Biology · Excretory Products and Their Elimination · NEET
When blood pressure in the glomerulus falls, the JG (juxtaglomerular) cells of the kidney release an enzyme called renin. Renin starts a chain: angiotensinogen turns into angiotensin I and then angiotensin II, which raises blood pressure and tells the adrenal cortex to release aldosterone, and aldosterone makes the tubule reabsorb Na+ and water. Memory hook: "Rain (Renin) makes Angie (Angiotensin) call Aldo (Aldosterone) to save water" - the whole system works to bring blood pressure and volume back up.
The RAAS cascade: low glomerular blood pressure triggers JG cells to release renin (an enzyme), which forms angiotensin II. Angiotensin II causes vasoconstriction and triggers aldosterone, which reabsorbs Na+ and water to restore blood pressure. This is the exact NCERT sequence NEET tests.
Your doubts, answered
Does renin raise or lower blood pressure?
Renin RAISES blood pressure. It is switched on exactly when blood pressure or blood volume FALLS. Through angiotensin II (a vasoconstrictor) and aldosterone (which reabsorbs Na+ and water), the whole RAAS chain works to bring low blood pressure back up. So the trigger is low BP, and the result is higher BP.
What is the correct NCERT sequence of the renin-angiotensin mechanism?
Fall in glomerular blood pressure/GFR then JG cells release renin then renin converts angiotensinogen to angiotensin I and then angiotensin II then angiotensin II causes vasoconstriction and activates adrenal cortex to release aldosterone then aldosterone causes reabsorption of Na+ and water from the distal tubule then blood pressure and GFR go back up. NEET loves to test this exact order (C-A-E-B-D style questions).
Is renin an enzyme or a hormone?
Renin is an ENZYME released by the JG cells, not a hormone. It acts on the plasma protein angiotensinogen to convert it into angiotensin I. Students lose marks by calling renin a hormone. Aldosterone and ADH are the hormones in kidney regulation; renin is the enzyme that starts the cascade.
What is the difference between renin and rennin?
Renin (one n before the i) is the kidney enzyme in the RAAS that regulates blood pressure. Rennin (double n) is a different, older term for the milk-clotting enzyme of the stomach in young mammals. In the excretory chapter, the answer is always renin from JG cells - do not confuse it with the digestive rennin.
Where exactly is renin secreted from?
Renin is secreted by the JG cells of the juxtaglomerular apparatus (JGA). The JGA is a special sensitive region formed by cellular modifications in the distal convoluted tubule (DCT) and the afferent arteriole where they touch. NEET 2026 tested this exact pairing: DCT and afferent arteriole.
What is the role of aldosterone in this mechanism?
Aldosterone is a hormone released by the adrenal cortex when angiotensin II signals it. It causes reabsorption of Na+ and water from the distal parts of the tubule. This retains water in the body, increases blood volume and blood pressure, and prevents diuresis (excess urine loss).
⚠️ The NEET trap ✗ Angiotensin II directly acts on the kidney tubule to reabsorb Na+ and water. ✓ Angiotensin II activates the adrenal cortex to release ALDOSTERONE, and it is aldosterone that causes Na+ and water reabsorption from the distal tubule. Angiotensin II itself mainly causes vasoconstriction. 🧠 Remember the two jobs are split: angiotensin II squeezes vessels (vasoconstriction) AND calls aldosterone; aldosterone does the actual Na+/water reabsorption. NTA rewards students who keep these two steps separate.
Real NEET questions
NEET 2023 (Phase 2)
Arrange the events of Renin-Angiotensin mechanism in correct sequence.
(A) Activation of JG cell and release of renin.
(B) Angiotensin II activates release of aldosterone.
(C) Fall in glomerular blood pressure.
(D) Reabsorption of Na+ and water from distal convoluted tubule.
(E) Angiotensinogen is converted to Angiotensin I and then to Angiotensin II.
A · (A), (D), (C), (B), (E)
B · (B), (A), (E), (D), (C)
C · (C), (A), (E), (B), (D) ✓
D · (A), (D), (E), (C), (B)
Solution: The cascade begins with a fall in glomerular blood pressure (C), which activates JG cells to release renin (A). Renin converts angiotensinogen to angiotensin I and then angiotensin II (E). Angiotensin II activates the adrenal cortex to release aldosterone (B). Aldosterone finally causes reabsorption of Na+ and water from the distal tubule (D). Correct order: C, A, E, B, D. NCERT Ch 16, p.212.
NEET 2020
Which of the following would help in prevention of diuresis?
A · Atrial natriuretic factor causes vasoconstriction
B · Decrease in secretion of renin by JG cells
C · More water reabsorption due to undersecretion of ADH
D · Reabsorption of Na+ and water from renal tubules due to aldosterone ✓
Solution: Diuresis means increased urine output, so preventing it means conserving body water. Aldosterone (released through the renin-angiotensin mechanism) causes reabsorption of Na+ and water from the distal tubule, retaining water and preventing diuresis. ANF causes vasodilation (not vasoconstriction), and ADH UNDERsecretion would increase urine, so those options are wrong.
NEET 2017
A decrease in blood pressure/volume will not cause the release of:
A · Renin
B · Atrial Natriuretic Factor ✓
C · Aldosterone
D · ADH
Solution: A fall in blood pressure/volume triggers renin (from JG cells), then angiotensin II and aldosterone, plus ADH, all working to conserve water and raise BP. ANF works oppositely - it is released when blood flow/volume to the atria INCREASES and causes vasodilation to LOWER BP. So a decrease in BP/volume will not release ANF.
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.
A fall in glomerular blood flow, glomerular blood pressure, or GFR activates the JG cells to release renin. In simple words, low blood pressure inside the kidney is the trigger.
What is the final effect of the RAAS on the body?
The final effect is an increase in blood pressure and GFR, because angiotensin II causes vasoconstriction and aldosterone causes reabsorption of Na+ and water, raising blood volume.
What is angiotensinogen?
Angiotensinogen is a protein present in the blood plasma. Renin converts it into angiotensin I, which is then converted into the active angiotensin II.
How is RAAS different from ADH and ANF?
RAAS and ADH both act to conserve water and raise BP when it falls. ANF (Atrial Natriuretic Factor) is the opposite - it is released when BP is high and causes vasodilation to lower BP, acting as a check on RAAS.
Why is this important for NEET?
NEET frequently asks the exact sequence of RAAS events (arrange in order questions in 2023 and 2026) and pairs it with ADH and ANF. It is a high-yield, almost every-year topic from Ch 16.
