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SMP - Renal > Lecture 4 - Dynamics of Glomerular Filtration > Flashcards

Lecture 4 - Dynamics of Glomerular Filtration Flashcards

1
Q

Is urine secreted?

A

NOPE - excreted

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2
Q

What is the glomerular substrate composed of?

A
  1. Limited plasma proteins
  2. NaCl
  3. HCO3-
  4. H2O
  5. Glucose
  6. AAs
  7. Urea
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3
Q

Does the glomerular substrate include any blood cells? Implication?

A

NOPE

PLASMA filtrate, not blood

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4
Q

Other than plasma proteins, are all other substances in the glomerular filtrate in approximately the same concentration as found in plasma?

A

YUP, except any substance that is bound to proteins in plasma in any significant amount (e.g. Ca++ - 40% bound to proteins in plasma and Mg++)

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5
Q

Describe the glomerular wall that the glomerular filtrate needs to pass. What do we call this as a whole?

A
  1. Glomerular endothelial fenestrations without diaphragms
  2. Thick glomerular basement membrane
  3. Filtration slits between adjacent podocyte foot processes, which is spanned by a slit diaphragm

=> glomerular pore

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6
Q

Size of glomerular pore?

A

20-30 Angstroms (10^-10 meters)

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7
Q

How did we determine the size of the glomerular pore?

A

Pass dextran molecules (starch) of different sizes through the pore and measure the fractional clearance for each - 50% of 30 Angstroms molecules made it through the pore

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8
Q

Can inulin make it past the glomerular pores? What else can it pass through?

A

YUP

Also can make it through peripheral capillaries to enter the interstitial space

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9
Q

If myoglobin was in plasma (it’s in the muscles), would it make through the glomerular pore?

A

YUP

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10
Q

When is myoglobin found in the blood? What can this lead to?

A

When muscle cells are damaged => makes it through the glomerular pore and then can get stuck in the tubules of the nephrons => leads to renal failure

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11
Q

Does the negative electrostatic barrier restrict the passage of all negatively charged substances?

A

NOPE - only large ones

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12
Q

Can positively charging large substances increase their fractional clearance through the glomerular pore?

A

YUP

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13
Q

Can glomerular injury affect the negative charge of the glomerular wall? What does this lead to?

A

YUP

Large proteins appear in the urine

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14
Q

Size of endothelial fenestrations in the glomerular wall?

A

20-100 nm

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15
Q

What determines if a fluid will be able to pass a capillary?

A

The 4 Starling forces:

  1. Capillary pressure (Pc) = hydrostatic pressure (HPc)
  2. Interstitial oncotic pressure (πi) = interstitial colloid osmotic (πif)
  3. Interstitial hydrostatic pressure (HPi or Pif)
  4. Plasma oncotic pressure (πc or πp) = plasma colloid osmotic pressure
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16
Q

How can you find the net filtration pressure across the length of a capillary wall?

A

Jv = Kf x [ (HPc-HPi) - (πc - πi) ]

Kf = Filtration coefficient = Surface area (SA) x Hydraulic permeability (Lp)

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17
Q

How does NET hydrostatic pressure change from the arterial to the venous side of a peripheral capillary?

A

It decreases

18
Q

How does NET oncotic pressure change from the arterial to the venous side of a peripheral capillary?

A

Constant

19
Q

What happens when net hydrostatic pressure is higher than net oncotic pressure in a peripheral capillary bed?

A

Filtration

20
Q

What happens when net hydrostatic pressure is lower than net oncotic pressure in a preripheral capillary bed?

A

Reuptake

21
Q

What determines if a fluid will be able to pass a GLOMERULAR capillary?

A
  1. Glomerular capillary hydrostatic pressure
  2. Bowman’s space hydrostatic pressure

=> Net hydrostatic pressure for filtration

  1. Plasma oncotic pressure
22
Q

How does glomerular hydrostatic pressure change from the efferent to the afferent side of a glomerular capillary? Explain

A

Constant, because arteriole to arteriole both with similar resistances

23
Q

Does plasma oncotic pressure help or oppose filtration through the glomerulus?

A

Opposes it

24
Q

How does the glomerulus net filtration pressure change throughout the glomerulus?

A

Under normal blood pressures in adults, the net hydrostatic pressure is constant throughout and the plasma oncotic increases throughout (so net decreases slightly), but overall the net hydrostatic pressure is higher than the plasma oncotic pressure throughout the glomerulus so that filtration happens throughout

25
Q

When do the net hydrostatic pressure and the plasma oncotic pressure in glomerulus reach equilibrium?

A

When there is hypotension

26
Q

How does plasma protein concentration vary throughout the glomerulus?

A

It increases

27
Q

What is the equation to calculate glomerular filtration rate?

A

GFR = Kf x [ (HPgc-HPbs) - πgc ]

Kf = Filtration coefficient = Surface area (SA) x Hydraulic permeability (Lp)

28
Q

Can hydraulic permeability change at any point in the glomerulus? Explain.

A

NOPE - it is always very permeable to water

29
Q

Can surface area change at any point in the glomerulus? Explain. How would this affect GFR?

A

YUP

  1. The actin and myosin within foot processes can cause these processes to change in shape and thereby regulate the size of intervening filtration slits and solute flow across the glomerular wall
  2. Loss of a kidney: GFR is halved, but with compensatory hypertrophy the glomeruli will increase in size and be able to increase the GFR to a certain % depending on the age of the patient (in adults: 50% increase within a month)

=> decrease in SA => decrease in GFR

30
Q

What is hydraulic permeability?

A

A measure of how permeable the membrane is to water

31
Q

What substances can cause the actin and myosin within foot processes to contract to decrease the size of intervening filtration slits?

A
  1. Angiotensin II

2. NE

32
Q

How does angiotensin decrease GFR? Which effect is greater?

A
  1. ***Constriction of both afferent and efferent arterioles (decrease in pressure drop)
  2. Decrease in Kf due to decrease in SA
33
Q

What is a way to treat HT using kidney physiology?

A

Blocking angiotensin so that the GFR can increase

34
Q

Why is the Bowman’s space oncotic pressure not included in the GFR equation?

A

Proteins do not get filtered through the glomerular pore

35
Q

What would cause an increase in HPgc? Effect on GFR?

A

Increase in BP => increase in GFR

36
Q

What would cause an increase in HPbs? Effect on GFR?

A

Obstruction in nephron (e.g. myoglobin, tumor, kidney stone) => decrease in GFR, which could reach 0 with a big enough obstruction

37
Q

What is hydronephrosis?

A

Swelling of a kidney due to a build-up of urine due to an obstruction in the urinary tract

38
Q

Effects of afferent arteriole resistance increase on GFR?

A

Decrease

39
Q

Effects of efferent arteriole resistance increase on GFR?

A

Increase

40
Q

What is the equation to calculate net filtration pressure at the glomerulus?

A

= [ (HPgc-HPbs) - πgc ]

41
Q

If a substance is freely filtered at the glomerular capillaries, would the concentration in the plasma, glomerular filtrate, afferent arteriole, and efferent arteriole all be the same?

A

YUP!!

42
Q

What is the most common uriniferous tubule segment found in the renal cortex?

A

PCT

SMP - Renal (20 decks)

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