Measuring Kidney Function Flashcards

1
Q

What is the role of the glomerulus?

A

Glomerulus and its surrounding Bowman’s capsule constitute a renal corpuscle, the basic filtration unit of the kidney

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2
Q

How is kidney function measured?

A

GFR = amount of filtrate prod from blood flow per unit time

Amount determined by the product of the average filtration of each nephron

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3
Q

What is normal GFR?

A

90-120

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4
Q

What factors does GFR depend on?

A
Gender
Age
Size
Size of kidney
Preg
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5
Q

Outline GFR in babies

A

Nephron development finishes 35th week of foetal devel

Premature often have lower nephron numbers

Birth GFR ~20

Normal GFR at ~18months

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6
Q

Outline GFR in advancing age

A

GFR starts declining after 30

Decline by 6-7ml per decade

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7
Q

How does age affect the kidney size?

A

Cortex volume and overall kidney volume falls

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8
Q

When do you get compensatory hypertrophy in the kidney?

A

Small nephrons/reduced number = compensatory growth

Occurs to a greater extent in childhood

Working hard = at greater risk of wearing out

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9
Q

How does GFR vary due to preg?

A

Increased = 130-180

Nephron number the same

But increased fluid vol = higher filtration rate

Back to normal ~6months post-partum

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10
Q

Broadly speaking if GFR decline what is this due to?

A

Decline in nephron number

Decline in GFR within individual nephrons

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11
Q

Why may GFR not fall until significant kidney damage has occurred?

A

Hypertrophy of nephrons

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12
Q

Define clearance

A

the volume of plasma cleared of a substance per unit of time where the substance is denoted as ‘x’

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13
Q

How is renal Cl calculated?

A

Renal Clearance of a substrate = excretion rate / plasma concentration

Excretion rate = U (amount in urine) x V (urine flow rate)

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14
Q

What factors are required of a substance in order for it to be used as a measure of GFR?

A

Be produced at a constant rate

Be freely filtered across the glomerulus

Not be reabsorbed in the nephron

Not be secreted into the nephron

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15
Q

What is the best substance to measure renal Cl?

A

51 Cr-EDTA = radio-active labelled marker, need to adjust for 10% lower Cl

Creatinine = collect urine over 24hs or serum levels, overestimation of GFR by 10-20%, used in preg

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16
Q

What factors affect creatinine levels?

A

Intake of cooked meat

Metabolism of muscle

Renal excretion

Extra-renal excretion

17
Q

How do creatinine levels change throughout life?

A

Foetus = same level as mother

After birth = quickly creatine drops

Reach adult levels at 15y

18
Q

What factors are measured in U+Es?

A
Urea
Sodium
Potassium
Bicarb
H = pH
Creatinine
19
Q

What is eGFR?

A

Computer model to estimate GFR

Underestimates true GFR = pts being labelled as having CKD

20
Q

When is eGFR inaccurate?

A

Kidney disease

Children/old age

Preg

Other ethnicities

Amputees/significantly reduced muscle mass

Pts with higher levels of kidney function

21
Q

Why is eGFR less accurate with mild kidney disease?

A

Reduced nephron number leads to nephron hypertrophy so no change in GFR

22
Q

What is an intravenous urograph?

A

X-ray examination of the kidneys, ureters and urinary bladder that uses iodinated contrast material injected into veins