Female Anatomy and Gametogenesis

ROSS UNIVERSITY SCHOOL OF VETERINARY MEDICINE

Female Anatomy and Gametogenesis

  • Major structures involved in female reproductive anatomy:

    • Vagina

    • Fornix vagina

    • Oviduct (also known as uterine tube)

    • Cervix

    • Bladder

    • Ovary

  • Structure of the ovary includes:

    • Tunica Albuginea

    • Surface (germinal) epithelium

    • Ovarian follicles:

    • Developing antral (tertiary) follicle

    • Secondary follicle

    • Primary follicle

    • Antral (dominant) follicle

    • Ovary cortical features:

    • Cortex

    • Medulla

    • Zona Pallucida

    • Granulosa cells

    • Theca Interna and Theca Externa

    • Hilus

    • Primordial follicles

    • Uterine Horn caruncles

Embryology: Sex Differentiation

  • Hypothalamus difference between male and female:

    • The female hypothalamus has two functional areas for the secretion of Gonadotropin-releasing hormone (GnRH):

    • Tonic center: Located in the arcuate/ventromedial region (ARC)

    • Surge center: Located in the preoptic area (POA)

  • The hypothalamus is inherently female, but testosterone during development:

    • “Defeminizes” the brain: Testosterone crosses the blood-brain barrier and is converted to Estradiol.

    • Estradiol roles: Defeminizes the hypothalamus, leading to the elimination of the surge center.

  • Fetal ovaries produce Estradiol, which is unable to cross the blood-brain barrier since it is bound to alpha-fetoprotein (αFP) which disappears rapidly after birth.

Freemartinism

  • Definition: A condition arising in bovine and sometimes other species when male and female co-twins experience:

    • Early fusion of placental circulation:

    • Anti-Mullerian Hormone (AMH) from the male is transferred to the female, leading to the regression of the paramesonephric (Mullerian) ducts.

    • Results in vestigial development of the vagina, cervix, uterus, and uterine tubes (mesoderm).

    • Formation of almost normal vulva and vestibulum derived from the urogenital sinus (ectoderm).

Fetal Maturation

  • The fetal stage is characterized by rapid growth and maturation of previously developed organs from the embryonic stage:

    • Gonads location:

    • In males: Testes descend into the scrotum, bringing two layers of peritoneum.

    • In females: Development of Broad ligament with ovaries migrating caudally due to fetal growth.

    • Metanephros: Enlarges and migrates cranially, impacting gonadal positioning within 6-9 weeks.

Testicular Descent Mechanism

  • Dilation of the inguinal canal involves two layers of peritoneum:

    • Visceral vaginal tunic

    • Parietal vaginal tunic

  • Inguinoscrotal phase:

    • Thickening of gubernaculum and increased abdominal pressure causes testicular descent through two phases:

    • Transabdominal phase

    • Retroperitoneal position: Upper layer attached to the diaphragm by the cranial suspensory ligament (CSL).

  • Testosterone causes degenerative processes in CSL, while Insulin-like hormone 3 (INSL3) influences gubernacular thickening.

    • INSL3 is produced by Leydig cells.

Vestigial Remnants in Females

  • Gubernaculum has two vestigial remnants in females:

    • Ovarian ligament

    • Round ligament of the uterus (ligamentum teres uteri):

    • These structures provide support for the ovaries and uterus.

Ectodermal vs. Mesodermal Structures

  • Ectoderm functions include fusion of paramesonephric ducts and development of the broad ligament, with the hymen membrane originating from the ectoderm.

External and Internal Genitalia

  • External genitalia: Vulva, mammary glands.

  • Internal genitalia:

    • Vestibule and vagina

    • Uterus (body and horns)

    • Oviduct

    • Ovaries

Clinical Applications Related to Female Anatomy

  • Functionality in terms of sperm propulsion and oocyte movement during embryonic development and parturition is critical:

    • Sperm propelled cranially, and embryos/fetuses propelled caudally.

    • Uterine residency during development and expulsion of fetal membranes (lochia) occurs caudally.

Vulva Description and Common Problems

  • Vulva Characteristics:

    • Size and position (vertical); must maintain a tight seal to prevent foreign material entry.

