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Clinical Immunology and Biochemistry > Renal Function > Flashcards

Renal Function Flashcards

1
Q

What are the major functions of the renal system?

A

Glomerular function
Tubular function
Endocrine function
Gluconeogenesis

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2
Q

What is the purpose of glomerular function?

A

Excretion of toxic end-products of metabolism

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3
Q

What is the purpose of tubular function?

A

Reabsorption of water, Acid-base and electrolyte balance

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4
Q

What is the purpose of endocrine function of the kidney?

A

1 Alpha Hydroxylase: Vitamin D metabolism
Erythropoetin: Haemoglobin synthesis
Renin: Renin-Angiotensin-Aldosterone Axis
Prostaglandins and endothelins

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5
Q

What is gluconeogenesis?

A

A metabolic pathway that results in the generation of glucose from non-carbohydrate carbon substrates such as pyruvate, lactate, glycerol, and glucogenic amino acids.

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6
Q

What are the physical features of the kidney?

A 
Afferent arteriole 
Efferent arteriole
Glomerulus 
Bowman's Capsule
Distal tubule
Proximal tubule
Capillary network
Loop of Henle
Collecting duct
Pelvis
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7
Q

What factors affect glomerular filtration?

A

Effective filtration pressure: -

- Increase resistance in efferent increases pressure in afferent vessels
- counter pressure = oncotic pressure 
- passage of blood through  glomeruli increase oncotic pressure so reduces filtration pressure

Molecular size and shape ( 70KD unlikely)

-ve charge. Basement membrane has a net -ve charge

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8
Q

What is glomerular filtrate?

A

Glomerular filtrate is an ultrafiltrate of plasma i.e plasma without most of the large proteins

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9
Q

What does glomerular function depend on?

A

Adequate renal blood flow and pressure

Number of functioning nephrons

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10
Q

What is the average glomerular filtration rate (GFR)?

A

120ml/min

170L/day

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11
Q

What is GFR related to?

A

Body surface area: higher in men

Age: decreasing in the elderly

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12
Q

What are the different structures in the tubule system of the kidney?

A

Proximal convoluted tubule
Loop of Henle
Distal convoluted tubule
Collecting duct

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13
Q

What is the function of the Proximal convoluted tubule?

A

Reabsorption of water, glucose, amino acids, K, HCO3 Na+

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14
Q

What is the function of the Loop of Henle?

A

Concentration of ultrafiltrate

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15
Q

What is the function of the Distal convoluted tubule?

A

Secretion of urate
Na+-K+ via aldosterone;
Na+-K+/H+ exchange

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16
Q

What is the function of the Collecting duct?

A

Water reabsorption under ADH control

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17
Q

What are the features of proximal renal tubular function?

A 
Reabsorption of:
	Water			
	Bicarbonate	
	Aminoacids		
	Phosphate
	Glucose	
	Electrolytes
	Proteins
Secretion of: 
	Drugs
	Small amounts of
		Creatinine 
		Urea
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18
Q

What is the function of the distal convoluted distal tubule?

A

Sodium reabsorption (Due to Aldosterone)

H+ excretion:

Water reabsorption (due to ADH)

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19
Q

How is the acid/base balance regulated?

A

Reabsorption of bicarbonate
Active secretion of hydrogen ions
Generation of bicarbonate.
Generation of ammonia.

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20
Q

What is clearance?

A

Clearance is the virtual volume of plasma completely cleared of a given substance per unit of time

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21
Q

What is the equation for calculating clearance?

A

Cs = (Us x V) / (Ps x T) ml/min

Where:
Us is the urine concentration of substance, s
Ps is the plasma concentration of s 
V is the urine flow rate in mL
T is the time in mins
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22
Q

How is clearance measured?

A

Renal clearance can be measured with a timed collection of urine and an analysis of its composition with the aid of the clearance equation.

When the substance is creatinine, an endogenous chemical that is excreted only by filtration, the calculated clearance is equivalent to the glomerular filtration rate.

Inulin clearance is also used to estimate glomerular filtration rate. However, it must be given intravenously and therefore impractical

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23
Q

What are the advantages of using creatinine clearance to measure kidney function?

A

Steady state endogenous creatinine production and its release into body fluids is at a constant rate

Robust plasma and urine assays

24
Q

What are the disadvantages of using creatinine clearance to measure kidney function?

A

Small quantities of creatinine are reabsorbed and secreted by the tubules.

Fluctuation of plasma levels – e.g protein meals, stenuous exercise

Creatinine clearance is ~7% greater than that of inulin

25
Q

What causes variation in creatinine clearance?

A

Greatest error in creatinine clearance is collection of timed urine samples.

Analytical and Biological variation is 8 - 20%

26
Q

What is the formula used to predict creatinine clearance from plasma creatinine?

A

CC = (Uc x V) / Pc

27
Q

What are the symptoms of Proximal Renal Tubular Dysunction?

A 
Polyuria
Metabolic acidosis
Aminoaciduria
Phosphaturia 
Glycosuria
Hypokalaemia 
Tubular proteinuria
28
Q

What are the symptoms of Distal Renal Tubular Dysunction?

A

Urine salt loss -> hyponatraemia
Alkaline urine -> Metabolic acidosis
Polyuria

29
Q

What are the 4 main mechanisms by which proteinuria occurs

A

Overflow: Excessive production & excretion of protein as in Bence-Jones protein, marked catabolism

Glomerular: Glomerular damage - albuminuria

Tubular: Tubular damage - α1 β2 microglobulinuria

Secretory: Tubular protein secretion – Tamm-Horsfall

30
Q

What do urine dipsticks test for?

