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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
How much of the entire endothelial surface do fenestrae constitute
20-50%
26
Diameter of fenestrae What does the diameter suggest
60 nm (albumin has a diameter of only 3.6 nm) Suggests that endothelial cells do not determine the PERMSELECTIVITY of the glomerular barrier
27
What does the endothelial cell coat have
Charge-selective properties and the barrier probably begins at the endothelial level
28
What are BV walls covered with on the luminal side
Endothelial cell surface layer (ESL)
29
What is the ESL composed of
Negatively charged glycoproteins, glycosaminoglycans (GAGs) and membrane-associated and secreted proteoglycans
30
What does the ESL seem to be
A thick, negatively charged structure that most likely contributes to the high permselectivity of the glomerular wall
31
What is the glomerular basement membrane (GBM)
Composed of a fibrous network with a backbone of type 4 collagen
32
What do mutations in the collagen chains give rise to
Severe pathological conditions - Alport's Syndrome (hereditary glomerulonephritis)
33
Components of GBM
PROTEOGLYCANS Agrin Perlecan GLYCOPROTEINS =\> Contribute to selective properties of barrier
34
What is the charge density within the glomerular barrier derived from
A combination of the endothelial cell layer and the GBM
35
Filtration membrane permeability
36
Filtration membrane permeability with charge
37
Equation for glomerular filtration rate (GFR)
GFR: Jv = Kf × [(PGC – PBS) – σ(πGC – πBS)] \<- oncotic pressure K = hydraulic conductivity (basically constant) -\> Kf = ultrafiltration coefficient
38
What are the 2 things filtration depends on
1. Kf - ultrafiltration constant 2. Net Starling forces
39
Glomerular Filtration Pressure Balance
40
Difference between oncotic and osmotic forces
Oncotic forces refer to plasma proteins The small amount of plasma proteins that get into Bowman's Space
41
Forces FILTERING FLUID OUT
1. PGC 2. πBS
42
Forces OPPOSING ULTRAFILTRATION
1. πGC (oncotic pressure) 2. PBS
43
Normal capillary balance between filtration and absorption
ARTERIAL END - filtration occuring to deliver O2 & nutrients to tissues VENOUS END - pulling waste products in =\> absorption 2 triangles are equal
44
Glomerular capillary P change (red line is oncotic pressure)
Glomerular capillaries are needed for filtration =\> no absorption Pressure stays high and constant Colloid oncotic pressure increases in the glomerular capillaries
45
Oncotic pressure in peripheral capillaries
46
PGC - loves filtration
55
47
πGC - hates filtration
30
48
PBS - hates filtration
15
49
Equation for net filtration pressure (NFP)
NFP - PGC - (πGC + PBS) NFP = 55 - (30 + 15) = 10 mmHg
50
What effect do kidney stones have on PBS
Make it increase
51
What controls PGC
Relative resistance of AA and EA
52
What controls resistance of AA and EA
Neural and hormonal inputs HORMONAL - local paracrine agents that are produced locally and act locally
53
Why is it important to control and maintain the PGC at a constant pressure
To ensure rate of filtration, GFR, is maintained constant
54
AA constriction
55
Efferent arteriole (EA) constriction
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
Definition of GFR
Volume of filtrate produced per minute
57
GFR in men vs women
MEN - 125ml/min WOMEN - 115ml/min =\> 180 L/day blood volume = 5.5L =\> entire blood vol is filtered every 40 minutes
58
Regulation of GFR - recall what filtration depends on
PGC, which is controlled by the relative resistance of AA and EA
59
Why must GFR be tightly regulated
25% increase in MAP 25% increase in GFR Loss of 40L/day [80-200 mmHg range] - GFR is tightly regulated
60
What are the 3 mechanisms for regulating GFR
1. Renin - angiotensin system 2. Autoregulation 3. Sympathetic nerves
61
Overall effect of RAS
Tends to increase BP in response to decreased BP at AA
62
AUTOREGULATION OF GFR Maintaining GFR in response to changes in MAP, venous pressure and obstruction
63
AUTOREGULATION OF GFR Sensing in tubule - macula densa of the juxtamedullary complex senses fluid flow in tubule
64
Response of macula densa
65
Sympathetic nerve response to regulate GFR (CV shock - GFR goes to 0)

Renal Physiology (8 decks)

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