  • Common Problems:

    • Perineal conformation issues, perineal lacerations, pneumovagina in mares, and tumors.

Reproductive Tract Positioning

  • The reproductive tract lies directly beneath the rectum in all reproductive species.

  • Surrounded by peritoneum continuous with the broad ligament:

    • Identified components:

    • BL = broad ligament

    • IlC = intercornual ligament

    • UH = uterine horn

    • O = ovary

    • OD = oviduct

    • R = rectum

Cervical Anatomy and Differences Among Species

  • Each reproductive species presents unique cervical structures:

    • Mares: Muscular layer with longitudinal folds; lack transverse cervical rings.

    • Cows/Ewes/Doe: Presence of cervical rings and a cartilaginous cervix.

    • Sow: Long corkscrew-shaped cervix.

    • Bitch: Firm tube-like sphincter with connective tissue and muscle.

  • The cervix performs critical anatomical roles and changes with reproductive cycle stages (estrus vs. diestrus vs. anestrus). It produces:

    • Thin mucus as a lubricant during estrus, thick mucus to occlude cervical lumen during diestrus and pregnancy.

Intrauterine Insemination Techniques

  • Involves laparoscopic or endoscopic insemination due to anatomical challenges:

    • Several cervical folds complicate the passage during standard artificial insemination (AI) procedures with frozen semen.

    • Manipulation of cervical rings is necessary for guiding passage of the insemination gun/pipette.

Uterus Conformation and Functionality

  • Composed of two horns and a singular body, the uterus functions primarily as:

    • The site of implantation and gestation.

  • Structure:

    • Layers:

    • Serosa

    • Myometrium

    • Endometrium

  • The uterine lumen plays a crucial role in reproductive processes.

Oviduct Description

  • Oviduct Functionality: Connects ovary to uterus; primary sites for fertilization and early embryo development. Contains:

    • Three parts: Infundibulum, Ampulla, and Isthmus

    • Ciliated epithelium aids in movement of both ovum and sperm.

  • Oviductal papilla: Plays a role in sperm reservoir and selection of morphologically normal sperm crucial for reproductive processes in equids.

Ovaries in Female Anatomy

  • Size Variability: Ovaries differ in size among species and are attached to the broad ligament (mesovarium).

  • Positioning and morphological traits: Located in the sublumbar area, occupy a caudally ventral placement in the pelvis for ruminants.

Equine Ovaries Structure

  • Distinctive features of equine ovaries:

    • “Inside-out” configuration with medullary zone superficial and cortical zone internal.

  • Identification of:

    • Ovulation fossa and Ovarian artery; larger size in mares.

Mammary Gland (Udder) Description

  • Importance of the mammary gland: often overlooked but crucial post-foaling. Common problems include:

    • Abnormalities such as lacerations, tumors, mastitis, and agalactia.

Gametogenesis Overview

  • Spermatogenesis vs. Oogenesis:

    • Overview of spermatogonial (2N) and oogonial (2N) processes involving meiosis locations and pathways.

  • Oocyte Development Stages:

    • Arrested at prophase I; majority of mammals are born with primary oocytes at this stage.

    • Postnatal events lead to resolution at the time of fertilization.

Oocyte and Follicle Development

  • Folliculogenesis: Primordial follicles develop with primary oocytes surrounded by varying layers of follicular cells through different stages (primary, secondary, antral/Graafian follicles). Antrum development leads to cumulus oophorus formation.

Ovulation Process

  • Defined as the release of oocyte from the follicle:

    • Cumulo mass moved into the uterine tube by fimbria.

    • Meiosis completes at the time of fertilization, with a limited fertilization window (6-12 hours).

Spermatogenesis and Testicular Development

  • Initial development in the fetal life includes:

    • Spermatogonia: initiated proliferation; diploid cells.

  • Sertoli and Leydig cells:

    • Sertoli as support cells providing hormones and forming the blood-testis barrier while Leydig provides testosterone.

Morphological Changes During Spermatogenesis

  • Essential stages as follows:

    • Morphological transitions through various types of cells—spermatogonia to primary/secondary spermatocytes, then to spermatids and finally spermatozoa.

  • Functional maturation of sperm occurs in the epididymis, leading to enhanced motility and fertilization capabilities.