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Renal I Midterm > Lecture 6: Elements of Renal Function > Flashcards

Lecture 6: Elements of Renal Function Flashcards

1
Q

What are the 2 populations of nephron and location?

A

1) Cortical (superficial)
2) Juxtamedullary (deep)

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2
Q

Each nephron has how many arteioles and capillaries?

A
  • Two arterioles
  • Two sets of capillaries
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3
Q

Which arteriole delivers blood to the glomerular capillaries?

A

Afferent arteriole

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4
Q

Arterial blood leaves the glomerulus through which arterial, which quickly subdivides into?

A

Efferent arteriole, which quickly subdivides into second set of capillaries, the peritubular capillaries (vasa recta).

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5
Q

What do the peritubular capillaries supply?

A

The renal tissue with blood

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6
Q

Where is blood flow rate highest and lowest in the kidney?

A
  • Highest in cortex (4-5 mL/min) = filtration is slow
  • Low in the medulla: helps maintain hyperosmolar enviornment in this region = filtration is high
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7
Q

What are some of the differences between the cortical and juxtamedullary nephrons?

A

Cortical: surrounded by extensive network of peritubular capillaries, rate of filtration is slow, larger diameter efferent arterioles

Juxta: longer loop of henle, longer thin loop, lower renin, different tubular permeability, high rate of filtration, and long (small diameter) efferent arterioles

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8
Q

Main function of the cortical nephron?

A

Excretion of waste products in the urine

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9
Q

Main function of the juxtamedullary nephron?

A

Concentration of urine

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10
Q

How many liters of fluid filters into the Bowman’s capsule each day at about what mOsM?

A

180 L at about 300 mOsM

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11
Q

What is the osmolarity of the filtrate leaving the proximal tubule as it enters the loop of henle, how about at the end of the loop of henle?

A

Start of loop: 300 mOsM

End of loop: 100 mOsM

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12
Q

What is the approximate osmolarity at the end of the collecting duct; why the variability?

A
  • 50-1200 mOsM
  • Depends on the body’s need to conserve or excrete water and solute
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13
Q

Where does filtration happen as opposed to absorption and secretion?

A
  • Filtration occurs in renal corpuscle as fluid moves from the glomerular capillaries into Bowman’s capsule
  • Reabsorption/secretion occur along remainder of tubule, material is transferred between the lumen and the peritubular capillaries
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14
Q

What happens to filtrate that remains in the lumen at the end of the nephron?

A

Excreted as urine.

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15
Q

What is the GFR is stages 1-5 of CKD?

A

Stage 1: >90 mL/min

Stage 2: 60-89 mL/min

Stage 3: 30-59 mL/min

Stage 4: 15-29 mL/min

Stage 5: <15 mL/min

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16
Q

The volume of filtrate formed by both kidneys per minute is the?

A

GFR

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17
Q

What percentage of the blood enters the kidney to be filtered per minute = how much filtrate per minute/per day in men vs women (GFR)?

A

Heart pumps 5L of blood per min. and 20% (1 liters) enters the kidney per minute.

Men: 125 mL/min of filtrate = 180 L/day

Women: 105 mL/min of filtrate = 150 L/day

18
Q

What percent of the filtrate is reabsorbed and returned to circulation?

A

99%

19
Q

Renal blood flow =

A

CO x % blood flow to kidney (usually 20%)

20
Q

Renal plasma flow =

A

Renal blood flow x (1-hematocrit)

*Hematocrit is typically 45 (.45) and 1-0.45 = 0.55

21
Q

GFR =

A

Renal plasma flow x % entering capsule (usually 19%)

22
Q

Urine per minute =

A

GFR x fraction of filtrate not reabsorbed (.008)

23
Q

What are the 3 possible outcomes of a substance as its filtered through kidneys

A

1) Substance is filtered and secreted, but NOT reabsorbed
2) Substance is filtered, and a fraction is reabsorbed
3) Substance is filtered and completely reabsorbed

24
Q

GFR will always be in what units of measurement?

A

mL/min

25
Q

The plasma clearance of any substance is defined as; importance

A

The volume of plasma completely cleared of that substance by the kidneys per minute; expresses the kidneys effectivness in removing various substances, which is more related to how they are functioning

26
Q

What is the equation that can be used which allows us to assess renal function using only analysis of the urine and the blood?

A

C(x) x P(x) = U(x) x V

C(x) = clearance rate of substance x (mL/min)

P(x) = plasma concentration of substance x

U(x) = urine concentration of substance x

V = urine flow rate (mL/min)

27
Q

What is the rearranged equation for renal clearance?

A
28
Q

What is the best marker for measuring GFR; what’s the issue with it?

A
  • Inulin
  • Is not made endogenously, must be administered by continous IV, expensive
29
Q

Filtered load =

A

GFR x Plasma concentration (P(x))

30
Q

Excretion rate =

A

Urine concentration (Ux) x Urine flow rate (V)

31
Q

How do the Cx and GFR relate in terms of absorbtion and excretion?

A

If C(x) < GFR = net tubular reabsorption of substance

If C(x) > GFR = net secretion of substance

If C(x) = GFR = no net secretion of reabsorption

C(x) = excretion rate

GFR = filtration rate

32
Q

GFR is routinely measured as the clearance of?

A

Endogenous Creatinine

33
Q

Problem with using creatinine as a marker?

A

There is typically an overestimation

34
Q

Normal serum creatinine is considered to be?

A

< 1.2 mg/dL = 0.012 mg/mL

35
Q

Why is serum creatinine concentration a good reflection of GFR?

A

Production of creatinine is typically constant over short periods.

36
Q

Why is PAH a good way to measure RPF?

A

Tubular secretory system for PAH is so efficient at low plasma concentrations it removes 90% + of PAH from thr plasma as it flows through the kidneys.

37
Q

Equation for RPF using PAH?

A
38
Q

How can we get RBF if we have RPF?

A

RBF = RPF/(1-Hct)

39
Q

What is Prerenal failure?

A
  • Failure of perfusion of the kidney
  • GFR falls because of volume depletion, decreased CO, or vasodilation
  • Increase BUN and creatinine (20:1 BUN/creatinine)
  • Decreased urinary output and urine sodium
  • Increased urine osmolality
  • Increased specific gravity
40
Q

What is Intrarenal failure?

A

Damage to kidney itself (traumatic, injury, burn, ect.)

  • Elevated BUN and creatinine
  • Decreased output,
  • increased sodium, and increased osmolarity
41
Q

What is Postrenal kidney failure?

A
  • Kidneys work, but obstruction distal to kidney
  • Increased pressure = decreased GFR
  • increased BUN and creatinine
  • Decreased output, decreased sodium
  • Normal sed rate, variable osmolarity, variable gravity

Renal I Midterm (8 decks)

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