Embryology Flashcards
At what weeks do sexual differentiation begin and end? At what week can sex be determined?
- begins week 7
- determined by week 12
- ends week 20
What happens to primordial germ cells during week 5 of development?
end up in yolk sac due to body folding and migrate up dorsal mesentery to enter genital ridge
What happens to primordial germ cells during week 6 of development?
move into the genital ridge and stimulate cells to separate from epithelium and migrate into ridge
What do the epithelial cells that migrate into the genital ridge develop into in males and females?
- somatic support cells
- males: sertoli cells
- females: follicle cells
What does the mesonephric duct make in males?
- epididymis
- vas deferens
- seminal vesicle
- efferent ductules
- ejaculatory duct
What does the paramesonephric duct make in females?
- oviduct
- uterus
- upper vagina
What gene is considered the sex-determining gene and where is it located?
SRY gene found on the sex-determining region of the Y chromosome
In what cells is the TDF (testis determining factor) from the SRY gene expressed?
somatic support cells (pre-Sertoli)
What is the function of the sertoli cells during development?
organize seminiferous tubules and recruit mesoderm cells to differentiate into fetal Leydig cells
What causes the loss of paramesoneprhic ducts in males? When do the ducts regress?
SRY gene -> Sox9 -> anti-mullerian hormone (AMH); regression between weeks 8-10
What do the remnants of paramesonephirc ducts in males produce?
- appendix testis
- prostatic utricle
What drives the mesonephric ducts to develop and what drives it?
Leydig-derived testosterone (driven by HCG of placenta)
What 2 things are produced by sertoli cells and what do they cause?
- AMH (regression of paramesonephric ducts)
- androgen binding factor during puberty (spermatogonia -> spermatozoa)
What 2 things are produced by fetal Leydig cells?
- testosterone
- 5 a-reductase (testosterone -> dihydrotestosterone)
When do fetal Leydig cells regress?
fetal/early post natal life
What is the function of dihydrotestosterone?
development of external genitalia (penis, scrotum, and prostate)
What germ layer does the mesonephric duct and everything it develops come from?
intermediate mesoderm
Where does the prostate gland come from?
endoderm of UG sinus around week 10
What forms the bulbourethral glands?
endodermal buds
What is the urogenital plate?
endoderm-lined plate that forms after rupture of the cloacal membrane opens the phallic portion of the UG sinus to the exterior
What is the glans plate?
remnants of cloacal membrane at ventral end of the urogenital plate; adjacent to genital tubercle
What is the genital tubercle?
ectodermal-covered mesodermal swelling at ventral end of urogenital plate
What happens to the urogenital folds in males?
as the penis develops, the folds behind it close off to develop the scrotum
What shortens and becomes the anchoring L. of the testis to the scrotum?
gubernaculum
What is cryptorchidism?
failure of the testis to descend in males
What is hypospadias?
open penile urethra on ventral side of penis (failure of urogenital folds to close)
What is epispadias?
- when the urethra opens on the dorsal side of the penis - associated w/ exstrophy of bladder (bladder exposed to outside)
- due to genital tubercle developing more dorsally
What 2 genes can be expressed in the absence of the SRY gene?
- WNT-4 (pro-female)
- FOXL2 (continually suppresses SOX-9 to prevent sertoli and leydig differentiation)
What do primordial germ cells differentiate into in females?
oogonia (stem cells) -> differentiate into oocytes
What do follicle cells do to oocytes?
surround them and block them in meiosis I
Why do females retain paramesonephric ducts and lose mesonephric ducts?
- no sertoli cells -> no AMH -> paramesonephric retained
- no Leydig cells -> no testosterone -> lose mesonephric
How are the uterus and uterine tubes formed? During which weeks?
- weeks 9-10
- uterus = fusion of inferior portion of paramesonephric ducts
- uterine tubes = unfused superior portion of paramesonephric ducts
What is vaginal agenesis?
failure of normal sinovaginal bulb to develop or failed canalization of vaginal plate
What are the upper/lower portions of the vagina derived from?
upper = mesoderm lower = endoderm
What does the lack of dihydrotestosterone in females cause?
lack of lengthening of the genital tubercle and no fusion of urogenital folds or labioscrotal swellings
What forms the broad L.?
peritoneum that is dragged into the pelvic cavity by the fusing paramesonephric ducts
What do the superior/inferior portions of the gubernaculum form in females?
- superior = round L. of ovary
- inferior = round L. of uterus
What is 46, XY DSD?
genotype of male and has testis but phenotype is female
What are 4 causes of 46, XY DSD?
- inadequate testosterone synthesis
- androgen insensitivity syndrome (can’t respond to testosterone)
- 5 a-reductase deficiency
- mutations n AMH receptor
What is androgen insensitivity syndrome? What happens at puberty?
- loss of functional androgen receptors -> high testosterone but body can’t respond to it
- at puberty, testosterone -> estradiol (female secondary sex characteristics); amenorrhea due to lack of uterus
Do pts with androgen insensitivity syndrome have a uterus or testis?
will have testis in inguinal or labial regions but no uterus (produce AMH from sertoli cells so no paramesonephric system)
What is 5 a-reductase deficiency?
AR disorder in 46, XY genotype w/ underdeveloped male external genitalia (no dihydrotestosterone)
What will still develop in pt’s with 5 a-reductase deficiency?
normal testis and duct system (due to AMH and testosterone)
What is a common cause of female DSD?
congenital adrenal hyperplasia (CAH) - virilization of female external genitalia due to excess androgen production
What are ovotesticular disorders?
true intersexuality disorders - have both testicular and ovarian tissue
What are some causes of ovotesticular disorders?
- translocation of piece of Y onto X (Barr body causes mosaicism)
- subset of cells may have mutation in Y
- anomaly in sex determination of primordial germ cells
What is the decidua?
functional layer of endometrium that separates from remainder of uterus after childbirth
Describe each of the parts of the decidua: decidua basalis, decidua capsularis, and decidua parietalis
- decidua basalis: deep to conceptus (part where embryo embedded)
- decidua capsularis: superficial to conceptus (closest to uterine cavity)
- decidua parietalis: remaining part of decidua
Describe syncytiotrophoblasts structurally. What do they produce?
- large grouping of nuclei with no detectable cell membrane (invade and displace decidual cells)
- produce hCG
What is the amnion and what creates it?
- thin tough membrane surrounding embryo and amniotic fluid
- derived from amnioblasts that separate from epiblasts
How does the embryo receive nutrients/O2 before complete production of the placenta?
primordial uteroplacental circulation where nutrients pass to embryo via diffusion through lacunar networks (maternal side of placenta)
What establishes the fetal part of the placenta?
the chorionic sac
