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CRR > L24 - Renal Perfusion and Glomerular Filtration > Flashcards

L24 - Renal Perfusion and Glomerular Filtration Flashcards

1
Q

What is the structure of the glomerulus?

A

A ball of capillaries which is inserted into the Bowman’s capsule

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2
Q

Describe the blood supply of the Glomerulus

A

1) Afferent Arterioles: supply the glomerulus.

2) Glomerulus is drains by the efferent arterioles.

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3
Q

What is the function of the glomerulus?

A

Initial site of urine production (where urine filtrate is initially produced)

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4
Q

Describe the structure of the Bowman’s Capsule?

A

1) Outer Parietal layer - continuous with the renal tubule outer layer
2) Capsular space - where filtrate collects.
3) Inner visceral layer - composed of podocytes with envelop glomerular capillaries.

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5
Q

What is the function of the glomerular filter?

A

Glomerular filtrate produced an ultra-filtrate of plasma.

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6
Q

What is ultra-filtration?

A

Ultra-filtration is molecular level filtration e.g. sodium, potassium are pushed across.

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7
Q

What happens to the glomerular ultrafiltrate before it reaches the collecting ducts?

A

The glomerular ultra-filtrate is modified along the renal tubule until it becomes urine in the collecting ducts.

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8
Q

Describe the structure of the glomerular filtrate?

A

1) Endothelium
2) Basement Membrane
3) Podocytes

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9
Q

What is a special feature of the podocytes? What is their purpose?

A

Podocytes have pedicels which increase the surface area for filtration

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10
Q

Describe the passage of substances across the glomerular filter?

A

Molecules from blood plasma must (passage of filtrate from the blood plasma into the capsular space)

1) pass through the fenestrated capillary epithelium (fenestrations are 50-100nm in diameter)
2) pass through the thick basement membrane (main filtration barrier)
3) pass though filtration slits between the podocyte feet into the capsular space

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11
Q

Deesribe the structure of the capillary endothelium?

A

They are fenestrated capillaries (which means that they are leaky and

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12
Q

Which type of cells are not allowed entry through the capillary endothelium?

A

Capillary endothelium blocks blood cells (RBC, WBC’s) and platelets - so you shouldn’t see blood in your urine.

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13
Q

What is the basement membrane’s function?

A

It is the main filtration barrier.

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14
Q

Which cells secrete the basement membrane?

A

Secreted by podocytes

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15
Q

Which molecules is the basement membrane made up of?

A

Collagen and glycoproteins

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16
Q

What is the charge on the basement membrane? Why is this useful?

A

Basement membrane is negatively charged. It repels negative ions so it is a barrier to proteins.

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17
Q

What are the functions of the podocytes ?

A

1) Maintain basement membrane
2) Act as a supplementary filtration berries via slit membranes.
3) Phagocytic - remove escaping cells and macromolecules.

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18
Q

Describe the structure of the podocytes?

A

1) Have pedicels (interdigitating foot processes

2) Negativly charged glycocalyx coating

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19
Q

What is the charge on the podocytes? Why is this?

A

Podocytes are negatively charged due to their glycococalyx coating.

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20
Q

Molecules of which sizes are allowed entry across the glomerular filter?

A

Free filtration below 7000Da

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21
Q

Molecules of which sizes are not allowed entry across the glomerular filter?

A

None above 70000Da

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22
Q

How is the entrance of proteins across the glomerular filter prevented?

A

Negative charge of the basement membrane prevents the filtration of proteins (which have a negative charge)

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23
Q

What is Pbc? (Bowman’s capsule hydrostatic pressure)

A

Forcing blood out of the Bowman capsule back into the glomerular capillaries.

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24
Q

What is Pcap? (Capillary Hydrostatic pressure)

A

Forcing fluid out of the glomerular capillaries and into the capsular space

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25
Q

What is πcap? (Capillary protein oncotic pressure)

A

Plasma proteins in the capillary which exerts osmotic pressure - which encourages fluid to move into the glomerular capillaries.

26
Q

Why is the value of πbc (Bowman’s capsule protein oncotic pressure) assumed to be 0?

A

Because, proteins are not filtered into the bowman’s capsule so can’t exert an osmotic pressure from within the bowman’s capsule.

27
Q

What is the equation for net filtration pressure (NFP)?

A 
NFP = (Pcap + πbc) – (Pbc + πcap)
NFP = (forces favouring filtration - forces opposing filtration)
28
Q

What is the equation for GFR (glomerular filtration rate)?

A

GFR is proportional to NFP.

So, GFR =(Pcap + πbc) – (Pbc + πcap)

As, πbc = 0 (because no protein enters the bowman’s capsule).

Therefore, GFR = Pcap – Pbc - πcap

29
Q

What is the filtration coefficient (Kf)?

A

Kf = function of glomerular capillary permeability and area available for filtration.

30
Q

What is Kf (filtration coefficient) used for? How does it change the GFR equation?

A

Kf is used to work out real GFR measurements.

So, GFR = Kf (Pcap - Pbc - πcap)

i.e. GFR = Kf (NFP)

31
Q

What is the average value for GFR?

A

Normal value is 125ml/min

32
Q

If GFR = 125 ml/min and NFP = 10, what is Kf?

A

Kf = 125/10 = 12.5 ml/min/mmHg

33
Q

Which factors affect the GFR?

