Female Reproductive System: Anatomy and Function

Female Reproductive Tract Overview

• The oviduct is the most terminal part of the female reproductive tract.
• This tract is highly responsive to the ovary.
• It is suspended in the abdominal cavity by the broad ligament.
• The recto-genital pouch physically separates the GI and reproductive tracts, aiding in palpation.

Litter Bearing

• Polytocous animals have litters, involving multiple ovulations and oocytes.
• Monotocous animals have single offspring.

Lower Reproductive Tract

• The lower reproductive tract's purpose is to facilitate penis insertion and serve as the birth canal.
• The labia closes the vaginal entrance to keep substances out.
• The vestibule is the outer vagina containing the urethral opening.
• The cranial vagina is between the vestibule and cervix, differing in musculature.
• Natural insemination usually occurs in the fornix vagina.

Cervix

• The cervix is a tough structure that separates the lower and upper reproductive tracts.
• The cervix is highly responsive to ovarian steroidal hormones.
• Progesterone constricts the cervix.

Uterus

• The uterine body occurs before the uterus bifurcates into horns.
• The uterus is very red due to an abundance of blood vessels supporting embryonic/fetal development and hormone transfer.
• Caruncles are internal structures, specific to ruminants, where the placenta forms.

Oviduct Function

• The oviduct is where fertilization and early embryonic development happens.
• The oviduct captures the oocyte via the infundibulum at its end.

Ovary Function

• The ovary has gametogenic roles that support oocyte development.
• Also, it has the endocrine roles of producing progesterone and estrogen to communicate with the brain.

Species-Specific Traits

• Cows ovulate a single oocyte at a time, alternating between ovaries.
• Pigs have a long, corkscrew-shaped cervix.
• The corkscrew shape is the result of interdigitating pads locking the penis in place.
• Ejaculation in pigs occurs in the cervix, facilitating easier sperm access to uterine horns.
• Sows ovulate multiple oocytes simultaneously from both ovaries, without a dominant horn.
• Highly folded uterine horns increase surface area for placenta attachment.
• In mares, copulation happens in the vagina, but sperm passes into the uterus.
• Mare cervixes have exaggerated longitudinal folds for expansion and contraction.
• Bitches have strong vaginas to withstand pressure from the dog's bone-containing penis and vascular structure during copulation.
• Queens require physical stimulation of the reproductive tract for induced ovulation, resulting from the barbs on the tom penis that stimulates the vagina.
• Spontaneous ovulation is driven by internal body functions and is common in most animals.

Internal Tract Tissue Layers

• The mucosa is the innermost tissue layer with a secretory epithelium lining the lumen.
• Cell type in the mucosa depends on function and responds to ovarian hormones and secretes hormones to tell the embryo when to grow.
• The Lumen is an open space where oocytes can travel through.
• The first 20 days of pregnancy have no placenta, so nutrients float around in the lumen.
• The submucosa surrounds and supports the mucosa, containing blood vessels, nerves, and lymphatics.
• The muscularis layer is composed of muscle cells in outer longitudinal and inner circular layers.
• It stimulates contractions for gamete/embryo transport and parturition.
• The serosa is the outer connective tissue that supports and prevents adhesions and responds to steroid hormones.
• The muscularis layer is especially thick around the uterus and vagina.
• The function of the mucosa depends on the cell type present.

Broad Ligament

• The broad ligament is suspensory tissue surrounding the reproductive tract in the body cavity.
• The peritoneum is abdominal connective tissue lining the body cavity.
• It supports, prevents adhesions, creates the rectogenital pouch for rectal palpation in cattle and horses, and carries a vascular supply of lymphatics and nerves.
• The development of the broad ligament involves part of the peritoneum.
• Mesometrium is the portion of the broad ligament supporting the uterus.
• The meso prefix refers to the broad ligament.
• The mesovarium supports and connects the ovary to the broad ligament.
• It forms the hilus and provides a vascular supply, lymphatics, and nerves to the ovary..
• The mesosalpinx surrounds and supports the oviduct
• In bitches, the mesosalpinx encloses the ovary, creating the bursa.
• The mesosalpinx is important for blood vessels, lymphatics, and nerves access because the embryo is in the oviduct for the first few days.

Ovary Roles

• The ovary develops oocytes and produces steroid hormones.
• Females are born with all the gametes they will ever have, but females don't make their own gametes.
• Oocytes at birth are not fully developed and only have 23 chromosomes which stay in G0 phase of meiosis.
• At puberty, oocytes resume meiosis.
• Menopause occurs when women run out of oocytes and cells that produce estrogen and progesterone, ending their reproductive life.
• The oocyte life cycle starts in fetal life and ends in fertilization.

