The reverse flow of the blood from the left systemic arch or from the pulmonary arch is prevented by

Options

A. Mitral valve
B. Tricuspid valve
C. Semilunar valves
D. Eustachian valve

Answer

To answer the question regarding what prevents the reverse flow of blood from the left systemic arch or from the pulmonary arch, we can follow these steps:

### Step-by-Step Solution:

1. **Understanding Blood Flow**: Blood flows through the heart and vessels in a specific direction. The systemic arch (aorta) carries oxygenated blood from the heart to the body, while the pulmonary arch (pulmonary arteries) carries deoxygenated blood from the heart to the lungs.

2. **Role of Valves**: The heart contains valves that ensure blood flows in one direction and prevents backflow. These valves open and close in response to pressure changes within the heart chambers and blood vessels.

3. **Identifying Relevant Valves**: The main valves in question are:
- Aortic semilunar valve (related to the systemic arch)
- Pulmonary semilunar valve (related to the pulmonary arch)
- Tricuspid valve (between right atrium and right ventricle)
- Mitral (bicuspid) valve (between left atrium and left ventricle)

4. **Focusing on the Semilunar Valves**: The aortic semilunar valve is located at the exit of the left ventricle and prevents backflow of blood from the aorta (systemic arch) into the left ventricle. The pulmonary semilunar valve is located at the exit of the right ventricle and prevents backflow from the pulmonary arteries into the right ventricle.

5. **Conclusion**: Since the question specifically asks about preventing reverse flow from the systemic arch and pulmonary arch, the correct answer is the **semilunar valves**. The aortic semilunar valve prevents backflow from the systemic arch, while the pulmonary semilunar valve prevents backflow from the pulmonary arch.

### Final Answer:
The reverse flow of blood from the left systemic arch or from the pulmonary arch is prevented by the **semilunar valves**.

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