Lec 2 | Female Reproductive Embryology PDF

EMBRYOLOGY FEMALE REPRODUCTIVE SYSTEM REPRODUCTIVE MODULE BY: Dr. Mohammed Emad MBChB, MSc, PhD (ANAT,HISTO,EMBRYO) I- THE INDIFFERENT EMBRYO At fertilization, the genotype of the embryo is established (46, XX or 46, XY) During weeks 1–6, the embryo remains in a sexually indif...

EMBRYOLOGY FEMALE REPRODUCTIVE SYSTEM REPRODUCTIVE MODULE BY: Dr. Mohammed Emad MBChB, MSc, PhD (ANAT,HISTO,EMBRYO) I- THE INDIFFERENT EMBRYO At fertilization, the genotype of the embryo is established (46, XX or 46, XY) During weeks 1–6, the embryo remains in a sexually indifferent or undifferentiated stage.(This means= genetically female embryos and genetically male embryos are phenotypically indistinguishable.) During week 7, the indifferent embryo begins phenotypic sexual differentiation. By week 12, female or male characteristics of the external genitalia can be recognized. By week 20, phenotypic differentiation is complete. And is determined by the SRY gene (sex-determining region Y) and may result in individuals with a female phenotype, an intersex phenotype, or a male phenotype. The SRY gene on chromosome Yp11.3 encodes for a sex-determining region Y protein (also called testes-determining factor [TDF]) As the indifferent gonad develops into the testes, Leydig cells differentiate to produce testosterone and Sertoli cells differentiate to produce Müllerian-inhibiting factor (MIF). Differentiate to Leyding produce cells testosterone Differentiate to Sertoli produce MIF cells  In the presence of TDF, testosterone, and MIF, the indifferent embryo will be directed to the male phenotype. In the absence of TDF, testosterone, and MIF, the indifferent embryo will be directed to the female phenotype. testesteron TDF testes e MIF Components of the indifferent embryo gonads, genital ducts, and primordia of external genitalia. Phenotypic sexual differentiation occurs in a sequence beginning with the gonads, then the genital ducts, and finally the primordia of external genitalia. GONADS GENITAL DUCTSPRIMORDIA OF THE EXTERNAL GENITALIA II- DEVELOPMENT OF THE GONADS A- THE OVARY: The intermediate mesoderm forms a longitudinal elevation along the dorsal body wall, the urogenital ridge. The coelomic epithelium and underlying mesoderm of the urogenital ridge proliferate to form the gonadal ridge. Primary sex cords develop from the gonadal ridge and incorporate primordial germ cells (XX genotype), which migrate into the gonad from the wall of the yolk sac.(The primordial germ cells originate from the epiblast in week 2 of development and then migrate into the endoderm and mesoderm layers of the yolk sac.)  Primary sex cords extend into the medulla and develop into the rete ovarii, which eventually degenerates. Later, secondary sex cords develop and incorporate primordial germ cells as a thin tunica albuginea forms. The secondary sex cords break apart and form isolated cell clusters called primordial follicles, which contain primary oocytes surrounded by a layer of simple squamous cells. The primary oocytes are derived from primordial germ cells. Whereas, the simple squamous cells of the primordial follicle and the ovarian connective tissue stroma are derived from mesoderm. primordial Primary sex secondary sex follicles: urogenital ridge. gonadal ridge. cords cords PRIMARY OOCYTES B- RELATIVE DESCENT OF THE OVARIES The ovaries originally develop within the abdomen but later undergo a relative descent into the pelvis as a result of disproportionate growth of the upper abdominal region away from the pelvic region. Other factors: gubernaculum: is a band of fibrous tissue along the posterior wall that extends from the medial pole of the ovary to the uterus at the junction of the uterine tubes, forming the ovarian ligament. The gubernaculum then continues into the labia majora, forming the round ligament of the uterus. The peritoneum evaginates alongside the gubernaculum to form the processus vaginalis, which is obliterated in the female later in development. III- DEVELOPMENT OF THE GENITAL DUCTS 1- Paramesonephric (Müllerian) ducts: develop as mesodermal invaginations of the lateral surface of the urogenital ridge. The cranial portions of the paramesonephric ducts develop into the uterine tubes. The caudal portions fuse in the midline to form the uterovaginal primordium, and thereby bring together two peritoneal folds called the broad ligament  The uterovaginal primordium develops into the uterus, cervix, and superior one third of the vagina. The paramesonephric ducts project into the dorsal wall of the cloaca and induce the formation of the sinovaginal bulbs. The sinovaginal bulbs fuse to form the solid vaginal plate, which canalizes and develops into the inferior two thirds of the vagina. Although the vagina has a dual origin, BUT the epithelial lining of the entire vagina is of endodermal origin. CRANIAL UTERINE TUBES PORTION Paramesonephric (Müllerian) ducts uterovaginal uterus, cervix, primordium superior 1/3 of (BROAD LIG) the vagina CAUDAL cloaca induced by inferior 2/3 of the vaginal plate sinovaginal bulbs. vagina 2- MESONEPHRIC (WOLFFIAN) DUCTS: develop in the female as part of the urinary system because these ducts are critical in the formation of the definitive metanephric kidney. However, they degenerate in the female after formation of the metanephric kidney. 3- VESTIGEAL REMNENTS:CYSTS FORMATION: hydatid cyst of Morgagni (1) (remnant of the paramesonephric duct). Kobelt cyst (2) (remnant of the mesonephric duct) cyst of the epoophoron (3) (remnant of the mesonephric tubules). cyst of the paroophoron (4) (remnant of the mesonephric tubules). Gartner duct cyst (5) (remnant of the mesonephric duct). IV- DEVELOPMENT OF THE PRIMORDIA OF THE EXTERNAL GENITALIA: A proliferation of mesoderm around the cloacal membrane causes the overlying ectoderm to rise up so that three structures are visible externally: the phallus, urogenital folds, and labioscrotal swellings. 1. The phallus forms the clitoris (glans clitoris, corpora cavernosa clitoris, and vestibular bulbs). 2. The urogenital folds form the labia minora. 3. The labioscrotal swellings form the labia majora and mons pubis. 5 WEEKS AT BIRTH