The normal duration of the menstrual cycle is 3-4 days.

Explanation:
The menstrual cycle is the natural process that occurs in females of reproductive age. It involves the monthly release of an egg from the ovaries, the thickening of the uterine lining, and the shedding of this lining if fertilization does not occur. The duration of the menstrual cycle can vary from woman to woman, but the average duration is around 28 days.

1. Menstrual Cycle Phases:
- Menstrual Phase: This is the phase when the uterine lining is shed. It typically lasts for 3-7 days, with an average duration of 3-4 days.
- Follicular Phase: This phase begins on the first day of the menstrual cycle and lasts until ovulation. During this phase, the follicles in the ovaries mature and prepare to release an egg.
- Ovulation: This is the phase when an egg is released from the ovary. It usually occurs around day 14 of the menstrual cycle.
- Luteal Phase: This phase begins after ovulation and lasts until the start of the next menstrual cycle. If fertilization occurs, the fertilized egg implants into the uterine lining. If not, the uterine lining begins to shed, marking the start of the next menstrual cycle.

2. Factors Affecting Menstrual Cycle Duration:
- Hormonal Imbalances: Imbalances in hormones such as estrogen and progesterone can affect the duration of the menstrual cycle. These imbalances can be caused by various factors including stress, certain medications, and underlying medical conditions.
- Age: The menstrual cycle duration can vary throughout a woman's life. It is typically longer in the beginning and end of reproductive age. In adolescence, it may take a few years for the menstrual cycle to become regular.
- Birth Control: The use of hormonal birth control methods can also affect the duration of the menstrual cycle. Some methods, such as certain types of oral contraceptives, can shorten the duration of the menstrual cycle.

In conclusion, the normal duration of the menstrual cycle is 3-4 days, but it can vary from woman to woman. It is important to note that any significant changes in the menstrual cycle, such as prolonged or irregular bleeding, should be discussed with a healthcare professional.

Mentruation and menstrual cycle are two different things later takes 28 days to complete