Loop of Henle, DT, and CD (Rao)

Question 1

What is the function of the DT?

Answer 1

to form urine w/ variable osmolarity

Question 2

According to physiologist, where does the DT start?

Answer 2

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

Question 3

What maintains the pH of urine from 4.5-8?

Answer 3

PO4 and H+

Question 4

What is the loop of Henle thin?

Answer 4

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

Question 5

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

Answer 5

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

Question 6

What is the function of the thin descending LOH?

Answer 6

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

Question 7

What are the transport properties of the thin ascending LOH?

Answer 7

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

Question 8

What happens to the osmolarity in the thin ascending LOH?

Answer 8

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

Question 9

What is the structure of the Thick Ascending LOH?

Answer 9

1. b/w medulla and cortex

2. thick epithelial cells w/ many mitochondria

Question 10

What are the transport properties of the thick ascending LOH?

Answer 10

1. serves in STRONG reabsorption of NaCl

2. impermeable to water

Question 11

What transporters are found at the thick ascending LOH?

Answer 11

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

Question 12

What can inhibit the NK2Cl channel?

Answer 12

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

Question 13

What is diuresis?

Answer 13

increased water loss in urine

Question 14

How does one form a collecting duct?

Answer 14

joining 6-8 DT together

Question 15

What do CDs do in the medulla?

Answer 15

join to form duct of Bellini

Question 16

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

Answer 16

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

Question 17

how much filtrate is received at the DT and CD?

Answer 17

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

Question 18

What is the net result of DT and CD?

Answer 18

dilution of tubular fluid

Question 19

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

Answer 19

1. electrically conductive Na channels (in both)

2. NaCl co-transporter (only in DT)

Question 20

What does amiloride and tramterene do?

Answer 20

block Na channels at DT and CD

- amiloride prevents membrane depolarization and has no increase on K secretion

Question 21

What do thiazide diuretics do?

Answer 21

inhibit NaCl cotransporters in DT –> doesn’t affect membrane potential though

Question 22

Which diuretic is more efficient?

Answer 22

loop –> increase K secretion

Question 23

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

Answer 23

more negative so membrane if depolarized and K is secreted

Question 24

What is the driving fore for K secretion?

Answer 24

1. high IC [K] caused by NKA

2. lumen-negative transepithelial voltage

Question 25

What effect does fluid flow have on K secretion?

Answer 25

if increased by diuretics –> increased K secretion

Question 26

How does aldosterone function?

Answer 26

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

Question 27

What is the MOA of aldosterone?

Answer 27

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

Question 28

What effect does aldosterone have on the cell?

Answer 28

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

Question 29

What is Addison’s disease?

Answer 29

• complete absence of aldosterone

- increased urinary excretion of NaCl

Question 30

What is Conn’s syndrome?

Answer 30

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

Question 31

What is Liddle’s Syndrome?

Answer 31

pseudo hyperaldosteronism

Question 32

What do principal cells do?

Answer 32

Na reabsoprtion and K secretion

Question 33

What do intercalated cells do?

Answer 33

alpha cells - proton channel in luminal membrane

beta cells - bicarb channel in luminal membrane

Question 34

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

Answer 34

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

Question 35

What transporter is used for H+ secretion?

Answer 35

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

Question 36

What drives HCO3- diffusion from cell to renal ISF?

Answer 36

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

Question 37

What happens during a high acidosis condition?

Answer 37

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

Question 38

What happens during Alkalosis?

Answer 38

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

Question 39

How is the directional switch of the channels activated?

Answer 39

by alpha and beta intercalated cells

Question 40

What stimulates distal nephron Ca reabsorption?

Answer 40

PTH