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BMS 242 - Phys and pharm of cells > Glomerular filtration > Flashcards

Glomerular filtration Flashcards

1
Q

What does the glomerulus do?

How?

A

Filter plasma:

  • ALLOWS the passage of H2O and small molecules
  • RESTRICTS the passage of blood cells and the majority of proteins
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2
Q

What happens to the molecular weight proteins during filtration?

A

Filtered but are REABSORBED by the proximal tubule

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3
Q

What is the structure of the glomuerulus?

A

Capillary bed:

  • Afferent arteriole - where blood enters the capillary bed
  • Capillaries - where filtration occurs
  • Efferent arteriole - where blood leaves the capillary bed
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4
Q

What % of the plasma moves into the tubule?

Where does it go?

A

20%

Bowman's capsule 
Proximal tubule 
Loop of henle 
Distal tubule 
Collecting duct
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5
Q

What happens to the plasma in the proximal tubule?

A

Modified

Turned into urine

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6
Q

Where is the filtration barrier present?

What happens here?

A

In the glomerular capillaries

Filtrate has to pass through 3 layers before getting into the Bowman’s capsule - if doesn’t pass through, it is not filtered

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7
Q

What is the structure of the filtration barrier?

A

3 layers:
1) Endothelial cells - wall of the capillary

2) Basement membrane
3) Epithelial cells (podocytes)

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8
Q

What are podocytes?

A

Cells in the Bowman’s capsule that wrap around capillaries of the glomerulus

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9
Q

What is the main site of determination if something is filtered or not?

A

The basement membrane in the filtration barrier of the glomerular capillaries - thin layer

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10
Q

What is the structure of the endothelial cell layer in the filtration barrier?

A

Flat cells with large nuclei

Cells in contact with each other

With circular fenestrations

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11
Q

What are fenestrations in endothelial cells?

What moves/doesn’t move through here?

A

Gaps between the cells

Filtrate moves through (ions, solutes)
Blood cells, platelets and large proteins don’t move through

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12
Q

What is the structure of the basement membrane?

A
  • Continuous layer that surrounds the glomerular capillaries
  • Comprised of many different glycoproteins
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13
Q

What are the glycoproteins that make up the base membrane?

A

Collagen

Laminin

Fibronectin

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14
Q

What charge does the basement membrane carry?

What is this important in?

A

-ve charge

Important in the determination of filtration

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15
Q

What 3 features determine if something crosses the filtration barrier or not?

A

1) Molecular shape
2) Molecular size (mass/weight)
3) Charge

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16
Q

What moves through the filtration barrier easily?

A

Small molecular weights

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17
Q

What happens when molecules have larger sizes?

A

Molecular shape becomes important to determine is something does/doesn’t cross the barrier:

  • Bulky shapes = not transported
  • Less bulky = transported
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18
Q

Do the podocytes determine if something is going to be filtered or not?

A

NO - everything that is going to be filtered is already determined

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19
Q

What are the 2 roles of the podocytes in the filtration barrier?

A

1) Provide STRUCTURAL SUPPORT of the glomerular capillaries and the filtration barrier
2) Play a role in PHAGOCYTOSIS of foreign bodies

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20
Q

What is the structure of the podocytes?

A

1) Trabeculae - projections out from the cell body

2) Pedicels - Small finger like projections from the larger . trabeculae

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21
Q

What do the pedicels form?

How?

A

Form SLIT PORES (gaps)

Interdigitate with each other (cross over but have gaps between them)

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22
Q

What charge is filtered more readily?

Why?

A

+ve charge

Basement membrane carries a negative charger - attracts +ve and repels -ve

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23
Q

What is the filtrate to plasma ratio?

A

How much of a substance is in the filtrate (In the Bowmann’s capsule) / how much is in the plasma

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24
Q

What is the filtrate/plasma ratio of something that is FREELY filtered?

Why?

