Hormones & Sexual

Development

Lecture 23

Sexual Dimorphism

Two forms male and female

What determines your sex? ~

Genetic determinants

XX or XY XO ?

Turner’s syndrome no ovaries

default = FEMALE MALE

Override genetic program ~

Genotype complete genetic makeup

Phenotype expression of genes ~

Genotypic vs Phenotypic Sex

Sexual Differentiation of Body

Chromosomal sex - XX or XY single gene

Sex-Determining Region on the Y Chromosome SRY ~

SRY

Turns on switch testes development

XX + SRY? male

XY - SRY female ~

Development of Reproductive Organs

Primordial Gonad

Indifferent gonadPotential for both sexes

Medullatestes

Cortexovaries ~

Differentiation

at 6 weeks SRY

medulla testes No SRY

cortex ovaries ~

Internal Reproductive Ducts

< 6 weeks 2 sets

Müllerian system = female upper vagina uterus fallopian tubes ~

Internal Reproductive Ducts

Wolffian system = male seminal vesicles vas deferens

3d month development 1 set withers

SRY testes testosterone Müllerian Inhibiting Hormone - MIH ~

Wolfian Müllerian

Müllerian Inhibiting Hormone Testes scrotum develops Mullerian degenerates

Testosterone stimulates wolffian Testosterone to female

get both systems No MIH

Critical periods No MIH Mullerian ~

External Genitalia

Dihydrotestosterone (DHT) critical period

testosterone ------------------------> DHT

5 - -reductase

M & F - same tissue ~

Sexual Differentiation of the Brain

Masculinization

Gonadotropin release patterns Female natural pattern

Brain masculinized by... testosterone? NO!ESTRADIOL

Structural differences? ~

Sexual Dimorphism of the Brain

Hypothalamus Sexually Dimorphic Nucleus - SDN Spinal Nucleus of the

Bulbocavernosus ~

testosterone -------------------> estradiol

aromatase

Aromatase present in neonates inject estradiol into neonate female

brain masculinized What protects females?

Rats - -fetoprotein Primates - placenta? ~

Masculinization of the Brain

Secondary sex characteristics Puberty Increased M/F sex hormone activity

Secondary characteristics maturation of genitals breasts body shape

Pubic & axillary hair females- androstenedione from adrenal cortex ~

Sexual Development Syndromes

Adrenogenital Syndrome Congenital adrenal hyperplasia

genotype: XX prenatal adrenal cortex hyperactivity high levels of androgens

partially masculinized external genitalia ~

Sex? Phenotype? Genotype?

Androgen Insensitivity Syndrome

Androgen Insensitivity Syndrome Genotype: XY

No androgen receptors Genetic mutation - X chromosome gene

Born with vagina, raised as female Undescended testes become functional at

puberty. NOW WHAT HAPPENS?

Female body, brain, & gender identity

5-alpha Reductase Syndrome

Genetically XY Fetal 5-alpha reductase

deficiency T not converted to DHT

Born with female external genitalia maybe raised as female

Dominican Republic 1:90 male births ~

At puberty

Undescended testes become functional at puberty testosterone 5-a-reductase present converts T DHT

Development of male genitalia including penis secondary sex characteristics ~