsorption of NaCl
2. impermeable to water


What transporters are found at the thick ascending LOH?

1. NaK2Cl - electroneutral, apical side
2. NaKATPase at basolateral side
3. Cl channel - BL side
4. K/Cl cotransporter - BL side
5. Apical K Channel


What can inhibit the NK2Cl channel?

furosemide, bumetanide -- have a high affinity for Cl site on channel --> block NaCl reabsoprtion --> leads to diuresis


What is diuresis?

increased water loss in urine


How does one form a collecting duct?

joining 6-8 DT together


What do CDs do in the medulla?

join to form duct of Bellini


What happens to the tubular fluid at the DT and CD?

1. Na is actively reabsorbed
2. K is secreted
3. Na reabsorption is greater than K secretion so Cl is reabsorbed


how much filtrate is received at the DT and CD?

10% of filtered load of water, <10% filtered load of NaCl and KCl, and 50% urea


What is the net result of DT and CD?

dilution of tubular fluid


What are the 2 distinct transport mechanism at DT and CD?

1. electrically conductive Na channels (in both)
2. NaCl co-transporter (only in DT)


What does amiloride and tramterene do?

block Na channels at DT and CD
- amiloride prevents membrane depolarization and has no increase on K secretion


What do thiazide diuretics do?

inhibit NaCl cotransporters in DT --> doesn't affect membrane potential though


Which diuretic is more efficient?

loop --> increase K secretion


What happens to the lumen voltage when all the Na is reabsorbed?

more negative so membrane if depolarized and K is secreted


What is the driving fore for K secretion?

1. high IC [K] caused by NKA
2. lumen-negative transepithelial voltage


What effect does fluid flow have on K secretion?

if increased by diuretics --> increased K secretion


How does aldosterone function?

- acts only on DCT and CD
- increases Na reabsorption
- increases K secretion


What is the MOA of aldosterone?

enters cell and binds to cytoplasmic and nuclear receptors to induce gene expression


What effect does aldosterone have on the cell?

1. increases Na channels (apical)
2. increases NaCl cotransporter
3. increases NKA
4. increased basolateral surface ara
5. increase synthesis of Krebs Cycle enzymes to make ATP
6. increase activity of apical K channel


What is Addison's disease?

- complete absence of aldosterone
- increased urinary excretion of NaCl


What is Conn's syndrome?

- aldosterone secreting tumor
- increased Na reabsorption and K secretion
- hypokalemia, hypernatremia, HTN


What is Liddle's Syndrome?

pseudo hyperaldosteronism


What do principal cells do?

Na reabsoprtion and K secretion


What do intercalated cells do?

alpha cells - proton channel in luminal membrane
beta cells - bicarb channel in luminal membrane


Why is proton secretion different in DT/CD than PT?

- H+ secreted against electrochemical gradient so needs high E active transport and epithelium is impermeant to diffusion


What transporter is used for H+ secretion?

Proton activated ATPase -- ATP hydrolysis drives transport of H from cell to lumen via apical channel


What drives HCO3- diffusion from cell to renal ISF?

increase in IC [HCO3-], diffused via HCO3-/Cl exchanger


What happens during a high acidosis condition?

cells express a new H transporter --> H/K ATPase or proton pump


What happens during Alkalosis?

H-ATPase and HCO3-/Cl exchange channels switch directionality


How is the directional switch of the channels activated?

by alpha and beta intercalated cells


What stimulates distal nephron Ca reabsorption?