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Psychobiology 5-1 chapter 10
Sex and Hormones
Steroid hormones are derived from cholesterol, contain four
carbon rings andexert their effects in three way
o 1. binding to membrane receptors like neurotransmitterso
2. entering, cells and activating certain kinds of proteins in
cytoplasm
o 3. binding to chromosomes where they activated or inactivate
certaingenes
The sex hormones are a special kind of steroid, released mostly
by the gonads andto a lesser degree by the adrenal glands.
o Affects the brain, genitals and other organs Two types of sex
hormones include:
o 1. Androgen (mainly testosterone)o 2. Estrogenso Both sexes
have these categories in varying quintiles
Sex limited genes are those activated by androgens or estrogens
and controlmost of the differences between male and female
o Example: estrogen activate the gene for breast growth and
androgensactivate the gene for the growth of facial hair
Sex hormones increase or decrease the rate of apoptosis in
various region of thebrain
o Certain areas are slightly larger in males or females Sex
hormones can have the following effect
o 1 occur mostly at sensitive stageo 2. Activities effects occur
at any time of life and temporally activate a
particular response
Sexual differentiation begins with the chromosomes Females
mammal has two x and a male has an x and a y in most cases but not
all During early stage of prenatal development both male and female
have a set of
Mullerian ducts and a set of Wolffian ducts as well as primitive
gonads
Wolffian duct are precursors to other male organso Develop into
the vas deferens and seminal vesicles
Mullerian ducts are the precursor to female oviducts uterus and
upper vagina 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 ans scrotum
Females are not exposed to high testosterone levels and their
gonads develop into
ovaries the egg producing organ
Sensitive periods are early periods are early periods when
hormones have long-lasting effects
Sexual differentiation depends mostly on level of testosterone
during a sensitiveperiod
The human sensitive period for genitals formation is about the
third and fourthmonth of pregnancy
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Alpha-fetoprotisis is found in the blood during early sensitive
period and binds toestrogen and prevents it from entering
developing cells
Testosterone does not bind to alpha-feto and freely enters the
cellSexual Desire and Hormones
Decreases in testosterone levels generally decrease males sexual
activity andinterest
o Example: castration Impotence inability to maintain an
erection
o Usually caused by impaired blood circulation not low
testosterone Erection partially depends on testosterone increasing
the release of nitric oxide
o Facilitates the hypothalamic neurons and increases blood flow
to the penisMenstrual Cycles and Hormones
After the end of menstrual of period The anterior pituitary
releases follicle stimulating hormone (FSH) FSH promotes the growth
of a follicle in the ovary The follicle nurtures the ovum and
produces estrogen
Towards the middle of the menstrual cycle the follicle builds on
receptors to FSH As a result the follicle produces increasing
amounts of estadiol a type pf estrogen Increased estradiol causes
pituitary to increase release of FSH and luetinizing
hormone (LH)
FSH an LH causes the follicle to release an ovum The remnants of
the follicle release the hormone progesterone
Prepares the uterus for implantation of a fertilized ovum
inhibits the further release of LH
Birth Control
birth control pills prevent pregnancy by interfering with the
usual feedback cyclebetween the ovaries and pituitary
the combination pill contains both estrogen and progesterone and
prevents thesurge of FSH and LH that would release an ovum
also thickens the mucus of the cervix making it harder for the
spearm to reach theegg
Parental Behavior and Hormones
oxytocin is a pituitary hormone also important for reproductive
behavior stimulates contraction of uterus during delivery of baby
stimulates the mammary gland to release milk released during orgasm
and triggers a state of complete relaxation facilitates bonds
between mating partners and mother and infant
Variation in Sexual Behavior gender identity refers to which
gender we identify as and what we call ourselves
in terms of man or woman
biological differences are generally referred to as sex
differences differences that result from peoples thoughts about
themselves as male or female
are referred to as gender differences
