Development of Reproductive System Flashcards
What is the normal number of chromosomes and the genotype for males and females?
- human cells have 22 pairs of autosomes and 1 pair of sex chromosomes
- female (46, XX): homogametic
- males (46, XY): heterogametic
What is the genetic determinant of sex?
- the presence or absence of a Y chromosome
- Y leads to male gonads (although many genes needed for it are found on the X)
- absence of Y leads to female gonads
How do the genes on the Y chromosome indirectly cause male gonadal development?
contains a regulatory gene (transcription factor) that binds DNA and controls some genes important for testes development on the other chromosomes
How can some females have an XY and some men have an XX genotype?
- Y chromosome retains regions of homology with X chromosome that permits pairing during meiosis but errors can occur
- part of short arm of Y chromosome is missing or mutates in females
- males with XX have section of Y chromosome translocated to an autosome or X chromosome
Describe the role of the SRY gene
- encodes a transcription factor that regulates expression of genes on the other chromosome
- turning on genes for testes differentiation, turning off ovarian genes
- responsible for sex determination
What makes up the male and female gonads?
- somatic mesenchyme
- primordial germ cells
Describe the formation of the sex cords in early gonadal differentiation
a genital ridge is formed by the proliferation of the surface epithelium and condensation of mesenchyme forming sex cords
Describe the movement and events of the primordial germ cells in early gonadal differentiation
- they migrate to genital ridge driven by chemotaxis
- by week 6 they invade genital ridges and are surrounded by the primitive medullary sex cords
Describe the male gonadal differentiation path
- under influence of SRY primitive sex cords differentiate and penetrate medulla forming testis cords
- they become looped, make contact with the ingrowing mesonephric tubule called rete testis and PGCs reside in developing testis cords
- mesodermal cells differentiate into sertoli cells in cords under influence of SRY
- mesenchyme tissue in interstitial space develop into Leydig cells and start to secrete testosterone by week 8
Describe the female gonadal differentiation path
- in the absence of Y chromosome, leads to degeneration of medullary cords
- cortical cords form from proliferating surface epithelium forming distinct cell clusters
- epithelial cells proliferate around each oogonium forming primordial follicles
Describe the formation of the genital ducts
- 7-8 weeks, embryos acquire dual ductal systems that are precursors to internal genitalia
- Wolffian (mesonephric) ducts give rise to male genital ductal system
- Mullerian (paramesonephric) ducts give rise to female genital ductal system
Describe the genes involved in the development of the internal genitalia
Males:
- SRY induces expression of SOX9 (which inhibits WNT4 preventing female pathway activation)
- activates SF1 and other genes
- promotes differentiation of testes
- promotes medullary cord development
- inhibits cortical cords
Females:
- WNT4 induces expression of DAX1 (inhibits male pathway) and other genes
- promotes differentiation of ovaries
- promotes cortical cord development
- degenerates medullary cords
Describe the formation of internal genitalia in females
- lower vagina forms from paramesonephric tubercle
- 2 envaginations grow out from pelvic side and proliferates forming vaginal plate
- 20 weeks, vaginal outgrowth is complete and expands around end of uterus
What is the determinant of the developmental path of the external genitalia?
depends on presence or absence of androgens
Describe Turner’s Syndrome
- chromosomal disorder
- (45, X0)
- oocytes degenerate since 2 X chromosomes are needed for full chromosomal development
- streaky ovary
