Female Reproductive System

Major Anatomical Components

The female reproductive system consists of several major anatomical components, each playing a crucial role in reproduction.

  1. Broad, Round, Suspensory Ligaments:
       - Function: These ligaments hold the reproductive organs in the abdominal cavity.

  2. Ovaries:
       - Description: Paired oval organs located in the abdomen.
       - Function: Responsible for hormone production and the production of ova (egg cells).

  3. Oviducts (Fallopian Tubes):
       - Function: Conduct ova from the ovary to either the uterine horn or the uterus, which varies by species.

  4. Uterus:
       - Description: Its presence or absence varies according to species, particularly in monolocous/uniparous animals (those giving birth to one embryo at a time).
       - Function: Embryos develop in the body of the uterus.
         - In polytocous/multiparous animals, such as dogs and cats, embryos develop in the uterine horns.

  5. Cervix:
       - Function: An opening to the uterus that serves as a muscular sphincter.
       - Note: Some species have a double cervix (e.g., rabbits).

  6. Vagina (Birth Canal):
       - Description: A tube extending from the cervix to the urethral opening.
       - Composition: Composed of muscular folds lined with mucus-producing glands.

  7. Vestibule:
       - Description: The entrance into the vagina, located between the labia and the vagina.
       - Contains: Urethral orifice and clitoris.

  8. Clitoris:
       - Location: Positioned on the floor of the vaginal vestibule in most mammals.
       - Description: The female equivalent of a penis, it contains erectile tissue, a glans, and many nerve endings, with a larger structure that extends into the labia.

  9. Hymen:
       - Description: A thin membrane that may partially cover the vaginal opening in some species.
       - Note: It may stretch or tear with intercourse or remain until parturition (e.g., elephants).

  10. Vulva:
        - Description: The external genital organ that includes the visible portion from the exterior.
        - Function: Many female animals have a common urogenital pathway.

Histological Layers

  1. Endometrium:
       - Description: Internal layer composed of epithelial cells, connective tissue, and glands.
       - Function: Varies in thickness during the reproductive cycle, reabsorbed in animals with an estrous cycle, and sloughed in those with a menstrual cycle.

  2. Myometrium:
       - Description: Composed of smooth muscle.

  3. Perimetrium:
       - Description: A serous outer covering that is continuous with the peritoneum.

Major Functions of the Female Reproductive System

  1. Oogenesis:
       - Function: The production of haploid germ cells (ova).

  2. Fertilization:
       - Definition: The union of the spermatozoa with the egg.

  3. Gestation (Implantation/Placentation):
       - Definition: The development of the embryo/fetus in the uterus, involving the attachment of the developing embryo to the uterine wall and the development of the placenta.

  4. Parturition:
       - Definition: The delivery of a fetus.

  5. Lactation:
       - Function: The development of mammary glands with the production of milk.

  6. Hormonal Influence on Reproductive Behaviours:
       - Description: Hormones fluctuate with the stage of the estrous cycle or pregnancy.

Ovarian Function

  1. Cytogenic:
       - Description: Develop oocytes (haploid germ cells) on a regular basis.
       - Detail: The maximum number present at birth can be in the millions.

  2. Endocrine:
       - Function: Produce a variety of hormones that are released into the bloodstream, responsible for physical and psychological reproductive behaviour.

Blood Supply

  1. Ovaries and Oviducts:
       - Supplied by the ovarian artery.

  2. Uterus:
       - Cranial Uterus: Supplied by the luteinizing branch of the ovarian artery.
       - Middle Uterus: Supplied by the middle uterine artery.
       - Caudal Uterus: Supplied by the branch of the vaginal artery.

Estrous Cycle Definitions

  1. Estrous (adjective) vs. Estrus (noun):
       - Definition of Estrous cycle: The interval from the beginning of one heat period (estrus) of sexual receptivity to the beginning of the next, describing the cycle.
       - Definition of Estrus: Refers to a particular hormonal stage of the estrous cycle.

Stages of the Estrous Cycle

  1. Follicular Phase:
       - Proestrus:
         - Definition: Period of preparation.
         - Under the influence of Follicle Stimulating Hormone (FSH) from the pituitary, reproductive tissue builds up, leading to new ovarian follicles growing and the release of estrogen.
       - Estrus:
         - Definition: True "standing heat"; the period of sexual receptivity when breeding occurs, and the uterus is prepared to receive an embryo.
         - Terminology: More estrogen is secreted during this phase, with the release of Luteinizing Hormone (LH) from the pituitary triggering ovulation.
         - Note: Spontaneous ovulators (e.g., cats, rabbits) only ovulate when bred, resulting in a longer estrus if not bred.
         - Dogs experience a bloody discharge during late proestrus into early estrus (diapedesis).
         - Cats exhibit behavioral changes during estrus, such as rubbing, lordosis, and vocalization, until ovulation is stimulated.

