Biochemistry of nervous system

1. “ Kidneys are dying silently”
The kidneys have considerable functional reserve
and abnormal laboratory tests are found when
50-60% OF NEPHRON HAVE BEEN LOST
Testing of the renal functions

2. Introduction
□ Diseases affecting the
kidney can selectively
damage:
□ (i) glomerular function
□ (ii) tubular function
(relatively uncommon)
□ In ARF & CRF there is a
loss of function of whole
nephrons.

3. Tests of glomerular
filtration

4. The principal functions of
glomeruli are:
□ (i) to filter water and low.
mol.wt.components of
the blood
□ (ii) retaining cells & high
mol.wt.components of
the blood

5. Glomerular filtration
testing

6. Plasma & urine
creatinine

7. Plasma creatinine
□ More accurate assessment of
glomerular function
□ Collection after overnight fasting
□ Plasma creatinine rises when GFR decreased 50% to normal

8. Normal level: 0.6-1.3 mg/dl
(85-120 micromol/L)

10. Urine creatinine
□ Amount of creatinine excreted:
□ (i) Is grater in muscular person
□ (ii) After severe exercise it may
increase, but total amount remains
constant from day to day
□ Normal level:
□ Females ………5.3-14.2 mmol/L
□ Male ……. 7.1-15.9 mmol/L

11. Urine creatine
□ Excretion of creatine in urine is called
creatinuria. Creatine excretion occurs:
□ (i) In children – reason probably lack
ability to convert creatine to creatinine
□ (ii) In adult females – in pregnancy and
maximum after parturition
□ (iii) In muscular dystrophies, myasthenia
gravis, myositis
□ (iv) In starvation
□ (v) DM

12. Blood urea (BUN)

13. Plasma urea (Blood urea
nitrogen-BUN)
□ Urea is freely filtered by the glomerulus
but is reabsorbed by the tubules.
□ Reabsorption of urea is dependent upon
the filtrate flow.
□ When filtrate flow is slow, 40% or more of
urea can be reabsorbed.
□ For this reason, urea (BUN) levels increase more than
creatinine level in pre-renal conditions (hypoperfusion,
shock) when the kidney is not damaged.

14. N.B.
□ When the tubules are
undamaged they reabsorb
a maximal amount
of urea
□ The reabsorption of
urea is decreased
when tubules are damaged.
□ But urine urea
increase

16. BUN (Blood urea nitrogen)

17. Measurement of GFR

18. Measurement of GFR
□ GFR measurement is required for:

19. For testing of GFR uses the
substances that:

20. N.B. (lat.: nota bene; note)
□ Creatinine is secreted by the renal tubule, and
creatinine clearance is higher
than the true GFR
□ The differences is little when
GFR is normal, but when the GFR is low
(< 10 ml/min) creatinine clearance significantly
overestimates the GFR

21. Creatinine clearance test
□ Three measurements is required:
□ 1. Plasma creatinine concentration
(P(Cr)-micromol/L
□ 2. Urinary creatinine concentration
(U(Cr)- micromol/L
□ 3. Collection of the timed urine
sample: 24-hours urine volume
(more difficult part)

22. Procedure:
□ At 8:00a.m. patient
empty the bladder and
urine discarded.
□ All urine produced of
that day and overnight
is added to the
specimen container.
□ At 8:00 next morning
last urine portion is
added to the container
to make up a complete
24-hours collection.

23. Clearance is the theoretical volume of
plasma from which a substance is
removed over a period of time

24. Normal level:

26. Formal measurement of
creatinine clearance
□ 3 measurements:
□ 1. Plasma creatinine (P(Cr)- micromol/L
□ 2. Weight of patient (kg) – M
□ 3. Age of patient (yr) – A

27. Stages of CRF

28. Assessment of
glomerular integrity

29. □ Impairment of glomerular integrity
results in the filtration of large
molecules.
□ -Proteinuria (can occur for other
reason)
□ - Hematuria
□ - RBCs cast (cells embedded in
protein matrix) in urinary sediment.

30. Tests of renal tubular
function

31. Indicators of tubular cells
damage
□ The presence of glucosuria in a patient with a
normal blood glucose implies proximal
malfunction which may be:
□ - isolated (renal glucosuria) or
□ - part of generalized tubular defect (Fanconi
syndrome)
□ Aminoaciduria can occur with tubular defect
□ Beta-2 or alpha-1-microglobulinuria –
sensitive indicators of renal tubular cells
damage

32. Other methods

33. □ US (including Doppler studies to assess
blood flow)
□ MRI (magnetic resonance imaging) –
anatomical information
□ Renal biopsy (histopatological
diagnosis)
□ Detection of specific antibodies (e.g.
antiglomerular basement membrane
Ab)