Which one of the following is the most likely root cause why menstruation is not taking place in regularly cycling human female ?

Options

A. Maintenance of the hypetrophical endometerial lining
B. Maintenance of high concentration of sex hormones in a the blood stream
C. Retention of well - developed corpus luteurm
D. Fertilisation of the ovum

Answer

**Step-by-Step Solution:**

1. **Understanding the Menstrual Cycle**: The menstrual cycle is a regular process that occurs in females, typically lasting about 28 days. It involves the preparation of the uterus for a potential pregnancy. If fertilization does not occur, menstruation takes place.

2. **Identifying Regular Cycling**: The question specifies a "regularly cycling human female," which indicates that her menstrual cycle has been normal and predictable until now.

3. **Considering Causes for Absence of Menstruation**: There are several reasons why menstruation might not occur, including:
- Pregnancy (fertilization of the ovum)
- Stress or environmental factors
- Health issues or poor nutrition

4. **Analyzing the Options**:
- **Option 1**: Maintenance of hypertrophical endometrial lining – This is related to pregnancy, not a cause for absence of menstruation.
- **Option 2**: Maintenance of high concentration of sex hormones – While hormones play a role in the menstrual cycle, this is not the direct cause of missed menstruation.
- **Option 3**: Retention of well-developed corpus luteum – This is also linked to pregnancy and does not explain the absence of menstruation in a regular cycle.
- **Option 4**: Fertilization of ovum – This is the most likely cause of missed menstruation, as it prevents the shedding of the uterine lining.

5. **Conclusion**: Based on the analysis, the most likely root cause for the absence of menstruation in a regularly cycling human female is the **fertilization of the ovum**.

**Final Answer**: The most likely root cause is the **fertilization of ovum**.

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