Question

Arrange the following events occurring in Renin-Angiotensin mechanism in the correct order :
A. Increase in blood pressure and Glomerular filtration rate.
B. Reabsorption of $Na^+$ and water from distal parts of tubule due to Aldosterone.
C. Fall in Glomerular filtration rate.
D. Vasoconstriction by Angiotensin II and release of Aldosterone.
E. Renin converts Angiotensinogen into Angiotensin I, followed by Angiotensin II.
Choose the correct answer from the options given below :

• A. C, E, D, B, A
• B. A, C, E, B, D
• C. A, D, B, E, C
• D. C, A, B, D, E

Hint:

Logic Tip: The mechanism is a classic negative feedback loop. The problem (Fall in GFR = C) must be at the very beginning, and the solution to the problem (Increase in GFR = A) must be at the very end. Only Option (1) follows this logic!

Answer 1

The Correct Option is A

Concept:
The Renin-Angiotensin-Aldosterone System (RAAS) is a complex multi-organ endocrine system involved in the regulation of blood pressure and fluid balance. It acts as a feedback mechanism triggered by a drop in kidney perfusion or glomerular filtration rate (GFR).
Step 1:
The entire RAAS cascade is initiated when there is a drop in blood volume, blood pressure, or a fall in Glomerular Filtration Rate (GFR). This stimulates the Juxtaglomerular (JG) cells of the kidney. First step: C
Step 2:
In response to the fall in GFR, the JG cells release the enzyme Renin into the blood. Renin acts on a plasma protein called Angiotensinogen (produced by the liver), converting it to Angiotensin I, which is further converted to the active hormone Angiotensin II (primarily in the lungs by ACE). Second step: E
Step 3:
Angiotensin II is a powerful vasoconstrictor. It constricts blood vessels directly. Additionally, it stimulates the adrenal cortex to release the hormone Aldosterone. Third step: D
Step 4:
Aldosterone acts on the distal parts of the renal tubule (DCT and collecting duct), promoting the active reabsorption of $Na^+$ and water back into the bloodstream, which increases blood volume. Fourth step: B
Step 5:
The combination of widespread vasoconstriction and increased blood volume leads to a restorative increase in blood pressure and GFR, returning the system to homeostasis and shutting off further renin release. Fifth step: A
Step 6:
The chronological sequence is C $\rightarrow$ E $\rightarrow$ D $\rightarrow$ B $\rightarrow$ A, which matches Option (1).