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Renal Physiology > Glomerular Filtration > Flashcards

Glomerular Filtration Flashcards

1
Q

Structure of each nephron

A
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2
Q

Renal blood flow accounts for how much of CO

A

20% = 0.8-1 L/min

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3
Q

What is the red cell mass % of blood

Therefore what is renal plasma flow rate

A

40%

0.5-0.6 L/min

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4
Q
  1. What is the filtration fraction
  2. Hence what is the normal glomerular filtration rate (GFR)
A
  1. 20-25%
  2. GFR = 125-150 ml/min
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5
Q

What is urine flow rate

A

1-2 ml/min

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6
Q

How much primary urine is produced per day

A

140L

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7
Q

How much of filtered fluid is reabsorbed

A

99%

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8
Q

If something has a relative permeability of 1, can it cross the filtration barrier easily

A

YES

However, FILTRATION FRACTION plays a role

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9
Q

What solutes are freely filtered but are not or not fully reabsorbed

A

Urea and creatine

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10
Q

Regulated reabsorption of water and solutes allows for

A
  • Regulation of EC fluid vol
  • Osmolality
  • Acid-base balance
  • Homeostasis of whole body phosphate, Ca2+, K+ conc
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11
Q

Na+

  1. Qty/min filtrate
  2. Qty/min urine
  3. % excreted
A
  1. 17 mEq
  2. 0.128 mEq
  3. 72%
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12
Q

Glucose

  1. Qty/min filtrate
  2. Qty/min urine
  3. % excreted
A
  1. 125 mg
  2. 0 mg
  3. 0
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13
Q

Urea

  1. Qty/min filtrate
  2. Qty/min urine
  3. % excreted
A
  1. 33 mg
  2. 18 mg
  3. 55%

Urea is saved because it is an OSMOLITE

=> pulls water around - helps loop of Henle with water reabsorption

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14
Q

Creatine

  1. Qty/min filtrate
  2. Qty/min urine
  3. % excreted
A
  1. 1.4 mg
  2. 1.8 mg
  3. 130%
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15
Q

What does the afferent arteriole supply

What does it then become

A

Supplies individual glomerulus

Breaks up into glomerular capillaries

INCREASES SA

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16
Q

What does the afferent arteriole reform to

A

Efferent arterioles

  • Key players in managing rate of filtration
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17
Q

What does the glomerular filtration barrier allow

A
  • High filtration rates of water
  • Non-restricted passage of small and middle-sized molecules
  • Almost total restriction of serum albumin and larger proteins
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18
Q

What is perselectivity

A

Restriction of permeation of macromolecules across the glomerular barrier on basis of molecular size, charge, physical configuration

ALSO molecular shape

[Anything big and negative gets pushed away

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19
Q

What is the unique properties of glomerular capillaries

A

They have FENESTRAE that allow size discrimination

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20
Q

Structure of a glomerular capillary

A

Garden hose stabbed with a fork

Painted with extracellular matrix

Podocytes lie on top

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21
Q

What charge do proteins have and what does this mean

A

Proteins are negatively charged

=> Reject negative charges at filtration membrane

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22
Q

How are podocytes structured

A

Stand up straight and narrow or lie flat, contributing to selection

  • highly differentiated
  • very specialised function
  • face the Bowman’s space and the primary urine
  • extending cytoplasmic foot processes, which are separated by a filtration slit that is 25-60 nm wide and covered by a diaphragm
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23
Q

What does the “beaded curtain” at the slit do

A

Filters based on chemical nature

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24
Q

What is the diaphragm of podocytes composed of

A

A number of proteins such as nephrin which when mutated causes massive leakage of protein and severe consequences for patients - congenital nephrotic syndrome

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25
Q

How much of the entire endothelial surface do fenestrae constitute

A

20-50%

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26
Q

Diameter of fenestrae

What does the diameter suggest

A

60 nm (albumin has a diameter of only 3.6 nm)

Suggests that endothelial cells do not determine the PERMSELECTIVITY of the glomerular barrier

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27
Q

What does the endothelial cell coat have

A

Charge-selective properties and the barrier probably begins at the endothelial level

28
Q

What are BV walls covered with on the luminal side

A

Endothelial cell surface layer (ESL)

29
Q

What is the ESL composed of

A

Negatively charged glycoproteins, glycosaminoglycans (GAGs) and membrane-associated and secreted proteoglycans

