Menstrual cycle occurs due to lack of:

Options

A. Progesterone
B. FSH
C. Oxytocin
D. Vasopressin

Answer

### Step-by-Step Solution:

1. **Understanding the Menstrual Cycle**: The menstrual cycle is a monthly process that occurs in females, typically lasting about 28 to 29 days. It involves changes in the ovaries and the uterus.

2. **Role of Hormones**: Several hormones regulate the menstrual cycle. Key hormones include Follicle Stimulating Hormone (FSH), Luteinizing Hormone (LH), estrogen, and progesterone.

3. **Ovulation**: Around the midpoint of the cycle (approximately day 14), an egg is released from the ovary. This process is known as ovulation.

4. **Preparation for Fertilization**: After ovulation, the uterus prepares for potential implantation of a fertilized egg by thickening its endometrial lining, which is influenced by progesterone.

5. **Fertilization or Lack Thereof**: If fertilization occurs, the fertilized egg (zygote) will implant in the thickened endometrium. If fertilization does not occur, the corpus luteum (which forms from the remnants of the follicle after ovulation) degenerates.

6. **Decrease in Progesterone**: The degeneration of the corpus luteum leads to a decrease in progesterone levels. Progesterone is crucial for maintaining the endometrial lining.

7. **Menstruation**: The lack of progesterone causes the endometrial lining to break down and shed, resulting in menstruation. This marks the beginning of a new menstrual cycle.

8. **Conclusion**: Therefore, the menstrual cycle occurs due to the lack of progesterone.

### Final Answer:
The menstrual cycle occurs due to the lack of **progesterone**.

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