The Menstrual Cycle / Menstruation

UPDATED ON Tue, 21 Jan, 2025 BY THOMPSON, RN RAEN.

Introduction:

The menstrual cycle is a complex physiological process that occurs in females, typically from puberty to menopause. It involves a series of hormonal changes that prepare the female body for potential pregnancy each month. Menstruation, or the menstrual period, is a key phase of this cycle, marked by the shedding of the uterine lining when pregnancy does not occur. Understanding the menstrual cycle is essential for recognizing normal reproductive health, identifying disorders, and managing reproductive health issues.

Phases of the Menstrual Cycle:

The menstrual cycle is typically divided into four main phases: the menstrual phase, the follicular phase, ovulation, and the luteal phase. The cycle usually lasts around 28 days but can range from 21 to 35 days in healthy women.

Menstrual Phase (Days 1-5):

  • The cycle begins with menstruation, which is the shedding of the endometrial lining of the uterus. This occurs when the egg released in the previous cycle is not fertilized.

  • The menstrual flow consists of blood, mucus, and tissue from the uterine lining.

  • Hormone levels (estrogen and progesterone) are at their lowest during this phase, which triggers the shedding process.

Follicular Phase (Days 1-13):

  • This phase overlaps with the menstrual phase and continues until ovulation.

  • The hypothalamus signals the pituitary gland to release follicle-stimulating hormone (FSH), which stimulates the growth of ovarian follicles.

  • One dominant follicle matures into an egg while others regress. The maturing follicle produces estrogen, which helps rebuild the uterine lining (endometrium) that was shed during menstruation.

  • Estrogen levels rise, peaking just before ovulation, preparing the body for the possibility of pregnancy.

Ovulation (Day 14):

  • Ovulation typically occurs around day 14 in a 28-day cycle but can vary depending on the individual.

  • The surge in luteinizing hormone (LH) from the pituitary gland triggers the release of the mature egg from the dominant follicle.

  • The egg travels down the fallopian tube, where it may meet sperm and become fertilized. Ovulation is the most fertile period of the cycle.

Luteal Phase (Days 15-28):

  • After ovulation, the ruptured follicle transforms into the corpus luteum, which secretes progesterone and some estrogen.

  • Progesterone prepares the endometrium for potential implantation of a fertilized egg by making it thick and nutrient-rich.

  • If fertilization does not occur, the corpus luteum degenerates, leading to a drop in progesterone and estrogen levels.

  • The decline in hormone levels causes the uterine lining to break down, leading to menstruation, and the cycle begins anew.

Hormonal Regulation:

The menstrual cycle is regulated by a delicate interplay of hormones, primarily:

  • Gonadotropin-Releasing Hormone (GnRH): Produced by the hypothalamus, it stimulates the pituitary gland to release FSH and LH.

  • Follicle-Stimulating Hormone (FSH): Promotes the growth and maturation of ovarian follicles.

  • Luteinizing Hormone (LH): Triggers ovulation and the formation of the corpus luteum

  • Estrogen: Helps thicken the uterine lining and regulates FSH and LH levels.

  • Progesterone: Stabilizes the endometrium and prepares it for a potential pregnancy.

Menstrual Disorders:

  • Dysmenorrhea: Painful menstruation, often caused by uterine contractions.

  • Amenorrhea: Absence of menstruation, which can be primary (never starting) or secondary (cessation after it has started).

  • Menorrhagia: Excessive menstrual bleeding.

  • Oligomenorrhea: Infrequent menstruation, often associated with hormonal imbalances or polycystic ovary syndrome (PCOS).