Assertion: During micturition, urine is prevented from flowing back into the ureters.
Reason: Urethral sphincters contract during micturition

Options

A. If both assertion and reason are true and reason is the correct explanation of assertion
B. if both assertion and reason are true but reason is not the correct explanation of assertion.
C. if assertion is true but reason is false
D. if both assertion and reason are false.

Explanation

**Step-by-Step Solution:**

1. **Understanding Micturition**: Micturition is the process of expelling urine from the urinary bladder. It is a reflex action that occurs when the bladder fills with urine and reaches a certain volume.

2. **Role of the Urinary Bladder**: The urinary bladder serves as a temporary storage reservoir for urine, which is produced by the kidneys and transported via the ureters to the bladder.

3. **Initiation of Micturition**: When the bladder fills with urine, stretch receptors in the bladder wall are activated. This leads to an increase in pressure within the bladder, which triggers a reflex action to initiate micturition.

4. **Contraction of Smooth Muscles**: During micturition, the smooth muscles of the bladder wall contract. This contraction helps to expel urine through the urethra, which is the duct through which urine exits the body.

5. **Prevention of Backflow**: The assertion states that urine is prevented from flowing back into the ureters during micturition. This is true because the ureters enter the bladder at an oblique angle, which creates a flap-like valve mechanism that prevents backflow when the bladder contracts.

6. **Urethral Sphincters**: The reason states that urethral sphincters contract during micturition. While the internal urethral sphincter (smooth muscle) does relax to allow urine to flow out, the external urethral sphincter (skeletal muscle) can be voluntarily controlled to prevent urination until an appropriate time.

7. **Conclusion**: Both the assertion and reason are true. However, the reason provided does not correctly explain the assertion because the prevention of backflow is primarily due to the anatomical arrangement of the ureters rather than the contraction of the urethral sphincters.

**Final Answer**: Both assertion and reason are true, but the reason is not the correct explanation of the assertion.

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