The Female Reproductive System

Functions

Secret mucus

Fertilization of the egg

Capture the egg

1. Produce egg;

2. produce estrogen and progesterone 1.Implantation of

fertilized egg;2.embryo developing3. Lining changes in menstrual cycle

1.Receive sperm;2. Discharge of fluid during menstruation;3. Birth of baby

The structure of one ovary and stages the developing egg

卵母细胞

卵泡

基质 输卵管伞

卵原细胞

颗粒细胞

Puberty

The Female Reproductive System – Oogenesis ( 卵子发生 )

卵泡膜细胞颗粒细胞

The Female Reproductive System – Oogenesis ( 卵子发生 )

The Female Reproductive System – Oogenesis ( 卵子发生 )

Oogenesis: production of haploid gametes in females;

The full sequence of meiosis is not completed until fertilization

Ovulation

Ovarian Hormones

Synthesis:

Granulosa cell: E,

Lutein cell: P, E

The two-stage model of estrogen synthesis:

1) androgen precursors are synthesized in the outer layer (theca cells) of the ovarian follicles and

2) diffuse to the inner layer (granulosa cells) for conversion to estrogens;

LH drives the former, FSH the latter.

Hormones of the Ovaries - Estrogen

Hormones of the Ovaries - Progesterone

Theca cells Granulosa cells

Estrogen and Progesterone

EstradiolSources: Ovary, adrenal cortex, placentaTypes:β-Estradiol: from ovary, the major estrogenEstrogenic potency: 12 times that of estrone and 80 times that of estriol

EstroneFormed in the peripheral tissues from androgenssecreted by the adrenal cortices and by ovarian thecal cells

Estriol: weakAn oxidative product derived from both estradiol and estrone mainly in the liver

Estrogens:

Estradiol; Estrone; Estriol

Progestins:

Progesterone

Progestins: Progesterone, secreted by the corpus luteum and placenta

Estrogen levels with age

Chemistry of Ovarian Hormones

Transport in the blood binding with albumin

Specific estrogen- and progesterone-binding globulins

Rapidly released to the tissues - about 30 mins

Fate of estrogens: Liver: estradiol and estrone → estriolLiver function↓ → ↑ estrogen activity

Fate of progesteroneLiver: P → pregnanediol ( 孕二醇 ) - estimate the rate of P formation from the rate of pregnanediol excretion in the urine

Functions of estrogens

Functions of Progesterone

Menstrual Cycle

Monthly rhythmical changes in the rates of secretion of the female hormones and corresponding physical changes in the ovaries and other sexual organs (e. g. the uterus)

Ovarian cycle: Only a single ovum is normally released

Endometrium cycle

Length: average about 28 days

Start at puberty - Menarche: 11 ~15 years of age

Stop at menopause 40 ~ 50 years of age

Follicular phase: FSH - Day 1 to day 14

Luteal phase: LH - Day 14 to day 28

Ovarian Cycle

Follicular phase: Primordial follicle, Primary follicle, Antral follicle, and mature follicle

Primordial follicle （始基卵泡、原始卵泡） :ovum + a single layer of granulosa cellsDuring childhood - Oocyte maturation-inhibiting factor

Primary follicles （初级卵泡） :After puberty, FSH causes accelerated growth of 6 to 12 primary follicles each month; granulosa cells + theca interna （内膜层）+ theca externa

Antral follicles （有腔卵泡）Follicular fluid (E)Vesicular folliclesE→granulosa cells → FSH-Rs↑E+ FSH → granulosa cells → LH-Rs↑E+ LH → proliferation and secretion of follicular thecal cells

Mature follicle

Before ovulation Only one each month D= 1 to 1.5 cm at the time of ovulationAtresia （闭锁、萎缩） of the remainder

Ovulation - 14 days after the onset of menstruationOvulatory Surge of LH, rising 6- to 10-fold, peak at about 16 hrs before ovulation

Ovum + corona radiata （放射冠）

Luteal phase

Luteinization - the remaining granulosa and theca interna cells →luteal cells- Depending on LH

Corpus luteumP and E (granulosa cells)Androgens (theca interna cells)

Corpus albicans （白体）-12 days after ovulation- Losing secretory function

InvolutionE and P→ strong feedback effects → FSH and LH↓ →involution

Inhibin (luteal cells) →FSH ↓ →involution

Onset of the next ovarian cycle2 days before menstruation begins

Sudden cessation of secretion of E, P and inhibin → removal of thefeedback inhibition → FSH and LH ↑ → initiate growth of new follicles

Involution （退化） of the corpus luteum and onset of the next ovarian cycle

Summary

After every 28 days, gonadotropic hormones cause about 8 to 12 new follicles to begin to grow in the ovaries.

