Female Reproductive System

• Components of the reproductive system

  • Primary internal sex organs (gonads like testes and ovaries), sex hormones, gametes (sperm and eggs), glands, ducts, external genitalia, particular brain parts
• Function of the reproductive system

  Mate, combine alleles, and make babies
• Female anatomy involves the vulva, mons pubis, labia majora, labia minora, vestibule, urethral and vaginal openings, and vagina
• The external sexual organs are the least important parts of the female reproductive system
• Ovaries


  Produce and release female gametes and sex hormones like estrogen and progesterone
• Gametes are haploid cells formed by meiosis
• When a sperm fuses with an egg, they make a diploid cell with all the genetic instructions required to make a baby
• Reproductive systems are designed to facilitate the fusion of sperm and egg
• Ovarian follicles


  Basic reproductive units in the cortex of the ovary that contain primary oocytes and supporting follicle cells
• Females are born with essentially all the early versions of eggs they will ever have
• Follicles


  Tiny-sac-like structures that hold a single primary oocyte along with supporting follicle cells
• Females are born with essentially all early versions of eggs in all primordial follicles they will ever have, around 1 million at birth
• Oocytes stop developing around birth and get stuck in the first stage of meiosis
• The process of egg creation, or oogenesis, is delayed until puberty
• Human eggs mature one-by-one, almost constantly, either fertilized or die to make way for a new egg
• Menstruation is only one part of the menstrual cycle, the other part being the ovarian cycle
• Ovarian cycle


  Ripens eggs and secretes sex hormones
• Menstrual cycle

  Prepares the uterus to capture and nourish any mature, fertilized eggs
• Puberty

  Regulates all the activity related to follicle maturation and egg development through sex hormones
• Ovulation


  The mature follicle ruptures, ejecting a single mature oocyte
• Corpus luteum formation

  The damaged follicle transforms into the corpus luteum, releasing hormones to prepare the uterus and eventually degenerating
• Puberty

  Regulates the ovarian and menstrual cycles through sex hormones
• FSH and LH secretion


  Stimulates follicle growth and maturation, and triggers oocyte division
• Estrogen surge


  Stimulates the pituitary to secrete LH to complete follicle maturation
• Corpus luteum formation

  Releases hormones to stop FSH and LH release and prepare the uterus for potential fertilization
• The fallopian tubes are about 10 centimeters long
• Final hormonal swan song

  Release of progesterone, a little estrogen, and some inhibin to stop the release of FSH and LH and prepare the uterus to receive the oocyte
• The fallopian tubes are about 10 centimeters long and are not connected to the ovaries
• When an egg pushes through the ovary, it has to float a short way through the peritoneal cavity before it's caught by a fallopian tube
• Only if and when an egg fuses with a sperm does it complete meiosis II and officially become an ovum
• The egg works its way down the tube until it enters the uterus, a hollow, thick-walled, and very stretchable muscular organ that sits anterior to the rectum and posterosuperior to the bladder, and ends with the cervix
• The uterine wall is composed of three layers: the perimetrium on the outside; the myometrium, a bulky, smooth muscle that contracts during labor; and the endometrium, the inner mucosal lining consisting of a thin, deep basal layer, and an outer functional layer
• If fertilization occurs, the embryo snuggles into the endometrium for gestation, but the uterus is only receptive to implantation for about a week after ovulation
• If the egg isn't fertilized, the outer functional layer of the endometrium sloughs off, marking the first phase of the uterine or menstrual cycle
• The shedding of the functional layer is triggered by the drop in progesterone and estrogens produced by the corpus luteum, about 10 days after ovulation, lasting about 5 days
• The rising FSH and LH stimulate the next round of follicles, which begin to make estrogen, heralding the start of the proliferative or pre-ovulatory phase of the menstrual cycle, typically lasting from days 6-14
• The rising estrogen levels stimulate the regeneration of the endometrium, building a well-vascularized habitat for a potential fertilized egg
• The final secretory or postovulatory phase begins when the ruptured follicle forms the corpus luteum, and if fertilization didn't occur, the corpus stops producing progesterone, leading to shedding of the functional layer of the endometrium
• If fertilization occurs, the pulse of progesterone from the corpus triggers further thickening of the functional layer of the endometrium and a secretion of nutrients to support the embryo until implantation