Biology

• Female Reproductive System


  • Major organs located inside the pelvic cavity
• External Female Genitals


  • Mons pubis
  • Labia majora
  • Labia minora
  • Clitoris
  • Hymen
  • Vaginal opening
  • Bartholin's glands
• Vulva


  Collective term for the external female reproductive structures
• Vagina


  Muscular canal (approximately 10 cm long) that serves as the entrance to the reproductive tract and the exit from the uterus during menses and childbirth
• Vagina


  • Outer walls formed into longitudinal columns or ridges
  • Superior portion (fornix) meets the protruding uterine cervix
  • Walls lined with outer fibrous adventitia, middle smooth muscle layer, and inner mucous membrane with transverse folds (rugae)
  • Allows expansion to accommodate intercourse and childbirth
  • Home to normal population of microorganisms that help protect against infection
• Ovaries


  Female gonads, paired ovals about 2-3 cm in length, located within the pelvic cavity
• Ovaries


  • Supported by the mesovarium
  • Contain the ovarian stroma with oocytes developing in follicles
  • Cortex contains the follicles, medulla contains blood vessels, lymph vessels, and nerves
• Ovarian cycle


  Set of predictable changes in a female's oocytes and ovarian follicles, occurs over approximately 28 days
• Oogenesis


  1. Oogonia form primary oocytes in fetal ovary

  2. Primary oocytes arrested in meiosis I, resume at puberty

  3. Meiosis produces secondary oocyte and first polar body

  4. Meiosis II completes to form haploid ovum if fertilized by sperm
• Maternal mitochondrial DNA is inherited, allowing tracing of ancestry through the female line
• Folliculogenesis


  1. Primordial follicles recruited to become primary follicles after puberty

  2. Primary follicles develop into secondary and tertiary follicles

  3. One follicle ovulates, others undergo atresia (death)
• Females are born with 1-2 million oocytes in primordial follicles, this declines to 400,000 at puberty and 0 by menopause
• Primordial follicles


  • Have only a single flat layer of support cells, called granulosa cells, that surround the oocyte
  • Can stay in this resting state for years—some until right before menopause
• Folliculogenesis


  1. Primordial follicles respond to a recruitment signal each day and join a pool of immature growing follicles called primary follicles

  2. Primary follicles start with a single layer of granulosa cells, which then become active and transition from a flat or squamous shape to a rounded, cuboidal shape as they increase in size and proliferate

  3. As the granulosa cells divide, the follicles—now called secondary follicles—increase in diameter, adding a new outer layer of connective tissue, blood vessels, and theca cells

  4. Within the growing secondary follicle, the primary oocyte secretes a thin acellular membrane called the zona pellucida

  5. A thick fluid, called follicular fluid, that has formed between the granulosa cells also begins to collect into one large pool, or antrum

  6. Follicles in which the antrum has become large and fully formed are considered tertiary follicles (or antral follicles)

  7. Several follicles reach the tertiary stage at the same time, and most of these will undergo atresia

  8. The one that does not die will continue to grow and develop until ovulation, when it will expel its secondary oocyte surrounded by several layers of granulosa cells from the ovary
• Hormonal control of the ovarian cycle

  • The process of development from primordial follicle to early tertiary follicle takes approximately two months in humans
  • The final stages of development of a small cohort of tertiary follicles, ending with ovulation of a secondary oocyte, occur over a course of approximately 28 days
• Hormonal regulation of the ovarian cycle

  1. The hypothalamus produces GnRH, which signals the anterior pituitary gland to produce the gonadotropins FSH and LH

  2. FSH stimulates the follicles to grow, and the five or six tertiary follicles expand in diameter

  3. The release of LH also stimulates the granulosa and theca cells of the follicles to produce the sex steroid hormone estradiol

  4. As a result of these large follicles producing large amounts of estrogen, systemic plasma estrogen concentrations increase

  5. The high concentrations of estrogen will stimulate the hypothalamus and pituitary to reduce the production of GnRH, LH, and FSH