One of these follicles finally becomes ‘mature’ and ovulates on the 14th day of the cycle.

During the growing of the follicles, estrogen is mainly secreted.

After ovulation, the secretory cells of the ovulating follicle develop into a corpus luteum that secretes large amount of P and E.

After another 2 weeks, the corpus luteum degenerates, whereupon P and E decrease greatly and menstruation begins.

Menstrual Cycle

Endometrial （子宫内膜） cycle - Phases

- Proliferative phase (estrogen phase) : 5 -14 days

- Secretory phase (Progestational phase): 15 - 28 days

- Menstruation: 1 – 5 days

Endometrial cycle – Proliferative phase: Before ovulation, under the influence of Es, stromal cells and epithelial cells proliferateNew blood vessels growEndometrium increases in thickness (3 - 5mm at the time of ovulation)Endometrial glands secret stringy mucus along the length of the cervical canal for help guide sperm

Endometrial cycle - Secretory phase: After ovulation, under the influence of Es and PEs cause additional cellular proliferation while P causes swelling and secretory development of the endometrium （子宫内膜）Glands increase in tortuosity （弯曲度）Increased deposits of lipid and glycogen in stromal cellsBlood vessels become highly tortuosityEndometrium increases in thickness – 5 - 6mm at the peak of this phase, with purpose of producing a highly secretory endometrium that contains large amounts of stored nutrients to provide appropriate conditions for implantation of a fertilized ovum

Endometrial cycle - Menstruation: 4 -7 days

Caused by the reduction of Es and P

Involution of the endometrium to 65%Vasospasm + ↓ nutrients + loss of hormonal stimulation →necrosis and hemorrhage→ all the superficial layers desquamate → uterine contraction

Menstrual fluid ：Necrotic material + blood + tremendous numbers of leukocytes40ml blood and 35ml serous fluid are lostNonclotting - release of fibrinolysin ( 纤溶酶 )Highly resistant to infection

Menses, days 0 to 7:

Levels of LH, FSH, estrogen, and progesterone are low.

The lining of the uterus cannot be maintained, and the uterine lining is lost.

The proliferative phase, days 7 to 14:

The follicle increases production of estrogen, causing LH to surge.

The follicle ruptures, and the egg is expelled.

Estrogen and progesterone stimulate growth of the uterine lining.

The secretory/luteal phase, days 14 to 28:

The follicle develops into corpus luteum and increases production of progesterone that prepares the uterus for implantation.

If fertilization and implantation do not occur, the corpus luteum degenerates into scar tissue called the corpus albicans and progesterone levels drop.

 

Positive feedback effect of E

Before ovulation↑ E → LH ↑ ↑Preovulatory LH surge

24-48 hrs before ovulationFor 1-2 days

Negative feedback effects ofE, P and inhibin

E in small amounts or E+P → anterior pituitary gland or hypothalamus (lesser) →LH and FSH↓

Inhibin → anterior pituitarygland → FSH and LH (lesser)↓

Regulation of menstrual cycle

Hypothalamic-pituitary-ovarian system

HypothalamusGnRH: ↑FSH and LH

PituitaryFSH: ↑ Follicular growth, E,P secretionLH: ovulation, corpus luteum formation, P secretion

Ovary E: negative and positive feedback effectsP: negative feedback effect

Release of GnRH

Hypothalamic centerMediobasal hypothalamus (arcuate nuclei)

Psychic factors → limbic system → arcuate nuclei → to modify the intensity and frequency of GnRH release → to modify female sexual function

Pulsatile secretion - in pulses lasting 5-25 mins which occur every 1-2 hrs- essential to its function- causes intermittent output of LH secretion about 90 mins →Pulsatile release of LH

Regulation of menstrual cycle ( 正负反馈调节机制 )

Small increases in thesecretion of gonadotropins (LH& FSH) lead to follicularmaturation, including anincrease in the synthesis andsecretion of ovarian steroidhormones (1-7).

