Renal function
The kidneys have three major functions
1)excretion of waste products
2)maintenance of extra cellular of fluids volume & compositions
3)hormone synthesis
The kidneys have a rich blood supply & normally recieve about
25% of the cardiac out put. The glomerula filtrate passes into the
proximal tubule where much of the filtrate is reabsorbed . Under
normal condition ; all glucose, amino acids , potassium &
bicarbonate and about 75% of the sodium reabsorbed by
energy- dependent mechanisms. on the other hand , urea ,
ammonia & other toxic substances all excreted into the urine,
to gather with waste products .
Normal glomarular filtrate rate (G F R ) passed a bout 120 ml./
min.
The kidneys also important as endocrine organ producing :
rennin ,erythro poietin & calcietriol . The secretion of these
hormones will be affected in the renal diseases.
DIseases affecting the kidney can selectively damage
glomullar or tubular function. In A cute and chronic renal
failure , there is a loss of the function of whole nephrone
as well as the gloerular filtration rate.
The Biochemical
Test of Renal function :
The most frequently used tests
are those that asses either the G F R or the integrity of
glomerula filtration barrier.
l) Measurment of G R F : The most frequently tests used as
clearance test : based on the measurement of creatinine .
This endogenus substance is derived mainly from turnover
of creatine in the muscle and the daily product is relatively
constant , being a function of total muscle mass. A small
amounts of creatinine is derived from meat in the diet.
Creatinine
=
U X V =
P
̃
ml. / min.
Normal range for Adult 120 ml./ min. corrected to a
standard body surface area of 1.73 m2 .
Urine sample should be colluted a 24 hr . the blood sample
should be taken from the patient during the urine collection .
Hence , any defect or dysfunction in the G F R will affect the
creatinine clearance .
2)B. urea :
Urea is synthesis in the liver as end product of the
deamination of the amino acids; its elimination in the urine
represent the major route for nitrogen excretion . It is filtered
from blood at the glomular . there fore, a measurement of
B. urea & S. creatinine give a good evidence for the renal
function. Urea production is increased by a high protein intake & by the absorption of amino acid & peptides after
gasterointestinal haemorrhage. On the other hand , B .urea
decreased in low protein in take & in liver diseases.
3)General urine analysis :
It is of value in detection renal disease as the presence of
Albumin in the urine indicate a defect in the capacity of G.
F.R . with sever glomular damage; RBCs are also detected
in the urine sample togather with granular cast which is
strongly suggestive a glomular dysfunction .
Renal disorders :
Failure of renal function may occur rapidly producing of the
syndrome of A cute renal failure . chronic renal failure
develops later on over many years & it is irreversibly leading
to end – stage renal failure . In this case require either long
– term renal replacement treatment ( e . g . dialysis or a
successful renal transplant in order to survive) . Here ,
biochemical tests are essential to the management of renal
failure . The clinical syndrome is usually associated with
nephorit ic syndrome hypertension , oedema & haematuria .
Acute renal failure :
ARF
This state is characterized by a rapid loss of renal
function , with retention of urea , creatinine , hydrogen ions
& other metabolic products & usually oliguria .
A R F is divided into three categories :1 )pre renal : which is a decrease in renal blood flow .
2)Renal : due to intrinsic damage to the kidney .
3)post renal : Here obstruction in renal tract .
Pre renal A . R . F : This caused by circulatory insufficiency ,
as may occur with severe haemorrhage , burns , fluid loss ,
cardiac failure or hypotension result in renal hypoperfusion &
a decrease in G F R . How ever , if adequate perfusion is
not rapidly restored prerenal ureamia may progress to
intrinisic failure result in
(A cute tubular necrosis ) .
In such cases B . urea is elevated greater than S . creatinine ;
due to increase reabsorption of the urea & also from in
crease synthesis of urea from amino acids released as aresult
of tissue damage .
Here , when given the patient extra fluid I . V
in dieresis ; b
. urea & S. creatinine will return to normal
Range within 48hr. By this way we can distingwish the pre
renal case from the intrinsic renal failure .
Intrinsic a cute renal failure :Many cases of A . R. F are due to nephrotoxic drugs e .g .
A mino glycosides & non- steroidal anti inflammatory drugs .
Renal disease & systemic disease are affecting the kindneys.
The characterstic biochemical changes in the plasma in A. R .
F. are : hyperkalemia , increased level of B . urea , S .
creatinine ,
phosphate & S . uric acid and a decrease level
of S. Sodium , bicarbonate & S. calcium . proteinuria is also
present .
Post renal failure :
Obstruction to the flow of urine
to an increase in hydrostatic pressure which acts in opposition to glomular
filtration & if prolonged , this will lead to secondary renal
tubular damage .
Causes of obstruction :
Either renal calculi , prostatic enlargement , other
neoplasma
of the urinary tract .
Chronic renal failure: Many diseases can lead to progressive ,
irreversible impairment of renal function : Glomerulo –
nephrites , diabetes mellitus .
Hypertension & polycystic kidneys account for the majority of
the cases . Here , dialysis or transplantation becomes
necessary to save the patient`s life.
Biochemical changes in such patients:
1) in Potassium , urea , creatinine , hydrogen ion , phosphate
& magnesium .
2) in S. calcium , bicarbonate & S . Sodium .