Female Reproductive System - Study Notes

Female Reproductive Tract

Introduction

• Content focuses on the female reproductive tract.
• Recap of the structure, oogenesis, folliculogenesis, fertilization, and the female reproductive cycle.
• Questions can be asked on the discussion board or via email.

Overview

• First half:
  • Uterus
  • Uterine tubes
  • Oogenesis
  • Folliculogenesis
  • Female reproductive cycle
• End: Fertilization (briefly)
• Final Kahoot

Functions of the Female Reproductive Tract

• Production of oocytes (oogenesis).
• Endocrine function: production of hormones (estrogen and progesterone).
• Receiving sperm and aiding its transport to the oocyte.
• Nurturing a pregnancy.

Components of the Female Reproductive Tract

• Primary organs:
  • Ovaries (paired):
    • Produce oocytes.
    • Produce hormones (estrogen and progesterone).
• Secondary organs:
  • Uterine tubes (oviducts, fallopian tubes).
  • Uterus.
  • Vagina.
  • Mammary glands (nourishing infants).

Ovaries

• Paired structure, almond-shaped.
• Functions:
  • Exocrine: secretes oocytes.
  • Endocrine: produces estrogen and progesterone.
• Structure (microscopic):
  • Capsule: outer layer, dense connective tissue, protects the ovaries.
  • Cortex: cortical region where follicles and oocytes develop.
  • Medulla: contains blood vessels and nerves for hormone transport.

Uterine Tubes (Oviducts)

• Paired structures connecting ovaries to the uterus; ovaries are not directly connected, but have fimbriae.
• Regions:
  • Infundibulum: has fimbriae (finger-like projections) to capture the oocyte during ovulation.
  • Ampulla: site of fertilization.
  • Isthmus: final maturation of sperm (capacitation).
• Oocyte Transport:
  • Uterine tubes are lined with ciliated epithelium.
  • Cilia beat to transport the oocyte.
  • Important to prevent ectopic pregnancy (implantation in the uterine tube).
• Ectopic Pregnancy
  • Occurs when the embryo implants in the uterine tube.
  • Non-viable pregnancy that requires surgical removal.
• Cilia Movement
  • Motility of cilia move the oocyte along the uterine tube.

Uterus

• Three Layers:
  • Endometrium: inner lining, responds to estrogen and progesterone, grows and sheds during the menstrual cycle.
    • Endometriosis involves endometrial cells growing outside the uterus.
  • Myometrium: thick smooth muscle layer, contracts during menstruation and childbirth.
    • Oxytocin acts on the myometrium to stimulate contractions during birth.
  • Perimetrium: outer layer that secretes fluid to reduce friction within the pelvic cavity.
• Endometrium Layers (Zoomed In):
  • Stratum Basales (Basal Layer): contains stem cells, gives rise to spiral arteries and glands in response to estrogen.
  • Stratum Functionalis (Functional Layer): builds up each month and is shed if pregnancy does not occur.

Folliculogenesis

• Development of follicles from primordial to mature stage.
• All primordial follicles are developed during embryonic development.
• Primordial follicles contain a primary oocyte and a single layer of cells.
• Stages:
  • Primordial Follicle:
    • Primary oocyte with a single layer of flat cells.
  • Primary Follicle:
    • Increased number of follicular cells, cuboidal shape, begins to produce estrogen.
  • Secondary Follicle:
    • Fluid-filled spaces with follicular fluid (nutrients for inner cells and oocyte).
  • Tertiary/Mature/Graafian Follicle:
    • Large fluid-filled space (antrum), cells directly around oocyte are granulosa cells which stay with oocyte after ovulation.
• Post-Ovulation:
  • Empty follicle luteinizes under LH influence to form the corpus luteum.
  • Corpus luteum produces both estrogen and progesterone to develop the endometrium.
  • If no pregnancy occurs within ten days, the corpus luteum dies off and forms the corpus albicans (scar tissue).
  • Menopause results as ovaries fill up with scar tissue because of multiple corpus albicans.

Oogenesis

• Development of oocytes, similar to spermatogenesis (mitosis, meiosis I & II); timing is different.
• Mitosis occurs during embryo development; stops around 3-4 months of pregnancy, giving a finite supply of oocytes.
• Process:
  • Mitosis: oogonia (stem cells) undergo mitosis to build up the stem cell supply (occurs during embryo development).
  • Primary Oocytes: oogonia differentiating after mitosis and begin meiosis but are arrested in prophase I until puberty.
    • Primary oocytes sit within the primordial follicle.
  • Puberty: GnRH stimulates FSH secretion, triggers follicle development.
    • Prior to ovulation, meiosis I is completed.
    • Two products: secondary oocyte and a polar body (uneven distribution of cytoplasm).
    • Secondary oocyte contains most cytoplasm, organelles, and half the DNA (haploid).
  • Secondary Oocyte: begins meiosis II but gets arrested at metaphase II.
    • Meiosis II completes only if fertilization occurs.
    • Results in a second polar body being expelled and a zygote (product of male and female DNA).