30
Q

What does the ESL seem to be

A

A thick, negatively charged structure that most likely contributes to the high permselectivity of the glomerular wall

31
Q

What is the glomerular basement membrane (GBM)

A

Composed of a fibrous network with a backbone of type 4 collagen

32
Q

What do mutations in the collagen chains give rise to

A

Severe pathological conditions - Alport’s Syndrome (hereditary glomerulonephritis)

33
Q

Components of GBM

A

PROTEOGLYCANS

Agrin

Perlecan

GLYCOPROTEINS

=> Contribute to selective properties of barrier

34
Q

What is the charge density within the glomerular barrier derived from

A

A combination of the endothelial cell layer and the GBM

35
Q

Filtration membrane permeability

36
Q

Filtration membrane permeability with charge

37
Q

Equation for glomerular filtration rate (GFR)

A

GFR: Jv = Kf × [(PGC – PBS) – σ(πGC – πBS)] <- oncotic pressure

K = hydraulic conductivity (basically constant)

-> Kf = ultrafiltration coefficient

38
Q

What are the 2 things filtration depends on

A
  1. Kf - ultrafiltration constant
  2. Net Starling forces
39
Q

Glomerular Filtration Pressure Balance

40
Q

Difference between oncotic and osmotic forces

A

Oncotic forces refer to plasma proteins

The small amount of plasma proteins that get into Bowman’s Space

41
Q

Forces FILTERING FLUID OUT

42
Q

Forces OPPOSING ULTRAFILTRATION

A
  1. πGC (oncotic pressure)
  2. PBS
43
Q

Normal capillary balance between filtration and absorption

A

ARTERIAL END - filtration occuring to deliver O2 & nutrients to tissues

VENOUS END - pulling waste products in => absorption

2 triangles are equal

44
Q

Glomerular capillary P change (red line is oncotic pressure)

A

Glomerular capillaries are needed for filtration => no absorption

Pressure stays high and constant

Colloid oncotic pressure increases in the glomerular capillaries

45
Q

Oncotic pressure in peripheral capillaries

46
Q

PGC - loves filtration

47
Q

πGC - hates filtration

48
Q

PBS - hates filtration

49
Q

Equation for net filtration pressure (NFP)

A

NFP - PGC - (πGC + PBS)

NFP = 55 - (30 + 15) = 10 mmHg

50
Q

What effect do kidney stones have on PBS

A

Make it increase

51
Q

What controls PGC

A

Relative resistance of AA and EA

52
Q

What controls resistance of AA and EA

A

Neural and hormonal inputs

HORMONAL - local paracrine agents that are produced locally and act locally

53
Q

Why is it important to control and maintain the PGC at a constant pressure

A

To ensure rate of filtration, GFR, is maintained constant

54
Q

AA constriction

55
Q

Efferent arteriole (EA) constriction

A

RPF - renal plasma flow rate

GFR is levelling off even though pressure is going up because of ONCOTIC FORCES

Proteins aren’t being flowed away, so fluid is being pulled back

56
Q

Definition of GFR

A

Volume of filtrate produced per minute

57
Q

GFR in men vs women

A

MEN - 125ml/min

WOMEN - 115ml/min

=> 180 L/day

blood volume = 5.5L => entire blood vol is filtered every 40 minutes

58
Q

Regulation of GFR - recall what filtration depends on

A

PGC, which is controlled by the relative resistance of AA and EA

59
Q

Why must GFR be tightly regulated

A

25% increase in MAP

25% increase in GFR

Loss of 40L/day

[80-200 mmHg range] - GFR is tightly regulated

60
Q

What are the 3 mechanisms for regulating GFR

A
  1. Renin - angiotensin system
  2. Autoregulation
  3. Sympathetic nerves
61
Q

Overall effect of RAS

A

Tends to increase BP in response to decreased BP at AA

62
Q

AUTOREGULATION OF GFR

Maintaining GFR in response to changes in MAP, venous pressure and obstruction

63
Q

AUTOREGULATION OF GFR

Sensing in tubule - macula densa of the juxtamedullary complex senses fluid flow in tubule

64
Q

Response of macula densa

65
Q

Sympathetic nerve response to regulate GFR

(CV shock - GFR goes to 0)

Renal Physiology (8 decks)

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