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Lecture 15

HMB200H1 Lecture Notes - Lecture 15: Pituitary Gland, Anterior Commissure, Labia Minora

Human Biology
Course Code
John Yeomans

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HMB200H1S L15; March. 06, 2012
Sex, Gender and the Brain
Sex and Gender
What is male/female?
Biological def’n: Large gamete = female (ovum)
o Female reproductive egg determines sex
o Until females reproductively active, then possible to determine
sex within species within ecosystem
Chromosomes: XX (female), XY (male)
o XO, XXY, XYY ?
o Y = male
o Dif ratios dif odd cases
Genitalia: Internal & external
o Primary sex characteristics which doctors look at to find sex of
o External genitalia can be misleading so have to analyze
Primary & secondary sex characteristics
o External genitalia become smaller in body percentage after birth
because surge of hormones decreases after birth
Hormones: androgens & estrogens
Brain changes
Gender identity
o Whether you are male or female determined by social factors
& internal biology
Bhvrs & social identity
o Ex. Partner preferences
o Hypothal projects to dif parts of limbic system by ascending
Sexual Differentiation (how primary sex characteristics are produced)
Y chromosome SRY gene
o Leads to hormone production in the gonads & male
differentiation of the gonads & Wolfian duct
o Without it get Mueller duct female
Male gonad produces testosterone & antimullerian hormone (AMH)
o Circulate in genitalia, go to brain to change organization
o Provides organizing factors secondary sex characteristics
triggered by hypothal (anterior pre-optic area)
Differentiates internal & external structures
o Wolfian duct for males
o Mueller duct for females
Changes brain via estrogen recs
In brain, testosterone converted to estradiol via aromatase
Female if no testosterone
If have SRY, gonads shift from undifferentiated to male 6wks after
gestation, shrinkage of female structures
Unisexual until 15wks of gestation
15-35wks: huge amt of changes in external genitalia
o Removal of genitalia doesn’t affect hormones, so male still
behaves like male
Male on left, female on right
o Male: testes move down abdomen to scrotal, then swells into
BNST = Bed N. of Stria Terminalis
o Sparse & lighter in females
o Dense & highly visible in males
o Most differentiated structure
Hormones can also change internal hypothal
Within anterior hypothal, boundary btwn anterior hypothalamic
nucleus & pre-optic nucleus
Middle of pre-optic area causes dif in bhvr btwn male & female
o Dramatic dif for secondary sex characteristics & sexual
bhvrs later in time
Suggests testosterone differentiating the brain; males have dense
cluster of cells
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