The Menstrual Cycle Overview

Study Notes

Menarche is the onset of menstruation, signaling the start of a female's reproductive life.
The menstrual cycle is a complex process with cyclical changes in the endometrium, controlled by estrogen and progesterone.
The average age of menarche is 12.8 years old.
Menstrual blood flow can vary between women, with blood clots and color ranging from bright red to dark maroon.
The menstrual cycle typically lasts for 25 to 32 days.
Hormones like FSH (follicle-stimulating hormone) and LH (luteinizing hormone) govern the menstrual cycle.
FSH stimulates the development of the Graafian follicle and estrogen production in the ovaries.
LH triggers the release of the mature egg from the Graafian follicle, causing ovulation.
LH also stimulates the development of the corpus luteum, which secretes progesterone.
This cycle is controlled by the hypothalamus-pituitary-ovarian axis (HPOA axis).

Menstrual phase: This is the first phase and lasts for 4-5 days. It involves sloughing off and discharge of the functional layer of the uterine wall.
Proliferative phase: This is a phase of repair and proliferation, lasting for 9 days. It is controlled by estrogen secreted by follicles and results in an increase in the thickness of the endometrium.
Secretory phase: This phase begins with ovulation and lasts until menstruation. It is controlled by progesterone and estrogen secreted by the corpus luteum.
If fertilization occurs, the fertilized egg implants in the endometrium and HCG (human chorionic gonadotropin) secreted by the developing placenta maintains the corpus luteum, ensuring continuous production of estrogen and progesterone.
If fertilization doesn't occur, the corpus luteum degenerates, leading to a drop in estrogen and progesterone levels. This causes the secretory endometrium to shrink and enter an ischemic phase, culminating in menstruation.
Ischemic phase: This phase occurs when estrogen and progesterone levels decrease. Glandular secretion stops, the endometrium shrinks, and damaged vessels rupture leading to bleeding and menstruation.

The Graafian follicle is a mature ovarian follicle, ready for ovulation.
Ovulation is the release of a mature egg from the Graafian follicle.
Labia minora: two erectile tissue folds located inside the labia majora that are more sensitive to touch than the labia majora.
Clitoris: a hooded body composed of erectile tissue located at the apex of the labia minora. It's rich in blood and nerve supplies, responsible for sexual pleasure and orgasm.

The Vestibule includes the urethral orifice (opening for urine), the vaginal orifice, the hymen, and the Bartholin glands.
Bartholin's glands: secrete mucus with an alkaline pH that enhances sperm viability and motility. These glands are not visible but can be palpated during infection.
Perineum: the muscle and tissue located between the vaginal opening and the anal canal. It holds the lower urinary and digestive tracts and is sensitive to touch.

Vagina: A passageway for menstrual flow, the birth canal during labor, and receives the penis during sexual intercourse.
Cervix: Connects the uterus to the vagina, acting as a barrier against foreign bodies entering the uterus and dilating during childbirth.
Uterus: A pear-shaped organ made up of three layers: the endometrium (inner layer), the myometrium (muscular layer), and the perimetrium (outer layer).
Fallopian tube: Pathway for the ovum to the uterus and the site of fertilization.
Ovaries: Female gonads or sex glands that develop and release an egg each month. They produce estrogen and progesterone.

The vaginal canal is acidic.
A woman is born with approximately 400,000 immature eggs (follicles), but only releases 400 to 500 during her lifetime.
The ovarian cycle cyclic changes in the ovaries influenced by FSH and LH.
Follcicular phase: primordial follicles begin to grow under the effect of FSH.