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_Physiology Exam 5 > 4/11: III - Glomerular Filtration > Flashcards

4/11: III - Glomerular Filtration Flashcards

1
Q

What is glomerular filtration rate?

A

Rate of production of glomerular filtrate

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2
Q

How often is entire plasma volume filtered?

A

Every 24 min (60x/day)

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3
Q

How does GFR occur?

A

Via bulk flow

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4
Q

Is GFR selective?

A

Unselective (Except for cells, proteins, Ca, fatty acids, and other protein-bound substances)

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5
Q

What is GFR regulated by?

A

Multiple systems

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6
Q

What is filtration fraction equation?

A

Filtration fraction = GFR/RPF

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7
Q

What does filtration fraction average?

A

20% of renal plasma flow (RPF)

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8
Q

Can filtration fraction be altered?

A

Yes

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9
Q

What are the functions of renal corpuscle?

A

Glomerular filtrate
contains:
1. Bowman’s capsule
2. Glomerular capillaries
3. Bowmans space

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10
Q

Where is protein free fluid filtered out of? into?

A

Glomerulas into bowman’s space

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11
Q

Where does filtrate flow?

A

Into proximal tubule

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12
Q

What is bowman’s space?

A

in between parietal and visceral layers of the capsule. Everything that gets filtered through the glomerular capillaries into the bowman’s space and then flows directly into the proximal tubule

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13
Q

What is filtered out of the glomerulus and into bowman’s space?

A

Protein free fluid
important it remains protein-free because if it is not it would lower the colloid osmotic pressure of plasma and would result in edema formation

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14
Q

How is blood in glomerular capillaries separated from Bowman’s space by?

A

Filtration barrier

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15
Q

What is glomerular filtration composed of?

A

Three layers (negatively charged)
1. Capillary endothelium (Fenestrated)
2. Basal Lamina (Basement Membrane)
3. Podocytes (Visceral Layer of Bowman’s
Capsule)

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16
Q

What are podocytes?

A

Foot-processes cover outside of basal lamina capillaries with filtration slits between them

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17
Q

What do podocytes create?

A

Filtration slits

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18
Q

Where are mesangial cells?

A

modified smooth muscle cells that surround glomerular capillary loops (not part of filtration barrier)

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19
Q

What do mesangial cells do?

A

Contract to modify size of filtration slits and alter the rate of filtrate production

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20
Q

What are determinants of the ability of a solute to penetrate the glomerular membrane?

A
  1. Molecular size
  2. Ionic charge
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21
Q

How does molecular size affect penetration of the glomerular membrane?

A

(small molecules filter better than large molecules)
- Molecules > 50 A are completely blocked
- Molecules < 20 A are completely filtered

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22
Q

How does ionic charge affect penetration of the glomerular membrane?

A

(cations (+) filter better than anions (-) because filtration barrier is negative drawing in cations)
- The more positive charge, the higher filterability
- At any given molecular weight, positively charged substances will be filtered better than neutral substances and neutral substances will be filtered better than negatively charged substances

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23
Q

What happens during minimal changes in nephropathy?

A

loss of negative charge in just one of the filtration barrier layers. This loss of charge causes proteins to be filtered through the membrane
- Causes proteinuria (protein in urine) which causes colloid osmotic pressure in blood to decrease and have volume distribution problems

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24
Q

What is capillary filtration coefficient (Kf)?

A

product of the permeability and surface area of the capillaries

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25
Q

What is net filtration pressure (NFP)?

A

balance of hydrostatic and colloid osmotic forces acting across the capillary membrane

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26
Q

How is GFR calculated?

A

GFRP = Kf x NFP (net filtration pressure)

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27
Q

Why is GFR high?

A

Because of high hydrostatic pressure and high Kf

28
Q

What are the values of NFP?

A

100mm Hg, 125 ml/min; 18- L/day

29
Q

How is Kf calculated?

A

Kf = hydraulic conductivity x surface area
- 400x higher than any other capillary bed. At any give pressure difference you’re going to have more fluid move because of the high Kf
- Normally not highly variable. Alterations in Kf are not used to regulate GFR (but can impact it in certain diseases)

30
Q

What are diseases that can lower Kf?

A

– Thickened basement membrane: hypertension,
diabetes mellitus
– Decreased capillary surface area: glomerulonephritis

31
Q

What is the primary control point for GFR?

