The opening of urinary bladder is guarded by

Answer

**Step-by-Step Solution:**

1. **Understanding the Urinary Bladder**: The urinary bladder is a muscular sac that stores urine from the kidneys before it is excreted from the body.

2. **Identifying the Openings**: The urinary bladder has two main openings:
- **Internal Opening**: This is where urine enters the bladder from the ureters.
- **External Opening**: This is where urine exits the bladder through the urethra.

3. **Guarding Mechanism**: The openings of the urinary bladder are controlled by muscles known as sphincters.

4. **Types of Sphincter Muscles**:
- **Internal Sphincter**: This sphincter is involuntary, meaning it operates automatically without conscious control. It guards the internal opening of the bladder.
- **External Sphincter**: This sphincter is voluntary, meaning it can be consciously controlled. It guards the external opening of the bladder.

5. **Conclusion**: Therefore, the opening of the urinary bladder is guarded by sphincter muscles, specifically the internal and external sphincters.

**Final Answer**: The opening of the urinary bladder is guarded by sphincter muscles (internal and external sphincters).

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