Body Changes During the Menstrual Cycle

During your menstrual cycle, your body's reproductive system undergoes changes beyond menses itself. The cycle typically follows a 28-day pattern with shifts in hormone levels, dysmenorrhea (menstrual cramps), and breast pain.

Uterus and ovaries model
ericsphotography / Getty Images

The Reproductive System

To understand and discuss these changes, it's important to remember the anatomical parts involved and their functions:

  • The uterus, or womb, is a pear-shaped organ, about the size of your fist, between your bladder and lower intestines.
  • The cervix is the lower third of the uterus. Its opening, called the os, is the entrance to the vaginal canal and permits your period to flow out.
  • The fallopian tubes extend from each side of the uterus and near the end of each one is an ovary.
  • The ovaries are almond-sized organs that produce eggs. Each ovary contains from 200,000 to 400,000 follicles, which contain the material necessary to produce eggs.
  • The endometrium is the inner lining of the uterus and this comes out as your menstrual flow.

In addition to endometrial tissue, your menstrual flow also contains blood and mucus from the cervix and vagina.

When you're pregnant, the endometrium thickens and fills with blood vessels that mature into the placenta.

Hormones and Your Menstrual Cycle

It all starts with your endocrine glands because they produce the hormones that determine when you get your period, the amount of menstrual flow, and what happens to your reproductive organs.

The area of the brain called the hypothalamus connects your nervous and endocrine system by way of the pituitary gland, which also is in the brain, and controls the hormones necessary for reproductive health and your period.

Six hormones serve as chemical messengers to your reproductive system:

  1. Gonadotropin-releasing hormone (GnRH)
  2. Follicle-stimulating hormone (FSH)
  3. Luteinizing hormone (LH)
  4. Estrogen
  5. Progesterone
  6. Testosterone

During your menstrual cycle, the hypothalamus first releases GnRH. This causes a chemical reaction in the pituitary gland and stimulates the production of FSH and LH.

Your ovaries produce estrogen, progesterone, and testosterone (yes, the "male" hormone) in reaction to stimulation by FSH and LH. When these hormones work harmoniously, normal menstrual cycles occur.

Four Phases of the Menstrual Cycle

Keep in mind the menstrual cycle can vary greatly from woman to woman or month to month and still be considered normal. Generally, the length of your menstrual cycle can fluctuate from three weeks to five weeks, without alarm.

Your menstrual cycle consists of four phases:

  • Menstrual: The menstrual phase starts the moment you get your period and typically lasts up to five days. During this time, your uterus sheds its lining through your vagina and you need a tampon or sanitary pad to absorb it.
  • Follicular: Next, the follicular phase usually occurs during days six through 14 of your cycle. Your estrogen levels rise, causing the endometrium to get thicker. FSH levels also rise, causing maturation of several ovarian follicles, one of which will produce a fully mature egg during days 10 to 14.
  • Ovulation: Around day 14, in a 28-day cycle, LH levels surge causing ovulation. This means one of the mature follicles burst and released the fully mature egg into one of the fallopian tubes.
  • Luteal: The fourth stage, called the premenstrual or luteal phase, lasts approximately 14 days. The egg travels through the fallopian tube to the uterus. If it's fertilized by a sperm, you get pregnant. If not, progesterone and estrogen levels decline, and the endometrial lining flows out as your period.

When counting the days in your cycle, always count the first day of your period as day one. The average period lasts three to five days, although some women may experience slightly shorter or longer periods.

3 Sources
Verywell Health uses only high-quality sources, including peer-reviewed studies, to support the facts within our articles. Read our editorial process to learn more about how we fact-check and keep our content accurate, reliable, and trustworthy.
  1. Thiyagarajan DK, Basit H, Jeanmonod R. Physiology, menstrual cycle. StatPearls Publishing.

  2. Office on Women's Health. What happens during the typical 28-day menstrual cycle?.

  3. Reed BG, Carr BR. The normal menstrual cycle and the control of ovulation., Inc.

Additional Reading

By Tracee Cornforth
Tracee Cornforth is a freelance writer who covers menstruation, menstrual disorders, and other women's health issues.