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

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Flashcards in Loop of Henle, DT, and CD (Rao) Deck (40):
1

What is the function of the DT?

to form urine w/ variable osmolarity

2

According to physiologist, where does the DT start?

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

3

What maintains the pH of urine from 4.5-8?

PO4 and H+

4

What is the loop of Henle thin?

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

5

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

6

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

7

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

8

What happens to the osmolarity in the thin ascending LOH?

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

9

What is the structure of the Thick Ascending LOH?

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

10

What are the transport properties of the thick ascending LOH?

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

11

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

12

What can inhibit the NK2Cl channel?

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

13

What is diuresis?

increased water loss in urine

14

How does one form a collecting duct?

joining 6-8 DT together

15

What do CDs do in the medulla?

join to form duct of Bellini

16

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

17

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

18

What is the net result of DT and CD?

dilution of tubular fluid

19

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)

20

What does amiloride and tramterene do?

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

21

What do thiazide diuretics do?

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

22

Which diuretic is more efficient?

loop --> increase K secretion

23

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

more negative so membrane if depolarized and K is secreted

24

What is the driving fore for K secretion?

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

25

What effect does fluid flow have on K secretion?

if increased by diuretics --> increased K secretion

26

How does aldosterone function?

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

27

What is the MOA of aldosterone?

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

28

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

29

What is Addison's disease?

- complete absence of aldosterone
- increased urinary excretion of NaCl

30

What is Conn's syndrome?

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

31

What is Liddle's Syndrome?

pseudo hyperaldosteronism

32

What do principal cells do?

Na reabsoprtion and K secretion

33

What do intercalated cells do?

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

34

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

35

What transporter is used for H+ secretion?

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

36

What drives HCO3- diffusion from cell to renal ISF?

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

37

What happens during a high acidosis condition?

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

38

What happens during Alkalosis?

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

39

How is the directional switch of the channels activated?

by alpha and beta intercalated cells

40

What stimulates distal nephron Ca reabsorption?

PTH