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FHB > Renal > Flashcards

Renal Flashcards

0
Q

What is a typical filtration fraction in the kidney?

What is a typical GFR?

A

20%

RPF = 625
625 * 20% = 125 mL/min

125 mL/min = GFR

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1
Q

What is renal plasma flow (RPF)?

A

RBF * (1-HCT) = RPF = 625 mL/min

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2
Q

How do afferent & efferent resistances affect GFR?

A

^ Afferent –> decreased GFR
^ Efferent –> increased GFR

Afferents are innervated 10x more than efferents.

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3
Q

What pressures can the kidney autoregulate between?

A

40-200 mmHg

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4
Q

What is inulin?

A

It is a molecule that is completely filtered, but not reabsorbed or secreted in the kidney.

It can be used to measure GFR.

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5
Q

What is PAH?

A

Its clearance is used a measurement of effective Renal Plasma Flow. 90% of it is cleared from the blood in one pass, thus:

1.1* ClearancePAH = RPF

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6
Q

How do BUN & Creatinine blood concentrations compare?

Which is more variable?

A 
BUN = 10 mg/dL
Creatinine = 1 mg/dL

BUN is more variable because high protein meals will affect it.

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7
Q

What is the formula for renal clearance?

A

C = UV/P

U = urine concentration
V = urine flow
P = plasma concentration
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8
Q

Where are proteins reabsorbed?

What percent of proteins are reabsorbed?

A

The proximal tubule

100% of proteins are reabsorbed in a healthy kidney.

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9
Q

What is solvent drag?

A

Salt is actively reabsorbed, and water follows into the interstitial space. The hydrostatic pressure created by this water pushes it into the capillary blood, carrying ions and molecules with it.

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10
Q

How much water is reabsorbed by the kidneys?

A

99.2%

GFR = 180 L/day but only 1 mL/min of urine is excreted each day.

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11
Q

What powers the renal reabsorption of glucose and amino acids?
How much are reabsorbed?

A

Na+-dependent secondary active transporters

They are 100% reabsorbed

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12
Q

What is the renal plasma threshold for glucose?

At what load are all glucose transporters saturated?

A

RPT = 200 mg/dL –> glucose will start to be seen in urine

All are saturated at 375 mg/dL. Above this point, excretion parallels filtration.

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13
Q

How are large proteins reabsorbed in the kidney?

Smaller peptides?

A

Large proteins are reabsorbed by pinocytosis in the proximal tubule. Smaller proteins/peptides are broken down into their constituent amino acids, which are then reabsorbed.

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14
Q

How does the pH of the renal tubule affect reabsorption of weak acids/bases?

A

They are reabsorbed more easily when uncharged, so acidification favors weak acid reabsorption, and akalination favors weak base reabsorption.

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15
Q

How much urea gets excreted?

A

50% of the filtered load

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16
Q

Where is sodium reabsorbed in the nephron?

A

99.9% total reabsorption.

65% proximal tubule
25% loop of Henle (ascending)
10% distal nephron

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17
Q

Why is bicarbonate preferentially absorbed in the first half of the proximal tubule?

A

The presence of carbonic anhydrase.

HCO3- is 80% complete by the end of the proximal tubule, Cl- is 60% complete.

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18
Q

What is reabsorbed paracellularly?

A

Water and chloride ions

19
Q

What is the osmolarity of plasma?

A

300 mosm/L

20
Q

What is the permeability of the thin descending limb of the loop of Henle?
The thin ascending limb?

A

Descending = permeable to water but not salts

Ascending = permeable to salts but not water

21
Q

How are salts reabsorbed in the thick ascending limb of the loop of Henle?

A

Na-K.2Cl symporter

This is the target of lasix/furosemide (loop diuretic)

22
Q

What is the water & salt permeability in the distal convoluted tubule?
What diuretics work here?

A

The DCT is water impermeable but contains ENaCs & the Na-Cl symporter (NCC).

The NCC is the target for thiazide diuretics.

23
Q

Describe reabsorption in the cortical collecting duct.

A

Sodium reabsorption is via ENaCs, which are controlled by aldosterone.

Water absorption is via aquaporins, which are controlled by ADH.

24
Q

How is the medullary osmolarity gradient affected by hydration status?

A

During diuresis, the gradient is low and urine is dilute.

During antidiuresis, the gradient is strong and urine is concentrated.

25
Q

Where does lasix/furosemide affect the nephron?

A

It blocks the NKCC pump in the thick ascending limb.

26
Q

Where do K+ sparing diuretics act on the nephron?

A

They block the Na+/K+ ATPase or block aldosterone’s effect on it, in the collecting duct.

27
Q

What does Angiotensin II do?

A

Causes vasoconstriction, release of ADH from pituitary, and release of aldosterone from the adrenals.

28
Q

How do macula densa cells respond to increased or decreased NaCl?

A

Increased NaCl –> they swell –> no renin released from granular cells

Decreased NaCl –> they shrink –> renin release from granular cells

29
Q

What is glomerulotubular balance?

A

Sodium reabsorption by the proximal tubule is a constant 67%, thus when GFR decreases, absolute reabsorption decreases but relative reabsorption goes up.

30
Q

What is tubuloglomerular feedback?

A

It is the regulation of the single nephron GFR.

JG apparatus senses increased distal tubular NaCl (flow) –>
vasoconstrictor release –> afferent arterioles constricted.

Vasodilators can also be released. This is the basis for autoregulation of the kidney as a whole.

31
Q

What facilitates renal afferent arteriole relaxation?

A

Prostaglandins

32
Q

What does stimulation of the renal nerve cause?

A

Renin secretion
Na+ reabsorption
Arteriolar constriction –> decreased GFR

33
Q

What are the two stimuli for ADH release and where are their receptors?

A
  1. Increased plasma osmolarity sensed by osmoreceptors in hypothalamus.
  2. Decreased plasma volume sensed by cardiac atrial receptors.
34
Q

Is sweat hyperosmotic or hyposmotic to plasma?

A

Hyposmotic, so the ECF that remains is hyperosmotic and can draw water out of cells –> dangerous.

35
Q

How does insulin affect K+ levels?

Exercise?

A

Insulin stimulates the Na+/K+ pump, leading to uptake of K+.

Exercise causes muscle cell release of K+ but other cells help to maintain EC K+ levels.

36
Q

What is the normal range of plasma K+?

A

3.3-5.1 meq/L

37
Q

What percent of K+ is normally reabsorbed?

A

85%

Allows wiggle room.

38
Q

Where is K+ secreted?

A

Distal tubule and cortical collecting duct, via ROMK channel and BK channel regulation.

It is reabsorbed everywhere else.

39
Q

What diuretic is K+ sparing?

A

Amiloride. It inhibits Na+ entry in the distal nephron, so that K+ is not secreted

40
Q

Are ROMK or BK channels the main method of K+ secretion regulation?

A

ROMK are. They can be sequestered in the cell or placed in the apical membrane.

BK channels are normally closed and only open when K+ needs to be avidly secreted.

41
Q

What condition can be induced b excessive use of most diuretics?

A

Hypokalemic metabolic alkalosis.

H+ is secreted along with K+

42
Q

How much Calcium is reabsorbed in the kidney?

A

97-99%

Proximal tubule, thick ascending limb, distal tubule, collecting duct.

43
Q

How does Calcitonin work?

A

It stimulates the formation of new bone and increases renal excretion of both calcium and phosphate.

44
Q

What is the renal plasma threshold for Phosphate like?

What does this mean?

A

Plasma levels are close to the RPT for phosphate, meaning that the kidney is constantly spilling a small amount of phosphate.

FHB (8 decks)

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