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Renal Exam 1 > DSA: Introduction to RBF and GFR > Flashcards

DSA: Introduction to RBF and GFR Flashcards

1
Q

What is the 3 layers of the glomerular capillary filtration barrier?

A
  1. Capillary endothelium
    • Biogel
    • Fenestrations
  2. Basement membrane
  3. Podocyte epithelium
    • Filtration slits
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2
Q

Glomerular endothelium forms a biogel in the lumen of the endothelium.

What is this?

A

Biogel is negatively charged and lines the inside of the capillary lumen, filling the fenestrations of the capillary.

Thus, it restricts movement of (-) charged proteins and large molecules.

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3
Q

Describe the filtration slits.

A

Filtration slits formed by the legs of the podocytes.

They are made up of: actin and cadherin (which bind the 2 foot processes) and nephrin, which prevent large proteins from going into Bowman’s capsule.

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4
Q

What size molecules are filtered via the filtration slits?

A
  1. Molecules less than 20 A are freely filtered.
  2. Molecules greater than 42 A are not filtered.
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5
Q

What is freely filtered at the filtration barrier?

A

1. Water

2. Small solutes, like glucose, AA and electrolytes

Thus, the concentrations are equal on both sides of the membrane .

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6
Q

What is not freely filtered at the filtration barrier?

A
  1. Large molecules, like proteins
  2. Formed elements, like cells
  3. V small amountsof protein are filtered.
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7
Q

Tamm-Horsfall protein is present in the urine.

However, proteins are not freely filtered. Thus, how is it present in the urine?

A

It is produced exclusively by renal tubular epithelial cells within the distal loop of Henle.

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8
Q

What is filtered depends on the size and charge and can be calculated based on its clearance ratio.

A clearance ratio close to 1 means that it is more freely filtered.

What has a higher clearer ratio?

A
  1. Molecules with a smaller radius
  2. Positive cations
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9
Q

What part of the filtration barrier is damaged in hematuria and proteinuria?

A

Hematuria–> thin basement membrane

Proteinuria–> caused by damage tothe structure of the podocyte foot processes and filtration slits.

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10
Q

What happens if we remove the negative charge from the biogel located in the fenestrations of the capillary endothelium?

A

Filtration of anions are increased from the blood–> urine, leads to proteinuria.

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11
Q

What would happen to the plasma oncotic pressure if we lost a bunch of albumin?

A

Plasma oncotic pressure would decrease.

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12
Q

How are the tubules and the vessels organized in the CTX and the medulla?

A

CTX has intertwined tubules and vessels

Medulla has straight blood vessels and straight tubules.

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13
Q

How often is renal blood flow (RBF) regulated?

A

RBF is regulated minute-to- minute.

For example, during an intense excercise, renal fraction of blood flow decreases because blood is being sent to the muscles.

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14
Q

—Equation—

Filtered Load of X

A
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15
Q

—Equation—

Urinary excretion

A
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16
Q

—Equation—

Tubular Reabsorption

A
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17
Q

How do we know if secretion occured?

A

Excretion> filtration

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18
Q

—Equation—

Urine excretion rate of x

A

-the concentration of X that we excrete

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19
Q

What is urine flow rate (V) dependent on?

A

1. Fluid intake

2. Fluid homeostasis

An increase in fluid intake, will increase urine flow.

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20
Q

What is renal clearance (C)?

What are the units?

A

Renal clearance (C) is the volume of plasma that is cleared of a substance by the kidneys, per unit time.

It is the ratio of [urinary excretion (Ux * V): plasma concentration].

Units: volume/time, which means that rate of plasma that is cleared of a substance per unit time.

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21
Q

Renal clearance can also be described as ___________

A

Flow rate

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22
Q

—Equation—

Renal Clearance

A
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23
Q

It is important to know that the [entrance of substance X must equal exit of substance X]

There is only 1 way to get to the kidney–> ___________

However, there are 2 ways to leave the kidney–>

  1. ______
  2. _______
A

It is important to know that the [entrance of substance X = exit of substance X]

There is only 1 way to get to the kidney–> arterial input

However, there are 2 ways to leave the kidney–>

  1. Venous output via the efferent arteriole
  2. Urine output
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24
Q

What is the arterial input equal to?

