Glucose Reabsorption

The embryonic and newborn animals, however, do not spill glucose into the urine, and bladder samples taken following glucose injection indicate that the sugar is completely reabsorbed. Segal et al (85) report that a rudimentary transport system is present in the newborn, as indicated by a decrease in accumulation in the presence of phloridzin. Thus, it seems possible that some more primitive mechanism for glucose reabsorption may operate in the embryonic kidney. 

In children with lead encephalopathy, a proximal tubule defect for glucose reabsorption (glycosuria without hyperglycemia) was first noted by McKhann in 1926 and aminoaciduria was described by Wilson et al. in 1953 [10,11]. The Fanconi syndrome (aminoaciduria, phosphaturia, and glycosuria) has been observed... 

Proximal tubular function is immature, and bicarbonate and glucose reabsorption is reduced. This leads to a low serum bicarbonate concentration. Glycosuria and aminoaciduria may be found in the normal neonate. A baby s ability to concentrate urine is poor. A urine osmolality of 600 mmol/kg is the maximum that can be produced. In the neonatal period, the kidney s ability to excrete water and electrolytes is limited. Thus, great care must be taken in the provision of intravenous fluids. 

Sodium SGLTl -dependent unidirectionai transporter Small intestine and kidney Active uptake of glucose from lumen of intestine and reabsorption of glucose in proximal tubule of kidney against a concentration gradient... 

Active reabsorption occurs when the movement of a given substance across the luminal surface or the basolateral surface of the tubular epithelial cell requires energy. Substances that are actively reabsorbed from the tubule include glucose amino acids and Na+, POy3, and Ca++ ions. Three generalizations can be made regarding the tubular reabsorption of sodium, chloride, and water ... 

Kanai, Y., et al. The human kidney low affinity Na+/glucose cotransporter SGLT2. Delineation of the major renal reabsorptive mechanism for D-glucose. J. Clin. Invest. 1994, 93, 397-404. 

Because the glomerular filtrate contains many important body constituents (e.g., glucose), there are specific active uptake processes for them. Also, lipid-soluble chemicals diffuse back from the tubule into the blood, especially as the urine becomes more concentrated because of water reabsorption. The pH of the urine is generally lower than that of the plasma, and therefore pH partitioning tends to increase the reabsorption of weak acids. The pH of the urine can be altered... 

Proximal tubule Cells of the PCT are responsible for bulk transport of solutes, with approximately 70-80% of the filtered load of sodium chloride (active processes) and water (passive, down the osmotic gradient established by sodium reabsorption) and essentially all of the amino acids, bicarbonate, glucose and potassium being reabsorbed in this region. 

A second form of diabetes is also recognized diabetes insipidus, which is caused by a deficiency of the pituitary hormone, vasopressin. Vasopressin promotes water reabsorption from the kidney, hence a deficiency also induces S5anptoms of excessive urination and thirst. A key diagnostic difference between the common diabetes meUitus and the rare diabetes insipidus, is the absence of glucose in the urine in the latter case. Until a few decades ago, a popular way to differentiate between the two diseases was to taste the patient s urine to see if it was sweet. 

---