sex and harmones.pdf

Copyright © 2007 by Allyn and Bacon
Chapter 11
Hormones and Sex
What’s Wrong with the
Mamawawa
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Developmental and Activational
Effects of Sex Hormones
 Developmental – “organizational”
- influencing the development of
anatomical, physiological and
behavioral characteristics that
differentiate the sexes
 Activational – activating
reproduction-related behavior in
mature individuals

Glands
 Exocrine – Release chemicals into ducts
which carry them to their targets.
Sweat glands, for example
 Endocrine – Ductless. Release hormones
directly into the circulatory system
Primary function is hormone release

Gonads
 Male testes produce sperm cells
 Female ovaries produce ova
 Sperm and ova each have 23 chromosomes
 Fertilization
 Sperm cell + ovum = zygote
 23 pairs of chromosomes
 X and Y – sex chromosomes
 XX = female, XY = male

Sex Hormones – Released by
Gonads
 Androgens - e.g., testosterone
 Estrogens - e.g., estradiol
 Adult testes tend to release more androgens
and ovaries tend to release more estrogens
 Progestins – also present in both sexes
 progesterone prepares uterus and breasts for
pregnancy
 Adrenal cortex – also releases sex hormones

Hormones
 Steroids
Synthesized from cholesterol (fat)
Fat-soluble – able to enter cells and bind to
receptors in cytoplasm or nucleus
 Amino acid derivatives
Epinephrine, for example (adrenal medulla)
 Peptides and proteins
Short and long chains of amino acids

Hormones of the Pituitary
 “Master gland”
 Tropic hormones influence the
release of hormones by other glands
 Posterior pituitary – hormones
synthesized in the hypothalamus
 Anterior pituitary – tropic hormones

Cyclic Vs Steady Gonadal
Hormone Levels
 Female hormones go through a 28-
day cycle, the menstrual cycle
 Male hormone levels constant
 Anterior pituitary activity is controlled
by the hypothalamus
 The hypothalamus determines
whether or not hormone levels cycle

Control of the Pituitary by the
Hypothalamus
 Posterior – neural input from hypothalamus
 Vasopressin – antidiuretic hormone
 Oxytocin – labor and lactation
 Synthesized in hypothalamic paraventricular and
supraoptic nuclei
 These nuclei have terminals in the posterior pituitary
 Anterior pituitary – hypothalamopituitary portal
system carries hormones from the hypothalamus
to the anterior pituitary

Hypothalamic Releasing Hormones
 Releasing and
inhibiting hormones
control production
and release of the
anterior pituitary
 All releasing and
tropic hormones are
peptides
Gonadotropins
(FSH and LH) –
stimulate
gonads
Gonadotropin-
releasing
hormone
Thyrotopin –
stimulates
thyroid
Thyrotropin-
releasing
hormone
Anterior
pituitary
Hypothalamus

Regulation of Hormone Levels
 Neural
All endocrine glands (except the anterior
pituitary) receive neural signals
From cerebral or autonomic neurons
 Hormonal
Tropic hormones, negative feedback

Sexual Development
 We are dimorphic – exist in 2 forms
 Initially there is a primordial gonad
 Cortex – potential to be ovary
 Medulla – potential to be a testis
 If XY, Y triggers the synthesis of H-Y
antigen and promotes development of the
medulla
 No H-Y antigen, cortex develops into ovary

Sexual Development
 6-weeks post-conception:
 H-Y antigen > testes
 No H-Y antigen > ovaries
 Both sexes begin with 2 sets of reproductive
ducts
 Wolffian system – male – seminal vesicles, vas
deferens
 Mullerian system – female – uterus, vagina, fallopian
tubes
 Differentiation occurs in the 3rd
prenatal month

Sexual Development
 6-weeks: gonads develop
 3rd
prenatal month: differentiation of ducts
Testes produce testosterone and Mullerian-
inhibiting substance
 Wolffian system develops, Mullerian degenerates,
testes descend
No testes – no testicular hormones
 Mullerian system develops, Wolffian degenerates

A terminology note
 Ovariectomy – removal of ovaries
 Orchidectomy – removal of testes
 Gonadectomy or castration – removal
of gonads, either ovaries or testes
 Such procedures are often used to
study the effects of sex hormones

Sexual Development
 External reproductive structures –
genitalia – develop from one
bipotential precursor
 Differentiation occurs in 2nd
month
 Testosterone > male
 No testosterone > female

Sex Differences in the Mammalian
Brain
 Pfeiffer (1936) – gonadectomized and
implanted gonads in neonatal rats
Gonadectomy > cyclic hormone release
Transplant of testes or ovaries > steady
 Perinatal hormones lead to male pattern
 Why do both ovaries and testes lead
to male pattern?

Aromatization and Sex Differences
in the Brain
 What masculinizes the brain?
 Sex steroids are all derived from
cholesterol and are readily converted
from one to the other
Aromatize testosterone > estradiol
 Evidence suggests that estradiol
masculinizes the brain

Evidence that Estradiol (E)
Masculinizes the Neonatal Brain
 Neonatal injections of E masculinize
 Dihydrotestosterone can’t be converted to
E – doesn’t masculinize
 Block aromatization or E receptors –
interferes with masculinizing effects of
testosterone
 Why doesn’t E masculinize female brains?

