Carbohydrate metabolism Blood glucose- 9 Glucosuria , glycosuria Blood is filtered by millions of nephrons. In each nephron, blood flows from the arteriole into the glomerulus. Bowmans capsule surrounds each glomerulus, and collects the filtrate that the glomerulus forms. The glomerular filtrate contains waste products (e.g. urea), electrolytes (e.g. sodium, potassium, chloride), amino acids, and glucose. The filtrate passes into the proximal renal tubules of the kidney where glucose is reabsorbed from the filtrate. Glucose inside the tubular cells is phosphorylated to glucose-6-phosphate. Glucose-6-phosphatase will set free glucose to the blood stream. Renal threshold of glucose The proximal tubules can only reabsorb a limited amount of glucose. The active reabsorption of glucose system is saturable at a certain level of blood glucose , above which, glucose will not be reabsobed and appears in urine. This is the renal threshold of glucose. Renal threshold of glucose is the blood concentration of glucose above which glucose appears in urine. It is 10 mmol/l (180 mg/dL) blood in normal individuals. In some old standing diabetics, the renal threshold of glucose may be higher than 180 mg/dl. The transport system of glucose in the renal tubules is saturable by a certain amount of glucose which will saturate the carrier molecules at a certain time which is called transport maximum for glucose (TmG). TmG is 325 – 370 mg glucose/minute. TmG depends on blood glucose as well as the glomerular filtration rate. Glycosuria or glucosuria is the excretion of glucose into the urine. Ordinarily, urine contains no glucose because the kidneys are able to reabsorb all of the filtered glucose back into the bloodstream if blood glucose is lower than the renal threshold. Hyperglycemia means high blood glucose than normal levels. Hypoglycemia means low levels of blood glucose Causes of glucosuria == Hyperglycemia; glycosuria is mainly caused by elevated blood glucose levels, most commonly due to untreated diabetes mellitus, provided that glomerular filtration rate and tubular reabsorption are normal. == Renal glucosuria, glucose appears in urine while blood glucose level is normal: - Congenital low renal threshold of glucose. - Diseases of the tubules. - Congenital deficiency of glucose-6-phosphatase (von-Gierke’s disease. - Inhibition of the active transport system by chemicals as phlorhizin and ouabain. Glycosuria leads to excessive water loss into the urine with resultant dehydration, a process called osmotic diuresis.
Posted on: Sat, 30 Nov 2013 19:21:14 +0000
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