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Renal and Endocrine Biology > REB 25. Renal Clearance > Flashcards

REB 25. Renal Clearance Flashcards

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1
Q

Why is measuring renal clearance important?

A

it is how renal function may be assessed

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2
Q

How is glomerular filtration rate (GFR) measured?

A
  • measured indirectly (NOT directly)

- measured indirectly via renal clearance

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3
Q

What are symptoms of patients with kidney disease?

A
  • hypertension
  • edema
  • bloody urine (hematuria)
  • OR asymptomatic
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4
Q

List the forces involved in glomerular filtration. [3]

A

[1] Glomerular Capillary Blood Pressure
[2] Plasma Colloid Osmotic Pressure
[3] Bowman’s Capsule Hydrostatic Pressure

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5
Q

What is the glomerular capillary blood pressure and does it favour or oppose filtration?

A
  • it is the pressure which pushes blood out of the capillary

- it FAVOURS filtration

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6
Q

What is the plasma colloid osmotic pressure and does it favour or oppose filtration?

A
  • it pushes the fluid from the tubules (Bownman’s capsule) back into the capillary
  • it OPPOSES filtration
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7
Q

What is the Bowman’s Capsulse hydrostatic pressure and does it favour or oppose filtration?

A
  • it pushes fluid out of the tubules (Bowman’s capsule) back into the capillary
  • it OPPOSES filtration
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8
Q

What is one method of assessing renal function (determining the clearance of the substance)?

A

it is to measure the rate of EXCRETION of a substance in relation to its PLASMA CONC.

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9
Q

What is the definition of renal clearance? What are the units involved?

A

Definition: “renal clearance is the volume of blood plasma from which a particular waste (hence clearance is substance specific) is completely removed in 1 minute”

units: Cs [mL/min]

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10
Q

What is the clearance formula (for any substance)?

A

Cs = (Us x V)/(Ps)

where:
U = concentration of substance (s) in urine (mg/mL)
V = volume of urine excreted/min (mL/min)
P = concentration of the substance(s) in plasma (mg/mL)

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11
Q

What is the unit of clearance?

A

mL/min

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12
Q

What is the measurement of glomerular filtration rate (GFR)? What is it representative of? What is it measured using? What is a decrease in GFR represents what?

A

Glomerular Filtration Rate: the rate at which plasma is filtered at the glomerular capillaries to form the tubular filtrate

  • GFR is an index of renal function
  • GFR is measured using clearance
  • a decrease in GFR is often the first clinical sign of renal disease
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13
Q

What may sometimes be the first and only clinical sign of renal disease?

A

a decrease in GFR

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14
Q

What qualities does a substance need to have to measure GFR by clearance? [6]

A

[1] it is freely filtered at glomerulus

[2] it is NOT reabsorbed from filtrate
- ultimately it is filtered out and exits straight into the urine

[3] it is NOT secreted into the filtrate

[4] it is NOT metabolised by the tubular cells

[5] it does NOT interfere with kidney function, NOT toxic

[6] easily measured

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15
Q

What is inulin? Why is it important?

A
  • inulin enters the tubular filtrate via filtration ONLY
  • it then flows through tubules and exits in urine

therefore:
rate at which it enters the filtrate = rate at which it enters the urine

it is a measure of GFR!!!

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16
Q

What is the formula for the rate of inulin entry into the filtrate?

A

Pin x GFR

- (plasma inulin conc)x(glomerular filtration rate)

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17
Q

What is the formula for the rate of inulin entry into the urine?

A

Uin x V

- (urine inulin conc)x(volume of urine excreted/min)

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18
Q

What is the overall formula to measure the amount of inulin that is excreted in the urine? (the glomerular filtration rate - GFR)

A

GFR = (Uin x V)/(Pin)

19
Q

The renal clearance of inulin is a measurement of what?

A

it is a measurement of GFR!!

20
Q

What is the difference between creatinine and inulin in measuring GFR?

A

INULIN:
- inulin does not occur in the body so it must be administered intravenously
(not often used for this reason)

CREATININE:

  • creatinine is a substance produced in the body and so may be used to measure GFR
  • HOWEVER, it does NOT fully meet the criteria as a small amount of creatinine is secreted into the tubule from the blood
21
Q

How are the errors involved in creatinine clearance cancelled out?

A

Cs = (Us x V)/(Ps)
[1] U in formula is high due to as there is a slight secretion into the filtrate

[2] the P is also high because the estimation of plasma creatinine concentration also detects another compound

– the 2 errors cancel each other out!

22
Q

What is the clearance value for inulin?

A

around 120 mL/min

23
Q

What is the clearance value for creatinine?

A

around 120 mL/min

24
Q

What is the clearance value for inulin and creatinine?

A

both are 120 mL/min

25
Q

What do you need to measure the GFR through creatinine? Do you need the concentration of creatinine in the plasma? Concentration of creatinine in the urine? Concentration of creatinine in both?