  6. Typically only one follicle, now called the dominant follicle, will survive this reduction in FSH, and this follicle will be the one that releases an oocyte

  7. When only the one dominant follicle remains in the ovary, it again begins to secrete estrogen

  8. The extremely high concentrations of systemic plasma estrogen trigger a regulatory switch in the anterior pituitary that responds by secreting large amounts of LH and FSH into the bloodstream

  9. The LH surge induces many changes in the dominant follicle, including stimulating the resumption of meiosis of the primary oocyte to a secondary oocyte

  10. The LH surge also triggers proteases to break down structural proteins in the ovary wall on the surface of the bulging dominant follicle, resulting in the expulsion of the oocyte surrounded by granulosa cells into the peritoneal cavity
• Corpus luteum


  • The collapsed follicle that is transformed into a new endocrine structure after ovulation
  • The luteinized granulosa and theca cells of the corpus luteum begin to produce large amounts of the sex steroid hormone progesterone
• Luteal phase


  The post-ovulatory phase of progesterone secretion
• Uterine tubes


  • Serve as the conduit of the oocyte from the ovary to the uterus
  • Divided into sections: isthmus, infundibulum with fimbriae, and ampulla
  • Have three layers: outer serosa, middle smooth muscle layer, and inner mucosal layer with ciliated cells
• Movement of the oocyte through the uterine tube

  1. High concentrations of estrogen induce contractions of the smooth muscle along the length of the uterine tube

  2. Coordinated beating of the cilia that line the outside and lumen of the uterine tube generates a current flowing toward the uterus

  3. These mechanisms pull the oocyte–granulosa cell complex into the interior of the tube and move it slowly toward the uterus
• If the oocyte is successfully fertilized, the resulting zygote will begin to divide into two cells, then four, and so on, as it makes its way through the uterine tube and into the uterus
• If the egg is not fertilized, it will simply degrade—either in the uterine tube or in the uterus, where it may be shed with the next menstrual period
• Uterus


  • Muscular organ that nourishes and supports the growing embryo
  • Has three sections: fundus, body, and cervix
• Sepsis is associated with sexually transmitted bacterial infections, especially gonorrhea and chlamydia
• Pelvic inflammatory disease (PID) can lead to infertility
• Movement of the oocyte through the ovary

  1. Cilia in the uterine tube promote movement of the oocyte

  2. If the cilia were paralyzed at the time of ovulation, the oocyte's movement would likely be impaired
• Uterus


  Muscular organ that nourishes and supports the growing embryo
• Uterus


  • Average size is approximately 5 cm wide by 7 cm long when a female is not pregnant
  • Has three sections: fundus, body of uterus, and cervix
• Cervix


  Narrow inferior portion of the uterus that projects into the vagina
• Cervical mucus


  Becomes thin and stringy under the influence of high systemic plasma estrogen concentrations, facilitating sperm movement
• Ligaments that maintain the position of the uterus

  • Broad ligament
  • Round ligament
  • Uterosacral ligament
• Uterine wall


  • Serous membrane (perimetrium)
  • Myometrium (smooth muscle)
  • Endometrium (connective tissue lining and epithelial tissue)
• Stratum basalis


  Part of the endometrium that is adjacent to the myometrium and does not shed during menses
• Stratum functionalis


  Thicker layer of the endometrium that contains the glandular portion and endothelial tissue, and grows and thickens in response to estrogen and progesterone
• Estrogen and progesterone levels


  Influence the growth and thickening of the stratum functionalis
• Progesterone declines


  Triggers the shedding of the stratum functionalis, leading to menses
• Menstrual cycle


  1. Menses phase

  2. Proliferative phase

  3. Secretory phase
• The menstrual cycle begins on day 1 with the start of menses
• Ovulation occurs around day 14 of a 28-day cycle, triggered by the LH surge
• Estrogen levels increase


  Stimulate the endometrial lining to rebuild during the proliferative phase