Why does menstruation occur?

Explanation

### Step-by-Step Solution:

1. **Understanding Menstruation**: Menstruation is the process where the thick lining of the uterus is shed. This shedding occurs along with blood vessels, resulting in vaginal bleeding.

2. **Role of the Uterus**: The uterus prepares for a potential pregnancy each month. The inner lining of the uterus thickens in anticipation of a fertilized egg.

3. **Ovarian Function**: At puberty, the ovaries start to produce female gametes (ova). This process occurs monthly, and each month an ovum is released.

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