Final answer:
Menarche refers to the first menstrual period in a pubertal female, indicating the start of reproductive maturity. It usually occurs at an average age of 12.5 years in the U.S. and is influenced by both genetic and environmental factors.
Step-by-step explanation:
The term menarche refers to the first menstrual period in a pubertal female. This event marks the onset of menstruation, signifying that the ovaries have begun the cyclic release of an egg. In the United States, the average age for menarche is approximately 12.5 years, but it can vary widely anywhere between 8 to 16 years. Factors influencing this variation include genetics and environmental aspects such as diet. Menarche is a pivotal moment in female reproductive development, representing the transition from childhood to reproductive maturity. The menstrual cycle, which includes ovulation and menstruation, is regulated by hormones from the hypothalamus, pituitary gland, and ovaries. During menstruation, the inner lining of the uterus, known as the endometrium, is shed through the vagina, a process that will occur throughout a woman's reproductive years until menopause.