Embryology Flashcards
how is the trilaminar disc formed during gastrulation?
invagination of the epiblast cells through the primitive streak to form the definitive endoderm and mesoderm
the mesoderm is organised into 3 main groups - what are these?
paraxial, intermediate and lateral plate
after gastrulation, which two types of folding occur in the embryo?
lateral folding and cranial folding
from which group of the mesoderm does the urogenital system develop?
intermediate mesoderm
*excretory ducts enter a common cavity (cloaca)
how are primitive sex cords formed within the embryo?
primordial germ cells within yolk sac migrate via dorsal mesentery to intermediate mesoderm (weeks 4-6)
coelomic epithelium proliferates and thickens to form genital ridges
proliferating epithelium will form somatic support cells with envelop the PGCs and form the primitive sex cords
what are the names of the genital ducts which connect to the posterior wall of urogenital sinus and make the ambisexual phase of development?
mesonephric (wollfian) duct
paramesonephric (mullerian) duct
at which week does sexual differentiation occur?
week 7
what triggers male development?
the presence of SRY (sex determining region of Y) transcription factor
what series of events occurs after the presence of SRY transcription factor?
somatic support cells develop into sertoli cells
primary sex cords form testis / medullary cords which engulf PGCs
rete testis connect the mesonephric tubules to the testis cords
between the coelomic epithelium and testis cords, a thickened layer of connect tissue forms the tunica albuginea
that is the role of sertoli cells in the presence of SRY protein?
secrere AMH (anti mullerian hormone) which causes degeneration of paramesonephric duct
stimulate the gonadal ridge cells to form leydig cells which produce testosterone which induces formation of epididymis, vas deferens and seminal vesicles - DHT then induces male genitalia and prostate
what causes persistent mullerian duct syndrome and how does it present?
mutations of AMH or AMH receptor genes (mullerian ducts fail to regress)
presents with:
- uterus, vagina and uterine tubes
- testes in ovarian location
- external male genitalia
where do testes originate and what pulls them caudally?
10th thoracic level
pulle caudally by gubernaculum
*failure to descend = cryptorchidism
how and when are the male accessory glands developed?
3 accessory glands spout near the junction of mesonephric duct and urethra, during week 10
prostate and bulbourethral glands form from endodermal invaginations from urethra
seminal vesicle develop from mesonephric duct
what triggers female development?
absence of SRY transcription factor
what series of events occurs in the absence of SRY transcription factor?
germ cells differentiate into oogonia and then into primary oocytes
somatic support cells differentiate into granulosa cells and surround the primary oocytes
this forms primordial follicles in the ovary
what structures do the paramesonephric (mullerian) ducts give rise to?
uterine tubes, uterus and superior vagina
*the female gonad forms primordial follicles and thecal cells (leydig homolog)
what is a gartners cyst?
remnant of mesonephric duct
what are the 3 parts of the paramesonephric (mullerian) duct?
cranial portion = opens up into coelomic cavity
horizontal portion = crosses mesonephric duct
caudal portion = fuses with paramesonephric duct on the opposite side
what gives rise to the uterovaginal canal?
the fused caudal portion of paramesonephric ducts give rise to uterus and superior vagina
how is the vaginal lumen and fornices produced?
by vacuolization of the paramesonephric portion of the vagina and the sinuvaginal bulbs
what different congenital disorders can result as dysfunction in female development?
between what weeks are the external genitalia indistinguishable?
4-7
describe the formation of the male external genitalia?
spongy urethra forms by proximal to distal zipping of urethral groove
ectodermal ingrowth at the tip of the glans penis, which meets spongy urethra
prepuce (foreskin) is formed by cicular ingrowth of ectoderm around the periphery of the glans (week 12)
what congenital disorder can result as a dysfunction in the development of the male genitalia?
hypospadias = external urethral opening lies in an abnormal position along the ventral aspect of the penis
describe the difference in female external genitalia between 5 months gestation and newborn?