Alpha fetoprotein
 In blood during perinatal period -
protects the female brain from E
 Binds to circulating E, so none gets to
the brain
 How does E get into male brain?
 In males, testosterone enters the
brain and then is converted to E

Sex Differences in the Brain: What
Do They Mean?
 Many differences, but their
significance is not known
 Links between structural
differences and functional
differences have not been
established

Perinatal Hormones and Behavioral
Development
 Masculinize – promoting male behavior,
mounting, etc.
 Defeminize – preventing female behavior,
lordosis
 Perinatal T masculinizes and defeminizes
 Neonatal castration of male rats –
feminizes and demasculinizes

Puberty
 Fertility achieved, secondary sex
characteristics develop
Features that distinguish sexually mature men
and women
 Increase in release of anterior pituitary
hormones
Growth hormone – acts on bone and muscle
Gonadoptrophic hormone
Adrenocorticotrophic hormone

Puberty
 Relative levels of androgens and
estrogens determine whether male or
female features develop
 Androstenedione – androgen
necessary for the growth of axillary
and pubic hair in both sexes

Anne S.
 Knowing how normal development occurs,
you should be able to understand what could
cause abnormal sexual development
 Why might a woman not cycle and have no
pubic or axillary hair?
 What determines whether male or female hormone
patterns develop?
 What causes the growth of pubic and axillary hair?

Anne S.
 Anne is chromosomally male, XY
 Internalized testes, but no ovaries
 Hormone levels are those of a man
 What happened?
 Androgenic insensitivity syndrome
 Normal male androgen levels, but no response to them
 She does respond to estrogens, so she effectively has more
estrogens than androgens – leading to the development of
female secondary sex characteristics

Adrenogenital Syndrome
 Androgenic insensitivity leads an XY individual
to look female (Anne S.)
 Andrenogenital Syndrome is caused by
congenital adrenal hyperplasia
 Too little cortisol leads to compensatory excessive
release of adrenal androgens
 No problem for males
 May masculinize female genitalia and behavior –
surgical and hormonal treatments needed at puberty

John/Joan
 A surgeon’s error led one of a pair of male twins
to be raised as a girl
 Artificial vagina created
 Estrogen administered at puberty
 John/Joan never felt or acted like a girl –
indicates that the key to one’s gender is in the
brain
 John/Joan chose to become John later in life,
but never recovered from the ordeal
 John took his life in May of 2004

Male Reproduction-Related
Behavior and Testosterone (T)
 Effects of orchidectomy Bremer (1959)
Reduced sexual interest and behavior
Rate and degree of loss varies
Still have adrenal T
 Level of male sexuality is NOT correlated
with T levels
 Increasing male T levels does NOT
increase sex drive

Female Reproduction-Related
Behavior and Gonadal Hormones
 Rats and guinea pigs – surges of estrogen
and progesterone initiate estrus, a period
of fertility and receptivity
 Women – sexual motivation and behavior
not tied to cycle
 Sex drive may be under androgenic
control

Human Female Sexuality and
Androgens
 T increases the proceptivity of
ovariectomized and adrenalectomized
female rhesus monkeys
 Correlations seen between sexual
motivation and T
 T found to rekindle sexual motivation in
ovariectomized and adrenalectomized
women

Anabolic Steroids
 Anabolic – growth-promoting
 No firm scientific evidence that muscularity and strength
are increased
 Sex-related side effects
 High circulating hormones cause a reduction of natural
release
 Men - testicular atrophy, sterility, gynecomastia (breast growth
in men)
 Women – amenorrhea (cessation of menstruation), sterility,
hirsutism (excessive growth of body hair)

Neural Mechanisms of Sexual
Behavior
 Sexually dimorphic nucleus (SDN)
medial preoptic area of rat hypothalamus
larger in males, due to estradiol shortly after
birth
size of male SDN correlated with T levels and
aspects of sexual activity
 Nuclei in preoptic, suprachiasmatic, and
anterior regions of the hypothalamus are
larger in men than in women

Medial Preoptic Area of the
Hypothalamus
 Contains the SDN
 Destruction abolishes sexual
behavior of all mammalian males
studied, but does not affect female
sexual behaviors females
 Stimulation elicits copulatory
behaviors

Ventromedial Nucleus of the
Hypothalamus
 Contains circuits critical for female rat
sexual behavior
 Lesion eliminates lordosis
 Microinjections of E and progesterone
induce estrus
 Lesions of periaqueductal gray (PAG)
or the tracts to it eliminate lordosis

Sexual Orientation
 Heterosexual – sexually attracted to
members of the other sex
 Homosexual – sexually attracted to
members of the same sex
 Bisexual – sexually attracted to
members of both sexes

Sexual Orientation
 Genetic basis established
 No differences in hormone levels
 Animal research suggests altered
hormone levels during development
may play a role, but there is no direct
human evidence of this

Sexual Body Type, Orientation, and
Identity
 All 3 are independent entities
 Consider Anne S. – chromosomally a
man, but a woman in every other way
 Consider John/Joan – a man’s brain
in a woman’s body
 How would you define male and
female?

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