Female Reproductive Cycle

• Governed by hormones from the brain and ovaries.
• Hormonal Control:
  • Hypothalamus secretes GnRH, which stimulates the pituitary gland to secrete FSH and LH.
  • FSH and LH act on the ovaries to produce estrogen and progesterone.
  • Estrogen and progesterone feedback to the hypothalamus and pituitary.
  • Estrogen and progesterone act on the uterine lining.
  • hCG comes from the embryo and is detected in pregnancy tests.
• Approximately a 28-day cycle (varies).
• Two phases (ovarian and uterine).

Ovarian Phase

• Follicular Phase (Pre-Ovulation):
  • Lasts about 10-12 days (days 6-14).
  • Hypothalamus secretes GnRH, stimulating FSH secretion.
  • FSH binds to follicles in the ovary, stimulating their development from primordial to tertiary follicles.
  • Developing follicles secrete estrogen, which acts on the uterus to build up the functionalis layer.
• Ovulation:
  • Occurs around day 14.
  • High levels of estrogen from the developing follicle have positive feedback on GnRH, leading to increased FSH and LH secretion.
  • Eventually, LH surges, triggering ovulation.
  • Oocyte completes meiosis I just before ovulation and is expelled as a secondary oocyte arrested in metaphase II.
• Luteal Phase (Post-Ovulation):
  • Follicle collapses and transforms into the corpus luteum under the influence of LH.
  • The corpus luteum secretes progesterone as well as estrogen.
  • Progesterone stimulates the endometrial glands to secrete factors that would support a pregnancy.
  • High levels of progesterone and low levels of estrogen cause a negative feedback to GnRH, preventing further follicle development.

Uterine Phase

• Proliferative Phase

  • Occurs at the same time as the Follicular Phase (Pre-Ovulation).
  • The basal layer of the uterine lining divides and the functionalis layer gets bigger and bigger in response to Estrongen.

• Secretory Phase

  • Occurs at the same time as the Luteal Phase (Post-Ovulation).
  • The corpus luteum is producing Progesterone to support a potential pregnancy. The endometrium becomes more lush.

• Menstrual Phase:

  • if there is no pregnancy, then the postovulatory will develop into the menstrual phase.
  • If there is no HCG, then no infant is detected, the corpus luteum degenerates and no estrogen and progesterone are produced.
  • Then the spinal arteries constrict, no blood is flowed in the uterine lining.
  • The funtionalist layer is shed, only the basale layer is left.
  • Then the levels of estrogen and progesterone cause GnRH.

Fertilization

• Sperm Transport
  • Sperm is deposited in the vagina and reaches the cervix in about one minute.
  • The cervix aids in sperm transport into the uterus if ovulation has occurred, producing mucus to nourish the sperm.
  • Sperm are stored in the cervix.
  • In about two to seven hours, Sperm reaches the isthmus region.
• Capacitation:
  • Secretes a fluid that causes motility of sperm tail to swim fast.
  • Speeds up the acrosome reaction when in the presence of ooctye.
    • Prepare it for a potential acrozone reaction to occur if it comes in contact with an olicite.
• Acrosome Reaction:
  • Sperm gets around the granulosa cells from follicular development. Connected to each other via tight junctions
  • Forces it's way to leaky some enyzmes break downt the tight junctions.
  • Breaks through the zona pelludica that protects the ooctye.
• Polyspermy Block:
  • Blocks multiple sperms from coming into the oocyte.
  • Depolarization: sperm contains a negative charge. Depolarization helps repel the sperm from the oocyte.
  • Cortical Granule Reaction: Small granules float and move to the outer layer and harden the zona pellulica. Not allowing other sperms through.
• Oocyte Completion:
  • Oocyte finishes meiosis 2
  • Expells it's second polar body
• Zygote Formation:
  • The Nuclei combines together to form the product of both the male and female contribution.
• Events
  • Zygote is formed
  • Days following division occurs to produce more cells
    • 1 day: transforms from one cell to two
    • 2 days: 2 to 4 cells
    • 3 days: 4 to 8 cells
    • 4 days: ball of cells makes morula
    • 5 days: the blastocyst is created. Outer cells are called trophoblast (create placenta) and then there is cell mass (creates the infant)
    • The trophoblast is covered by a zona pellicula that is cracked by the zona pellicula to implant into the surface endometrium. This then uses the gyclogen, all secretions, etc. This is the development of the placenta