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CRAAB 7 > Katz: Loop of Henle, Distal Tubule and Cortical Collecting Duct > Flashcards

Katz: Loop of Henle, Distal Tubule and Cortical Collecting Duct Flashcards

1
Q

What are juxtamedullary nephrons?

A

Nephrons that send their loops into the medulla and consist of the descending limb and the thin and THICK ascending limb

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2
Q

What is the difference between the descending limb of the loop of Henle and the ascending limb?

A

Descending limb- NO net solute transport, just WATER

Ascending limb- no permeability to water, just SOLUTE

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3
Q

What happens to the concentration of solute as it passes through the loop of henle?

A

Enters from the proximal tubule at 300 mOsms.

At the lowest point it reaches 1400 mOsms.

Enters DCT at 100 mOsms.

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4
Q

What type of cell if found in the TAL?

A

Big cuboidal epithelial cell

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5
Q

What is the primary transporter in the TAL?

A

Na/K/2CL co transporter

Moves Na DOWN its gradient while moving K and 2Cl UP the gradient.

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6
Q

Why is the osmolality of the luminal fluid in the TAL only 100 mOsms?

A

TAL has NO permeability to water. Solutes are transported out while water stays in the tube resulting in a hypo-osmolar solution.

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7
Q

Describe how Na,Cl and K are ultimately reabsorbed in the peritubular capillaries from the TAL?

A
  1. Na/K/2Cl co transporter brings them from the lumen into the cuboidal cell of the TAL.
  2. Na/K ATPase antiporter allows Na to be reabsorbed.
  3. Cl diffuses through a channel and is reabsorbed.
  4. K/Cl symporter allows K and Cl to be reabsorbed.
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8
Q

What percent of Na/Cl are reabsorbed in the peritubular capillaries?

A

20% of the filtered load

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9
Q

What does the export of K into the lumen in the TAL do?

A

Generates a + lumen that pushes ions like Na, Ca and Mg through tight junctions.

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10
Q

What is Bartter’s syndrome? What does it cause?

A

Loss of fxn of any of the transport components in the TAL

Salt wasting–> HYPOVOLEMIA
Na/K/2Cl transporters don’t work, leading to the excretion of NaCl and water. This causes the pt to pee a lot, get thirsty and become HYPOvolemic.

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11
Q

What does a loop diuretic do?

A

Blocks the Na/K/2Cl co transporter in the TAL

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12
Q

What are examples of loop diuretics and what are the good at treating?

A

Furosemide (lasix)

EDEMA

Most powerful!

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13
Q

Where does luminal fluid move after the loop of Henle? Is it permeable to water?

A

Early distal tubule

IMPERMEABLE to water

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14
Q

What is the key element in the early distal tubule?

A

NaCl symporter

Moves Na down it’s gradent while moving Cl up it’s gradient.

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15
Q

What percent of filtered NaCl is reabsorbed here?

A

5%

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16
Q

What is Gitelman’s syndrome?

A

Loss of function of the NaCl symporter that leads to SALT wasting.

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17
Q

What drug blocks the NaCl symporter in the early distal tubule?

A

Thiazide diuretics (HCTZ)

Increase Na, Cl and Water excretion

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18
Q

Thiazide diuretics are useful in treating what conditions? How do they compare to loop diuretics?

A

HTN- decrease fluid volume> decrease in BP

Only lose 5% vs. 20% so they are MILDER

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19
Q

Where is Na reabsorbed in the nephron?

A
  1. PCT- 65%
  2. TAL- 20%
  3. DCT- 5%
  4. CCD- 0-4.9%
  5. MCD- 5%
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20
Q

What causes variable reabsorption of Na in the CCD?

A

ALDOSTERONE sensitive PRINCIPLE CELLS in the DCT and CCD

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21
Q

What is the FENa when 4.9% of the filtered lad is reabsorbed in the CCD?

A

It’s possible to reabsorb 99.9% of total filtered Na so FENa is .1% and Na excretion is only 25 mM/day.

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22
Q

What is the FENa when 0% of the filtered load is reabsorbed in the CCD?

A

You only reabsorb 95% of the total filtered Na so FENa is 5% and Na excretion is 1250 mM/d.

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23
Q

What does the variable abosrption rate allow for in the CCD?

A

It allows for Na BALANCE across a wide range of intakes (25- 1,250 mM/d)

24
Q

What is FENa?

A

Fraction Excreted Na

25
Q

What causes a small Na?

A

Hemorrhage–> lose Na

26
Q

What is aldosterone and what effects does it have on the late distal tubule and CCD?

A

A steroid hormone that causes increased TRXN of genes leading to INCREASED expression of luminal Na and K channels as well as basolateral channels and the Na/K pump that leads to INCREASED saving of NaCl.

27
Q

What happens when aldosterone targets it’s receptor?

