Lecture 19 - Reproductive Tract Development PDF

DEVELOPMENT OF REPRODUCTIVE TRACTS Thomas Wilson Graphics from Grant’s Method of Anatomy, Netters Atlas of Human Embryology, Larsen’s Anatomy, Human Embryology and Developmental Biology, Moore’s Before We Are Born, Analysis of Vertebrate Structure, McMinn’s & Abrahams Clinical Atlas of Anatomy, Hum...

DEVELOPMENT OF REPRODUCTIVE TRACTS Thomas Wilson Graphics from Grant’s Method of Anatomy, Netters Atlas of Human Embryology, Larsen’s Anatomy, Human Embryology and Developmental Biology, Moore’s Before We Are Born, Analysis of Vertebrate Structure, McMinn’s & Abrahams Clinical Atlas of Anatomy, Human Anatomy Colour Atlas & Textbook [email protected] Goal: Why are there peculiar differences between the reproductive tracts? Outline: Outcomes: Describe the process of urogenital development in the male and Development of the gonads female, including external genitalia, relating the gonadal and tubular migrations to the adult anatomy. Development of the genital Describe the migration and differentiation of primordial germ cells tracts and somatic support cells of the urogenital ridge, in both males and females. How they’re sexually dimorphic Identify and describe the connections of the related ligaments, which accompany urogenital development Result of development Begin to understand how a person could develop a Disorder of Sexual Development, from a morphological standpoint. Development of the gonad 3wks 5wks Comprises 2 tissue types: 1. Primordial germ cells (PGC)  Gametes 2. Mesenchyme  Stroma of gonad PGC from yolk sac Chromosomal and genetic sex lineage is already set ~6wk migrated into dorsal body wall mesenchyme (IMM) Somatic support cells differentiate and proliferate Induced by overlying coelomic epithelial cells (~T10) Initially forms an ‘indifferent’ gonad Morphologically indifferent 6wks PGC  Gamete Mesenchyme  stroma Male Spermatogonia Sertoli & Leydig cells Female Oogonia Follicle (granulosa) & thecal cells Gonadal differentiation SRY expression in somatic support cells  Sertoli cells form cords of the testis and enclose PGC  spermatogonia Surrounding mesenchyme forms tunica albuginea Cords become seminiferous tubules (at puberty)  rete testis Maintains connection to mesonephric tubules Leydig cells different from mesenchyme ~9-10wks Secrete testosterone under influence hCG not LH, as in the adult Induces mesonephric duct development Sertoli cells produce Anti-Mullerian Hormone (AMH) Supresses paramesonephric duct system No SRY-gene: PGC  Oogonia  Primary oocyte & enter meiosis 1 Support cells differentiate into follicle cells (induced by oocyte) Follicle cells surround the oocyte to form a primordial follicle Loss of mesonephric tubule connections Development of genital ducts Gonads of primitive vertebrates release eggs & sperm directly into the coelomic cavity Pass through pores into the cloaca Male: Mesonephric duct and ductules Adjacent to genital ridge  Indifferent gonad Morphological differences emerge between 10-13 weeks Mesonephros (not duct) is regressing at this point Urinary component Female: Para-mesonephric duct appears ~6wks (AKA Műllerian duct) Formed by the coelom folding in on itself (B ) A specialised cloacal pore Note that mesonephros and duct, paramesonephric duct, gonad, and metanephric duct coexist at this time Female genital ducts Mesonephric duct degenerates ‘completely’ in females Eggs of higher vertebrates still released into peritoneal cavity Human: Closely adjacent to a developing specialised ‘cloacal pore’ Uterine tube remains open to peritoneal cavity: Mechanism for ectopic pregnancy Para-mesonephric duct gives rise to: Uterine tubes Ducts fuse caudally to form uterus, & cervix Paramesonephric duct never had a tubular connection to mesonephros Fold in the coelom that connects to the urogenital sinus Hence, uterine tubes and uterus are derived from lateral plate mesoderm components: Most of Urethra Vagina (?) (sinusal tubercle  vaginal plate  caudal growth & canalisation) Paraurethral gland Greater vestibular gland Variations in caudal paramesonephric fusion Male genital ducts Sperm of higher vertebrates is NOT released into a cavity Paramesonephric duct disintegrates in males Male reproductive tract is connected to the distal urinary system Mesonephric duct originally drained urine into cloaca  urogenital sinus Urinary function now replaced by metanephric duct Growth of urogenital septum: Mesonephric duct remains connected to the bladder, but grows caudally towards urethra Gives rise to: (from IMM) Efferent ductules  Epididymis  Vas deferens  Seminal vesicles  ejaculatory ducts components: Urethra Most of prostate (glandular part) Surrounding SM and CT from mesenchyme Bulbourethral gland Surrounding SM and CT from mesenchyme Descent of the gonads Gonads develop in upper abdomen in both sexes Gubernaculum (governor):Fibrous cord attached to labioscrotal fold & caudal pole of the gonad Fetus grows and ‘Cord draws gonad caudally’ Ligamentous remnants: Males: Testis is drawn through the inguinal canal creating the scrotum Held in scrotum by  Scrotal lig. Male gonads external because no paramesonephric duct to get in the way Descent of the gonads Ligamentous remnants: Females: 2 remnants Uterus grows into the path of the gubernaculum  Lig. of Ovary ‘Traps’ the gonad internally Caudal end still dragged through inguinal canal  Round lig. AKA Lig. Teres Suspensory lig of ovary: a mesenteric ligament Ovary is ‘intra-peritoneal’ Continuous with the cranial pole of the gonad  continues into broad ligament Formation of external genitalia From week 5: Cloacal urogenital sinus develops Separated from anus Top: Genital tubercle (body of erectile tissue) Bottom: Urethral fold Before week 9: indifferent Males: Genital tubercle elongates (forms the phallus) Urethral folds close to form a penile urethra Labioscrotal swells into a scrotum and accepts the descending testicles Females: Tubercle does not lengthen & urethral folds do not close Results in short clitoral body and labia minora Open to both urethra and vagina (eventually) Cloacal septation completed by week 12 Females have urethral, vaginal, and anal openings Scrotal heat exchange: Sperm viability is temperature dependent 1. Dartos muscle: Smooth muscle under autonomic control Contraction wrinkles the scrotum = …. 2. Counter-current heat exchange Paramesonephric duct disintegrates in males…. Persistent Müllerian Duct Syndrome XY person with testes Has a cervix, uterus, and uterine tubes, as well as normal male mesonephric ducts mesonephric gonad tube D * N - para-mesonephric tube