Transcript Sex Hormones

Chapter 11
Reproductive Behaviors
Variations in Sexual Behavior
• Gender identity: how we identify sexually and
what we call ourselves
• Sex differences: Biological differences
between males and females
• Gender role: refers to the activities and
dispositions that a particular society
encourages for one sex or the other
Gender Identity
• Most people have a
gender identity that
matches their
external
appearance.
• Some people have a
gender identity that
is opposite their
biological sex.
• Psychologists and
researchers once
believed that gender
identity was learned
and more a product of
rearing and
experience.
• Current evidence
strongly suggests that
biological factors,
especially prenatal
hormones, play a
large role in gender
identity.
Variations in Sexual Development
• True hermaphrodite: someone who has both
testicular and ovarian tissue—very rare
• Hermaphrodites: individuals whose genitals
do not match the normal development for
their genetic sex
• Intersex people are people are intermediate
between being male or female (AKA:
pseudohermaphrodite)
• Video: Is It a Boy or a Girl?
Sex Hormone
• A chemical that is
secreted by a gland,
conveyed by the blood,
and affects other organs
Endocrine glands
• Glands that produce
hormones
Sex Hormones
Two types of sex hormones include:
1. Androgens
2. Estrogens
• Both sexes have both hormones
Sex and Hormones
• Androgens are a groups of male sex
hormones that include testosterone
• Generally referred to as “male hormones”
because men have higher levels than women
Sex and Hormones
• Estrogens include estradiol
and others and are referred
to as “female hormones”
because women have higher
levels.
• Progesterone is a type of
hormone that prepares the
uterus for the implantation of
a fertilized ovum and
promotes the maintenance of
pregnancy.
Sexual Differentiation
• Begins with the chromosomes
• At six weeks of development, both sexes have primitive
gonads as well as:
– Mullerian ducts (precursors to female reproductive
organs-- oviducts, uterus, and upper vagina) and
– Wolffian ducts (precursors to male reproductive organs-vas deferens and seminal vesicles).
Sexual Differentiation
• The male Y chromosome includes the SRY
gene which causes the primitive gonads to
develop into testes, the sperm-producing
organ.
• The developed testes produce the hormone
testosterone.
• Testosterone induces the development of the
penis and scrotum.
• Females are not exposed to high
testosterone levels and their gonads develop
into ovaries, the egg-producing organs.
Sex and Hormones
• Sensitive periods are early periods when
hormones have long-lasting effects.
• Sexual differentiation depends mostly on the
level of testosterone during a sensitive
period.
• The human sensitive period for genital
formation is about the third and fourth month
of pregnancy.
Sex and Hormones
•
Sex hormones can have the following
effects:
1. Organizing effects- occur mostly at sensitive
stages of development.
-Determine whether the brain and body
will develop male or female
characteristics
2. Activating effects- occur at any time of life
and temporarily activate a particular
response.
Congenital adrenal hyperplasia (CAH)
• XX female’s cortisol
production leads to
overstimulation of the
adrenal gland.
• Overstimulation of the
adrenal gland leads to
extra testosterone
production.
– The female fetus
becomes partly
masculinized.
Congenital adrenal hyperplasia (CAH)
• Research indicates that
CAH girls show a greater
preference for boy-typical
toys than do other girls.
• During adolescence and
early adulthood, they also
show partly masculinized
interests.
• Sexual interest and
activity also differs for
CAH girls as well.
Androgen insensitivity or testicular feminization
• XY male has the genital
appearance of a
female.
• Production of
androgens remains
normal but they lack the
androgen receptor that
enables it to activate
genes in a cell’s
nucleus.
• Condition occurs in
various degrees from a
smaller than average
penis to genitals that
develop a female
appearance.
Four siblings with testicular
feminization syndrome
(recessive sex-linked allele)
5 alpha-reductase 2 deficiency
• XY males fail to produce an enzyme that
converts testosterone to dihydrotestosterone.
• Most look female at birth but a penis
develops during adolescence and puberty.
• Most then accept a male gender identity.
– Brain is exposed to testosterone during
early development.
Biological Bases of Sexual Orientation
• Research suggests that certain brain structures
differ in size between heterosexual and
homosexual men and women, due to the early role
of sex hormones.
• Sexually dimorphic nucleus (SDN): an area in the
anterior hypothalamus that is larger in the male
and contributes to control of male sexual behavior,
(e.g., being attracted to a female).
– Study of homosexual male brains found that
their SDN was similar to those found in females.
Biological Bases of Sexual Orientation
• Twin studies suggest genetic
factors.
• Probability is highest in
monozygotic twins and lower in
dizygotic twins, and even lower
in siblings and adopted brothers
or sisters.
• Because monozygotic twins can
have opposite sexual
orientations, genes are not the
only factor.
Biological Bases of Sexual Orientation
• Sexual orientation
may be influenced by
testosterone levels
during sensitive
periods of brain
development.
• Male animals
deprived of
testosterone early in
life show sexual
interest in other males
as adults.
• Female animals
exposed to
testosterone during
early development
show an increased
likelihood of mounting
behavior.
Biological Bases of Sexual Orientation
• Laboratory research has
also shown that prenatal
stress can alter sexual
development.
• Male subjects subjected to
either prenatal stress or
alcohol developed male
sexual behavior in addition
to female sexual behaviors.
• Male subjects exposed to
both stress and alcohol
during prenatal
development had
decreased sexual behavior.
Biological Bases of Sexual Orientation
• The probability of
homosexual orientation
is higher among men
with older brothers.
• Results suggest that a
mother’s immune
system may react
against a protein in a
son and attacks
subsequent sons to
alter development.
[Prenatal Influences,
p337]