1- Sexual Differentiation Flashcards
define sexual determination
- dependent on the ‘switch’ on the Y chromosome
- genetically controlled process for chromosomal determination of male or female
define sexual differentiation
- internal and external genitalia developing into male or female
- development of gonadal sex
define the role of the Y chromosome in determining sexual differentiation
in males, short arm of the Y chromosome has the SRY gene
SRY gene is activated during week 7 and transcribed into SRY protein
SRY protein acts as a transcription factor - causes its own transcription through positive feedback amplification, and transcribes other genes causing a TF cascade for testes development
in females, the SRY gene isn’t present, isn’t expressed, and thus female embryos are on the ovary development pathway
why are the genital ridges bipotential gonads?
can develop into ovaries or testes depending on if SRY is expressed
describe the sequence of gonad/ genital ridge development
three waves of cells invade: primordial germ cells, primitive sex cords and mesonephric cells
primordial germ cells invade and populate the genital ridges - can become spermatozoa or oocytes depending on SRY expression
primitive sex cords - for males invade deeply and become Sertoli cells (produce AMH)
- for females don’t invade as deeply and become granulosa cells
mesonephric cells - from the lateral edges of the genital ridges
- for males = can become Leydig cells (produce testosterone) and vascular tissue
- for females = can become theca cells (produce oestrogen) and vascular tissue
what can primordial germ cells become?
spermatozoa or oocytes
what can primitive sex cords become?
sertoli cells (male) or granulosa cells (female)
what can mesonephric cells become?
leydig cells and vascular tissue in males
theca cells and vascular tissue in females
what hormone do Sertoli cells produce? why is it important?
AMH
Mullerian ducts degenerate in presence of AMH - allows Wolffian ducts to grow and develop into male internal genitalia structures
what hormone do Leydig cells produce?
testosterone
what hormone do theca cells produce?
oestrogen
describe the process of internal sexual differentiation
gonad have developed, pathway determined by SRY expression - male gonads produce testosterone and AMH, female gonads only produce oestrogen
if AMH is present from Sertoli cells, Mullerian ducts will degrade = Wolffian ducts will develop into internal male genitalia
if testosterone is absent because of no Leydig cells, Wolffian ducts degenerate and Mullerian ducts will develop into internal female genitalia
Mullerian ducts if AMH is present, Wolffian ducts degenerate in testosterone absence
describe the process of external sex differentiation for external genitalia in males and females
in males:
Leydig cells produce testosterone, a substrate for 5-alpha-redutase - converted to DHT
stimulates development of male external genitalia such as the scrotum and glans penis
in females:
absence of Leydig cells and testosterone - causes development of female external genitalia such as clitoris and labia
what is 5-alpha-reductase?
an enzyme that converts testosterone into DHT
present on the genital skin of both sexes