A

a mathematical formula can be used to estimate creatinine clearance from a measurement of PLASMA [CREATININE] ONLY

26
Q

What is creatinine derived from?

A

the breakdown of creatine in skeletal muscles

- the amount entering the plasma each day is dependent on skeletal mass (which is dependent on age)

27
Q

What is the Cockroft and Gault relationship? What is the formula associated with it?

A
  • it is representative of renal function (as it measures creatinine clearance and so, glomerular filtration rate [GFR])

MALES:
creatinine clearance = [(140 - age) x (weight in kg)]/[72 x (serum creatinine in mg/dL)]

FEMALES:

  • multiply result by 0.85
  • as the lower proportion of body weight is due to muscle mass
28
Q

When substances whose clearance is LESS than that of inulin what does this mean (about the substance)?

A

it means that the substances are FILTERED + REABSORBED

- e.g. glucose + urea

29
Q

When substances whose clearance is GREATER than that of inulin what does this mean (about the substance)?

A

it means that the substances are FILTERED (glomerulus) and SECRETED (tubular
- e.g. PAH (para-amino-hippuric acid)

30
Q

What is renal plasma flow (RPF)?

A

it is the volume of blood plasma delivered to the kidneys per unit time

31
Q

Why is autoregulation of renal plasma flow (RPF) and glomerular filtration rate (GFR) important?

A
  • usually RPF and GFR happen in parallel
  • if RPF increases, then GFR increases
  • autoregulation maintains a relatively constant blood flow which allows for GFR to remain constant
32
Q

What is used to measure the Renal Plasma Flow (eRPF)? Why is it used?

A

PAH is used to measure the renal plasma flow.

  • PAH is freely filtrable and non-reabsorbable!!
  • all PAH that escapes from filtration is secreted by the organic anion secretory pathway in proximal tubule
  • PAH COMPLETELY REMOVED from all the plasma that flows through kidney
33
Q

What value is the estimated renal plasma flow (eRPF) at?

A

around 625 mL/min

34
Q

If there is continous decrease in GFR what does this mean? If there is continous increase in GFR what does this mean?

A

Continous Decrease:
- means that the renal disease is getting worse

Continous Increase:
- means that the renal disease is getting better

35
Q

What is the definition of renal failure?

A

it is the reduction in glomerular filtration rate so that the kidneys can no longer maintain salt and water balance nor excrete nitrogenous waste products

36
Q

What are the 3 types of renal failure?

A

[1] Acute
[2] Subacute
[3] Chronic

37
Q

Describe the traits of acute renal failure.

A
  • abrupt/rapid decline in renal function (12 to 72 hour onset)
  • usually reduced urine formation
  • kidneys stop working entirely or almost entirely
  • may be reversible or fatal
38
Q

What are the possible causes of acute renal failure?

A

[1] Pre

  • altered blood supply to kidney
  • e.g. hemorrhage, heart failure, hypotension

[2] Intra

  • damage to the kidney due to toxins/inflammation
  • e.g. glomerulonephritis or tubular necrosis

[3] Post

  • urinary tract abnormalities
  • e.g. urethral obstruction, prostate enlargement or stones
39
Q

What tests/measurements can be done to assess ACUTE renal failure?

A
  • urea and electrolyte (U+E) measurements

- e.g. sodium, potassium, chloride, bicarbonate, urea, creatinine…

40
Q

What are the consequences of acute renal failure?

A 
[1] Salt and Water Retention
[2] Potassium Retention
[3] Metabolic Acidosis
[4] Hyperphosphataemia
[5] Increased Plasma Urea and Creatinine
41
Q

Describe the traits of chronic renal failure?

A
  • gradual and irreversible loss of large numbers of functioning nephrons
  • normally electrolyte homeostasis possible and normal fluid balance maintained with 20 to 30% renal function
  • asymptomatic until functioning nephrons <70% - insidious disease process (pretty late into the disease)
  • end stage > 90% function lost (only 10% functioning kidneys)
  • urea/creatinine may indicate level of impairment/progression
42
Q

What are causes of chronic renal failure?

A

[1] Metabolic Disorders
- e.g. diabetes mellitus

[2] Renal Vascular Disorders

[3] Immunological Disorders

[4] Infection

[5] Urinary Tract Obstruction

[6] Congenital Disorders

43
Q

What are the consequences of chronic renal failure?

A
  • inability to concentrate or dilute urine appropriately
  • water retention
  • increase in urea and creatinine (uraemia)
  • anaemia in chronic disease
  • acid and ion imbalances
  • osteomalacia
  • secondary hyperparathyroidism
44
Q

What is the treatment of chronic renal failure?

A
  • chronic renal failure is irreversible
  • treatment aimed at maintaining renal function + preventing side effects
  • management of hypertension
  • management of underlying cause (infections + medications)
  • dialysis (haemodialysis and CAPD)
  • renal transplantation

Renal and Endocrine Biology (25 decks)

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