Final answer:
The menstrual cycle is regulated by hormones and involves the follicular phase, ovulation, the luteal phase, and menstruation. Estrogen levels rise before ovulation, while progesterone levels increase afterward, leading to the thickening of the uterine lining. Menstruation occurs when pregnancy does not happen, with menarche and menopause marking the beginning and end of the reproductive years, respectively.
Step-by-step explanation:
The menstrual cycle is a complex process involving hormonal changes that prepare the female reproductive system for the possibility of pregnancy. The cycle is regulated by hormones such as estrogen and progesterone, produced by the ovaries, as well as hormones from the anterior pituitary gland, including luteinizing hormone (LH) and follicle-stimulating hormone (FSH). The menstrual cycle has several distinct phases, including the follicular phase, ovulation, the luteal phase, and menstruation.
Estrogen levels rise before ovulation, triggering a surge of LH that leads to the release of an egg from the ovary. After ovulation, during the luteal phase, progesterone levels increase, promoting the thickening of the uterine lining (endometrium) in preparation for potential pregnancy. If pregnancy does not occur, progesterone levels fall, leading to the shedding of the endometrium as menstruation.
The first occurrence of menstruation is called menarche, and it signifies the beginning of a female's reproductive years. The process of menstruation ceases temporarily during pregnancy, as the hormonal environment shifts to support the developing fetus. Eventually, women reach menopause, which marks the end of the menstrual cycle, typically around the age of 50.