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rainage from the kidney to the bladder during the process of urine formation. Bladder acts by means of contraction to expel urine from the body. In order for the kidney to work properly the renal arteries deliver about 25% of resting cardiac out put.

Glomerular filtration (GF) normally occurs at rate of about 120-150 ml/min. There are significant forces which are involved in glomerular filtration, glomerular capillary blood pressure which induced a blood pressure within the glomerular capillary depending on the heart contraction and on the peripheral resistance provided by efferent arterioles. The other significant force is the plasma colloid osmatic pressure which occurs due to impermeability to protein through the glomerulus. The permeability depends on the molecular size and the electrical charges. The positively charged molecules easily filtered than the negatively charged one because the glomerular endothelium layer carry negative charges that repel the protein particles and not allowing them to be filtered.

In Bowman's capsule hydrostatic pressure, there will be high force to push fluid out of Bowman's capsule into glomerulus. Any changes occur in these forces will lead to change in glomerular filtration rate (GFR).

Glomerular filtration rate (GFR) is a measurement of the amount of glomerular filtrate (a substance similar to blood plasma but without proteins) formed in the kidneys each minute. It can be assessed by measuring the excretory ability and the substance level in plasma that freely filtered through the glomerulus. Some of the substances will not appear in the glomerular filtrate unless they have reached a certain concentration in blood. Glucose is such a substance that does not appear in the urine until it reaches high concentration in the blood (11.0 mmol/L). Whereas other substances like creatinine excreted without appreciable reabsorption.

Creatinine is an endogenous substance, an end product of nitrogen metabolism formed through a series of enzymatic reaction in the liver. The contraction of skeletal muscle involves both creatine and ATP (adenosine triphosphate) in the presence of creatine kinase enzyme. The creatine formed from phosphocreatine gives the final end product creatinine which is instantly filtered at glomerulus without any tubular reabsorption. Therefore creatinine can be used to estimate the clearance ability of kidney, but it is not a perfect marker as it is secreted. This involves the measurement of substance concentration in urine and plasma using the following clearance formula:

(U/P) * (V/T) = mls/min

Renal failure

Diseases affecting the kidneys can damage glomerular or tubular function. Failure of renal function may occur rapidly producing the syndrome of acute renal failure which is characterized by rapid loss of renal function with retention of urea, creatinine, hydrogen ions and other metabolic products. However chronic renal failure develops often over many years leading to end-stage of renal failure where patients require either long term dialysis or a successful renal transplant to survive. Diabetes and hypertension are the two commonest causes of chronic renal failure with other causes including glomerulonephritis of any type

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