Why is there no glucose in urine?

Glucose is actively reabsorbed in the renal proximal convoluted tubule and loops of Henle through a process called glucose reabsorption. The glucose transporters SGLT2 (sodium-glucose transporter 2) and GLUT1 (glucose transporter 1) are responsible for this reabsorption. SGLT2 is located in the luminal membrane of the proximal tubule cells, and GLUT1 is located in the basolateral membrane. Glucose binds to SGLT2 and is transported into the proximal tubule cells, where it then binds to GLUT1 and is transported into the bloodstream. This process ensures that glucose is reabsorbed back into the bloodstream and not lost in the urine.

In healthy individuals, the reabsorption process is highly efficient, and there is no significant amount of glucose in the urine. However, in certain conditions, such as diabetes mellitus, the reabsorption of glucose can be impaired, leading to the presence of glucose in the urine, a condition known as glucosuria.