Main function of eustachain tube is to

Options

A. protect membranous labyrinth
B. support the bones of middle ear
C. equalize pressure on two sides of tympanic membrane
D. prevent infection entering ear drum

Answer

### Step-by-Step Solution:

1. **Identify the Structure**: The Eustachian tube is a tube that connects the middle ear to the nasopharynx.
- **Hint**: Think about where the Eustachian tube is located and what it connects.

2. **Understand Its Function**: The primary function of the Eustachian tube is to equalize the atmospheric pressure in the middle ear.
- **Hint**: Consider why pressure equalization is important for hearing.

3. **Pressure Equalization**: When the Eustachian tube opens, it allows air to flow into or out of the middle ear, which helps to balance the pressure on both sides of the tympanic membrane (eardrum).
- **Hint**: Reflect on how changes in altitude or underwater activities might affect ear pressure.

4. **Protection Role**: The Eustachian tube also plays a protective role by preventing unwanted fluctuations in pressure and shielding the middle ear from very high-frequency sounds.
- **Hint**: Think about what could happen if the middle ear was exposed to extreme pressure changes or loud sounds.

5. **Conclusion**: Therefore, the main function of the Eustachian tube is to equalize pressure on both sides of the tympanic membrane.
- **Hint**: Summarize the key points about the Eustachian tube’s role in ear health.

### Final Answer:
The main function of the Eustachian tube is to equalize pressure on both sides of the tympanic membrane.