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Block 2; Week 4 > Keef 4 > Flashcards

Keef 4 Flashcards

1
Q

What is the concept of transport maximum?

A

the highest rate @ which a substance can be transferred back & forth b/w the tubular lumen & the interstitial fluid.

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2
Q

A large amount of glucose is reabsorbed in the PCT…b/c remember: it’s not normal to have glucose in your urine! How is glucose transported?

A

Glucose is transferred from the tubular lumen into the epithelial cell by a symport w/ sodium (driven by the sodium gradient).
Glucose goes into the peritubular space by a glucose channel.
The sodium gradient is maintained w/ a sodium potassium pump.

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3
Q

What is the equation for calculating the reabsorption rate (Tx)?

A 
Tx = Filtered Load - Excretion Rate
Reabsorption = Filtration - Excretion
Tx = (GFR X Px) - (Ux X V)
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4
Q

How does the transport maximum relate to the reabsorption rate, Tx?

A

Tx will max out at some point. At this point you will start getting excretion in the urine, Ux. Once the Tx maxes out it is the transport maximum.

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5
Q

If you are below the Tm, what happens to the glucose in the plasma?

A

20% of it is filtered.

In the PCT…all of it goes back thru to the blood.

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6
Q

If you are above the Tm, what happens to the glucose in the plasma?

A

20% of it is filtered.
In the PCT…much of it goes back into the blood.
Some of it is disposed of in the urine.

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7
Q

T/F As the plasma conc’n of glucose increases, the filtration rate of glucose will increase until you reach a plateau that represents Tm.

A

False. The filtration rate will increase without limit as the plasma conc’n increases.

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8
Q

T/F As the plasma conc’n of glucose increases, the reabsorption rate of glucose will increase until you reach a plateau that represents Tm.

A

True.

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9
Q

What is splay?

A

It explains that you start seeing a little bit of urine formation even before you reach your Tm.

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10
Q

T/F As soon as your reabsorption rate reaches Tm…you will start excreting urine w/ glucose.

A

False. There is a little bit of urine formation before you reach Tm: it is called splay.

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11
Q

What class of inhibitors has emerged as an anti diabetic drug?

A

Sodium-glucose co transporter-2 (SGLT2) inhibitors.
Idea is w/ diabetes…you really want to excrete more glucose b/c there is too much in your plasma. So this keeps the glucose from being reabsorbed in the PCT. It blocks the transporter.

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12
Q

What is phlorizin?

A

A non-selective blocker. It will block the sodium glucose transporters in the PCT, causing glucose excretion before reaching Tm.

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13
Q

The excretion of what substance looks similar to the excretion of glucose in the presence of phlorizin?

A

Inulin.
Remember: inulin is not secreted or reabsorbed. The greater the plasma conc’n of inulin–the greater the filtration/excretion.
Glucose is not secreted. It is only reabsorbed. When this is blocked by phlorizin…it acts like inulin.

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14
Q

Why is it that ppl w/ Diabetes Mellitus experience polyuria?

A

B/c they have increased plasma conc’n of glucose.
This means that more glucose will be reabsorbed in the PCT & w/ the transporter used…more sodium will be reabsorbed.
B/c there is less sodium left in the filtrate, the macula densa cells in the DCT will think–OH no! We have low NaCl–we must have low GFR!
Afferent arteriole dilation.
JG cells release renin, Ang II contracts the efferent arteriole.
GFR increases
urine output increases–polyuria

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15
Q

What is the best measurement of GFR?

A

The clearance of inulin.

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16
Q

If the clearance of a substance is less than that of inulin…what does this indicate?

A

Perhaps this substance is reabsorbed, giving it a lower clearance rate. Or maybe the substance is too large to make it thru the pores for filtration.

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17
Q

If the clearance of a substance is greater than that of inulin, what does this indicate?

A

This substance is secreted.

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18
Q

If you were looking at a graph w/ an x-axis: plasma conc’n of a substance & a y-axis: clearance:
What is the slope like of inulin?

A

It is a flat, horizontal line.
This means that its clearance is constant regardless of plasma conc’n. Whatever is filtered is excreted/cleared.
Clearance of Inulin=125 ml/min=GFR.

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19
Q

Probenecid is an endogenous substance/drug that is reabsorbed/secreted by the PCT/DCT?

A

Probenecid is a drug that is secreted by PCT.

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20
Q

How & where is PAH secreted?

A

It is secreted in the late PCT. It uses an antiport & is replaced by an anion. Once it gets into the epithelial cell it uses a similar transporter to get into the lumen (exchanged w/ an anion).

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21
Q

How does transport maximum relate to secretion?

A

This is the maximum amount of the substance that can be secreted into the proximal tubule lumen. After you exceed this conc’n of a substance in the plasma…it will not be totally cleared from the plasma.

22
Q

What is the equation for calculating the secretion rate?

A 
Secretion Rate (Tx) = Excretion Rate - Filtered Load
Tx = (Ux X V) - (GFR X Px)
23
Q

What will happen to the slope of your excretion rate line when you hit the Tm of the secretion rate line?

