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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 ~