A 
Protein
Glucose
Blood
pH
Nitrite
Bile pigments
Ketones
31
Q

What is microalbuminuria?

A

24 h urine albumin 30mg - 300mg.

Therefore, increased urine albumin excretion but urine Dipstick –ve

32
Q

What new marker can be used to test for clearance?

A

Cystatin C

  • Small protein produced by all nucleated cells
  • Not affected by muscle mass, age, gender or race

NGAL- Neutrophil Gelatinase Associated Lipocalin

  • Marker of acute kidney injury (urine & serum)
  • Early detection of AKI
33
Q

What are the problems with urine dipstick tests?

A

Detect ~ 300mg/L albumin

Protein error of indicators

  • don’t detect Bence Jones protein
  • False positives (alkaline urine, various contaminants)
34
Q

What is the criteria for stage 1 AKI?

A

Creatinine increase ≥ 26μmol/L within 48hrs or increase ≥1.5 to 1.9 X reference Serum Creatinine

Urine output 6 consecutive hrs

35
Q

What is the criteria for stage 2 AKI?

A

Creatinine increase ≥ 2 to 2.9 X reference SCr

Urine output 12hrs

36
Q

What is the criteria for stage 3 AKI?

A

Creatinine increase ≥3 X reference SCr or increase ≥354μmol/L or commenced on renal replacement therapy (RRT) irrespective of stage

Urine output 24hrs or anuria for 12hrs

37
Q

What is reference serum creatinine?

A

The reference serum creatinine should be the lowest creatinine value recorded within 3 months of the event

If a reference serum creatinine value is not available within 3 months and AKI is suspected repeat serum creatinine within 24 hours

38
Q

What are the stages of CKD

A 
1
2
3A
3B
4
5
39
Q

Describe stage 1 CKD

A

Normal kidney function, but urine findings or structural abnormalities or genetic trait point to kidney disease

40
Q

Describe stage 2 CKD

A

Mildly reduced kidney function and other finding (as for stage 1)

41
Q

Describe stages 3A and 3B CKD

A

Moderately reduced kidney function

42
Q

What is the difference between stages 3A and 3B?

A

Stage 3A - GFR=45 - 59

Stage 3B - GFR=30 - 44

43
Q

Describe stage 4 CKD

A

Severely reduced kidney function

44
Q

Describe stage 5 CKD

A

Very severe, or endstage kidney failure (sometimes called established renal failure)

45
Q

What is the GFR for the different stages of CKD?

A 
Stage 1 - 90+
Stage 2 - 60-89
Stage 3A - 45-59
Stage 3B - 30-44
Stage 4 - 15-29
Stage 5 -
46
Q

What are the metabolic effects of AKI?

A

Retention of:

Urea & creatinine
Water: Oliguria/Anuria
            Pulmonary oedema
H+: Metabolic Acidosis 
Electrolytes:   K+  - hyperkalaemia
                        Na+
47
Q

What tests can be done to differentially diagnose the causes of acute renal failure?

A

Ultrasound:
To exclude obstruction
May show intrinsic renal disease

Renal Biopsy:
Identify cause of renal disease

48
Q

Describe the features of AKI

A

Characterised by oliguria (

49
Q

What happens after AKI?

A

May proceed to Chronic Renal Failure

50
Q

What are the clinical features of Chronic Renal Failure?

A 
Skin:
  - Pruritis
  - Purpura
CNS and PNS:
  - Lethargy
  - Peripheral Neuropathy
CVS:
  - Hypertension
  - Pericarditis
  - Anaemia
GIT:
  - Nausea and vomiting
  - Anorexia
GUS:
  - Impotence
  - Nocturia
Musculoskeletal:
  - Myopathy
  - Stunted growth
  - Bone pain
51
Q

Describe the features of CRF

A

Similar to ARF

  • Increased serum urea /creatinine
  • Increased serum K+
  • Metabolic acidosis
  • Hyperphosphataemia

But also loss of endocrine function

  • Hypocalcaemia & Osteodystrophy (secondary or tertiary hyperparathyroidism)
  • Normochromic normocytic anaemia
52
Q

Why do patients develop anaemia with CRF?

A

In chronic renal failure lack of erythropoetin (stimulates haemogloblin synthesis) causes anaemia.

53
Q

Why do patients develop hypocalcaemia with CRF?

A 
Loss of 1 alpha hydroxylase  
leads to 
Decreased 1,25 (OH)2 Vitamin D 
leads to 
Hypocalcaemia: due to decreased gut Ca2+ absorption
leads to 
Increased parathyroid hormone (PTH) 
leads to 
Bone disease (renal osteodystrophy)
54
Q

What are the different phases of AKI?

A

Oliguric Phase: Predominantly impaired glomerular function
Diuretic phase: Improved glomerular function but impaired tubular function
Recovery phase

55
Q

How is CRF managed?

A 
Water and salt: Low salt diet avoid dehydrate or volume overload
Dietary protein restriction
Hyperphosphataemia: Oral phosphate binders
Hypocalcaemia: 1 (OH) Vitamin D
Treat hypertension vigorously
Anaemia: Erythropoetin
Dialysis
 - Haemodialysis
 - Peritoneal dialysis
Renal transplantation
56
Q

What is acute on chronic renal failure?

A

Patients with chronic renal failure may develop acute renal failure

Anaemia and hypocalcaemia in subjects with acute renal failure is indicative of underlying Chronic Renal failure i.e Acute on chronic renal failure

Clinical Immunology and Biochemistry (14 decks)

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