  2. Luteal Phase:
       - Metestrus/Diestrus:
         - Definition: The postovulatory phase where corpus hemorrhagicum develops after ovulation.
         - Each ruptured follicle transitions into a corpus luteum (CL), which inhibits the development of new follicles.
         - If pregnancy does not occur, the corpus luteum degenerates, and some species can display pseudopregnancy, entering a resting phase known as anestrus.
         - If pregnancy occurs, the corpus luteum continues to secrete hormones, with different species exhibiting varying durations of secretions.
       - Anestrus:
         - Description: A long period of reproductive inactivity in seasonally polyestrous animals or a period of least reproductive activity.

Types of Estrous Cycles

  1. Monestrous Cycles:
       - Description: Usually one cycle per year, typical in seasonal breeders such as minks and bears.

  2. Diestrous Cycles:
       - Description: Cycles occurring in spring and fall, as seen in dogs.

  3. Polyestrous Cycles:
       - Description: More than one estrous cycle per year; specific examples include pigs.
       - Seasonally Polyestrous:
         - Definition: Cycle continuously in specific seasons, as seen in cats, horses, and sheep.

Types of Ovulators

  1. Reflex/Induced Ovulators:
       - Definition: Ovulate only after mating, found in felines, rabbits, ferrets, and camelids.

  2. Spontaneous Ovulators:
       - Definition: Ovulation occurs naturally regardless of coitus. Examples include dogs, pigs, cows, horses, and humans.

Estrous Cycle of Pig/Cow

  • Overall cycle: 21 days

  • Proestrus: Lasts 4 days, stimulated by FSH with 4 follicles developing.

  • Estrus: In cows, lasts 1 day; in pigs, lasts 2 days.

  • Metestrus: Lasts 2-3 days.

  • Diestrus: Lasts approximately 12-13 days.

Female Reproductive Hormones

  1. Hypothalamus:
       - Secretes Gonadotropin-Releasing Hormone (GnRH).
       - Function: Controls the secretion of other hormones from the pituitary gland.

  2. Pituitary Hormones:
       - Produced in the anterior lobe of the pituitary gland.
       - Follicle Stimulating Hormone (FSH):
         - Function: Promotes follicle growth and estrogen production.
       - Luteinizing Hormone (LH):
         - Function: Induces maturation of the follicle, ovulation, and stimulates corpus luteum formation along with progesterone production level spikes just prior to ovulation.
       - Prolactin:
         - Description: A luteotrophic hormone responsible for milk synthesis and development of the mammary gland.

  3. Ovarian Hormones:
       - Produced by the ovaries, typically in response to the levels of pituitary hormones.
       - Estrogen: Includes estradiol, estriol, and estrone, involved in the manifestation of mating behaviour, cyclic changes in the female reproductive tract, and development of secondary female sex characteristics.
       - Levels of estrogen peak during estrus, and when present, the corpus luteum of the ovary produces progesterone.

  4. Progesterone:
       - Function: Maintains pregnancy, increases thickness of the uterine lining, promotes development of glands in the uterine wall, and stimulates the development of the alveoli in the mammary gland.

  5. Ovarian Placental Hormones:
       - When present, both the corpus luteum and the placenta produce relaxin.
       - Relaxin:
         - Function: Causes relaxation of pelvic ligaments and the cervix, preparing the body for birth.

Summary of Hormonal Sequencing

  1. Pituitary: FSH, LH, prolactin

  2. Ovaries: Estrogen
       - a. Corpus luteum: Progesterone
       - b. Corpus luteum + placenta: Relaxin

From Ovum to Ovulation

  1. Primary Oocyte:
       - Surrounded by a single layer of cells.

  2. Secondary Oocyte:
       - Surrounded by multiple layers of cells.

  3. Tertiary Oocyte:
       - Formation of a fluid space around the oocyte.

  4. Mature Follicle:
       - A fluid-filled, mature follicle with an oocyte surrounded by gelatinous glycoprotein.

  5. Atretic Follicle:
       - Any follicle which fails to develop.

  6. Corpus Hemorrhagicum:
       - Recent ovulation site on the ovary, characterized by a blood-filled space.

  7. Corpus Luteum:
       - Mature yellow body that secretes progesterone.

  8. Corpus Albicans:
       - The old corpus luteum, forming a white scar (white body).

Fertilization to Embryo Development

  1. Zygote:
       - A fertilized egg that contains half the necessary chromosomes.

  2. Copulation/Copitus:
       - The act of mating or sexual intercourse whereby the male mounts the female and inserts his penis.

