In a regularly cycling human female, which can be the root cause of menstrual failure?

Options

A. Maintenancy of high concentration of sex-hormones in the blood stream
B. Retention of well-developed corpus luteum
C. Fertilisation of the ovum
D. Maintenancy of the pypertrophical endometrial lining

Answer

### Step-by-Step Solution

1. **Understanding the Question**: The question asks for the root cause of menstrual failure in a regularly cycling human female. This implies that the female does not have any underlying pathological conditions affecting her menstrual cycle.

2. **Hormonal Regulation of the Menstrual Cycle**: The menstrual cycle is regulated by hormones, primarily estrogen and progesterone. These hormones are crucial for the development of the ovarian follicles and the preparation of the uterine lining for potential implantation of a fertilized egg.

3. **Role of the Ovum and Corpus Luteum**: During the menstrual cycle, an ovum (egg) is released from the ovary (ovulation). After ovulation, the ruptured follicle transforms into the corpus luteum, which secretes progesterone to maintain the uterine lining for a possible pregnancy.

4. **Fertilization and Menstrual Failure**: If the ovum is fertilized by sperm, the corpus luteum is maintained, and menstruation does not occur. If the ovum is not fertilized, the corpus luteum degenerates, leading to a decrease in progesterone levels, which triggers menstruation.

5. **Analyzing the Options**:
- **Maintenance of High Concentration of Sex Hormones**: This is typically a pathological condition and not applicable to a regularly cycling female.
- **Retention of Well-Developed Corpus Luteum**: This occurs only if fertilization has taken place. In a regularly cycling female, this would indicate a pregnancy, not menstrual failure.
- **Fertilization of the Ovum**: If fertilization occurs, menstruation will not happen, making this a plausible cause of menstrual failure.
- **Maintenance of Hypertrophical Endometrial Lining**: This is also a pathological condition and not typical in a regularly cycling female.

6. **Conclusion**: The most logical root cause of menstrual failure in a regularly cycling human female is the **fertilization of the ovum**. This prevents the menstrual cycle from occurring as the body prepares for pregnancy.

### Final Answer
The root cause of menstrual failure in a regularly cycling human female is the **fertilization of the ovum**.