Female reproductive system

I.  Introduction

- female reproductive system far more complex than male:

• production of sex cells
• production of sex hormones
• create environment for implantation
• create environment for embryo development

- sex organs:  ovaries;  produce eggs and sex hormones

- accessory ducts:  uterine tubes, uterus, vagina

- external sex organs:  external genitalia, vulva

II.  Anatomy of female reproductive system

A.  Ovaries

- paired, flank uterus on each side, almond (2X size)

- surrounded by tunica albunigea

- X-section:  outer cortex with forming gametes at different stages of development; inner medullary region has blood vessels, nerves

- in cortex see ovarian follicles:  one or more layer(s) of cells surrounding an immature egg, oocyte

• surrounding cells called follicle cells if single layer is present
• surrounding cells called granulosa cells if more than one layer is present

- stages of follicular development:

• primordial follicle:  single layer squamous cells surrounds oocyte
• primary follicle:  two or more layers cuboidal/columnar granulosa cells surround oocyte
• secondary follicle:  fluid-filled spaces appear between granulosa cells; fluid-filled cavity is antrum
• vestibular or Graafian follicle:  oocyte sits on stalk of cells on side of antrum; other side burst, ovulation
• corpus luteum:  follicle after ovulation , really an endocrine gland

B.  Uterine tubes

- receive ovulated oocyte, provide site where fertilization occurs; very muscular walls

- fimbrae with cilia draw egg into tubes; peristalsis moves egg to uterus

- ectopic pregnancy -- fertilization and implantation in peritoneal cavity

C.   Uterus

- hollow, thick walled organ:  receive, retain, nourish fertilized ovum

- size/shape of inverted pear; during pregnancy up to 60X original size

- regions of uterus:

• fundus
• body
• isthmus
• cervix:   mucosal glands in lining of cervix; mucus filled cervical canal; protection of uterus and rest of tract

- layers:

• perimetrium: outermost, visceral peritoneum
• myometrium:  bulky, interlacing bundles of smooth muscle
• endometrium:  mucosal lining of uterine cavity; simple columnar epithelium with thick lamina propria -- where embryo implants
  • has  two layers:  stratum functionalis that undergoes cyclical changes in response to blood levels of ovarian hormones; stratum basalis that forms new functionalis after latter is shed.
  • rich vascular supply -- spiral arteries of s. functionalis undergo degeneration/regeneration during uterine cycle; their spasms causes shedding of functionalis.

D.  Vagina:  thin-walled tube, 8-10 cm long, extends from vestibule to cervix

- receives penis/semen during intercourse and prides passageway for delivery during childbirth; highly distensible wall

- acidic mucosa to prevent infection

E.  External genitalia

1. mons pubis:  rounded area overlying pubic symphysis
2. labia majora:  two hair-covered skin folds; homologous to male scrotum
3. labia minora:  two hairless skin folds, enclose space called vestibule; homologous to ventral penis
4. vestibule:  space within labia minora that contains external openings of urethra and vagina; flanking vagina are vestibular glands that release mucous into vestibule:   moisten, lubricate, facilitate intercourse, homologous to bulborethral glands in male
5. clitoris:  anterior to vestibule; erectile tissue, homologous to penis; covered by thin fold, prepuce

F.  Mammary glands:  present in both sexes only functional in female; modified sweat glands

- internally divided into 15-20 lobes by CT; lobes divided into lobules that contain secretory units or alveoli that empty secretion into lactiferous duct system ----> unites at lactiferous sinus in nipple

III.  Physiology of female reproduction

A.  Oogenesis

- note that in male gamete production begins at puberty; in female preparation for gamete production begins in fetus

1. cells that develop into eggs migrate from yolk sac to ovaries, develop into oogonia
2. oogonia divide mitotically (several million) enlarge, mature
3. cells become primary oocytes when they begin first meiotic division (DNA replicated), division is stalled prior to birth;  primary oocyte enclosed by follicle cells, flat primordial follicle
4. at puberty under appropriate stimulation:  follicle growth, completion of first meiotic division (secondary oocyte); ovulation; when fertilized second meiotic division takes place

-  thus at birth all of women's potential eggs formed:  of about 2 million primordial follicles at birth about 700,000 remain; by puberty about 300-400,000 left

B.  Ovarian cycle

follicular phase:  period of follicular growth, d1-d14

luteal phase:  period of corpus luteum activity, d14-d28

1.  follicular phase

1. starting at puberty a group of primordial follicles stimulated to continue development every 28 days
2. follicle cells become cuboidal, divide ----> primary follicle (multi layered);
3. follicle cells begin to produce estrogen
4. liquid accumulates ---> secondary follicle ---> vestibular follicle

- primary oocyte within completes meiosis 1 -- secondary oocyte; hours later ovulation; secondary oocyte completes meiosis 2 only if fertilization occurs

2.  luteal phase:  antrum space fills with blood, corpus hemorrhagium

1. remaining granulosa cells begin producing  progesterone, estrogen -- corpus luteum
2. if fertilization occurs, the embryo produces human chorionic gonadotrophin (HCG) which maintains CL until placenta can kick in its own progesterone/estrogen production
3. if fertilization does not occur, CL degenerates as no HCG

C.  Hormonal regulation of ovarian cycle

-  feedback inhibition patterns:

• very low levels of estrogen stimulate FSH
• moderate level of estrogen inhibit FSH/LH
• high level of estrogen stimulate LH/FSH release

D.  Uterine cycle:  menstrual cycle, regulated by ovarian hormones

1. d1 of cycle, est/prog very low, shed endometrium; FSH level begin to increase due to lack of feedback inhibition
2. FSH stimulates follicle growth --> follicles produce estrogen ---> uterine build up, proliferative phase
3. as estrogen levels increase, LH/FSH spike ---> ovulation ---> estrogen levels begin to drop ---> corpus luteum develops ---> progesterone/some estrogen ---> secretory phase of uterine cycle (enriches endometrium blood supply, provides nutrients to prepare endometrium for implantation) ---> depending if HCG present or not CL maintained or degenerates and likewise endometrium

- shedding of endometrium produced by spasms of spiral arteries -- deprive endometrium of nutrients, oxygen; cells die, lysosomes rupture; spiral arteries constrict, relax massively, capillaries fragment -- functionalis sheds

E. Extra-uterine estrogen effects

- female secondary sex characteristics:  increased deposits of subcutaneous fat, widening, lightening of pelvis; growth of axillary and pubic hair.

- maturation of reproductive structures