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Block 1 CTB > Glomerular Filtration > Flashcards

Glomerular Filtration Flashcards

1
Q

What percentage of cardiac output do the kidneys receive?

A

22%

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2
Q

What is cardiac output in l/min?

A

5 l/min

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3
Q

What is renal blood flow in ml/min?

A

1,100 ml/min

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4
Q

Haematocrit makes up what percentage of renal blood flow?

A

40%

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5
Q

How many ml/min is renal plasma flow?

A

660 ml/min

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6
Q

What percentage of renal plasma flow passes through the filtration barrier?

A

20% (132ml)

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7
Q

How many l/day of filtrate is formed?

A

180 l/day

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8
Q

The ultrafiltrate does not contain which 2 things?

A

Proteins and blood cells

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9
Q

What are the 3 layers of the glomerular filtration barrier?

A

Glomerular capillary endothelium

Basement membrane

Epithelial cells (podocytes)

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10
Q

Which substances pass through the glomerular capillary endothelium? What is not filtered through this layer?

A

Water, solutes, and plasma proteins are all filtered across.

Blood cells and platelets are not as they are too big.

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11
Q

What is the basement membrane made up of? Give 4 examples.

A

Extracellular matrix proteins and negatively charged glycoproteins.

Type IV collagen
Laminin
Fibronectin
Entactin

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12
Q

Describe the charge of plasma proteins and what this means for the filtration of them.

A

Plasma proteins have a net negative charge, and they will be repelled and restricted from filtration by the negative charge of the basement membrane.

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13
Q

Describe the arrangement of the primary processes of the podocytes and their function.

A

Wrap around the glomerular capillaries to strengthen them against high pressures.

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14
Q

Describe the arrangement of the secondary processes of the podocytes.

A

Interdigitate to form filtration slits

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15
Q

The slit diaphragms which bridge the filtration slits are made of which protein?

A

Nephrin

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16
Q

Define glomerular filtration rate (GFR).

A

The volume of filtrate formed by all the nephrons in both kidneys per unit time

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17
Q

What is the equation of GFR (the 2 factors which determine GFR)?

A

GFR = Kf x NFP

(glomerular capillary filtration coefficient x net filtration pressure)

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18
Q

What is the filtration coefficient?

A

A measure of the permeability and surface area of the glomerular capillary wall

19
Q

Which 2 factors contribute to the filtration coefficient?

A

Hydraulic conductivity (permeability) of the filtration barrier per unit of surface area

Total surface area available for filtration

20
Q

The filtration coefficient for glomerular capillaries is greater than that of systemic capillaries because of the combination of what?

A

Higher total surface area

Higher intrinsic water permeability of the barrier due to holes in the basement membrane and fenestrated endothelium

21
Q

Which forces are involved in net filtration pressure?

A

Starling forces / pressure - 2 hydrostatic pressures and 2 oncotic pressures

22
Q

What are hydrostatic pressures?

A

Forces that push water and solutes out of the compartment they are in

23
Q

What are colloid osmotic (oncotic) pressures?

A

Forces holding water and solutes in the compartment they are in

24
Q

Most physiological regulation of GFR occurs due to changes in which factor?

A

Glomerular hydrostatic pressure

25
Q

What 3 things is glomerular hydrostatic pressure dependent on?

A

Systemic arterial pressure

Afferent arteriole resistance

Efferent arteriole resistance

26
Q

What effect does angiotensin II have on glomerular hydrostatic pressure and how?

A

Increases glomerular HP by preferentially constricting the EA

27
Q

What effect do prostaglandins and atrial natriuretic peptide (ANP) have on glomerular hydrostatic pressure and how?

A

Increases glomerular HP by dilating the AA

28
Q

What effect do noradrenaline, adenosine, and endothelin have on glomerular hydrostatic pressure and how?

A

Reduces glomerular HP by constricting AA

29
Q

What are the 2 mechanisms of autoregulation of GFR?

A

Myogenic response

Tubuloglomerular feedback

30
Q

Define the myogenic response.

A

The inherent ability of smooth muscle cells in afferent arterioles to respond to changes in vessel diameter by contracting or relaxing

31
Q

Tubuloglomerular feedback works by linking what?

A

Changes in NaCl in the tubule lumen to the control of its own afferent arteriole resistance in the same nephron

32
Q

In tubuloglomerular feedback, which cells sense a change in the concentration of NaCl and where are they located?

A

Macula densa cells in the early part of the DCT

33
Q

How are Na+ and Cl- transported into the macula densa cells?

A

NKCC transporter

34
Q

Once inside the macula densa cells, how do increased levels of Cl- lead to constriction of the AA and subsequent decrease in GFR?

A

The Cl- depolarizes the basolateral membrane of the macula densa cells, which opens Ca2+ channels and causes increased intracellular Ca2+ concentration. This increased intracellular Ca2+ releases adenosine from macula densa cells. The adenosine acts locally, by a paracrine mechanism, to cause constriction of the nearby AA.

35
Q

Which 3 tests are routinely used to assess renal function?

A

Estimated GFR (eGFR)

Serum creatinine

Serum Urea

36
Q

eGFR is relatively inaccurate for what? But is useful for what?

A

As a point measure of GFR.

But useful for monitoring trends.

37
Q

How would an amputation affect eGFR and why?

A

Increase eGFR due to lower creatinine levels in the blood

38
Q

How would the consumption of meat affect eGFR and why?

A

Decreased eGFR due to higher creatinine levels in the blood

39
Q

Most calculations which are used to calculate eGFR consider which 3 factors?

A

Serum creatinine, age, and sex

40
Q

What is the name of the equation recommended by NICE to calculate eGFR?

A

CKD-EPI

41
Q

Newer tests used to calculate eGFR measure which substance?

A

Serum Cystatin C

42
Q

Give a limitation of using the CKD-EPI equation to calculate eGFR.

A

Does not include a measure of body size (amputations, malnutrition etc).

43
Q

eGFR cannot be used for drug dose calculation for highly toxic drugs such as chemotherapy drugs. In these circumstances, where a more accurate eGFR is required, what test should be used?

A

Inulin infusion

Block 1 CTB (14 decks)

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