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Physiology and Pharmacology of Cells > L2 - Glomerular Filtration > Flashcards

L2 - Glomerular Filtration Flashcards

1
Q

What is the role of the glomerulus?

A

Glomerulus filters plasma
180l/day filtrate
Total plasma passes filtration barrier 65 times a day

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2
Q

What does the glomerulus allow the passage of?

A

Water and small molecules

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3
Q

What does the glomerulus restrict the passage of?

A

Blood cells and proteins

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4
Q

What is the structure of the glomerulus?

A

Capillary bed
Filtration occurs within the capillaries
Plasma enters via the afferent arteriole and leaves via the efferent arteriole

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5
Q

What are the 3 layers of the filtration barrier?

A

Endothelial cells
Basement membrane
Epithelial cells - podocytes

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6
Q

What does the endothelial cell filtration barrier consist of?

A

Flat large nuclei
Circular fenestrations
In contact with each other
Filters blood cells and platelets

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7
Q

What does the basement membrane filtration barrier consist of?

A

Continuous - main barrier for filtration
Composed of glycoproteins - collagen, laminin, fibronectin
Negatively charge
Filtration based on molecular shape, size and charge

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8
Q

What does the epithelial cell filtration barrier consist of?

A

Trabecula – projections from cell body
Pedicles – projections from trabecula
- They interdigitate creating slit pores
- Slit pores allow filtrate to move through
Maintenance of structure
Phagocytosis of foreign bodies

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9
Q

If the filtration: plasma ratio is 0 what does this show?

A

None of the plasma has been filtered

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10
Q

If the filtration: plasma ratio is 0.5 what does this show?

A

Half of the plasma has been filtered

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11
Q

What 3 things determine what is filtered?

A

Molecular size
Charge
Shape

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12
Q

How does molecular size affect filtration?

A

As the mass of the molecule increases the likelihood of filtration decreases
At 70,000 Daltons it will not be filtrated

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13
Q

How does charge affect filtration

A

Negatively charged molecules are less likely to be filtered
- Tested this by removing the negative charge of dextran molecule
This becomes insignificant if the molecule is very small

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14
Q

What is the filtration co-efficient?

A

Kf

A measure of the permeability of the filtration barrier

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15
Q

What are starling forces?

A 
GFR alpha
= forces favouring – forces opposing
= (Pcap + OPbc) – (Pbc + OPcap)
- P = hydrostatic pressure
- OP = oncotic pressure
- cap = capillary
- bc = Bowman’s capsule
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16
Q

Which two pressures favour filtration?

A

Hydrostatic pressure capillary

Oncotic pressure in Bowmans capsule

17
Q

Summary of forces in the Bowmans capsule?

A

Volume of fluid is constant

Pressure is constant

18
Q

Summary of forces in the glomerular capillary?

A

Hydrostatic pressure averages at 60 mmHg
- Along the capillary as plasma volume decreases as does the pressure
Oncotic pressure starts at 20 mmHg and rises to 30 mmHg
- Determined by the concentration of proteins
- Losing fluid from the capillary increases protein concentration

19
Q

GFR equation

A

GFR
= Kf (Pcap + OPbc)–(Pbc + OPcap)
= 125 ml/min

20
Q

What is the single nephron GFR?

A

50 nl/min

21
Q

What helps in autoregulation?

A

Afferent arteriole resistance?

22
Q

What series of events happens after an increase in arterial BP?

A

Increase RBF
Increase GFR
Autoregulation increases resistance afferent arteriole Decrease RBF and Pcap
Decrease GFR

23
Q

What series of events happens after a decrease in arterial BP?

A

Decrease RBF
Decrease GFR
Autoregulation decreases resistance afferent arteriole Increase RBF and Pcap
Increase GFR

24
Q

Autoregulation of GFR - what is the myogenic theory?

A

Response is a property of afferent arteriole smooth muscle

  1. Increase arterial BP
  2. Stretches afferent arteriole
  3. Afferent arteriole constriction
  4. Increase afferent arteriole resistance
25
Q

Autoregulation of GFR - what is the tubuloglomerular feedback theory?

A

Response is a property of juxtaglomerular apparatus
Macula densa cells in the distal tubule
- Have cilia that detect the rate of flow of tubular fluid
- Release vasoactive chemicals

26
Q

What do macula densa cells do in response to and increase in GFR and flow?

A

Release vasoconstrictors

Leads to afferent arteriole constriction

Physiology and Pharmacology of Cells (13 decks)

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