What happens to glucose in the kidneys?

The glomerulus is the filtering system of the nephron , the functional unit of the kidney. The blood coming from the afferent arteriole pushes blood into the glomerulus where ultrafiltration takes place. After that blood leaves via efferent arteriole with plasma proteins such as albumin, globulin and red blood cells, platelets, etc.

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The filtered part of blood that is collected into the Bowman's space is called glomerular filtrate . It is composed of glucose, salts, vitamins, amino acids, water and bicarbonate along with nitrogenous waste products like urea. Once the filtrate passes through the proximal convoluted tubule , the primary site of absorption, 100% of the glucose is reabsorbed back into the blood, including other nutrients and molecules.

Please note that 100% reabsorption of glucose from filtrate by PCT may take place only when blood glucose level is below 180 mg/dL: when blood sugar level shoots above this renal threshhold, glucose will appear in urine (i.e. 100% reabsorption will not be possible).

Normally, the kidneys filter glucose from the blood and then reabsorb it back into the bloodstream. But, in cases where blood glucose levels are excessive—such as in diabetes—the kidneys may not be able to reabsorb all of the glucose, which can result in glucose excreted in the urine, a condition called glucosuria.

Glucose in the kidneys is typically reabsorbed back into the bloodstream through the renal tubules. Normally, all glucose filtered by the glomeruli is reabsorbed in the proximal convoluted tubules. However, if blood glucose levels are abnormally high, as in cases of diabetes mellitus, the capacity of the renal tubules to reabsorb glucose may be exceeded, leading to glucose appearing in the urine, a condition known as glucosuria. This occurs because the renal threshold for glucose reabsorption is exceeded, resulting in the spillage of glucose into the urine.