Ovulation is provoked by a surge inLH and marks the transition to theluteal phase of the cycle,characterized by high levels ofprogesterone (8-14).

Eventually, (15) a decrease in LHleads to luteolysis, and thewithdrawal of steroid supportfor a thick, active uterus.

Menstrual Cycle: hormones

Anovulatory cycles

The preovulatory surge of LH is not of sufficient magnitude

No ovulation

Failure of development of the corpus luteum

Almost no secretion of P

Cyclical variations of the sexual cycle continue

Cycle is shortened by several days

Rhythm continues

The first few cycles after the onset of puberty

Several months to years before menopause （绝经）

Menopause

40 ~ 50 yearsSexual cycle: irregular →ceaseThe remaining primordial follicles become atretic （闭锁）

Female sex hormones↓FSH and LH are produced in large and continuous quantities

Physiological changes in the function of the body because of loss of Es:

Hot flushes （潮热）Psychic sensation of dyspneaIrritabilityFatigueAnxietyStrength and calcification of bones ↓

To avoid severe symptoms - Daily administration of an E in small quantities and gradually decrease the dose

Female fertility

Fertile period of each sexual cycle

Intercourse must occur sometime between 4 and 5 days before ovulation up to a few hours after ovulation in order to fertilize

Ovum remains viable and capable of being fertilized after it is expelled no longer than 24 hrs

A few sperm can remain fertile in the female reproductive tract for up to five days

Female sterility

About 1/6 ~ 1/8 marriages is infertile - ~ 60% of which: female sterility

The most common causes

1) Anovulation: Hyposecretion of gonadotropic hormones (treated by hCG); Abnormal ovaries; Thick ovarian capsules

Methods to determine whether ovulation occurs: to chart a woman’s body temperature throughout the cycle; T rises abruptly at the time of ovulation

2) Endometriosis （子宫内膜异位） : Endometrial tissue grows and even menstruates in the pelvic cavity surrounding the uterus, fallopian tubes and ovaries, causing fibrosis throughout the pelvis and occluding the fallopian tubes

3) Other causes-Salpingitis （输卵管炎） : Inflammation of the fallopian tubes → occluding; - Secretion of abnormal mucus by the uterine cervix: E → mucus secretion ↑ → mucous ‘threads’ Viscous mucus plug (low-grade infection or inflammation, or abnormal hormonal stimulation of the cervix)

Pregnancy桑葚胚

囊胚

Fertilization of the ovumImplantation of the blastocyst（胚泡）

The morula is differentiated into two groups of cells: a small group of internal blastomeres （分裂球） called the inner cell mass or embryoblast （成胚细胞） which gives rise to the embryo; the surrounding cells, termed the outer cell mass or trophoblast （滋养层） , which give rise to the placenta and membranes.

After the end of the first trimester, the placenta is more fully developed, including its nutritive/exchange relationship between the maternal and fetal circulations, and its steroid products provide hormonal support for the uterus.

绒毛膜

Placental hormones: Human chorionic gonadotropin (hCG ，人绒毛膜促性腺激素 ) ; Human chorionic somatomammotropin (hCS ，人绒毛膜生长催乳素 )Metabolites of hCG in the urine are an ‘early indicator’ of pregnancy. The critical transition from uterine-ovarian to placental steroids occurs at the end of the first trimester, a period with the largest risk of miscarriage.

Parturition

The onset of labor and delivery is typically heralded by the ‘breaking of the waters’ in reference to the loss of amniotic fluid (c) through the rupturedamniotic sac.

Uterine contractions, coupled with the mother’s abdominal contractions, move the newborn into its own world.

Factors that influence the process of parturition

Parturition

A series of positive feedback events involving neural and chemical cues promotes the cascade of uterine contractions (smooth muscle) that help to propel a neonate into the world.

Lactation

The hormones of pregnancy, including prolactin, estrogens, and progestins, stimulate development in the mammary glands