menstrualcycle-100515015456-phpapp02

7/30/2019 menstrualcycle-100515015456-phpapp02

1/14

The Menstrual Cycle

www.freelivedoctor.com


2/14



3/14

The Menstrual Cycle: Two Phases

Ideally 14 days each

Follicular and Luteal

Describe changes in the ovary Proliferative and Secretory

Describe changes in the endometrium



4/14

Hormones in the Menstrual Cycle



5/14

Follicular phase

Begins with the onset of menses and ends on the day ofthe luteinizing hormone (LH) surge

During late luteal phase/ early follicular phase: withdrawal of estrogen and progesterone in late luteal phase

In early follicular phase, ovary is least hormonally active lowserum estradiol and progesterone

release from negative feedback effects of estrogen +progesterone increase in GnRH pulse frequency in earlyfollicular phase

Increased GnRH pulse 30% increase in serum FSHconcentrations

FSH release from the pituitary stimulates growth of 5-15primordial follicles By late follicular phase, a single dominant follicle has been

selected.



6/14

Follicular Phase

The developing dominant follicle producesestrogen in a 2-cell process Theca interna cells produce androstenedione in

response to LH stimulation

Granulosa cells convert androstenedione estradiolwhen stimulated by FSH

Estrogen causes the uterine lining to thicken /proliferate

GnRH pulse frequency increase rise in LH

Rise in LH also stimulates androgen synthesis androgens are converted to estrogens



7/14

Follicular Phase

Serum estradiol concentrations peak

approximately 1 day before ovulation

Midcycle (~day 14) there is an LH spike in

response to this estrogen surge

Ovulation occurs as increase in LH level

causes the follicle to rupture and release

mature ovum



8/14

LH Surge Involves a poorly-understood

neuroendocrine phenomenon in whichthere is a switch from negative feedback

control of LH secretion by estradiol and

progesterone to positive feedback

Rising estradiol levels at the end of the

follicular phase result in a 10-fold increase

in serum LH concentration



9/14

LH Surge: Effect on the Ovary

In response to LH:

Oocyte in the dominant follicle completes 1st meiotic

division

Increase in local secretion of plasminogen activatorand cytokines required for ovulation

Oocyte released from follicle at ovarian surface ~ 36

hrs after LH surge.

Even before oocyte is released, granulosa cellsaround it begin to luteinize and produce

progesterone. Progesterone slows LH pulses/

decreases LH pulse frequency



10/14

Ovulation LH spike stimulates ovulation, the release of the ovum from the follicle

After ovulation, the luteal phase begins, and remnants of the follicle leftbehind in the ovary develop into the corpus luteum



11/14

Ovulation

Ovum usually passes into adjoining

fallopian tube and is swept down to the

uterus by the cilia lining the tube

Takes 3-4 days for ovum to travel down

tube to the uterus

Fertilization must occur within 24 hrs of

ovulation or ovum degenerates



12/14

Luteal Phase

After ovulation, granulosa and theca

interna cells lining the wall of the follicle

form the corpus luteum cyst (stimulated by

LH)

The corpus luteum synthesizes estrogen

and large amounts of progesterone

Progesterone stimulates the endometrium to

become more glandular/secretory in

preparation for implantation of fertilized ovum



13/14

Luteal Phase

If fertilization occurs:

developing trophoblast synthesizes human

chorionic gonadotropin (hcg)

hcg maintains the corpus luteum so it may

continue producing estrogen and

progesterone to support the endometrium

By ~ 8-10 weeks gestation, the placenta isdeveloped, and takes over production of

estrogen and progesterone



14/14

Luteal Phase

If fertilization does not occur: corpus luteum is not maintained by hcg

Corpus luteum degenerates after ~ 14 days

Estrogen and progesterone levels fall

Withdrawal of progesterone causes secretoryendometrium to slough

FSH levels slowly rise again in absence of negativefeedback

MENSTRUATION


menstrualcycle-100515015456-phpapp02

Documents

Transcript of menstrualcycle-100515015456-phpapp02