Physiology of Menstruation

mentrual cycle1

Menstruation – is the periodic discharge of blood, mucus and epithelial cells from the uterus.

Menstrual Cycle – periodic uterine bleeding in response to cyclic hormonal changes. A process that allows for conception and implantation of new life.

It is usually determined by counting as day 1 the 1st day of a menstrual period until the last day before the next menstrual period.


  • To bring an ovum to maturity
  • To renew a uterine tissue bed that will be responsive to fetal growth
  • To prepare the uterus for pregnancy

Characteristics of Normal Menstrual Cycles



Beginning (Menarche) average age of onset: 12 or 13 years;
average range of age: 9-17 years
Interval between cycles average 28 days; cycles of 23 to 35 days not usual
Duration of Menstrual flow average flow: 2-7 days; ranges 1-9 days not normal
Amount of menstrual flow difficult to estimate; average 30 to 80 ml. per menstrual period; saturating a pad in less than an hour is considered heavy bleeding.
Color of menstrual flow dark red; a combination of blood, mucus, and endometrial cells
Odor of menstrual flow marigold

Discomforts of Menstruation

  1. Breast tenderness and feeling of fullness
  2. Tendency towards fatigue
  3. Temperament and mood changes – because of hormonal influence and decreased levels of estrogen and progesterone
  4. Discomfort in pelvic area, lower back and legs
  5. Retained fluids and weight gain

Abnormalities of Menstruation

  1. Amenorrhea – absence of menstrual flow
  2. Dysmenorrhea – painful menstruation
  3. Oligomenorrhea – scanty menstruation
  4. Polymenorrhea – too frequent menstruation
  5. Menorrhagia -excessive menstrual bleeding
  6. Metrorrhagia – bleeding between periods of less than 2 weeks
  7. Hypomenorrhea – abnormally short menstruation
  8. Hypermenorrhea – abnormally long menstruation

Four body structure involved in the physiology of the menstrual cycle:

mentrual cycle

  1. Hypothalamus
  2. Pituitary gland
  3. Ovaries
  4. Uterus

Reproductive Hormones:

  1. Gonodotropin-Releasing Hormone (GnRH)
    • Stimulates release of FSH and LH initiating puberty and sustaining menstrual cycle.
  2. Follicle-stimulating Hormone (FSH)
    • secreted by anterior pituitary gland during the 1st half of menstrual cycle
    • stimulate growth and maturation of graafian follicle before ovulation
    • thins the endometrium
  3. Luteinizing Hormone (LH)
    • secreted by the anterior pituitary gland
    • stimulates final maturation of graafian follicle
    • surge of LH about 14 days before next menstrual period causes ovulation
    • stimulates transformation of graafian follicle into corpus luteum
    • thickens the endometrium
  4. Estrogen
    • secreted primarily by the ovaries, corpus luteum, adrenal cortex and placenta in pregnancy
    • considered the Hormone of Women
    • stimulates thickening of the endometrium; causes suppression of FSH secretion
    • responsible for the development of secondary sex characteristics
    • stimulates uterine contractions
    • increases water content of uterus
    • high estrogen concentration inhibits secretion of FSH and Prolactin but stimulates secretion of LH7.
    • low estrogen concentration after pregnancy stimulates secretion of Prolactin
  5. Progesterone
    • secreted  by the ovary, corpus luteum and placenta during pregnancy
    • inhibits secretion of LH
    • has thermogenic effect (increases body temperature)
    • relaxes smooth muscles thereby decreases contractions of uterus
    • causes cervical secretion of thick mucus
    • maintain thickness of endometrium
    • allows pregnancy to be maintained = Hormone of Pregnancy
    • prepares breasts for lactation
  6. Prolactin
    • secreted by the anterior pituitary gland
    • stimulates secretion of milk
  7. Oxytocin
    • secreted by the posterior pituitary gland
    • stimulates uterine contractions during birth and compress uterine blood vessels and control bleeding
    • stimulates let-down or milk-ejection reflex during breastfeeding
  8. Prostaglandins
    • fatty acids’ categorized as hormones
    • produced by many organs of the body, including the endometrium
    • affects menstrual cycle
    • influences the onset and maintenance of labor

Daisy Jane Antipuesto RN MN

Currently a Nursing Local Board Examination Reviewer. Subjects handled are Pediatric, Obstetric and Psychiatric Nursing. Previous work experiences include: Clinical instructor/lecturer, clinical coordinator (Level II), caregiver instructor/lecturer, NC2 examination reviewer and staff/clinic nurse. Areas of specialization: Emergency room, Orthopedic Ward and Delivery Room. Also an IELTS passer.

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