Embryology of the Reproductive Tract Flashcards
What does gastrulation lead to?
Formation of the trilaminar disc
What occurs in gastrulation?
Invagination of the epiblast cells through the primitive streak to form the definitive endoderm and mesoderm
How is the mesoderm organised?
Into 3 main groups = paraxial, intermediate and lateral plate
What is special about the urogenital system?
Made from two functionally distinct systems which are developmentally and anatomically interwoven
What do the urinary and genital systems arise from?
The intermediate mesoderm
Where do the excretory ducts of the urogenital system enter?
A common cavity called the cloaca
What happens to the primordial germ cells in weeks 4-6?
Primordial germ cells within the yolk sac migrate via dorsal mesentery to the intermediate mesoderm
How are the genital ridges formed?
From the proliferation and thickening of the coelomic epithelium
How are the primitive sex cords formed?
The proliferating coelomic epithelium forms somatic support cells which envelop primordial germ cells
What happens in the bipotential phase?
Development of the genital ducts = mesonephric (Wolffian) and paramesonephric (Mullerian) ducts
Where do both genital ducts connect to?
The posterior wall of the urogenital sinus
What makes up the bipotential phase?
Genital ducts and indifferent gonads
When does sexual differentiation occur?
From week 7 onwards
What triggers development of the male genital system?
Presence of SRY transcription factor
What do somatic support cells develop into in males?
Sertoli cells
What do the primary sex cords form in males?
Testis/medullary cords = engulf the primordial germ cells
What do the rete testis connect?
The mesonephric tubules to the testis cords
What is the tunica albuginea?
Thickened layer of connective tissue between the coelomic epithelium and testis cords
What do sertoli cells secrete?
Anti-Mullerian hormone = causes degeneration of the paramesonephric (Mullerian) duct
What stimulates gonadal ridge cells to form leydig cells?
Sertoli cells
What do leydig cells produce?
Testosterone = induces formation of epididymis, vas deferens and seminal vesicle
What does dihydrotestosterone induce?
Development of male specific external genitalia and prostate
What causes persistent Mullerian duct syndrome?
Mutations of AMH or AMH receptor genes = Mullerian ducts fail to regress
How does persistent Mullerian duct syndrome present?
Present with uterus, vagina and uterine tubes
Testes are in ovarian location
Have male external genitalia
Where do the testes originate before they descend?
Originate at 10th thoracic level and are pulled caudally by the gubernaculum
What is cryptorchidism?
Failure of one or both testes to descend
What causes development of female genital system?
Absence of SRY transcription factor
What do germ cells differentiate into in females?
Oogonia and then into primary oocytes
What do somatic support cells differentiation into in females?
Granulosa cells which then go on to surround the primary oocytes = forms primordial follicles and thecal cells
What forms the primordial follicles and thecal cells?
Female gonad
What do influences of the ovarian oestrogens and from maternal sources stimulate?
Formation of the female external genitalia and development of the paramesonephric (Wolffian) ducts
What do the Mullerian ducts give rise to in females?
Uterine tubes, uterus and superior vagina
What are the three parts of the Mullerian duct?
Cranial portion = opens into coelomic cavity
Horizontal portion = crosses mesonephric duct
Caudal portion = fuses with Mullerian duct on opposite side
What forms the uterovaginal canal?
Fused caudal portion of the Mullerian ducts = gives rise to uterus and superior vagina
How is the vaginal lumen created?
By vacuolisation of the Mullerian portion of the vagina and the sinuvaginal bulbs = produces the fornices
What are some abnormalities of the female genital system?
Double uterus and double vagina
Double uterus, bicornate uterus or septated uterus
Unicornate uterus or cervical atresia
What is the indifferent stage of external genitalia development?
Between week 4-7 the external genitalia are indistinguishable
How does the spongy urethral form?
By proximal to distal zipping of urethral groove
What is present at the tip of the glans?
Ectodermal ingrowth which meets the spongy urethra
How is the foreskin formed?
By circular ingrowth of ectoderm around the periphery of the glans = occurs in week 12
What is hypospadias?
External urethral opening lies in abnormal position along ventral aspect of penis = occurs with varying degrees of severity
