Chapter 9. THE HUMAN MENSTRUAL CYCLE Reid L. Norman, PhD Professor, Pharmacology and Neuroscience, TTUHSC

Learning Objectives Know the hormonal changes that occur throughout a menstrual cycleKnow the hormonal changes that occur throughout a menstrual cycle List the reproductive hormones and where they are producedList the reproductive hormones and where they are produced Diagram how secretion of pituitary and ovarian hormones is regulatedDiagram how secretion of pituitary and ovarian hormones is regulated Explain how birth control pills workExplain how birth control pills work

Hypothalamus Releases GnRH (gonadotropin releasing hormone) in pulses to stimulate pituitary FSH (follicle stimulating hormone) and LH (luteinizing hormone) secretion.Releases GnRH (gonadotropin releasing hormone) in pulses to stimulate pituitary FSH (follicle stimulating hormone) and LH (luteinizing hormone) secretion. The hypothalamus is under the control of higher brain centers and feedback from ovarian steroidsThe hypothalamus is under the control of higher brain centers and feedback from ovarian steroids

Pituitary Secretes LH and FSH in response to GnRHSecretes LH and FSH in response to GnRH Estrogen, inhibin and progesterone from the ovary regulate the amount of LH and FSH released in a feedback relationshipEstrogen, inhibin and progesterone from the ovary regulate the amount of LH and FSH released in a feedback relationship The pituitary also secretes prolactin, particularly during pregnancy and lactationThe pituitary also secretes prolactin, particularly during pregnancy and lactation TSH (thyroid stimulating hormone), ACTH (adrenocorticotripic hormone) and GH (growth hormone) are secreted by the pituitary and important for normal fertilityTSH (thyroid stimulating hormone), ACTH (adrenocorticotripic hormone) and GH (growth hormone) are secreted by the pituitary and important for normal fertility

Ovary Responds to FSH and LHResponds to FSH and LH Follicular growth and maturationFollicular growth and maturation Secretion of estrogen, progesterone and inhibinSecretion of estrogen, progesterone and inhibin Ovulation in response to LHOvulation in response to LH Corpus luteum functionCorpus luteum function Progesterone secretionProgesterone secretion

Hormonal changes in cycle Days from LH peak E P LH FSH

Feedback relationships HYPOTHALAMUS OVARY PITUITARY (GnRH) (LH, FSH) (Inhibin) (Estradiol, Progesterone) negative feedback negative and positive feedback

Hormonal birth control Birth control pills contain estrogens and/or progestinsBirth control pills contain estrogens and/or progestins Act by suppressing LH and FSH through negative feedback mechanismsAct by suppressing LH and FSH through negative feedback mechanisms Formulated to mimic the changes that naturally occur during the menstrual cycleFormulated to mimic the changes that naturally occur during the menstrual cycle Stimulate the uterus so menstruation occursStimulate the uterus so menstruation occurs

Fallopian tube Ovum is transported to the uterus through the fallopian tubesOvum is transported to the uterus through the fallopian tubes Responds to estrogen and progesterone by altering motility (muscular contractions)Responds to estrogen and progesterone by altering motility (muscular contractions) Fertilization occurs in fallopian tubeFertilization occurs in fallopian tube Early embryo does not enter uterus for several days – until the hormonal conditions are right for implantationEarly embryo does not enter uterus for several days – until the hormonal conditions are right for implantation

Uterus Uterus has a muscular layer (myometrium) and an epithelial lining (endometrium)Uterus has a muscular layer (myometrium) and an epithelial lining (endometrium) Endometrium responds to estrogen in the follicular phase by growth and to progesterone in the luteal phase by becoming secretory in preparation for implantationEndometrium responds to estrogen in the follicular phase by growth and to progesterone in the luteal phase by becoming secretory in preparation for implantation Menstruation – if pregnancy does not occur, progesterone levels fall and the endometrium dies and is discharged through the vaginaMenstruation – if pregnancy does not occur, progesterone levels fall and the endometrium dies and is discharged through the vagina The cycle begins again with FSH stimulationThe cycle begins again with FSH stimulation

Pregnancy When fertilization occurs, the embryo implants in the endometrium and secrets hCG (human chorionic gonadotropin)When fertilization occurs, the embryo implants in the endometrium and secrets hCG (human chorionic gonadotropin) hCG stimulate the corpus luteum to produce progesterone to maintain pregnancyhCG stimulate the corpus luteum to produce progesterone to maintain pregnancy Placenta eventually produces progesterone to maintain pregnancyPlacenta eventually produces progesterone to maintain pregnancy

Lactation After delivery, prolactin is secreted to stimulate milk productionAfter delivery, prolactin is secreted to stimulate milk production Follicular development can be suppressed which results in amenorrhea by suckling and this is lactational amenorrheaFollicular development can be suppressed which results in amenorrhea by suckling and this is lactational amenorrhea Pituitary tumors that secrete prolactin can also cause amenorrheaPituitary tumors that secrete prolactin can also cause amenorrhea