Loop of Henle, DT, and CD (Rao) Flashcards
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?
- hyperosomotic to plasma
- increases progressively b/w cortex and medulla
- reaches max of 1200 mOsm
What is the function of the thin descending LOH?
- concentrates tubular fluid
- no active transepithelial transport
- highly permeable to water - due to lots of AQP
- minimal permeability to NaCl and Urea
- osmotic gradient is the driving forces
What are the transport properties of the thin ascending LOH?
- extremely water IMPERMEABLE
- Impermeable to urea
- 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?
- b/w medulla and cortex
2. thick epithelial cells w/ many mitochondria
What are the transport properties of the thick ascending LOH?
- serves in STRONG reabsorption of NaCl
2. impermeable to water
What transporters are found at the thick ascending LOH?
- NaK2Cl - electroneutral, apical side
- NaKATPase at basolateral side
- Cl channel - BL side
- K/Cl cotransporter - BL side
- 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?
- Na is actively reabsorbed
- K is secreted
- 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?
- 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?
- 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?
- increases Na channels (apical)
- increases NaCl cotransporter
- increases NKA
- increased basolateral surface ara
- increase synthesis of Krebs Cycle enzymes to make ATP
- 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?
PTH
