Ovarian and menstrual cycle

Ovarian cycle

Cycle in the ovary where a mature ovum is produced each month; includes periodic changes every 28 days during the fertile period of a nonpregnant female.

Uterine cycle

Cycle in the uterus involving the shedding of the outer endometrial layer each month if fertilization does not occur.

Target population for ovarian and uterine cycles

Females from postpuberty until menopause.

Phases of the ovarian cycle

Preovulatory (follicular) phase, ovulation, postovulatory (luteal) phase.

Preovulatory phase hormone

Controlled by FSH (Follicle Stimulating Hormone).

Ovulation phase hormone

Controlled by LH (Luteinizing Hormone).

Postovulatory phase hormone

Controlled by LH which stimulates the corpus luteum to secrete progesterone.

GnRH function

Secreted by the hypothalamus; stimulates anterior pituitary to release FSH and LH.

FSH function in ovary

Induces maturation of primary follicle into Graafian follicle and stimulates follicular cells to secrete estrogen.

LH functions in ovary

Induces final maturation of Graafian follicle, triggers ovulation, and converts ruptured follicle into corpus luteum to secrete progesterone.

Effect of FSH at start of ovarian cycle

Stimulates development of primordial follicles.

Inhibition of FSH secretion

Caused by estrogen secretion from a mature follicle.

Atretic follicles

Degeneration of remaining follicles under LH influence after one reaches maturity.

Uterine phase corresponding to follicular phase

Proliferative phase.

LH and follicle rupture

LH activates collagenase to digest collagen around Graafian follicle and increases prostaglandins to cause ovarian contraction.

Ovulation product

Secondary oocyte with corona radiata and zona pellucida is released from the ruptured Graafian follicle.

Corpus luteum formation

After ovulation, granulosa and theca interna cells become luteal cells forming corpus luteum under LH influence.

Hormone secreted by corpus luteum

Progesterone.

Uterine phase affected by luteal phase

Secretory phase.

Corpus luteum fate without fertilization

Degenerates after 9 days into corpus albicans; progesterone levels drop.

Corpus luteum fate with fertilization

Becomes corpus luteum of pregnancy, maintained by hCG from embryo until 4th month, then placenta takes over progesterone secretion.

Uterine cycle phases

Menstruation, proliferative (estrogenic/postmenstrual), secretory (premenstrual/progestational).

Endometrium changes in uterine cycle

Undergoes monthly cyclical changes influenced by ovarian hormones.

Three layers of uterine wall

Perimetrium (outer), myometrium (muscular middle), endometrium (inner mucosa).

Endometrial strata

Stratum functionalis (inner, shed), stratum basalis (outer, regenerates).

Arterial supply of endometrium

Stratum functionalis: spiral arteries (progesterone-sensitive), stratum basalis: short straight arteries.

Menstrual phase hormonal trigger

Decrease in progesterone and estrogen at the end of the luteal phase.

Effect on spiral arteries in menstruation

They constrict and burst, leading to shedding of the superficial endometrial layer.

Expelled material during menstruation

Mucus, unclotted blood, and necrotic tissue from ulcerated superficial endometrium.

Intact layer during menstruation

Stratum basalis remains and regenerates the endometrium.

Hormone controlling proliferative phase

Estrogen from developing follicle.

Ovarian phase corresponding to proliferative phase

Last 10 days of the preovulatory phase.

Endometrial changes in proliferative phase

Increased thickness, vascularization, glandular enlargement, mucus secretion.

Hormones in secretory phase

Mainly progesterone (from corpus luteum), minor estrogen.

Endometrial changes in secretory phase

Thickened endometrium, spiral arteries, distended mucus glands with secretion.

Purpose of secretory phase

Prepare endometrium to nourish a potential blastocyst.

No fertilization: corpus luteum

Becomes corpus albicans, progesterone drops, spiral artery vasoconstriction, functional layer ischemia and shedding.

Fertilization: corpus luteum

Becomes corpus luteum of pregnancy, continues secreting progesterone.

Endometrium in fertilization

Becomes decidua of pregnancy, prepared to receive blastocyst ~6 days post-fertilization.

Decidua definition

Endometrium of pregnancy; consists of three regions.

Formation time of decidua

Forms 6 days after fertilization.

Decidua basalis

Between fetus and myometrium; becomes maternal part of placenta.

Decidua capsularis

Covers rest of the fetus.

Decidua parietalis

Lines the uterine cavity.