A

Arterial input= [venous output + urine output]

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25
Q

—Equation—

Arterial Input

A

Plasma concentration of X * RPF (the amount of plama that flows through our kidneys at once)

26
Q

When will clearance (C) = RPFa?

A

clearance (C) = RPFa when venous output is 0.

27
Q

A substance is present in the blood at 1mg/mL and in the urine at 100mg/mL. Urine flow rate is 1mL/minute. What is the renal clearance?

A

Cx= 100mL/min

28
Q

What is the glomerular filtrate?

Compared to plasma, it is isosmotic, hyposmotic, hyperosmotic?

A

Glomerular filtrate (aka plasma ultrafiltrate) is the plasma filtered from [GC–> BC] in all nephrons in both kidneys/ unit time. The filtrate should not have cells or proteins in it.

Compared to plasma, it is isoosmotic.

29
Q

____% of the RBF is filtered (becomes our glomerular filtrate).

A

20%

30
Q

GFR is about 20% of the RBF and is determined by what?

A

1. Hydrostatic forces

2. Oncotic forces

31
Q

Normal RBF (amount of blood going to the kidneys) is about 625 mL/min.

The filtration fraction (FF) is 20% of RBF, which results in a GFR of what??

Do we excrete this all?

A

Normal RBF= 625 mL/min

FF= 20% of RBF

GFR= 125 mL/minute (180L/day)

However, 99% of this is typically reaborbed (124 mL/min), thus we typically only excrete 1mL/minute.

32
Q

—Equation—

Filtration fraction

​(fraction of RBF that is filtered across glomerulus)

A
33
Q

Changes in FF are due to ___________.

What happens to the oncotic pressure of the efferent arteriole as FF increases?

A

Changes in FF are d/t ultrafiltration pressure (BP).

Increase in FF= increase in oncotic pressure of the efferent arterioles, promoting reabsorption because the decrease in H20 increases the concentration of plasma proteins relative to the amount of water.

34
Q

GFR depends on what 2 factors?

A
  1. Permeability of the membrane
  2. SA

When calculating GFR, these are included in the equation as Kf (permeability * SA).

35
Q

As we go along the glomerular capillary, what happens to the glomerular colloid/oncotic pressure as FF increases and decreases?

A

Increase FF= increase glomerular colloid oncotic pressure

Decrease FF= decrease glomerular colloid oncotic pressure

36
Q

How can we change the FF?

A

Changes in GFR or RBF.

37
Q

What happens when we have a severe hemorrhage or renal artery stenosis?

A

RBF is reduced

GFR must increase to maintain homeostasis, making the FF increse.

38
Q

What is the difference between [filtered load] and [filtration fraction]?

A

Filtered load–> rate in mg/min at which filtration occurs.

Filtration fraction–> ratio of GFR to RBF.

39
Q

___________________ (what we filter) will eventually become the urine that we expel.

A

Iso-osmotic ultrafiltrate (primitive urine)

40
Q

—Equation—

Filtered load (of Na+)

A

Filtered load= GFR * PNa+

Normally, about 25,200 mEq/day

41
Q

—Equation—

Reabsorption (when given filtered load)

A

Reabsorption= [filtered load]- [excretion]

-should be around 99% of the filtered load-

42
Q

—Equation—

Excretion

A

Excretion= Urine Flow Rate * UrineNa+

Excretion= V * UrineNa+

Usually around 100 mEq/day

43
Q

When calculating the net reabsorption, what variables are at play?

A

1. GFR

2. Plasma concentration of x (PNa+)

3. Urine concentration of x (UNa+)

4. Urine flow rate

44
Q

When does [GFR= renal clearance (Cx)]?

