The Menstrual Cycle

The menstrual cycleinvolves many changes in the uterus, ovaries, vagina, and breasts. The average length is about 28 days but it varies from month to month among individuals and in the same individual.

Phases

Menses—about the first 4 or 5 days of the cycle; varies somewhat

  • Characterized by sloughing of bits of endometrium (uterine lining) with bleeding
  • Initiated by lower levels of progesterone
  • First day of flow is day 1 of menstrual cycle

Proliferative phase—days between the end of menses and secretory phase; varies in length

  • The shorter the cycle, the shorter the proliferative phase; the longer the cycle, the longer the proliferative phase
  • Characterized by repair of endometrium
  • Follicles mature
  • Estrogen secretion increases to its highest level

Secretory phase—days between ovulation and beginning of next menses

  • Characterized by further thickening of endometrium and secretion by its glands in preparation for implantation of fertilized ovum
  • Ovary secretes its highest levels of progesterone
  • Combined actions of the anterior pituitary hormones FSH and LH cause ovulation
  • Sudden sharp decrease in estrogen and progesterone bring on menstruation if pregnancy does not occur


The Human Menstrual Cycle

The anterior pituitary gland secretes the follicle stimulating hormone (FSH) and the luteinizing hormone (LH).

  • FSH stimulates several immature ovarian follicles to start growing and secreting estrogens. As the estrogen content of the blood increases, it stimulates the anterior pituitary gland to secrete LH.
  • LH (ovulation hormone) causes maturation of the follicle and its ovum, ovulation, and luteinization (formation of the corpus luteum).
  • Birth control pills that contain estrogen substances suppress FSH secretion. This indirectly prevents ovulation.

Corpus luteum

  • Yellowish tissue in the follicle
  • Forms after ovulation (rupturing of mature follicle)
  • Secretes estrogen and progesterone to promote build-up of the uterine lining

Sequence of the Menstrual Cycle

1. Anterior pituitary gland secretes increasing amounts of FSH

2. Maturation of the follicle

3. Estrogen stimulates uterine lining to thicken

4. Secretion of LH

5. Ovulation occurs

6. Formation of corpus luteum

7. Secretion of progesterone (If pregnant: will continue to secrete progesterone)

8. Corpus luteum degenerates

9. Uterine lining degenerates

10. Menstruation occurs

Hormonal and Menstrual Disorders

  • Menstrual cramps or dysmenorrhea—painful menstruation
  • Amenorrhea—absence of normal menstruation
  • Dysfunctional uterine bleeding (DUB)—irregular or excessive bleeding resulting from a hormonal imbalance
  • Premenstrual syndrome (PMS)—symptoms that occur before menstruation

Infection and Inflammation

  • Exogenous infections often sexually transmitted; endogenous infections caused by organisms already in or on the body
  • Pelvic inflammatory disease (PID)—acute inflammatory condition of the uterus, uterine tubes, or ovaries caused by infection
  • Vaginitis—infection of vaginal lining, it most often results from STDs or yeast infections

Tumors and Related Conditions

  • Myoma, or fibroids—benign tumors of the uterus
  • Polycystic ovary syndrome (PCOS)—enlarged ovaries with many fluid-filled cysts

•Affects 10% of reproductive-age women

•Most common cause of female infertility

  • Ovarian cysts—fluid-filled enlargements; usually benign

•Follicular cysts—most common

•Luteal cysts—most symptomatic

•Most resolve in 60 days

  • Endometriosis is the presence of functioning endometrial tissue outside the uterus.
  • Breast cancer is the most common type of cancer in women.
  • Ovarian cancer can result from metastasis of breast cancer or can arise independently.
  • Cervical cancer is often detected by a Papanicolaou test (Pap smear).
  • Infertility can result from factors such as infection and inflammation, tumors, and hormonal imbalances.