Menstrual Cycle Flashcards
Menstrual cycle
General
Cyclic pattern of hormonal and tissular activity that prepares a suitable uterine environment for the fertilization and implantationof an ovum
Involves both an ovarian and endometrial (uterine) cycle that are dependent on one another
Normal cycle length: 21-35 days
Average cycle length: 28 days
Menarche
1st menstrual period; starting on average age at 12years
Perimenopause
interval of menstrual irregularities leading up to the total cessation of cycles
Menopause
cessation of menses for 12 months or more; average age 51
Ovarian phases
Follicular phase
Represents the time during which the ovarian follicle and its oocyte develop
Spans from menses onset (day 1) to the day before the surge of luteinizing hormone (LH), leading to ovulation
Length: 14-21 days
Intervals in cycles usually remain consistent until perimenopause
Follicular phases become shorter and more frequent
Ovarian phases
Luteal phase
Represents the time after ovulation when the ovary produces hormones to support a potential pregnancy and maintain a healthy endometrium
Spans from the day of LH surge until the onset of the next menses
Length: 15 days
Endometrial (uterine) phases:
Menses:desquamation/shedding of the endometrial lining
Proliferative phase: endometrial proliferation
Secretoryphase: preparation for potential oocyte implantation
Regulation of the Menstrual Cycle
HPO Axis
Regulated by thehypothalamic-pituitary-ovarian (HPO) axis
Hypothalamus:
Releases GnRH in a pulsatile fashion → stimulates gonadotropes of the anterior pituitary
Anterior pituitary:
Stimulated by GnRH → releasesFSH and LH
FSH and LH → stimulate theovaries
FSH:
Stimulates follicular development and ovum maturation
Stimulates the ovary (granulosa cells) to produce estradiol
LH:
Stimulatesthe ovary (theca cells) to producetestosterone; most is converted toestradiol
A surge of LH midcycle triggers ovulation
Regulation of the Menstrual Cycle
negative and positive feedback of Ovaries
Ovaries:
Negative feedback:During most of the menstrual cycle, estrogens inhibitfurther secretions of FSH, LH, and GnRH
Positive feedback:For a short time midcycle,estradiolstimulatesFSH and LHsecretionfrom the pituitary → results in ↑estrogenproduction in theovariesand causes the surge of LH, which triggers ovulation
Regulation of menstrual cycle
Ovaries and Progestins
Progestins:
Progesterone secreted by the corpus luteum (stimulated by LH)
Effects on reproductive organs:
Stabilizes and causes maturation of theendometrium→ prepares theendometriumforimplantation
↑ Endometrial secretions (↑ secretion thickness)
Lobular breast development
↑ Body temperature
Regulation of the Menstrual Cycle
Activins and Inhibins
Activins:
Secreted by the granulosa cells of the ovarian follicles (stimulated by FSH)
Providespositivefeedback to gonadotropes
Inhibins:
Secreted by the granulosa cells of the ovarian follicles (stimulated by FSH)
Providesnegativefeedback to gonadotropes
Follicular phase
general
Represents the time during which the follicle (and the oocyte it contains) develop, leading up to ovulation
Occurs within the ovaries
Coincides with menses and the proliferative phase of the endometrium
days1–14of the menstrual cycle
Primarily under the control ofestradiol
Increasing amounts of estradiol will lead to negative feedback near the end of the phase
The purpose of the follicular phase is to:
Grow the endometrial layer of the uterus (increased number of stroma and glands, increasing depth of the spiral arteries that supply the endometrium)
Create an environment that is friendly and helpful to possible incoming sperm (creation of channels within the cervix, allowing for sperm entry)
develop a primordial follicle (a primordial follicle matures into the Graafian follicle that is ready for ovulation)
Follicular phase
GnRH
Gonadotropin-releasing hormone(GnRH) is released from thehypothalamus→ stimulates the release ofFSH from the anterior pituitary → stimulates the primary follicles of the ovary to begin developing
Maturing primary follicles produce:
Inhibin A→ inhibits the release of FSH from the anterior pituitary (negative feedback)
Estradiol →stimulates development of a dominant follicle → the follicle secretesestradioluntil just before the LH surge
Follicular phase
Primary and dominant follicles
Primary ovarian folliclesdevelop due to ↑ FSH
Dominant follicle (Graafian follicle)continues to develop and secrete estradiol
follicular phase
LH surge
Estradiol levels will peak and ~12 hours later, the anterior pituitary releases aluteinizing “surge”→ triggers ovulation
During ovulation, a mature oocyte is released from the dominant follicle
The LH surge ends the follicular phase
Luteal phase
general
Represents the time after ovulation when the ovary produces hormones to support a potential pregnancy and maintain a healthy endometrium
Occurs within the ovaries
Coincides with the secretory phase of the endometrium
Takes place typically during days15-28of the menstrual cycle
Under the control ofprogesterone
luteal phase
corpus luteum and potential of this phase
The corpus luteum of the mature oocyte producesprogesterone
Progesterone feedback inhibits LH secretion from the anterior pituitary
If conception does not occur, LH levels continue to ↓ and thecorpus luteum recedes into acorpus albicans
Ifpregnancyoccurs, the secretion of human chorionic gonadotropin (hCG) saves the corpus
luteum and allows it to continue to secrete progesterone
Oocyte migrates to the fimbria of theFallopian tube
Potential offertilizationby sperm at this phase
Endometrial Cycle
phases
There are 3 phases of the endometrial (uterine) cycle:
Desquamation or menses
Proliferative phase
Secretory phase
Normal menstrual cycle
S/Sx
Sign
Vaginal bleeding
Acne
Symptoms
Bloating
Abdominal or pelvic cramping
Lower back pain
Breast tenderness
Mood swings/irritability
Headache
Fatigue
