Hormones Sexual Development Lecture 23 Sexual Dimorphism Two

Hormones & Sexual Development Lecture 23

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

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

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

Sexual Differentiation of Body n Chromosomal sex - XX or XY l single gene n Sex-Determining Chromosome l SRY ~ Region on the Y

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

Development of Reproductive Organs

Primordial Gonad n n n Indifferent gonad l. Potential for both sexes Medulla ltestes Cortex lovaries ~

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

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

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

Müllerian Inhibiting Hormone 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 ~ n

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

Sexual Differentiation of the Brain

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

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

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

Secondary sex characteristics 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 ~ n

Sexual Development Syndromes

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

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

Androgen Insensitivity Syndrome 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 n

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

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