The Menstrual Cycle and Menstrual Disorders

You need the normal cycle cold before you can spot the disorders. Know the hormones, the phases, and the numbers that define normal flow, then the common disorders fall into place.

What is Menstruation?

Menstruation is the female reproductive cycle marked by uterine bleeding in response to hormonal change. Over the cycle the ovum matures and a new uterine bed is prepared for implantation of a fertilized ovum.

Characteristics

What normal flow looks like:

• Average age at onset: 12.4 years.
• Usual range of onset: 9-17 years.
• Average interval between cycles: 28 days; 23-35 days is also normal.
• Average duration of flow: 2-7 days, with 1-9 days not unusual.
• Average volume: 30-80 mL.
• Normal color: dark red, a mix of blood, mucus, and endometrial cells.
• Normal odor: likened to marigolds.

Physiology

• The cycle is initiated by luteinizing hormone-releasing hormone, released mainly by the hypothalamus.
• At puberty the hypothalamus becomes less sensitive to estrogen feedback, which triggers release of gonadotropin-releasing hormone (GnRH).
• GnRH travels from the hypothalamus to the pituitary, signaling release of follicle-stimulating hormone (FSH) and luteinizing hormone (LH).
• FSH matures the ovum. LH drives ovulation and thickens the uterine lining.
• FSH activates one primordial follicle to grow and mature. At full maturity it is the Graafian follicle.
• The pituitary releases LH, and prostaglandins rupture the Graafian follicle. Ovulation occurs and the ovum is swept into the fallopian tube.
• LH acts on the ovarian follicle cells to produce a yellow fluid, lutein, which fills the empty follicle (now the corpus luteum).
• Without conception, the unfertilized ovum atrophies after 4 to 5 days and the corpus luteum persists for 8 to 10 days, then is replaced by the corpus albicans, a white fibrous tissue.

The Phases of the Menstrual Cycle

Proliferative Phase

• After 4 to 5 days, the uterine lining is one cell layer deep and very thin.
• The ovary produces estrogen and the endometrium proliferates to roughly eightfold its usual thickness.
• From day 5 to 14, the endometrium keeps thickening.

Secretory Phase

• LH drives progesterone formation in the corpus luteum, giving the endometrium a twisted appearance.
• Capillaries increase and the lining becomes rich and spongy.

Ischemic Phase

• Without fertilization, the corpus luteum regresses by its tenth day.
• Progesterone and estrogen fall, the uterine lining sloughs off, and capillaries rupture.
• The discharge contains blood, mucus, endometrial tissue, and the unfertilized ovum. Menses is the only external marker of the cycle and marks day one of the next cycle.

Menstrual Disorders

Dysmenorrhea

Painful menstruation. Prostaglandins released during the ischemic phase cause the contractions and pain.

Menorrhagia

Abnormally heavy flow, greater than 80 mL. Without subsequent progesterone secretion and ovulation, estrogen production continues and the endometrium overproliferates.

Metrorrhagia

Bleeding between periods, usually from decreased progesterone and endometrial sloughing.

Mittelschmerz

Pain when follicular fluid drops into the abdominal cavity and releases prostaglandins. It is a clear ovulation marker because the pain is felt on one side of the abdomen, near the ovary.

Endometriosis

Extrauterine endometrial cells grow abnormally on the uterine ligaments or ovaries. Excessive endometrial production plus backflow of blood and tissue into the fallopian tube during the cycle drives it.

Absence of menstrual flow from a non-definitive cause can occur in any female who is pregnant or has other related conditions.