Download BN23 hormones & sexual development

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 ~

Genotypic vs Phenotypic Sex
Genotype
 complete genetic makeup
 Phenotype
 expression of genes ~

Sexual Differentiation of Body

Chromosomal sex - XX or XY
 single gene
 Sex-Determining
Chromosome
 SRY ~
Region on the Y
SRY
Turns on switch
 testes development
 XX + SRY?
 male
 XY - SRY
 female ~

Development of Reproductive
Organs
Primordial Gonad



Indifferent gonad
Potential for both
sexes
Medulla
testes
Cortex
ovaries ~
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
Wolfian
Müllerian
Wolffian system = male
 seminal vesicles
 vas deferens
 3d month development
 1 set withers
 SRY  testes
 testosterone
 Müllerian Inhibiting Hormone - MIH ~

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 ~

Masculinization of the Brain
testosterone -------------------> estradiol
aromatase
Aromatase present in neonates
 inject estradiol into neonate female
 brain masculinized
 What protects females?
 Rats - -fetoprotein
 Primates - placenta? ~

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 ~
Androgen Insensitivity Syndrome
Sex?
 Phenotype?
 Genotype?

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 ~