Hormones & Sexual Development Lecture 23

Sexual Dimorphism n Two forms l male and female n What determines your sex? ~

Genetic determinants n XX or XY n XO ? l Turner’s syndrome l no ovaries n default = FEMALE n MALE l Override genetic program ~

n Genotype l complete genetic makeup n Phenotype l expression of genes ~ Genotypic vs Phenotypic Sex

Sexual Differentiation of Body n Chromosomal sex - XX or XY l single gene n S ex-Determining R egion on the Y Chromosome l SRY ~

SRY n Turns on switch l testes development n XX + SRY? l male n XY - SRY l female ~

Development of Reproductive Organs

Primordial Gonad n Indifferent gonad l Potential for both sexes n Medulla l testes n Cortex l ovaries ~

Differentiation n at 6 weeks n SRY l medulla  testes n No SRY l cortex  ovaries ~

Internal Reproductive Ducts n < 6 weeks l 2 sets n Müllerian system = female l upper vagina l uterus l fallopian tubes ~

Internal Reproductive Ducts n Wolffian system = male l seminal vesicles l vas deferens n 3d month development l 1 set withers n SRY  testes l testosterone l Müllerian Inhibiting Hormone - MIH ~ Wolfian Müllerian

Müllerian Inhibiting Hormone n Testes  scrotum develops n Mullerian degenerates l Testosterone stimulates wolffian n Testosterone to female l get both systems l No MIH n Critical periods l No MIH  Mullerian ~

External Genitalia n Dihydrotestosterone (DHT) l critical period testosterone > DHT 5 -  -reductase n M & F - same tissue ~

Sexual Differentiation of the Brain

Masculinization n Gonadotropin release patterns l Female natural pattern n Brain masculinized by... l testosterone? l NO!  ESTRADIOL n Structural differences? ~

Sexual Dimorphism of the Brain n Hypothalamus n Sexually Dimorphic Nucleus - SDN n Spinal Nucleus of the Bulbocavernosus ~

testosterone > estradiol aromatase n Aromatase present in neonates n inject estradiol into neonate female l brain masculinized n What protects females? l Rats -  -fetoprotein l Primates - placenta? ~ Masculinization of the Brain

Secondary sex characteristics n Puberty n Increased M/F sex hormone activity Secondary characteristics l maturation of genitals l breasts l body shape n Pubic & axillary hair l females- androstenedione l from adrenal cortex ~

Sexual Development Syndromes

Adrenogenital Syndrome n Congenital adrenal hyperplasia l genotype: XX l prenatal adrenal cortex hyperactivity l high levels of androgens n partially masculinized external genitalia ~

n Sex? n Phenotype? n Genotype? Androgen Insensitivity Syndrome

n Genotype: XY l No androgen receptors l Genetic mutation - X chromosome gene n Born with vagina, raised as female l Undescended testes become functional at puberty. l NOW WHAT HAPPENS? n Female body, brain, & gender identity

5-alpha Reductase Syndrome n Genetically XY n Fetal 5-alpha reductase deficiency l T not converted to DHT n Born with female external genitalia l maybe raised as female n Dominican Republic l 1:90 male births ~

At puberty n Undescended testes become functional at puberty l  testosterone l 5-a-reductase present l converts T  DHT n Development of male genitalia l including penis l secondary sex characteristics ~