Major portion of glomerular filtrate is reabsorbed in

The correct answer is Proximal tubule

Concept:

• The nephron is the functional unit of the kidney, responsible for filtering blood and forming urine. It consists of various structures, including the glomerulus, proximal tubule, loop of Henle, distal convoluted tubule, and collecting tubule.
• The process of urine formation involves three main steps: filtration, reabsorption, and secretion.
• Glomerular filtration occurs in the glomerulus, where blood is filtered, and the filtrate enters the nephron tubules for further processing.
• Reabsorption is the process by which essential substances such as water, glucose, amino acids, and ions are absorbed back into the bloodstream from the filtrate.

Explanation:

Proximal tubule:

• The majority of the glomerular filtrate is reabsorbed in the proximal tubule (approximately 65-70%).
• This portion of the nephron is highly specialized for reabsorption. Key substances reabsorbed here include:
  • Water: Reabsorbed due to osmotic gradients created by solute reabsorption.
  • Glucose and amino acids: Reabsorbed completely under normal physiological conditions via active transport.
  • Electrolytes such as sodium, chloride, potassium, bicarbonate, and calcium are reabsorbed through various transport mechanisms.
• The proximal tubule also plays a role in secretion, removing substances like hydrogen ions, ammonia, and certain drugs from the blood into the filtrate.

Other Options:

• Loop of Henle: The loop of Henle is primarily responsible for concentrating the urine by creating a countercurrent system.
• Only a small amount of reabsorption occurs here, mainly of water in the descending limb and sodium and chloride in the ascending limb.
• Distal convoluted tubule: The distal convoluted tubule is involved in the fine-tuning of reabsorption and secretion, especially for electrolytes like sodium and potassium, and in maintaining acid-base balance.
• Collecting tubule: The collecting tubule is mainly involved in the reabsorption of water under the influence of antidiuretic hormone (ADH) and in the secretion of potassium and hydrogen ions.