Final answer:
Glycosuria is the presence of glucose in the urine. It is associated with diabetes mellitus and occurs when the concentration of glucose in the blood exceeds the renal threshold.
Step-by-step explanation:
Glycosuria is the presence of glucose in the urine. It occurs when the concentration of glucose in the blood exceeds the renal threshold. The renal threshold is the level of glucose in the blood at which the kidneys start excreting glucose into the urine. The typical reabsorption percentage of glucose is almost 100% in the proximal convoluted tubules of the kidney.
The major disorder associated with glycosuria is diabetes mellitus, which is characterized by a defect in the uptake of glucose by cells due to insulin deficiency or defective insulin receptors. Insulin is the hormone responsible for facilitating the uptake of glucose by cells. At a cellular level, insulin acts on cells by promoting the insertion of glucose transport proteins, called GLUTs, into the cell membrane. These transporters facilitate the movement of glucose from the extracellular fluid into the cell through facilitated diffusion.
The renal transport maximum (Tm) is the maximum rate at which a substance can be reabsorbed by the renal tubules. The Tm for glucose is about 350 mg/min. If the concentration of glucose in the glomerular filtrate exceeds the Tm, the excess glucose is not reabsorbed and ends up being excreted in the urine.