Embryology Flashcards
what is gastrulation
formation of the trilaminar disc- invagination of the epiblast cells through the primitive streak
ectoderm, mesoderm and endoderm
what are the 3 groups of mesoderm
paraaxial (axis of body), intermediate and lateral plates
what part of mesoderm forms the urogenital system
intermediate mesoderm
when does gastrulation happen
week 3
what common cavity do the urogenital system enter via the mesonephric duct
the cloaca (hindgut endoderm)
what makes up the renal system in embryos
pronephrons - not functional
mesonephrons - produce urine, arent end stage kidney
metanephrons - form the kidneys, start low in pelvis then rise up
what does the cloaca form
rectum, bladder and genitalia
how is the indifferent gonad formed
primordial germ cells within yolk sac migrate via dorsal mesentary (via allatoic stalk) into intermediate mesoderm
stimulates body epithelium to proliferate and thicken to form the genital ridges. will also form somatic support cells which envelop the PGCs
this forms primitive sex cords
what are somatic support cells
e.g. sertoli and follicular cells
what do primdorial germs cells form
gametes
what are the two primitive genital ducts
mesonephric (wollfian)
paramesonephric (mullerian)
where do the mesonephric and paramesonephric ducts connect to
the posterior wall of the urogenital sinus
when does sexual differentiation start to occur
week 7 onwards
what triggers male development in an embyro
the presence of SRY (sex determining region of Y) transcription
what do somatic support cells form in male development
develop into serotil cells which start to produce primary sex cords
what do the primary sex cords from in males
testes and medullary cords - these engulf the PGCs
what are the rete testes
connect the mesonephric tubules to the testis cords
what is the tunica albguinae
thickened layer of connective tissue between the coelomic epithelium and the testis cord
what is order of structures in the developing embryo testis
mesonephric duct- mesonephric tubules- retes testis- testis cords- tunica albuginea- epithelium
in the developing testis there is an outer cortex and inner medulla, which of these degenerates
the cortex
what is the function of sertoli cells in male development
secrete AMH (anti mullerian hormone) which causes the degeneration of the paramesonephric duct
stimulate gonadal ridge cells to form leydig cells (testosterone secreting).
- testosterone induces the formation of the epididymis, vas deferens and seminal vesicles.
- dihydrotestosterone (DHT) induces male specific external genitalia development and prostate
what causes persistent mullerian duct syndrome and what does it result in
mutation of AMH or AMH receptor gene- mullerian (paramesonephric ducts fail to regress)
present with uterus, vagina and uterine tubes, testes in ovarian location, male external genitalia
what fascilitates the descend of the testes
pulled caudally by the gubernaculum (on anterior body wall) through the inguinal canal
where do the testes start before the descend
10th thoracic level
what is cryptorchidism
failure of one/ both testes to descend
what does the vaginal pouch of the parietal peritoneum allow
the testis to protract and move
when and where do the male accessory glands start to form
sprout near the junction of the mesonephric duct and urethra during week 10
what do the prostate and bulbourethral glands form from
endodermal invaginations from the urethra
what do the seminal vesicles form from
outpouches form the mesonephric duct (intermediate mesoderm)
what stimulates femal development of an embryo
the absence of the SRY transcription factor
what do germ cells form in females
oogonia and then into primary oocytes
what do somatic support cells form in females
granulosa cells which surround the primary oocytes
what forms the primordial follicles in the ovary
the primary oocytes surrounded by the granulosa cells
what stimulates the formation of granulosa cells from somatic support cells in female embryos
germ cells
does the medulla or cortex of the indifferent gonad degenerate in females
the medulla degenerates- means you dont get ret testis/ connection to mesonephric duct
why does the paramesonephric duct remain in females
as dont get AMH from serotli cells
what is important about the anatomy of the paramesonepheric duct
is onto at top into peritoneal cavity
what does the female gonad form
primaoridal follicles and thecal cells (leydig homonlog, increases oestrogen and progesterone)
what does oestrogen stimulate in an embryo
formation of female external genitalia and development of paramesonephric ducts
what do the paramesonephric ducts form
uterine tubes and fimbria
uterus
superior vagina
what can remain in females of the mesonephric duct
epophoron and parophronon- not functional but can form cysts and adenomas
what are the three parts of the paramesonephric duct
cranial (opens to coelomic cavity)
horizontal (crosses mesonephrc duct)
caudal (fuses with paramesonephric duct on the opposite side to make uterovaginal cavity)
what is the uterovaginal canal
the fused caudal portion of the paramesonephric ducts create this= the uterus and superior vagina
what is the vaginal lumen created
vacuolisation of the paramesonephric portion of the vagina and the sinuvaginal bulbs (this also produces the fornices)
what cell origin make up vagina and cervix
bottom 2/3rds of vagina endoderm
upper 1/3rd and cervix mesoderm
what are female external genitalia distinguishable
after week 7
what cell origin forms the glans and prepuce (foreskin)
ectoderm
what is hypospadias
where external urethral opening lies in an abnormal position along the ventral aspect of the penis
urine exits this cavity
what does the genital tubercle form in both men and women
men- glans penis
women- clitoris
(these have same innervation and vascular supply)