A

1) Kf
2) Capillary Hydrostatic Pressure
3) Capillary Oncotic Pressure
4) Bowman’s Capsule Hydrostatic Pressure
5) Bowman’s Capsule Oncotic Pressure

34
Q

How is GFR compared across adults? How does this change the units for GFR?

A

GFR is normalised to 1.73m2.

GFR = 125 ml/min/1.73m2

35
Q

How much blood enters the kidneys (RENAL BLOOD FLOW)?

A

Renal blood flow (RBF) = 1.1 litres/min

36
Q

What proportion of cardiac output does renal blood flow account for?

A

20-25% of Cardiac Output is Renal Blood Flow.

37
Q

What is renal plasma flow (RPF)? What is the value?

A

The proportion of RBF that is filtered = 600ml of the 1.1 litres is filterable.

38
Q

Why is the renal plasma flow lower than the renal blood flow?

A

Aside from the filterable 600ml RPF value, the rest of the renal blood flow volume is composed of cells (which can’t be filtered = blocked by capillary endothelium)

39
Q

If GFR = 125ml/min, what percentage of the renal blood flow is filtered per minute? (What is the filtration fraction?)

A

125/600 x 100 = 20% (= Filtration Fraction).

So 80% of RPF is unfiltered after 1 minute.

After 5 minutes = all RPF is filtered

40
Q

What does auto regulation of RBF and GFR mean?

A

The kidney regulates RBF and GFR (auto regulation = local blood flow regulation) to ensure that they are constant throughout normal ranges of of blood pressure?

41
Q

Between which blood pressure range are the RBF and GFR values constant?

A

90mmHg - 200mmHg

42
Q

At which blood pressure does GFR and RBF begin to increase?

A

Blood pressures above = 200 mmHg = GFR and RBF increase.

43
Q

At which blood pressure does GFR and RBF begin to decrease?

A

Blood pressure below = 90mmHg = GFR and RBF = decrease.

44
Q

Which auto regulation mechanisms are used to keep RBF and GFR constant?

A

1) Myogenic Feedback

2) Tubuloglomerular Feedback

45
Q

What is myogenic feedback?

A

Regulation of the RBF and GFR by the smooth muscle cells in the afferent arteriole.

46
Q

Describe the myogenic feedback mechanism when there is high systolic blood pressure?

A

1) High systolic blood pressure causes stretch on the afferent arteriole.
2) Afferent arteriole vasoconstricts (diameter of lumen decreases)
3) This decreases renal blood flow which decreases GFR (less blood flowing through = less filtration occurs).

47
Q

Describe the myogenic feedback mechanism when there is low systolic blood pressure?

A

1) Low systolic blood pressure detected by stretch receptors on afferent arteriole.
2) Afferent arteriole dilates
3) This increases RBF which increases GFR (more blood flowing through = more filtration occurs)

48
Q

What is the effect of a dilated efferent arteriole on the RBF and GFR?

A

Dilation of the renal blood flow will increase renal blood flow and decreases blood pressure at the glomerulus = this means that GFR decreases.

49
Q

What is the effect of a constricted efferent arteriole on the RBF and GFR?

A

Constriction of the efferent arteriole = decreases renal blood flow = increases blood pressure at the glomerulus = means that GFR increases.

50
Q

What is the juxtaglomerular apparatus?

A

The region of contact between the macula dense cells at the distal tubule and the afferent and efferent arterioles.

51
Q

What process is the juxtaglomerular apparatus involved in?

A

The Tubuloglomerular feedback mechanism for regulating (keeping constant) RBF and GFR.

52
Q

Which cells are involved in the Tubuloglomerular feedback mechanism?

A

1) Macula Densa cells - at the distal tubule.
2) Juxtaglomerular Cells - at the afferent/efferent arterioles

These cells are in contact.

53
Q

What is the role of the Macula Densa cells in the tubuloglomerula feedback mechanism?

A

Macula dense cells regulate GFR by monitoring the fluid flow at the distal tubule and the NaCl content of the filtrate fluid.

54
Q

Describe the action of the tubuloglomerular feedback mechanism when GFR is high.

A

1) Macula Densa cells detect a high GFR as there is a high NaCL conc and high fluid flow in the distal tubule.
2) Macula Densa cells inhibit nitric oxide secretion (NO = causes vasodilation)
3) Decreased NO causes vasoconstriction of afferent arterioles.
4) GFR returns to normal
5) Normal NaCl and fluid flow in the distal tubule is restored

55
Q

Describe the action of the tubuloglomerular feedback mechanism when GFR is low.

A

1) A low GFR means a low NaCl and low fluid flow in the distal tube
2) This is detected by the macula densa
3) This means that more NO is secreted.
4) This causes vsodilation of the afferent arteriole.
5) This causes NaCL and fluid flow to increase = back to normal.

56
Q

What type of nerve innervation does the kidney receive?

A

The kidney recieves rich sympathetic innervation to the kidney.

57
Q

Does denervation of the kidney have an effect on the kidney?

A

Denervation has little effect on the kidney (e.g. transplantation)

58
Q

Which part of the kidney does the sympathetic nerves innervate?

A

The smooth muscle fibres of the afferent arteriole of the kidney.

59
Q

What is the effect of increased sympathetic (nerve) innervation/activation of the kidney?

A

1) Vasoconstriction of afferent arteriole.

2) Reduces RBF and GFR.

60
Q

How can you increased the activation of nerves in the kidney?

A

1) Exercise

2) Circulatory Shock (leads to increased activation of nerves in the kidney)

CRR (3 decks)

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