How does the menstrual cycle work?

The menstrual cycle is a complex series of events that occur in the female reproductive system, typically lasting around 28 days, although it can vary from person to person. It involves the coordination of hormonal changes, follicle development, ovulation, and changes in the uterine lining. 

The primary function of the menstrual cycle is to prepare the female reproductive system for the possibility of pregnancy. It involves a series of complex hormonal and physiological changes that contribute to the reproductive process. The menstrual cycle serves several important functions, including:

• Egg Production. The menstrual cycle facilitates the production and release of eggs (ova) from the ovaries. Each month, one mature egg is typically released during ovulation, providing the opportunity for fertilization by sperm.

• Hormonal Regulation. The menstrual cycle involves intricate hormonal interactions. Hormones like estrogen and progesterone play crucial roles in regulating the cycle, influencing the growth and development of the uterine lining, and preparing it for potential implantation of a fertilized egg.

• Uterine Lining Preparation. The menstrual cycle ensures that the uterus develops and maintains a suitable environment for a potential pregnancy. The uterine lining, or endometrium, thickens during the cycle under the influence of hormones. This thickened lining provides nourishment and support for an embryo if fertilization occurs.

• Fertilization and Implantation. The menstrual cycle creates optimal conditions for fertilization and subsequent implantation of a fertilized egg in the uterus. Ovulation, the release of a mature egg, occurs during the cycle, allowing for the opportunity for sperm to fertilize the egg in the fallopian tubes. The thickened uterine lining provides a receptive site for the fertilized egg to implant and develop.

• Menstruation. If pregnancy does not occur, the menstrual cycle culminates in menstruation. Menstruation involves the shedding of the uterine lining that was prepared during the cycle. The purpose of menstruation is to eliminate the unneeded tissue and start a new cycle in preparation for potential future pregnancies.

By going through these cyclic changes, the menstrual cycle ensures the reproductive system’s readiness for conception, pregnancy, and childbirth. It plays a vital role in the overall reproductive health of individuals assigned female at birth. Additionally, tracking the menstrual cycle can provide valuable insights into fertility, health, and the identification of potential underlying issues or irregularities.

The menstrual cycle can be divided into several phases:

Menstrual Phase. The cycle begins with menstruation, marked by the shedding of the uterine lining (endometrium). Menstrual bleeding occurs as a result of decreased hormone levels, specifically progesterone. This phase typically lasts for 3 to 7 days.

Follicular Phase. As menstruation ends, the follicular phase begins. The pituitary gland releases follicle-stimulating hormone (FSH), which stimulates the growth and development of follicles in the ovaries. The follicles contain eggs, and as they grow, they produce estrogen. Estrogen causes the uterine lining to thicken in preparation for a potential pregnancy. This phase usually lasts around 10 to 14 days.

Ovulation. A surge in luteinizing hormone (LH) triggers ovulation, which usually occurs around day 14 of the menstrual cycle. The dominant follicle releases a mature egg from the ovary into the fallopian tube. Ovulation is a relatively short-lived event, typically lasting for 24 to 48 hours.

Luteal Phase. After ovulation, the ruptured follicle in the ovary transforms into a structure called the corpus luteum. The corpus luteum produces progesterone, which prepares the uterine lining for potential implantation of a fertilized egg. Progesterone levels rise and reach their peak during this phase. If fertilization does not occur, the corpus luteum eventually degenerates, leading to a decrease in hormone levels. The luteal phase lasts around 10 to 14 days.

Menstruation (Repeat). If pregnancy does not occur, hormone levels drop, causing the uterine lining to shed once again. This marks the start of a new menstrual cycle.

Variations in cycle length, hormone levels, and timing of ovulation are normal, and can be influenced by factors such as stress, illness, hormonal disorders, and certain medications.

The menstrual cycle represents a delicate interplay of hormonal signals and structural changes within the female reproductive system. Understanding this process is essential for comprehending fertility, contraception, and various menstrual cycle-related concerns.