A

Glomerular (PG)

32
Q

What is glomerular pressure the determinant of?

A

GFR most subject to physiological control

33
Q

What are factors that influence PG?

A
  • arterial pressure (effect is
    buffered by autoregulation)
  • afferent arteriolar resistance
  • efferent arteriolar resistance
34
Q

What is not a physiological regulator of GFR?

A

Bowman’s capsule presure (PB)

35
Q

What are diseases that can affect GFR via PB

A
  • Tubular Obstruction
    (kidney stones, tubular
    necrosis)
  • Urinary tract obstruction
    (prostate
    hypertrophy/cancer)
36
Q

When does osmotic pressure increase?

A

Along length of glomerular capillary
(from afferent to efferent): this occurs because of the filtration

37
Q

What does glomerular capillary colloid osmotic pressure oppose?

A

Hydrostatic pressure

38
Q

When does GFR decrease?

A

Along length of capillary

39
Q

How is hydrostatic pressure in glomerular capillaries be altered by?

A

altering the resistance of the afferent and efferent arterioles
- leads to changes in GFR

40
Q

What happens to Pg if flow in > flow out?

A

Increase in PH

41
Q

What happens to Pg if flow in < flow out?

A

Decrease in PG

42
Q

How can flow in and out be altered by?

A

altering the resistance of the afferent and efferent arterioles, which can lead to changes in GFR

43
Q

Describe

A
44
Q

Describe

A
45
Q

Describe

A
46
Q

Describe

A
47
Q

What happens to Renal blood flow and GFR when afferent arterioles are constricted (increasing resistance)?

A

Afferent constriction causes flow in to go down, decreasing PG and GFR

48
Q

What happens to renal blood flow and GFR when efferent arterioles are constricted?

A

Efferent constriction causing flow out to go down, increasing PG and GFR
- GFR is only increased -> then it will start to fall due to increased concentration of plasma proteins from increased filtration fraction (only occurs with severe resistance (3-4x normal) Pa-PV

49
Q

What are factors that can decrease GFR?

A
50
Q

What is the equation for renal blood flow?

A
51
Q

What controls renal blood flow?

A

Kidneys via renal autoregulation

52
Q

What is vascular resistance regulated by?

A

Factors acting on afferent and/or efferent arterioles

53
Q

How much of blood flow in medulla is total RBF?

A

<10%
Very low flow in vasa recta contributes to generation of osmotic gradient for
concentration/dilution

54
Q

Describe the pressure during renal blood flow

A

High pressure coming in through renal artery. Pressure drops as you pass through afferent arteriole due to lots of resistance. Glomerular capillaries (high pressure vessels) have high plateaued pressure around 60 mmHg. It then drops again as it passes through efferent arterioles due to increased resistance. It then passes through peritubular capillaries (low pressure vessels)

55
Q

What happens with high RBF?

A

high energy cost of active transport that the kidney needs to do. Is an index of amount of energy that the kidneys need to expend

56
Q

What does O2 consumption reflect?

A

ATP consumption

57
Q

What does ATP consumption reflect?

A

Active transport

58
Q

What are primary active transporters seen in the kidneys?

A

Na+/K+ ATPase, H+ ATPase, H+/K+ ATPase, Ca2+ ATPase

59
Q

What are the three levels of control of RBF and GFR?

A
  1. autoregulation
  2. local control
  3. systemic control
60
Q

What is autoregulation control?

A

Prevents moment to moment changes in GFR

61
Q

What is myogenic autoregulation?

A

functions to keep RBF and GFR relatively constant in spite of changes in MAP
- Reflex vessel constriction in response to increased MAP
- intrinsic to blood vessels

62
Q

Describe the renal autoregulation of RBF and GFR in normal , lowered, and raised pressure

A
63
Q

What is the function of tubuloglomerular feedback?

A

functions to help ensure a nearly constant delivery of Na+ and Cl- to the distal nephron (you don’t want to deliver too much filtrate to distal nephron)

64
Q

What does the tubuloglomerular feedback prevent?

A

spurious fluctuations in renal excretion
* If we start over running the distal nephron, we will excrete things we don’t want to excrete

65
Q

What is tubuloglomerular feedback carried out via?

A

juxtaglomerular apparatus (afferent and efferent arteriole resistance related to flow rate of NaCl by macula densa)

_Physiology Exam 5 (10 decks)

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