Follicular Development

• The primordial follicle is the first stage; a single flat layer of granulosa cells surrounds the oocyte to protect it.
• A fixed number of primordial follicles exist at birth.
• The primary follicle is when the follicle wakes up, and granulosa cells become cuboidal but remain one layer.
• Granulosa cells increase in layers (>2) and become more cuboidal, the oocyte grows, and the zona pellucida develops in the secondary follicle stage.
• The developing antral (tertiary) follicle becomes responsive to brain signals, and granulosa cells produce estrogen/estradiol, signaling the brain and preparing the oocyte for ovulation.
• It produces fluid to fill the antrum, during the developing antral follicle.
• The antral (dominant) follicle is when granulosa cells produce maximum estradiol concentrations.
• This stage signals to the brain that it is ready to ovulate and becomes the dominant follicle, and competing follicles are lost and reabsorbed.
• The antrum bursts, and the fluid pushes out the oocyte, to escape from the ovary, at the point of the dominant follicle ovulating.
• The entire process from primordial to ovulating follicle takes 120 days, so the process is continuous.
• After ovulation, granulosa cells from the ovulated oocyte become luteal cells, producing progesterone instead of estrogen, forming the corpus luteum.
• The corpus luteum is yellow due to its high cholesterol content, which is used to make progesterone.
• High ovary-produced progesterone levels signal the brain that the body is pregnant, which prevents ovulation.
• If the oocyte is not fertilized, the corpus luteum stops producing progesterone, regresses, and sinks into itself, becoming the white body.

Ovary Anatomy

• Germinal epithelium is on the ovary surface, continuous with the peritoneum.
• It is a single layer of cuboidal cells preventing adhesions and is broken at ovulation.
• Germinal epithelium is not the origin of germ cells.
• Tunica albuginea is a dense connective tissue providing structure to the ovary.
• The preantral phase includes the oogonia, primordial, primary, and secondary follicular phases.
• The antral phase includes the tertiary and preovulatory phases.
• The cortex is the outer 2/3 of the ovary that contains the follicles.
• The theca externa surrounds the developing follicle and consists of connective tissue where blood vessels end.
• The theca interna is follicular cells that produce testosterone (estrogen precursor) and have receptor sites responsive to gonadotropin.
• Granulosa cells are ovarian cells that produce estrogen and lead to follicle development.
• The zona pellucida is a thick, transparent coating rich in glycoproteins surrounding the oocyte to separate it from granulosa cells.
• The cumulus-oocyte complex (COC) consists of granulosa cells around the oocyte, which is released at ovulation and aids in oviduct transport.
• The corpus hemorrhagicum (CH) is a bloody body/ovulation cavity containing blood vessels, granulosa, and theca cells.
• Luteal cells originate from theca interna and granulosa cells and produce progesterone.
• Progesterone is the hormone of pregnancy, which blocks myometrial contractions and behavioral estrus, increases endometrial secretions, and regulates luteinizing hormone.
• Endometrial secretions from progesterone provide nutrients for the early embryo.
• The corpus albicans is a white body, a degenerated CL, scar tissue with no function.
• The medulla is the inner, looser layer of the ovary that contains blood vessels, nerves, and lymphatic vessels.
• In horses, the cortex is inside, and the medulla is on the outside, and they only ovulate at the ovulation fossa.
• The ovulation fossa is a conspicuous depression in the ovarian surface, which is the site of each ovulation in the mare.

Ovary Roles

• The gametogenic role of the ovary involves the development, maturation, and ovulation of oocytes.
• The endocrine role of the ovary involves producing and responding to estrogen, progesterone, oxytocin, relaxin, inhibin, and activin.

Oviduct Parts

• The parts of the oviduct include the infundibulum, ostium, ampulla, and isthmus.

Oviduct Functions

• The ovarian infundibulum captures the ooctye (COC).
• Fimbriae (cilia) line the inner infundibulum to increase surface area and aid in COC capture.
• The ostium is the opening to the ampulla.
• The ampulla is the first 1/2 of the oviduct and has a large diameter with increased mucosal folds and ciliated epithelium, and low muscle presence.
• It moves the oocyte to the isthmus using cilia.
• The isthmus is the last 1/2 of the oviduct, has a small diameter, a thick muscular wall, few mucosal folds and ciliated cells, high muscle presence, and connects to the uterus.
• Contractions in the isthmus move sperm to the ampullary-isthmic junction (AIJ), which it a possible sperm reservoir.
• The ampullary-isthmic junction (AIJ) is the fertilization site in most mammals.
• In mares, the AIJ regulates that only fertilized oocytes pass into the isthmus and uterus.
• Uterotubal junction (UTJ) regulates sperm into the oviduct and the embryo into the uterus.
• In pigs, the UTJ prevents polyspermy.
• Increased estrogen kinks the UTJ, and increased progesterone removes the UTJ kink.
• Oviduct functions include gamete transport, sperm capacitation, early embryo development, and embryo transport.
• The oviduct facilitates gamete transport through muscle contractions to move sperm and ciliated epithelial cells to move the oocyte.

Overview of the female reproductive tract, including the oviduct, lower tract, and cervix. Discussion of litter bearing in polytocous and monotocous animals. Explanation of the vagina's structure and function in facilitating insemination.