A 
Aldosterone enters cytosol>
Aldosterone receptor complex translocates to the nucleus>
binds specific SREs (steroid response elements)>
Increased trxn, trln and INSERTION of:
1.luminal Na (ENaC) 
2. K channels
3. Basolateral Na/K pumps
>
Reabosrb MORE Na
28
Q

What happens to FENa when more Na is absorbed?

A

FENa moves towards .1%

29
Q

What stimulates aldosterone secretion? Where is it secreted from?

A

LOW Na or HIGH K>

increased aldosterone secretion from adrenal cortical cells (zona glomerulosa)

30
Q

What leads to an increase in renin?

A

Low Na diet
hypovolemia (low NaCl/H20)
Low BP> BR reflex> Increased SNS activity

31
Q

How does low Na lead to an increase in aldosterone?

A 
Low Na>
increases renin>
Coverts Ang to ANG I>
ACE converts Ang I to Ang II>
Aldosterone
32
Q

What is the primary secretion stimulus for aldosterone?

33
Q

What are secondary aldosterone stimuli?

A

Decrease in plasma Na
Increase in plasma K
Increase in ACTH

34
Q

What are aldosterones actions?

A

Increased trxn, trln, insertion of the following channels in PRINCIPLE CELLS:

  1. Epithelial Na channels (ENaC) and K channels (ROMK)
  2. Basolateral Na/K pumps and K channels
35
Q

What are ROMK channels?

A

Aldosterone sensitive renal outer medullary K channel

36
Q

How does aldosterone cause Na to be reabsorbed? What happens to K?

A

Aldosterone> increased ENaC/K channels>
brings Na into cell>
Na/K ATPase allows Na to move into the ISF>
reabsorbed into the peritubular capillaries

K is secreted into the lumen and the ISF.

37
Q

What is Type I pseudo-hypoaldosteronism?

A

Loss of function of luminal epithelial Na channels (ENac) in principle cells or collecting duct cells. This leads to SALT WASTING.

38
Q

What is Liddle’s syndrome?

A

Gain in fuctionof the ENaC d/t inefficient removal from cell surface (can’t get rid of ENaC)> always reabsorb Na> HTN, Edema, hypevolemia

39
Q

What is salt sensitive HTN?

A

Liddle syndroome

Can’t get rid of ENaC channels so you over reabsorb water/Na.

40
Q

What does Amiloride do?

A

Blocks ENaC channels.

41
Q

What leads to an increase in renin?

A
  1. Low Na diet/low body NaCL> sensed at JGA via load or delivery signal mediated by macula densa cells
  2. Hypovolemia> aff arteriolar baroreceptor
  3. Increased SNS activity
  4. Low circulating Ang II
42
Q

What secretes renin?

A

Granular cells located in the JGA located in the aff arterioles

43
Q

What are the many actions of Ang II?

A
  1. Aldosterone secretion
  2. VASOCONSTRCITOR
  3. Na/H exchange to reabsorb more Na
  4. Vasopressin> reabsorb more water
  5. Increases SNS activity by Ang II binding to cicumventricular organs
44
Q

What happens when ang II is too high for a situation?

A

GROWTH:
LV hypertrophy
Glomerular sclerosis (collapse of glomerular capillaries> decreased GFR)

45
Q

What are the three mechanisms used to maintain Na balance?

A
  1. GFR
  2. Principal cells and aldosterone
  3. Proximal Na/H antiporter activity
46
Q

How does GFR respond to high Na?

A

Hi Na intake> GFR/filtered load of Na increase> Increase Na EXCRETION.

47
Q

How does aldosterone respond to high Na?

A

Hi Na intake> aldosterone levels fall> Na reabsorption falls> Na EXCRETION increases

48
Q

How does the proximal Na/H antiporter activity respond to high Na intake?

A 
Hi Na intake>
renin, angII, NE fall>
proximal Na/H antiport activity decreases>
Na reabsorption falls>
Na excretion increases
49
Q

How do ANP and BNP help to maintain Na balance?

A

Both cause increased Na excretion

High salt intake>
distension of atria/increased EDV>
ANP/BNP secretion increase>
aff arteriole dilation/inhibition of renin secretion/direct tubular actions>
GFR/filtered load of Na increase>
Na reabsorption falls>
Na excretion increases
50
Q

Where do ANP and BNP come from?

A

ANP- atria

BNP- ventricles

51
Q

How do you calculate RPF?

A

Flow in Aff arteriole x plasma Na

52
Q

How do you calculate the filtered load of Na?

A

GFR x plasma Na

53
Q

How do you calculate the concentration of Na in the eff plasma flow?

A

Eff flow x conc of Na

54
Q

How do you calculate the Na reabsorptive rate?

A

Filtered load of Na- Na excretion rate

55
Q

How do you calculate the Na excretion rate?

A

Urine flow x urine Na concentration

56
Q

How do you calculate FENa?

A

Na excreted/ Total filtered load of Na

57
Q

How do you calculate Na clearance?

A

Excretion rate/ concentration of Na in the plasma

CRAAB 7 (4 decks)

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