Reabsorption of useful substances from the glomerular filtrate occurs in the proximal convoluted tubule (PCT).

Proximal Convoluted Tubule (PCT):
The proximal convoluted tubule is the first part of the renal tubule system in the nephron. It is responsible for the reabsorption of a majority of the useful substances from the glomerular filtrate, which is the fluid that is formed in the glomerulus of the kidney.

Reabsorption in the PCT:
1. Reabsorption of water: The PCT reabsorbs around 65% of the filtered water from the glomerular filtrate. This is important for maintaining the body's water balance.

2. Reabsorption of electrolytes: The PCT reabsorbs a majority of the electrolytes, including sodium, potassium, calcium, and magnesium ions, from the glomerular filtrate. This reabsorption helps in maintaining the body's electrolyte balance.

3. Reabsorption of glucose and amino acids: The PCT actively reabsorbs glucose and amino acids from the glomerular filtrate. These substances are essential for energy production and protein synthesis in the body.

4. Reabsorption of bicarbonate ions: The PCT reabsorbs bicarbonate ions, which helps in maintaining the acid-base balance in the body.

5. Reabsorption of vitamins and other organic molecules: The PCT also reabsorbs various vitamins, hormones, and other organic molecules from the glomerular filtrate, ensuring their availability for the body's metabolic processes.

6. Reabsorption of urea: The PCT reabsorbs a small amount of urea, which is a waste product of protein metabolism. This helps in conserving water and maintaining the concentration gradient in the medulla of the kidney.

Conclusion:
The proximal convoluted tubule plays a crucial role in the reabsorption of various useful substances from the glomerular filtrate. This reabsorption process is essential for maintaining the body's water and electrolyte balance, as well as ensuring the availability of important molecules for metabolic processes.

Useful substance like glucose amino acid minerals absorbed in PCT it is nearby 70%reabsorptiom take place bcz it has brush border epithelium