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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
Q

What does a filtrate/plasma ratio of 0 mean?

A

Nothing in the filtrate

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26
Q

What does a filtrate/plasma ratio of 0.5 mean?

A

There is restrictions on what is filtered (only 50%)

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27
Q

As mass increases, what happens to the chance of filtration?

A

It decreases

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28
Q

Above what molecular weight are molecules not filtered?

A

About 70,000 daltons

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29
Q

When ARE -vely charged ions filtered?

A

When they are in the very SMALL molecular weight range

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30
Q

What is Dextran?

A

Chain of glucose molecules with a negative charge

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31
Q

What can Dextran be used for?

How?

A

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

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32
Q

When does the charge of the molecule passing the filtration barrier become an important factor to determine if something is filtered or not?

A

Large molecular weight proteins

33
Q

For the same molecular weight but a molecule with and without a -ve charge, what crosses the filtration barrier easier?

34
Q

What is filtration in the kidney movement from –> where?

A

FLUID from the plasma –> Bowmann’s capsule

35
Q

What is the glomerular filtration rate proportional to?

A

Forces that favour filtration - forces that oppose filtration

36
Q

What are the 4 different forces that need to be considered in order to calculate the GFR?

A

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
Q

What is GFR proportional to?

A

(Pcap + Πbc) - (Pbc + Πcap)

38
Q

What factors FAVOUR filtration?

A

Hydrostatic pressure in the capillaries

Oncotic pressure in the bowmann’s capsule

39
Q

What factors OPPOSE filtration?

A

Hydrostatic pressure in the bowmann’s capsule

Oncotic pressure in the capillary

40
Q

What is hydrostatic pressure?

A

Pressure of the FLUID in a compartment

41
Q

What oncotic pressure generated by?

What does this gradient do?

A

The PROTEINS in a the plasma which form an OSMOTIC gradient

Osmotic gradient - driving force for fluid movement (from high –> low

42
Q

What does oncotic pressure in the capillaries cause?

A

The RETENTION of fluid

43
Q

What does oncotic pressure in the Bomann’s capsule cause?

A

The FILTRATION of fluid

44
Q

What is the hydrostatic pressure in the capillaries?

A

The pressure of the plasma that pushing out on the capillary wall

45
Q

What is the hydrostatic pressure in the Bowmann’s capsule?

A

The pressure of the plasma pushing on the basement membrane of the podocytes (against the capillary wall)

46
Q

Why is the oncotic pressure in the Bowmann’s capsule NOT considered in the GFR equation?

A

Proteins are NOT filtered

It is the proteins that form an oncotic gradient

47
Q

What is the filtration coefficient?

What is it a measure of and what does it determine?

A

Kf

Measure of the PERMEABILITY of the filtration barrier
Determines how much filtration occurs

48
Q

What does a high Kf mean?

A

More filtration

49
Q

What does a low Kf mean?

A

Less filtration

50
Q

What is the value of Pbc?

How does this change down the length of the glomerular capillary?

A

Approx. 20mmHg

Doesn’t change

51
Q

Why doesn’t the Pbc change down the length of the GC?

A

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
Q

What is the AVERAGE value of Pcap?

How does this change down the length of the glomerular capillary?Why?

A

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
Q

What happens to the Πcap as travel down the GC?

Why?

A

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
Q

What is the average filtration pressure in the GC?

A

At the start - just above 10mmHg

At the end - just below 10mmHg

55
Q

Where does filtration occur in the GC?

How is this different to other capillaries in the body?

A

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
Q

How GFR calculated?

A

GFR = Kf (Pcap + Πbc) - (Pbc + Πcap)

57
Q

How can Kf be estimated?

A

Using the CLEARANCE technique

58
Q

What is the value of GFR?

59
Q

What is the SNGFR?

What is the value?

A

Single nephron glomerular filtration rate

50nl/min

60
Q

Why is it important to maintain a relatively CONSTANT glomerular filtration rate?

A

If drops - not filtering enough plasma

This can cause renal faliure

61
Q

What 2 things is the kidney the site of?

A

1) EXCRETION of toxins from the body

2) REGULATION of the COMPOSITION and VOLUME of the fluids in the body

62
Q

What 2 things can affect the GFR?

A

1) Filtration rate

2) Renal blood flow

63
Q

When filtration rate or renal blood flow change, what must be regulated?

When can this regulation occur?

When can’t this regulation occur?

A

GFR

Can occur with arterial BP change within 80-200mmHg

Can’t occur with arterial BP change outside of 80-200mmHg

64
Q

What happens is renal blood flow decreases below 80mmHg?

A

GFR decreases

65
Q

What happens is renal blood flow increases above 200mmHg?

A

GFR increases

66
Q

How does the body compensate for changes in GFR?

A

By changing the resistance in the AFFERENT arteriole

67
Q

How does the afferent arteriole resistance change when GFR decreases?

What does this cause?

A

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
Q

How does the afferent arteriole resistance change when GFR increases?

What does this cause?

A

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
Q

What is the control of GFR through the afferent arteriole resistance called?

A

Autoregulation

70
Q

When is GFR increased?

What does this stimulate?

A

When arterial BP increase

Stimulate auto regulation which decreases GFR

71
Q

When is GFR decreased?

What does this stimulate?

A

When arterial BP decrease

Stimulate auto regulation which increases GFR

72
Q

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?

A

1) Myogenetic theory
2) Tubuloglomerular theory

Likely that BOTH of these theories work TOGETHER

73
Q

What is the myogenetic theory?

A

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
Q

What are macular densa cells?

A

Cells of the distal tubule that are located NEXT TO the afferent arterioles

75
Q

What structures do macula densa cells have?

What do these do?

A

Cilia:

  • Project from the apical membrane and detect the rate of flow of the tubular fluid
76
Q

What is the tubulo glomerular theory?

A
  • 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
Q

What are released from the cilia of the macular densa cells when there is an increase in GFR and blood flow?

A

Release vasoCONSTRICTORS

78
Q

What are released from the cilia of the macular densa cells when there is an decrease in GFR and blood flow?

A

Release vasoDILATORS

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

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