VT 111 Lec 19 Female Reproductive System

Female Reproductive System

• more complex than male reproductive system

• functions:

  • produces sex hormones

  • develops gametes

  • receives male gametes

  • furnishes a site for male gametes to fertilize the ovum

  • provides environment for embryo to grow and develop

  • carries embryo for entire pregnancy

  • pushes offspring out when fully developed

  • supply nutrients to newborn(s)

Female Reproductive System

• ligaments

• ovaries

• oviducts

• uterus

• cervix

• vagina

• vulva

Ovarian Cycle 

• Development of ovum within follicle

• Release of ovum from follicle – ovulation

• Formation of corpus luteum (CL) produces progesterone

• Degeneration of unripened follicles

• Degeneration of corpus luteum

Follicle Development

• Primary or primordial follicle

  • Immature gamete (oocyte - 1) surrounded by single layer of flat follicular cells

  • Female had thousands in ovaries

• FSH released from anterior pituitary

  • A few of primordial follicles begin to develop

    • Now called growing follicle – cells multiply

    • As it grows, forms glycoprotein zona pellucida layer outside cell membrane

    • Follicular cells form around zona pellucida (2) – granulosa cells (3)

      • Produce estrogen

      • Granulosa cells multiply → follicle grows in size

Follicle Development Continued… 

• Follicle continues to enlarge

  • Produces more estrogen

  • Fluid filled spaces form between granulosa cells

    • → merge to form antrum (1)

      • Fluid filled space

  • At maximum size, called a mature follicle

    • AKA: Graafian follicle, vascular ovarian follicle

  • Ovulation (rupture of follicle) takes place due to

    • Rising levels of LH (with or without breeding) or

    • Breeding takes place

      • Induced ovulators (rabbits, cats, camelids)

  • Gamete released from follicle à now call ovum

Follicle Development Continued… 

• Ruptured follicle fills with blood

  • Corpus hemorrhagicum

• Granulosa cells of corpus hemorrhagicummultiply

  • → form corpus luteum (CL)

    • Formed under the influence of LH

    • Produces progestins

      • Primary one: progesterone

        • Maintains pregnancy if ovum is fertilized and implants

        • If no pregnancy, CL degenerates

Ovulation

• Whole: ovary

• mature follicle ruptures

• gamete released into oviduct – now called an ovum

• empty follicle fills with blood to form corpus hemorrhagicum

Corpus Luteum 

• formed from cells lining corpus hemorrhagicum

• produces the progestins needed to maintain pregnancy if ovum is fertilized

Progestins

• Progestins produced by CL

• Principle progestin – progesterone

  • “pregnancy-promoting steroid hormone”

  • Helps to prepare uterus to receive fertilized ovum (ova)

    • Necessary for pregnancy to be maintained

• If no pregnancy, CL regresses and disappears

Ovulation

• occurs spontaneously in most species

  • result of rising levels of LH

• induced ovulators

  • ovulation occurs after breeding

    • cats, camels, rabbits, ferrets

• Other factors?

  • Koala, alpaca

Follicular Atresia

• not all follicles activated in a single ovarian cycle will fully develop and ovulate

  • follicles may degenerate at any stage of development

  • normal part of each ovarian cycle

Oviducts = Fallopian Tubes = Uterine Tubes

• Oviduct (animal) = fallopian tubes (human)

• guide ova from ovary to uterus

• serve as usual site for fertilization of ova by spermatozoa

• extend from tips of uterine horns

• fimbriae “catch” ova in infundibulum

• walls composed of smooth muscle

  • lining cells have cilia

  • both work to move ovum to uterus

The Uterus 

• hollow muscular organ, usually Y-shaped

• forms part of placenta

• suspended from dorsal abdomen by mesometrium

• 3 layers:    

  • endometrium 

  • myometrium 

  • perimetrium

Species Variation 

Uterus

• Endometrium

  • Simple columnar epithelium

  • Simple tubular glands à secrete mucus

• Myometrium – thickest layer

  • Layers of smooth muscle

• Perimetrium

  • Covered by visceral layer of peritoneum

• Implantation of fertilize ovum - zygote

The Cervix

• smooth muscle sphincter between body of the uterus and the vagina

• normally tightly closed

  • except during estrus

    • “heat”

  • except during parturition

    • “birth”

    • Pressure of fetus against relaxed cervix causes it to dilate

The Vagina and the Vulva

• vagina

  • muscular tube that receives penis during breeding time

  • acts as birth canal at parturition

• vulva

  • vestibule

    • space between labia and opening of vagina

    • urethra opens on floor of vestibule

  • clitoris

    • also on floor of vestibule

  • labia

    • external boundary of vagina

Estrous Cycle 

• Estrous cycle - entire reproductive cycle

  • the time from the beginning of one heat period to the beginning of the next

  • controlled by hormones FSH and LH

  • different animal species have different patterns of estrous cycles

• Specific period in estrous cycle when breeding can take place

  • Estrus

    • Female is receptive to male

    • Highest chance or successful pregnancy

Intervals & Stages

Proestrous & Estrus

Metestrus & Diestrus

The Estrous Cycle Continued… 

• Pseudopregnancy – under influence of CL, animal may exhibit signs of active pregnancy (e.g. enlarged mammary glands)

  • Occurs more commonly in species with a prolonged diestrus

  • Usually resolves spontaneously

• Anestrus

  • Period of temporary ovarian inactivity in seasonally polyestrous, diestrous and monoestrous species

Cycle of the Dog 

Vaginal cytology 

Vaginal Cytology continued…

Estrous (Heat Cycle in Female Dogs

Hormonal Changes

• Luteinizing hormone :

  • anterior pituitary (LH)

• Follicle stimulating hormone:

  • anterior pituitary (FSH)

• Progesterone:

  • Corpus luteum (CL)