A

As soon as you have a conc’n of PAH in your plasma…you get an excretion rate.
Once you hit your Tm for secretion…your excretion rate slope will decrease to the same slope as your filtration rate.

24
Q

What happens to PAH before you hit the Tm of secretion?

A

100% of the plasma is cleared of the PAH.

25
Q

What happens to the PAH after you hit the Tm of the secretion?

A

Not 100% of the plasma is cleared of the PAH. There is still PAH in the plasma.

26
Q

Which has the higher clearance rate of PAH & the higher excretion rate of PAH?
Before you reach the Tm of PAH secretion.
After you reach the Tm of PAH secretion.

A 
Before you reach Tm: 
Higher clearance rate of PAH
Lower Excretion Rate of PAH
After you reach Tm:
Lower clearance rate of PAH
Higher Excretion Rate of PAH
27
Q

Is the clearance of PAH lower or higher than the clearance of inulin?

A

It is higher. This is b/c it experiences secretion.

28
Q

T/F The renal plasma flow is the same as the renal blood flow.

A

False. Renal blood flow includes RBCs etc.

29
Q

Why does it make sense that the clearance of PAH is about 5X that of inulin?

A

Because inulin approximates GFR. PAH clearance approximates RPF b/c it has to do w/ secretion & clearance from the plasma.

30
Q

How can you estimate the filtration fraction?

A

Filtration Fraction = GFR/RPF = Cinulin/CPAH=20%

31
Q

To summarize: Equations
What is the Tm for reabsorption?
What is the Tm for secretion?

A

Tm for reabsorption:
Tx=Filtered Load - Excretion Rate
Tm for secretion:
Tx = Excretion Rate - Filtered Load

32
Q

What is gout?

A

a painful condition caused by the buildup of uric acid crystals in the tissues & joints

33
Q

What are 2 problems that patients w/ gout have in terms of dealing w/ their uric acid crystals?

A

One is increased uric acid production

Another is decreased uric acid excretion (maybe increased reabsorption or decreased secretion).

34
Q

T/F Uric acid could be used to determine both reabsorption & secretion rates via the Tm equations b/c it exhibits both reabsorption & secretion.

A

False.

B/c it exhibits both, you can’t isolate either & it can’t be used at all to determine these rates.

35
Q

For a normal person…what happens to their uric acid from filtration to excretion?

A 
After filtration
99% of the filtrate-->reabsorbed.
49% is secreted back.
40% is reabsorbed back.
10% is left & is excreted in a normal person.
36
Q

Which of these could explain why a drug causes an increase in uric acid excretion?
An increase in the formation of uric acid.
An increase in the transport maximum for uric acid reabsorption.

A

An increase in the formation of uric acid could explain the effects of this drug.
An increase in the ability to reabsorb uric acid would NOT explain increased excretion of it.

37
Q

About what percentage of urea is reabsorbed?

A

~60%

38
Q

What are 4 factors that affect the passive reabsorption of urea?

A
  1. Tubular area
  2. Urea permeability
  3. Conc’n gradient
  4. tubular flow
39
Q

What happens to reabsorption as tubular flow increases?

A

Reabsorption decreases.

40
Q

Explain how passive reabsorption is dependent on the conc’n gradient of urea.

A

As sodium is reabsorbed w/ the use of energy…water naturally gets reabsorbed too. The absence of water…causes an increase in the conc’n gradient of chloride & of urea. By this mechanism a conc’n gradient is created & chloride & urea are both passively reabsorbed.

41
Q

T/F The clearance of urea, like inulin, is dependent upon tubular flow.

A

False.
Inulin isn’t dependent on tubular flow.
The clearance of urea is dependent on tubular flow–>the higher this is; the higher the clearance b/c the less reabsorption.

42
Q 
If you have a person who drinks a ton of water...what happens to:
V?
Uurea?
Curea?
%Urea Reabsorbed?
A

V–>increases
Uurea–>decreases
Curea–>increases
%Urea Reabsorbed–>decreases

43
Q 
If you have a person who has been thirsty for 12 hours & NOT drinking...what happens to:
V?
Uurea?
Curea?
%Urea Reabsorbed?
A

V–>decreases
Uurea–>increases
Curea–>decreases
%Urea Reabsorbed–>increases

44
Q

Does the following favor reabsorption or secretion or neither?
Lowering the pH?
Raising the pH?

A

Lowering the pH: provides more H+s & favors reabsorption

Raising the pH: provides fewer H+s & favors secretion.

45
Q

How would you treat a man who presented to the ER after having consumed large amounts of phenobarbitol?

A

Bicarbonate…want to favor excretion

Osmotic Diuretic like mannitol…

46
Q

What is the fractional excretion of Na?

A

less than 1%

47
Q

What is the fractional excretion of inulin?

A

100%

48
Q

What is the fractional excretion of creatinine?

A

120%

49
Q

What is the fractional excretion of glucose?

A

0%

50
Q

What is the fractional excretion of PAH?

A

500%

51
Q

What is the fractional excretion of Uric Acid?

A

10%

52
Q

What is the fractional excretion of potassium?

A

10-20%

Block 2; Week 4 (6 decks)

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