A

1. Freely filtered

2. Not reabsorbed or secreted

3. Not made/broken down by the kidney or accumulated by the kidney.

4. Inert, meaning that it is not toxic or affect renal function

45
Q

Does inulin meet the criteria to allow GFR= Cx?

A

Yes.

Inulin is freely filtrered at the glomerulus (Pln *GFR), is not secreted or reabsorbed.

Thus, the amount excreted in the urine (Uln * V)= amount filtered at the glomerulus.

46
Q

When GFR= Cx, how do we calculate GFR of inulin?

A

GFR= (Uln) * (V)/ Pln

47
Q

Does creatinine meet the criteria to allow GFR= Cx?

Why is it used to measure GFR?

A

Sort of.

Inulin is freely filtered at the glomerulus, however around 10% of creatinine excreted is secreted from the peritubular capillaries.

Even though it is not an ideal indicator of our GFR, we use it to measure GFR because it is made endogenously by the skeletal muscle and does not require infusion.

48
Q

What is the values of creatinine dependent on?

A

Age and muscle mass.

We can use it for long term monitoring of renal fx.

49
Q

Sympathetic NS stimulation increases BP through 3 mechanisms.

What are they?

A
  1. Vasoconstriction of afferent* and efferent arteriole via A1 receptors.
  2. Release of renin from JGC via B1 receptors.
  3. Increased Na+ reabsorption via Na-K ATPase pumps by binding onto A1 receptors on tubular epithelial cells.
50
Q

Renal sympathetic nerve stimulation causes the biggest change in which of the 3 mechanisms?

A

1. Plasma renin activity.

51
Q

What are the immediate effects of sympathetic stimulation?

Eventual effects?

A

Immediately;

  1. Renin is secreted from JGC
  2. Angiotensin II is made and causes thirst, vasoconstriction of the efferent arteriole
  3. Na+ is reabsorbed in the PCT and DCT via the Na-K+ ATPase.
  4. GFR is stabilized–> raising our systemic BP

_______

Eventually;

  1. Decrease urine output; causing decrease Na+ excretion and increased water intake.
52
Q

How are [plasma creatine] and [GFR] related?

A

Inverselely proportional.

As GFR increases, plasma creatine decreases; because it is being filtered as well.

53
Q

What is the BUN: Creatinine ratio used for?

A

Used to determine is physiological conditions in the kidney are normal.

54
Q

Normal BUN/Cr ratio

A

A normal BUN/Cr level is 10-20:1.

However, this can also indicate post-renal diseases, such as those that occur in the ureter, bladder or urethra.

55
Q

BUN/Cr ratio: >20:1

High, low or normal?

How does this occur?

Examples we will find this in:

A

HIGH, indicating a pre-renal problem.

BUN reabsorption is increased and disproportionally elevated relative to creatinine in the serum.

Examples this occurs in is: hypovolemia, dehydration, reduced renal perfusion and high protein diet.

56
Q

BUN/Cr ratio: <10:1

High, low or normal?

How does this occur?

Examples we will find this in:

A

Low, indicating an intrarenal problem.

Mechanism: Renal diseases reduced BUN reabsorption, thereby decreasing plasma levels and decreasing the ratio.

Examples: Liver dz and a low protein diet.

57
Q

PAH (para-aminohippuric acid) can give us a good estimate of what?

A

Renal plasma flow, because it is freely filtered at the glomerulus and that that is not filtered, is secreted from the [peritubular capillaries–> tubule] (10% remains in blood)

Thus, the amount in the renal artery= amount excreted in urine.

58
Q

Why is creatinine used to indicated GFR and not PAH?

A

Because PAH is an organic acid not normally present in our bodies.

It must be administered intravenously.

It is so effcient that as long as we do not saturate the transporters (12 mg/dl), almost no PAH stays in the blood.

59
Q

They majority of PAH is filtered/secreted into the tubular lumen.

A

Secreted

60
Q

There is a limit to how much PAH can be filtered/secreted.

A

Secreted,

based on the saturation of the transporters.

Renal Exam 1 (10 decks)

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