The Menstrual Cycle PHS 208

This set of vocabulary flashcards covers the physiological definitions, hormonal shifts, and phases of the ovarian and endometrial cycles as described in the PHS 208 lecture on the Menstrual Cycle.

Menstrual Cycle

Regular cyclic changes in the female reproductive system that serve as the body’s periodic preparation for ovulation and potential pregnancy.

Menarche

The first beginning of menstruation, typically starting around puberty with a median age of $12.4\,yrs$.

Menopause

The cessation of menstrual cycles, having an average onset around age $50/51\,yrs$.

LMP

An acronym for Last Menstrual Period.

Normal Menstrual Frequency

Cycles occurring every $24$ to $38\,days$ as defined by FIGO.

Infrequent Menstruation

Menstrual cycle lengths defined as being longer than $38\,days$.

Frequent Menstruation

Menstrual cycle lengths defined as being shorter than $24\,days$.

Amenorrhea

The complete absence of menstrual bleeding.

Normal Menstrual Duration

Bleeding that lasts for $8\,days$ or less.

Prolonged Menses

Menstrual bleeding that lasts beyond $8\,days$.

Heavy Menstrual Bleeding (Research Definition)

Blood loss exceeding $80\,mL$ per cycle based on weighed menstrual products.

Heavy Menstrual Bleeding (NICE Definition)

Excessive menstrual bleeding that interferes with a person's physical, social, emotional, and/or material quality of life.

Light Menstrual Bleeding (Research Definition)

Commonly defined as less than $5\,mL$ of blood loss per cycle.

Menstrual Regularity (Ages 26 to 41)

Cycles are considered regular if the difference between the shortest and longest cycle lengths is $7\,days$ or less.

Menstrual Regularity (Ages 18 to 25 or 42 to 45)

Cycles are considered regular if the difference between the shortest and longest cycle lengths is $9\,days$ or less.

Intermenstrual Bleeding

Bleeding that occurs between cyclically regular menstrual periods, which can be random (unpredictable) or cyclic.

Ovarian Cycle Phases

The cycle within the ovary comprising the follicular phase, ovulation, and the luteal phase.

Endometrial Cycle Phases

The cycle within the uterus comprising the proliferative phase, the secretory phase, and the menstrual phase.

Follicular Phase

The ovarian phase beginning on day 1 of the cycle (first day of bleeding) and ending with ovulation, during which FSH stimulates follicle maturation.

Proliferative Phase

The uterine phase that starts after menstrual bleeding ends and continues until ovulation, corresponding to the ovarian follicular phase.

FSH (Follicle-Stimulating Hormone)

A hormone that stimulates primordial follicles to mature into Graafian follicles and promotes the production of $17\text{-}\beta\text{ estradiol}$ and inhibin B.

Dominant Follicle

The follicle that matures and grows approximately $2\,mm/d$ until reaching an average diameter of $23.6\,mm$ ($18$ to $29\,mm$).

Decidual Basalis

The basal layer of the endometrium from which the stroma and glands develop during the proliferative phase.

Ovulation

The rupture of the mature follicle and release of the oocyte, typically occurring $36$ to $44\,hours$ after the onset of the LH surge.

GnSAF

Gonadotropin surge-attenuating factor; a nonsteroidal ovarian product believed to counteract the sensitizing effects of estradiol on the pituitary during the follicular phase.

Luteal Phase

The ovarian phase beginning with ovulation and ending when menses starts; it is relatively consistent and typically lasts $14\,days$.

Secretory Phase

The uterine phase corresponding to the luteal phase, characterized by the maturation of the endometrium under the influence of progesterone.

Progesterone

The dominant hormone of the luteal phase that prepares the endometrium for implantation, thickens cervical mucus, and slightly raises basal body temperature.

hCG (Human Chorionic Gonadotropin)

Hormone released by a fertilized ovum that stimulates the corpus luteum to maintain progesterone production.

Menses

The shedding of the endometrium triggered by the abrupt decline in progesterone and estradiol levels at the end of the luteal phase.