Which of the following diagrams is correct with regard to the proximal (P) and distal (D) tubule of the Nephron. 
 

The correct answer is Option 2 

Explanation:

• The nephron is the structural and functional unit of the kidney. It is responsible for filtering blood, reabsorbing essential nutrients, and excreting waste as urine.
• The nephron consists of various parts:
  • Bowman's capsule
  • Proximal tubule
  • Loop of Henle
  • Distal tubule.
  • Collecting duct. 
• The proximal tubule (P) is closer to Bowman's capsule and is primarily involved in reabsorbing water, ions, glucose, and amino acids.
• The distal tubule (D) is farther along the nephron and plays a role in the selective reabsorption of ions and water, influenced by hormones like aldosterone and ADH (antidiuretic hormone).

PCT is lined by simple cuboidal brush border epithelium which increases the surface area for reabsorption.

• Nearly all of the essential nutrients, and 70-80 per cent of electrolytes and water are reabsorbed by this segment.
• PCT also helps to maintain the pH and ionic balance of the body fluids by selective secretion of hydrogen ions and ammonia into the filtrate and by absorption of HCO₃ ^– from it.

Distal Convoluted Tubule (DCT): Conditional reabsorption of Na+ and water takes place in this segment. DCT is also capable of reabsorption of HCO₃ ^– and selective secretion of hydrogen and potassium ions and NH₃ to maintain the pH and sodium-potassium balance in blood.