- developmental processes
- development of body systems
- week 1
- week 2
- week 3
- weeks 4-8
- weeks 9-40
- teratogens
- problems with development
Section Links
Sexual Differentiation
Development of Genital Systems
The development of the genital systems is complex and mediated primarily by...
- SRY gene
- effect of differentiation on brain
- Turner's syndrome
- Klinefelter's syndrome
- Adrenogenital syndrome
- Androgen insensitivity syndrome
SRY Gene
- presence of SRY gene (and associated genes), which codes for testis-determining factor, on Y chromosome induces primordial gonads to differentiate into fetal testes: Sertoli cells and Ledig cells
- Ledig cells produce testosterone, inducing Wolffian duct structures and external genetalia
- Sertoli cells produce Mullarian-inhibiting substance (MIS) which induces regression of Mullerian ducts
Female Differentiation
- Absence of SRY gene and therefore testosterone and MIS leads to development of outer genitalia and Mullerian ducts and regression of Wolffian ducts.
Effect on Brain
- there are differences in brains re: ie reading tasks
- there are differences in neurological/psychiatric disorders differentially affecting men and women
- different responses to various medications
- there appear to be sexual dimorphism in hypothalamus, including in brains of homosexuals
- could be genes, could be hormones....
Chromosomes, Gonads, and Syndromes
During meiosis,
| XO | ovary | Turner's |
| XX | ovary | healthy |
| XXX | ovary | super female |
| XXY | testis | Klinefelter's |
| XYY | testis | super male |
| XY | testis | healthy |
Turner's Syndrome
- XO chromosomes + 44 autosomes
- 1:2000 live births
- no ovaries (streaks)
- no estrogen
- no breasts
- no cycles
- short stature, webbed neck, shield chest, low hairline, widely spaced nipples
- treated with:
- growth hormone
- estradiol/progesterone can induce menstruation
- but sex hormones need to be given after GH so as not to stop growth at the epiphyseal plate, which is what estrogen does
Klinefelter's Syndrome
- XXY chromosomes; nondisjunction is most common cause
- incidence - 1:1000
- low fertility
- low testosterone
- small testes and low spermatogenesis
- feminine features and gynecomastia due to low testosterone:esterogen ratio
- poor-reading skills (dyslexia-like)
- osteoporosis due to low testosterone
Adrenogenital Syndrome
- affects 1:14,000 female
- due to enzyme defect, adrenals shunt cholesterol away from cortisol to androgens
- begins in utero and results in masculinization of external genetalia and behaviour
- treatment with dexamethasone decreases the shunt to androgens
- female pseudo-hermaphrodite
Androgen Insensitivity Syndrome
- XY, but psychosexually female
- caused by defects of the dihydrotestosterone receptor (androgen receptor) on the X chromosome
- male pseudo-hermaphrodites
Hermaphrodites
- hermaphrodites are 46 XX, have both ovarian and testicular tissue, often have a uterus, and usually have ambiguous or predominantly female external genitalia.
Male Pseudoheramptodites
- male pseudo-hermaphrodites are 46 XY and have testes
- usually caused by underactivity of androgens and MIS
- can be due to maternal ingestion of progestens and estrogens
Female Pseudoheramptodites
- female pseudohermaphrodites are 46 XX and have ovaries
- usually caused by overactivity of androgens
- congenital adrenal hyperplasia can lead to excessive androgen production and masculinization of external genitalia and secondary sexual characteristics
- aromatase deficiency can block the conversion of androgens to estrogens