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Renal > Glomerular Filtration and Renal Blood Flow > Flashcards

Glomerular Filtration and Renal Blood Flow Flashcards

1
Q

What are some barriers to filtration in the kidneys?

A

Glomerular capillary endothelium = red blood cell barrier
Basement membrane = plasma protein barrier
Slit processes of podocytes = plasma protein barrier

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2
Q

What must fluid filtered from the glomerulus into the Bowman’s capsule pass through?

A

The three layers that make up the glomerular membrane

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3
Q

What are the forces that make up the net filtration pressure?

A

Glomerular capillary blood pressure (BPgc)
Bowman’s capsule oncotic pressure (COPbc)
Bowman’s capsule hydrostatic pressure (HPbc)
Capillary oncotic pressure (COPgc)

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4
Q

How is the net filtration pressure calculated?

A

(BPgc + COPbc) - (HPbc + COPgc)

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5
Q

What is the oncotic pressure equal to?

A

The colloid osmotic pressure

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6
Q

What is the balance of hydrostatic forces and osmotic forces?

A

Staring forces

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7
Q

What is the glomerular filtration rate (GFR)?

A

Rate at which protein-free plasma is filtered from the glomeruli into the Bowman’s capsule per unit time

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8
Q

How can the glomerular filtration rate be calculated?

A

GFR = Kf x net filtration pressure

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9
Q

What is Kf?

A

The filtration coefficient = how holey the glomerular membrane is

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10
Q

What is the normal glomerular filtration rate?

A

125 ml/min

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11
Q

What is the major determinant of glomerular filtration rate?

A

Glomerular capillary fluid (blood) pressure (BPgc)

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12
Q

How is GFR regulated extrinsically?

A

Sympathetic control via baroreceptor reflex

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13
Q

How is GFR regulated intrinsically?

A

Autoregulation = myogenic mechanism and tubuloglomerular feedback mechanism

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14
Q

How does increased arterial blood pressure affect the GFR?

A

Increases blood flow into glomerulus = glomerular blood pressure and net filtration both increase, which increases GFR

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15
Q

What happens to the glomerular filtration rate if the glomerular blood pressure (BPgc) falls?

A

GFR decreases = occurs after constriction of afferent arteriole

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16
Q

Why don’t changes in systemic blood pressure always result in changes in GFR?

A

Autoregulation prevents short term changes in systemic arterial pressure affecting GFR

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17
Q

If GFR protected form changes in mean arterial blood pressure over a wide range of values?

A

Yes = as is renal blood flow

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18
Q

What occurs in the myogenic mechanism in the kidneys?

A

If vascular smooth muscle is stretched (increases arterial pressure), it contracts to constrict the arteriole

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19
Q

What occurs in the tubuloglomerular feedback mechanism?

A

If GFR rises then more NaCl flows through the tubule leading to constriction of the afferent arteriole

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20
Q

What part of the kidney is involved in the tubuloglomerular feedback mechanism?

A

The juxtaglomerular apparatus

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21
Q

What senses the NaCl of tubular fluid?

A

The macula densa

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22
Q

What are some things that may cause a decrease in GFR?

A 
Increased HPbc (i.e due to kidney stone)
Increased COPbc (i.e diarrhoea)
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23
Q

What are some things that may cause an increase in GFR?

A 
Decreased COPgc (e.g severely burned patient)
Decreased Kf = due to change in surface area available for filtration
24
Q

What is plasma clearance a measure of?

A

How effectively the kidneys can clean the blood of a substance

25
Q

What is the plasma clearance equal to?

A

The volume of plasma completely cleared of a substance per minute

26
Q

Is plasma clearance unique to each substance?

A

Yes

27
Q

How can plasma clearance be calculated?

A

Rate of excretion/plasma concentration

Urine concentration x urine volume/plasma concentration

28
Q

What is the clearance of inulin equal to?

A

The GFR = measurement of clearance can be used to clinically determine GFR

29
Q

What are some features of inulin?

A

Freely filtered at the glomerulus, neither absorbed nor secreted, not metabolised by kidney

30
Q

How does inulin enter the urine?

A

By filtration alone

31
Q

Where can inulin be measured?

A

Easily measured in urine and blood

32
Q

What can be used instead of inulin to measure GFR?

A

Creatine clearance

33
Q

How are the plasma and urine concentrations of inulin related?

A

Plasma inulin x GFR = Urine inulin x urine volume

34
Q

What is the clearance of substances which are filtered, completely reabsorbed and not secreted?

A

Clearance = 0 (e.g glucose, also applies to substances not filtered and not secreted)

35
Q

What is the clearance of substances which are filtered, partly reabsorbed and not secreted?

A

Clearance < GFR (e.g urea, only portion of plasma is cleared)

36
Q

What is the clearance of substances which are filtered, secreted but nor reabsorbed?

A

Clearance > GFR (e.g H+, all of filtered plasma is cleared of a substance, as is the peritubular plasma from which it was secreted?

37
Q

What happens of clearance is less than GFR?

A

Substance is reabsorbed

38
Q

What happens if clearance equals GFR?

A

Substance is neither reabsorbed nor secreted

39
Q

What happens if clearance is greater than GFR?

A

Substance is secreted

40
Q

What is used to calculate renal plasma flow?

A

Para-amino hippuric acid (PAH) = exogenous organic anion, used clinically to measure RPF (= 650ml/min)

41
Q

What are some features of PAH?

A

Freely filtered at the glomerulus, secreted into tubule (not reabsorbed), and completely cleared from plasma

42
Q

What happens to the PAH that escapes filtration?

A

Secreted from the peritubular capillaries

43
Q

What are some example clearance values?

A 
Glucose = 0
PAH = 650 ml/min
Inulin = 125 ml/min
Creatine = 125 ml/min
44
Q

What are some benefits of measuring creatine clearance?

A

Produced at near constant rate, freely filtered and not reabsorbed but is slightly secreted, gives close approximation of GFR

45
Q

What is the drawback of using inulin clearance as a marker for GFR?

A

Requires constant infusion to insure constant plasma concentration

46
Q

What are the features of a good clearance marker?

A

Non-toxic, inert (doesn’t metabolise) and easy to measure

47
Q

What are some features of a good GFR marker?

A

Filtered freely, not secreted or reabsorbed

48
Q

What are some features of a good RPF marker?

A

Should be filtered and completely secreted

49
Q

What is the filtration fraction?

A

Fraction of plasma flowing through the glomeruli that is filtered into the tubules

50
Q

How is the filtration fraction calculated?

A

GFR/Renal plasma flow

51
Q

How does GFR compare to the plasma volume?

A

GFR is much greater

52
Q

How is renal blood flow calculated?

A

RPF x (1/1-Hct)

53
Q

What is Hct?

A

Haematocrit

54
Q

Does the afferent or the efferent arteriole have a wider diameter?

A

The afferent arteriole

55
Q

Where are the pores in the glomerular capillaries located?

A

In between endothelial cells = exclude red blood cells

56
Q

What is the basal lamina (basement membrane) made of?

A

Collagen and glycoproteins = confer net negative charge which acts as barrier to large plasma proteins

Renal (36 decks)

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