Glucose and albumin are both normally absent in the urine but reason for their excluison differs explain absence of glucose?

Glucose

There are two reasons for the absence of glucose in urine.

1. The kidneys have specialized structures called nephrons that are responsible for filtering waste products from the blood and producing urine. Within the nephrons, there is a network of tiny blood vessels called glomeruli that act as filters. These filters allow water, electrolytes, and small molecules to pass through while retaining larger molecules, such as glucose.

2. Glucose is actively reabsorbed from filtered urine back into the blood by specialized cells called proximal tubular cells. The proximal tubular cells have glucose transporters that facilitate the movement of glucose from the tubular lumen back into the blood.

When the blood glucose level exceeds a certain threshold, known as the renal threshold for glucose, the reabsorption capacity of the proximal tubular cells is overwhelmed, leading to the presence of glucose in the urine. This condition is called glucosuria. Glucosuria is commonly observed in individuals with diabetes mellitus, where blood glucose levels are chronically elevated.

Albumin

In contrast, the absence of albumin in the urine is primarily due to the size of the albumin molecule. Albumin is a relatively large protein with a molecular weight of approximately 69,000 Daltons. The pores of the glomerular filters in the kidneys are normally too small to allow such large molecules to pass through, thereby preventing albumin from entering the urine.

Therefore, the absence of glucose in urine is a combination of filtration and reabsorption processes, while the absence of albumin is primarily due to size-based exclusion by the glomerular filters.