Embryo Flashcards
Where does the indifferent gonad develop from?
Intermediate mesoderm
- along posterior wall of abdominal cavity
The primordial germ cells arise from ________________ then migrate ____________ to arrive at __________.
From wall of yolk sac close to allantois
Migrate along dorsal mesentery of hindgut
Arrive @ primitive gonads in wk5
Invade gonadal ridge in wk6
Indifferent gonads appear initially as longitudinal gonadal ridges before the epithelium penetrates the mesenchyme to form ______________, which connect to the ___________.
Epithelium penetrate mesenchyme → sex cords → connected to surface epithelium
How far in embryological development do male and female characteristic form?
7th week
Describe the formation of the testes in an embryo.
1) Under SRY gene influence, primitive sex cords proliferate and penetrate deep into medulla
2) Become horseshoe-shaped in 4th month
3) Cords near testes hilum break up → form network (Rete testes)
True or false:
The testes cords are solid throughout childhood/infancy.
True.
At puberty, solid testes cords acquire lumen → seminiferous tubules
What is the embryological origin of Sertoli cells?
Gonadal surface epithelium
What is the embryological origin of Leydig cells?
Mesenchyme of gonadal ridge
Leydig cell develop from ____________ shortly after onset of ___________ but only produce testosterone from _________ onwards.
From mesenchyme of gonadal ridge
shortly after onset of testis cord differentiation
produce testosterone 8th week onwards
What do the abdominal structures that are brought down during the descent of the testis form?
1) Processes vaginalis → parietal and visceral tunica vaginalis
2) Transversalis fascia → Internal spermatic fascia
3) Internal oblique muscle → cremasteric fascia and muscle
4) External oblique muscle → external spermatic fascia
What are the 4 controlling factors for the descent of the testes?
1) Outgrowth and regression of gubernaculum
2) ↑intra-abdominal pressure due to organ growth
3) Androgens
4) Mullerian inhibiting substances
What is a congenital inguinal hernia?
Descent of intestinal loops into scrotum
What does an unobliterated processes vaginalis result in?
Communicating hydrocele
What are the 2 pairs of indifferent genital ducts?
1) Mesonephric (Wolffian) ducts
2) Paramesonephric (Mullerian) ducts
What are 3 factors that influence the development of indifferent genital ducts?
1) Androgens (testosterone, DHT)
2) Oestrogens
3) Anti-mullerian hormone (mullerian inhibiting substance)
What are the structures that form the mesonephric duct and how are they formed?
1) Epididymis
- mesonephric ducts elongate and become highly convoluted
2) Ductus deferens
- from tail of epididymis to seminar vesicles
- ducts obtain thick muscular coat
3) Ejaculatory ducts
- from beyond seminar vesicles
What are the structures that arise from the cloaca?
1) Urinary bladder
2) Anal canal
Describe how the cloacal/urogenital folds develop into the urethral and anal folds.
1) Cranial to caudal membrane unite → genital tubercle
2) Caudally: Cloacal membrane subdivides into urogenital and anal membranes @ wk6 → urethral and anal folds
During the development of male external genitalia, the genital swellings are separated by ______________
Scrotal septum
Describe the development of the male external genitalia.
Rapid elongation of genital tubercle
→ pull urethral folds forward
→ form urethral groove
- extends along caudal aspect of elongated phallus
- lined by endodermal cells → form urethral plate
- urethral folds close over urethral plate → penile urethra (end of 3rd mth)
What is hypospadias?
Opening of penile urethra is located on the underside/along shaft of the penis
- due to incomplete closure of urethral folds over urethral plate
Describe the formation of the ovary from indifferent sex cords.
1) Primitive sex cords dissociate into irregular cell clusters → occupy ovary medulla
2) Primitive germ cells replaced by vascular stroma → ovarian medulla
3) Surface epithelium of female gonad proliferates → cortical/secondary cords @ wk7
What are the structures that are formed by the cortical/secondary cords in an ovary?
1) Penetrate underlying mesenchyme
2) Split into isolated cell clustered & surround primitive germ cells
3) Germ cells form oogonia
4) Surrounding epithelial cells → follicular cells
Where does the paramesonephric/Mullerian ducts that form the main female genital ductal system arise from?
Longitudinal invagination of epithelium on anterolateral surface of urogenital ridge
What are the structures that arise from the paramesonephric ducts?
1) Uterine tubes
2) Uterus
3) Upper part of vagina
What are the 3 parts of the paramesonephric duct and what do they form?
1) Cranial vertical part
- opens into abdominal cavity w funnel-like structure
- fimbriae
2) Horizontal part
- broad ligament of uterus
- divides pelvic cavity into uterorectal & uterovesical pouches
3) Caudal vertical part
- contact opposite paramesonephric duct in midline
- caudal tip projects into posterior wall of urogenital sinus
- sinus separated by septum fuse → uterus and cervix
Where does the myometrium arise from?
Surrounding mesenchyme of paramesonephric duct
Where does the perimetrium arise from?
Peritoneal covering of paramesonephric duct
What are the 2 origins of the vagina?
Upper: paramesonephric/mullerian ducts
Lower: Urogenital sinus
How do the upper and lower parts of the vagina form 1 continuous lumen?
1) Sinovaginal bulbs from pelvic part of urogenital sinus proliferate to form solid vaginal plate
2) Completely canalise by 5th mth → lower part of vagina
3) Lumen separated from urogenital sinus by hymen
What happens if the 2 paramesonephric ducts do not fuse?
Double uterus
What causes a “rudimentary horn” in the uterus of a young px?
Underdevelopment of 1 of the paramesonephric ducts
Describe the development of the female external genitalia.
1) Genital tubercle elongates slightly → Clitoris
2) Urethral folds → Labia minora
3) Genital swellings enlarge → Labia majora
4) Urogenital groove remains open → form vestibule
What is a possible genital presentation of congenital adrenal hyperplasia in a female?
Development of male external genitalia
- elongation of penile tubercle
- formation of scrotum
