Biology · Excretory Products and Their Elimination · NEET
The proximal convoluted tubule (PCT) is the main reabsorption site of the nephron. It takes back nearly all glucose, amino acids and other nutrients, plus about 70 to 80 percent of the water and electrolytes from the filtrate, and it secretes H+ and ammonia while reabsorbing HCO3- to keep blood pH and ion balance normal. Memory hook: "PCT = the Pick-up and Cleaning Tubule" — it picks up the good stuff and cleans up acid.
The PCT reabsorbs glucose, amino acids, Na+ (active), most water and HCO3- back into blood, while secreting H+ and ammonia into the filtrate. Its cuboidal brush-border lining maximises surface area for this reabsorption.
Your doubts, answered
What exactly does the PCT reabsorb?
The PCT reabsorbs nearly all the essential nutrients (glucose, amino acids) and about 70 to 80 percent of the electrolytes and water from the glomerular filtrate. Because it takes back the useful things, only wastes and a small part of water move on to the loop of Henle. This large reabsorption is why the PCT is called the main reabsorbing segment of the nephron.
Why does the PCT have a brush border, and why does NEET keep asking about it?
The PCT is lined by simple cuboidal brush border epithelium. The brush border is a layer of tiny finger-like microvilli that greatly increases the surface area, so more reabsorption can happen. NEET repeatedly tests two exact words here: cuboidal (not columnar) and brush border. A common wrong option writes 'simple columnar brush border' — that single word 'columnar' makes the statement false.
Does the PCT only reabsorb, or does it secrete too?
It does both. Besides heavy reabsorption, the PCT also secretes hydrogen ions (H+) and ammonia into the filtrate and absorbs HCO3- (bicarbonate) from it. This two-way action keeps the pH and ionic balance of body fluids steady, so the PCT is a control point for blood acidity, not just a sponge for water.
Is sodium reabsorption in the PCT active or passive?
Sodium (Na+) reabsorption in the PCT is active — it uses energy to pump Na+ out of the filtrate. This is a favourite NEET fact: when asked 'the part of nephron involved in active reabsorption of sodium', the answer is the PCT. Water then follows the reabsorbed salts, but the Na+ movement itself is active.
How is the PCT different from the DCT for reabsorption?
The PCT does bulk, unconditional reabsorption — it always takes back most water, ions and all nutrients. The DCT does conditional reabsorption of Na+ and water, meaning it is controlled by hormones like ADH and aldosterone. So PCT = fixed large clean-up, DCT = fine, hormone-adjusted tuning.
⚠️ The NEET trap ✗ The PCT is lined by simple columnar brush border epithelium. ✓ The PCT is lined by simple cuboidal brush border epithelium. 🧠 NCERT says CUBOIDAL. NTA swaps in 'columnar' to make a false statement (NEET 2024 did exactly this). The brush border part is true; only the cell shape word is the trap.
Real NEET questions
NEET 2016 Phase 2
The part of nephron involved in active reabsorption of sodium is
A · Distal convoluted tubule
B · Proximal convoluted tubule ✓
C · Bowman's capsule
D · Descending limb of Henle's loop
Solution: Active reabsorption of Na+ is a key function of the PCT, which has a brush-border cuboidal epithelium that increases surface area. The PCT reabsorbs nearly all essential nutrients and 70-80% of electrolytes and water. Bowman's capsule and the limbs of Henle's loop are not the primary site of active Na+ reabsorption.
NEET 2020
Cuboidal epithelium with brush border of microvilli is found in:
A · Proximal convoluted tubule of nephron ✓
B · Eustachian tube
C · Lining of intestine
D · Ducts of salivary glands
Solution: NCERT states the PCT is lined by simple cuboidal brush border epithelium; the microvilli (brush border) increase surface area for reabsorption. The intestine has columnar epithelium, and the Eustachian tube and salivary duct linings are not described with this microvillar brush border. So the brush-bordered cuboidal epithelium is characteristic of the PCT.
NEET 2024
Statement II: The proximal convoluted tubule is lined by simple columnar brush border epithelium and increases the surface area for reabsorption. (Judged as part of a two-statement question.)
A · Statement II is true
B · Statement II is false ✓
Solution: Statement II is FALSE. The PCT is lined by simple CUBOIDAL brush border epithelium, not columnar. The brush border correctly increases surface area for reabsorption, but the cell shape word 'columnar' makes the whole statement wrong — a classic NTA word-swap.
Solved Excretory Products and Their Elimination NEET PYQs
Try the real previous-year questions from this chapter — each with the answer and a full solution.
What is the main function of the proximal convoluted tubule?
Its main function is reabsorption: it takes back nearly all nutrients and about 70 to 80 percent of the water and electrolytes from the filtrate. It also secretes H+ and ammonia and absorbs HCO3- to maintain blood pH and ionic balance.
Is the PCT lined by cuboidal or columnar epithelium?
Simple cuboidal brush border epithelium. This is a high-frequency NEET fact — the answer is cuboidal, never columnar. The brush border (microvilli) increases the surface area for reabsorption.
How much water and electrolytes does the PCT reabsorb?
About 70 to 80 percent of the electrolytes and water in the filtrate, along with almost all essential nutrients such as glucose and amino acids.
Does the PCT help control blood pH?
Yes. By secreting hydrogen ions and ammonia into the filtrate and reabsorbing HCO3- from it, the PCT maintains the pH and ionic balance of body fluids.
Which part of the nephron actively reabsorbs sodium?
The PCT actively reabsorbs sodium. This is why 'active reabsorption of Na+' points to the proximal convoluted tubule in NEET questions.
