Proximal Information and Courses from MediaLab, Inc.

In the healthy individual, almost all of the glucose filtered by the renal glomerulus is reabsorbed in the proximal convoluted tubule. The amount of glucose reabsorbed by the proximal tubule is determined by the body's need to maintain a sufficient level of glucose in the blood. If the concentration of blood glucose becomes too high (160-180 mg/dL), the tubules no longer reabsorb glucose, allowing it to pass through into the urine. It is important to note that glucose may appear in the urine of healthy individuals after consuming a meal that is high in glucose. Fasting prior to providing a sample for screening eliminates this problem.

Fructose makes up 99% of the reducing sugar present in semen. This sugar is produced in the seminal vesicles and its absence may indicate an obstruction proximal to these glands. Although a fructose test is NOT part of a routine semen analysis, the clinician may want to measure this in cases of azoospermia. In azoospermia secondary to obstruction of the ejaculatory ducts or absence of the vas deferens, fructose is usually absent. When azoospermia is caused by failure of the testes to produce sperm, fructose is present. Measuring fructose levels can thus help the clinician determine the cause of azoospermia, although measurement of pH is often more useful in this regard. The procedure for determining the amount of fructose in semen involves heating semen in a strong acid in the presence of resorcinol. Fructose gives a red color to this solution when present.

Renal epithelial fragments of collecting duct origin are composed of three or more cuboidal cells. These fragments indicate a more severe form of renal tubule injury with basement membrane disruption. Proximal and distal convoluted tubule renal epithelial cells are not found in fragment form. In addition to the indication of severe tubule damage, proper identification of these fragments is important to avoid a false positive diagnosis of low-grade transitional cell carcinoma. Transitional cell carcinoma is a type of cancer seen in 71% of cases of malignant tumors of the ureter.