A

1

Concentration in the filtrate is the same as the concentration in the plasma

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25
What does a filtrate/plasma ratio of 0 mean?
Nothing in the filtrate
26
What does a filtrate/plasma ratio of 0.5 mean?
There is restrictions on what is filtered (only 50%)
27
As mass increases, what happens to the chance of filtration?
It decreases
28
Above what molecular weight are molecules not filtered?
About 70,000 daltons
29
When ARE -vely charged ions filtered?
When they are in the very SMALL molecular weight range
30
What is Dextran?
Chain of glucose molecules with a negative charge
31
What can Dextran be used for? How?
Used to show what types of molecules can/can't cross the membrane Can add/remove glucose molecules to increase/decrease the molecular weight Can modify Dextran/remove charge
32
When does the charge of the molecule passing the filtration barrier become an important factor to determine if something is filtered or not?
Large molecular weight proteins
33
For the same molecular weight but a molecule with and without a -ve charge, what crosses the filtration barrier easier?
No charge
34
What is filtration in the kidney movement from --> where?
FLUID from the plasma --> Bowmann's capsule
35
What is the glomerular filtration rate proportional to?
Forces that favour filtration - forces that oppose filtration
36
What are the 4 different forces that need to be considered in order to calculate the GFR?
Pcap - Hydrostatic pressure in the capillary Pbc - HP in the bowmann's capsule Πcap - Oncotic pressure in the kidney Πbc - Oncotic pressure in the bowmann's capsule
37
What is GFR proportional to?
(Pcap + Πbc) - (Pbc + Πcap)
38
What factors FAVOUR filtration?
Hydrostatic pressure in the capillaries Oncotic pressure in the bowmann's capsule
39
What factors OPPOSE filtration?
Hydrostatic pressure in the bowmann's capsule Oncotic pressure in the capillary
40
What is hydrostatic pressure?
Pressure of the FLUID in a compartment
41
What oncotic pressure generated by? What does this gradient do?
The PROTEINS in a the plasma which form an OSMOTIC gradient Osmotic gradient - driving force for fluid movement (from high --> low
42
What does oncotic pressure in the capillaries cause?
The RETENTION of fluid
43
What does oncotic pressure in the Bomann's capsule cause?
The FILTRATION of fluid
44
What is the hydrostatic pressure in the capillaries?
The pressure of the plasma that pushing out on the capillary wall
45
What is the hydrostatic pressure in the Bowmann's capsule?
The pressure of the plasma pushing on the basement membrane of the podocytes (against the capillary wall)
46
Why is the oncotic pressure in the Bowmann's capsule NOT considered in the GFR equation?
Proteins are NOT filtered It is the proteins that form an oncotic gradient
47
What is the filtration coefficient? What is it a measure of and what does it determine?
Kf Measure of the PERMEABILITY of the filtration barrier Determines how much filtration occurs
48
What does a high Kf mean?
More filtration
49
What does a low Kf mean?
Less filtration
50
What is the value of Pbc? How does this change down the length of the glomerular capillary?
Approx. 20mmHg Doesn't change
51
Why doesn't the Pbc change down the length of the GC?
Fluid moves into the BC at the SAME rate as fluid moves out (into the nephron) So the volume of fluid in the BC remains constant Pbc --> constant
52
What is the AVERAGE value of Pcap? How does this change down the length of the glomerular capillary?Why?
Approx. 60mmHg (at the start - just above, at the end - just below) Changes slightly - plasma volume determines the Pcap - Plasma moves down the GC --> filtration occurs
53
What happens to the Πcap as travel down the GC? Why?
Starts at 25mmHg and INCREASES to 30mmHg - Π pressure is set by the CONCENTRATION of the proteins - Proteins don't move but fluid is lost from the capillary due to filtration - Concentration of the proteins increase, oncotic pressure increase
54
What is the average filtration pressure in the GC?
At the start - just above 10mmHg At the end - just below 10mmHg
55
Where does filtration occur in the GC? How is this different to other capillaries in the body?
Throughout the ENTIRE length In other capillary beds: - Half way down the capillary, move from net FILTRATION (fluid out of capillary) to a MINUS value (fluid into the capillary)
56
How GFR calculated?
GFR = Kf (Pcap + Πbc) - (Pbc + Πcap)
57
How can Kf be estimated?
Using the CLEARANCE technique
58
What is the value of GFR?
125ml/min
59
What is the SNGFR? What is the value?
Single nephron glomerular filtration rate 50nl/min
60
Why is it important to maintain a relatively CONSTANT glomerular filtration rate?
If drops - not filtering enough plasma This can cause renal faliure
61
What 2 things is the kidney the site of?
1) EXCRETION of toxins from the body | 2) REGULATION of the COMPOSITION and VOLUME of the fluids in the body
62
What 2 things can affect the GFR?
1) Filtration rate | 2) Renal blood flow
63
When filtration rate or renal blood flow change, what must be regulated? When can this regulation occur? When can't this regulation occur?
GFR Can occur with arterial BP change within 80-200mmHg Can't occur with arterial BP change outside of 80-200mmHg
64
What happens is renal blood flow decreases below 80mmHg?
GFR decreases
65
What happens is renal blood flow increases above 200mmHg?
GFR increases
66
How does the body compensate for changes in GFR?
By changing the resistance in the AFFERENT arteriole
67
How does the afferent arteriole resistance change when GFR decreases? What does this cause?
Decrease resistance of the afferent arteriole (through VASODILATION) - Increases renal BF through the arteriole - Larger volume of blood through the GC - Increase in Pcap - Increases GFR (through the equation)
68
How does the afferent arteriole resistance change when GFR increases? What does this cause?
Increase the resistance of the afferent arteriole (through VASOCONTRACTION) - RBF decreases - Smaller volume of blood through the GC - Decrease in Pcap - Decrease in GFR (through eqn)
69
What is the control of GFR through the afferent arteriole resistance called?
Autoregulation
70
When is GFR increased? What does this stimulate?
When arterial BP increase Stimulate auto regulation which decreases GFR
71
When is GFR decreased? What does this stimulate?
When arterial BP decrease Stimulate auto regulation which increases GFR
72
What are the 2 theories in how the kidneys detect changes in the GFR and mediate the changes in resistance in the afferent arteriole? What is the likely mechanism?
1) Myogenetic theory 2) Tubuloglomerular theory Likely that BOTH of these theories work TOGETHER
73
What is the myogenetic theory?
Response is a property of the afferent arteriole smooth muscle: - Changes in arterial BP that change RBF - Stimulate or inhibit STRETCH RECEPTORS in the muscle of the afferent arteriole - Leads to signalling which change the degree of afferent arteriole constriction - Increase/decrease afferent arteriole resistance
74
What are macular densa cells?
Cells of the distal tubule that are located NEXT TO the afferent arterioles
75
What structures do macula densa cells have? What do these do?
Cilia: - Project from the apical membrane and detect the rate of flow of the tubular fluid
76
What is the tubulo glomerular theory?
- Cilia of the macula densa cells detect the rate of fluid flow - When there is a change in the flow - cilia release vasoactive chemicals - These chemicals cause the afferent arteriole to constrict/dilate
77
What are released from the cilia of the macular densa cells when there is an increase in GFR and blood flow?
Release vasoCONSTRICTORS
78
What are released from the cilia of the macular densa cells when there is an decrease in GFR and blood flow?
Release vasoDILATORS

BMS 242 - Phys and pharm of cells (13 decks)

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