  3. Artificial Insemination (AI):
       - The placement of semen into the vagina without the presence of a male.

  4. Fertilization Process:
       - After fertilization, the cell undergoes mitotic divisions as it travels through the uterine tubes.
       - Initial divisions lead to rapid increases in cell size until a morula (too many cells to count) forms.
       - Early nourishment derives from the oviduct/uterus, after which viability during nutrient secretion ceases.

  5. Differentiation:
       - The zygote undergoes mitotic divisions, leading to cellular differentiation with the inner cell mass evolving into an embryo and the outer layer forming the embryonic sac or fetal membranes.
       - Implantation of the embryo occurs within the uterine horns or uterine wall, depending on the species.

  6. Placenta Formation:
       - This allows for the exchange of nutrients and waste products between the mother and the fetus without mixing fetal and maternal blood.

Fetal Development in Pregnancy

During the time from implantation to parturition, the developing organism is referred to as a fetus.

  • Stage 1: Ovum:
       - Represents the zygote or blastula phase from fertilization until the first signs of organ formation.

  • Stage 2: Embryo:
       - Characterized by organogenesis, the period during which organs form.

  • Stage 3: Fetus:
       - The stage of growth and completion of organ differentiation followed by parturition.
       - Specific duration examples:
         - Canine: 84 days
         - Bovine: 45 days
         - Mare: 55 days.

Fetal Membranes

  1. Chorion:
       - The outermost layer, which attaches to the endometrium externally and fuses with the outer layer of the allantois on the opposite side.

  2. Allantois:
       - A two-layered membrane that adheres externally to the chorion and internally to the amnion, creating a fluid-filled cavity known as the allantoic sac that becomes prominent during birth.

  3. Amnion:
       - Closest to the fetus, fused to the inner layer of the allantois, and filled with amniotic fluid to form the amniotic sac.

Placental Attachment

  • The type of attachment is determined by the number of tissue layers separating the mother's blood from fetal blood, with a maximum of six layers.

Types of Placental Attachment

  1. Diffuse:
       - Present in species like horses and pigs, where it attaches diffusely across the entire surface via villous structures (finger-like projections).

  2. Cotyledonary:
       - Identification in cows, sheep, and goats, involving specialized button-like structures known as placentomes.

  3. Zonary:
       - Observed in dogs and cats, indicating attachment by a narrow band around the placenta's central area.

  4. Discoid:
       - Seen in primates, including humans, with attachment via a round, single, disc-like structure.

Umbilical Cord

  1. Umbilical Arteries:
       - They carry poorly oxygenated blood from the fetus to the dam.

  2. Umbilical Veins:
       - They carry oxygenated blood from the dam to the fetus.

  3. Urachus:
       - A duct connecting the fetal urinary bladder to the allantoic sac, containing waste products.

Act of Parturition

Parturition refers to the process of birth, encompassing both physical and behavioral changes.

  1. Physical Changes:
       - Includes an enlarged abdomen, relaxation of abdominal musculature causing a dropped belly, prominence of the tailhead, expansion of the pelvic girdle due to the hormone relaxin, softening and swelling of the vulva, thick mucus seen at the vulva, enlarged mammary glands, and edema along the ventral abdomen.

  2. Behavioral Changes:
       - Include restlessness, frequent urination, and seeking seclusion.

Stages of Labour

  1. Active Phase:
       - Triggered by oxytocin secretion from the pituitary gland, initiating contractions of the uterus or uterine horns, leading to the dilation and softening of the cervix as the fetus presses against it.

  2. Delivery of the Fetus:
       - The breaking of the allantoic or amniotic sacs marks this stage (commonly known as water breaking) and results in the pushing of the fetus through the cervix and vagina to the exterior.

  3. Delivery of the Placenta:
       - After the birth of each fetus, the placenta is typically delivered within 24 hours, and it may be necessary to remove it to prevent the dam from consuming it.

Parturition Presentation

This describes how the fetus is positioned during delivery.

  1. Normal Presentation:
       - The head-first position with the head positioned between extended legs.

  2. Abnormal Presentation:
       - Tail-first or any non-standard positions; the normal position is the back of the fetus aligned with that of the dam.

Gestation Periods

Gestation refers to the length of time from fertilization to birth, varying among different species:

  • Sow: 114 days (3 months, 3 weeks, and 3 days).

  • Ewe: 148 days (5 months).

  • Cow: 285 days (approximately 9 months).

  • Mare: 336 days (approximately 11 months).

  • Bitch (female dog): 63 days (approximately 2 months).

  • Queen (female cat): 56-63 days (approximately 2 months).

  • Rabbit Doe: 30 days.