LECTURE 5
FEMALE REPRODUCTIVE SYSTEM--MAMMALIAN

PLEASE PRINT OUT ALL FIGURES AND BRING THEM TO LECTURE

I. Introduction

a. Function

  • Production of ovum (oogenesis) and release of oocyte (ovulation)--OVARIES



  • Production of sex steroid hormones (estrogens)



  • Serve as a site or fertilization (oviduct) and implantation (uterus) (ALL DUCT SYSTEMS)





    b. General anatomy of mammalian female reproductive system

    See Figure 1.


  • Paramesonephric duct (Mullerian duct) is probably derived from a ridge in the lining of dorsolateral body wall. Its origin is different from archinephric (mesonephric or Wolffian) duct.




  • In mammals, paramesonephric duct is devoted exclusively to reproductive function (as in the case of most vertebrates).





    II. Ovaries

    a. Macroscopic anatomy

  • In humans and most other mammals, a paired organ situated in the dorsal-lateral aspect of the abdominal cavity. About 3 cm x 1 cm x 1.5 cm in humans.




  • Ovarian surface is smooth in prepubertal animals, but becomes scarred and pitted from the release of ova after reaching puberty.





    b. Microscopic anatomy

    See Figure 2.

  • General structures

    -Cortex




    -Medulla




    -Granulosa cells--nourish ova and produce estrogen




    -Theca cells (theca folliculi)--produce androgen. Can be theca externa or interna.




    -Oogonia and oocytes




    -Follicles--oocytes and the enclosing sacs with multiple cell types




    -Zona pellucida--glycoprotein coat surrounding oocyte




    -Antrum--fluid-filled cavity in maturing follicles




    -Corpus luteum




    -Two-cell model of estrogen production:



  • Sequence of follicular development in human ovaries

    -Follicular phase (about 10-14 days in human)

    *from before birth to end of reproductive years, the ovarian cortex contains thousands of primordial follicles (single oocyte surrounded by a thin layer of follicular cells).




    *at the start of each cycle, 6-12 follicles start to grow, depending on hormonal stimulation, becoming primary follicles.




    *Primary follicles grow bigger to form a stratified layer of follicular cells surrounding the oocyte, forming granulosa cells.




    *oocyte develops glycoprotein coat (zona pellucida). Theca cells are formed.




    *a clear liquid gathers between granulosa cells and form an antrum. Oocyte now sorrrounded by corona radiata (a stalk of granulosa holding oocyte to the follicle, forming secondary follicles. High levels of estrogen are being produced.




    *Only ONE secondary (dominant) follicle will be selected for ovulation. This follicle grows to reach a diameter of about 2 cm = Graafian follicle.




    -Ovulation (about midway in cycle)

    *In response to ovulatory hormone (LH), large amounts of enzymes (collagenase) are made. Surface of ovary is weakened, releasing the oocyte in the Graafian follicle.




    *Oocyte exits the ovary, surrounded by corona radiata.




    -Luteal phase (about 10-14 days in humans)

    *the remains of ruptured follicle (both granulosa and theca cells) undergo cellular and biochemical changes, turn yellow, and become filled with smooth endoplasmic reticulum, forming corpus luteum (yellow body).




    *corpus luteum produces progesterone and some estrogen.




    *if no fertilization and implantation occur within the next 2 weeks, luteolysis occurs, and corpus luteum is destroyed. The cycle repeats.





    c. Oogenesis

    See Figure 3.

    III. Estrous vs. Menstrual cycles

    a. Female reproduction is cyclic, unlike males. Females are fertile only once during the cycle, whereas males are constantly producing sperm.



    b. Estrous cycle-most female mammals are receptive to males only around the time of ovulation. This period of "heat" is accompanied by behavioral change (e.g., lordosis in rodents). This stage is called "estrus". Day one of estrous cycle is the day of first appearance of estrous behavior (~time of ovulation).



    c. Menstrual cycle-in higher primates. They shed uterine lining once a month. The is called menstruation (monthly event). Day one of menstrual cycle is the day of menstruation (~time of initiation of follicular phase).



    d. Although both estrous and menstrual cycle reflect ovarian cycles, the starting days for each cycle occur at different time points in the ovarian cycle.



    IV. Length of ovarian cycles


    a. In the absence of mating (cervical stimulation), mice and rats undergo a very short luteal phase. This shortens the duration of "unproductive" estrous cycle and enhances fertility.



    b. In the absence of mating, rabbits do not even have a luteal phase. Rabbits are called "induced ovulators". Female rabbits ovulate and develop luteal phase only if mating occurs. This is similar to rats and mice but carried to greater extreme.



    V. Length of ovarian cycles

    a. Human anatomy--schematic

    See Figure 4


    b. Pathway of oocyte transport and fetal delivery

    Ovary------------->peritoneal cavity----->uterine tube (fertilization occurs here)--->uterus (implantation occurs here)---->vagina