Renal function
The kidneys have three major functions1)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 = ml. / min.
PNormal 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 in- take & 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 hydro- static 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 .