The menstrual cycle is a complex series of hormonal and physiological changes that occur in the female reproductive system, primarily to prepare the body for pregnancy. It typically lasts about 28 days, though it can vary from 21 to 35 days in adults. The cycle is divided into several phases:
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Menstrual Phase (Days 1-5):
- This phase starts on the first day of menstruation, marking the shedding of the uterine lining (endometrium) along with blood and mucus. This occurs if implantation of a fertilized egg does not take place in the previous cycle.
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Follicular Phase (Days 1-13):
- Along with menstruation, this phase also begins on the first day of the cycle. The pituitary gland releases follicle-stimulating hormone (FSH), stimulating the ovaries to produce several follicles, each containing an immature egg. As the follicles mature, they release estrogen, which helps to rebuild the endometrium in preparation for a potential pregnancy.
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Ovulatory Phase (Day 14):
- Around the middle of the menstrual cycle, a surge in luteinizing hormone (LH), triggered by rising estrogen levels, leads to ovulation. This is the release of a mature egg from a dominant follicle in the ovary. The egg then travels down the fallopian tube, where it may meet sperm for fertilization. Ovulation is often marked by an increase in basal body temperature and changes in cervical mucus.
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Luteal Phase (Days 15-28):
- After ovulation, the ruptured follicle transforms into the corpus luteum, which secretes progesterone. Progesterone helps to further prepare the uterine lining for a potential implantation of a fertilized egg. If fertilization occurs, the embryo produces human chorionic gonadotropin (hCG), signaling the corpus luteum to continue producing progesterone. If fertilization does not occur, the corpus luteum disintegrates, leading to a decrease in progesterone levels.
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Premenstrual Phase:
- A few days before menstruation, if no pregnancy has taken place, hormone levels (estrogen and progesterone) drop, leading to the breakdown of the uterine lining. This hormonal shift can result in premenstrual syndrome (PMS), characterized by physical and emotional symptoms like bloating, mood swings, and cravings.
Overall, the menstrual cycle is regulated by a delicate balance of hormones and is crucial for reproductive health. Each woman's cycle can be unique in terms of length, symptoms, and flow. Understanding this cycle is essential for managing menstrual health, engaging in fertility awareness, and identifying potential health issues.