PSY-2 Ch08 Hormones & Sex

Ch08: Hormones & Sex
➔The Endocrine System
➔The Pituitary Gland
➔Reproductive Behavior
➔Sexual Differentiation
➔Sexual Dimorphism
➔Sexual Orientation

THE ENDOCRINE SYSTEM
• HORMONES: chemicals that travel through the
bloodstream to act on target tissue
• ENDOCRINE GLANDS: release hormones within the
body
• EXOCRINE GLANDS: use ducts to secrete fluid
outside the body

Types of Chemical
Communication:
1. ENDOCRINE
2. SYNAPTIC
3. PHEROMONE: released outside
the body to affect others of the
same species
1. ALLOMONE: released outside
the body to affect another
species

Hormones are Classified by Chemical Structure:
1. PEPTIDE HORMONE: string of amino acids
EX: growth hormone, insulin, oxytocin
2. AMINE HORMONE: modified version of a
single amino acid
EX: epinephrine, melatonin
3. STEROID HORMONE: derived from
cholesterol
EX: estradiol, testosterone, cortisol,

Peptide & Amine Hormones:
1. Bind to receptors that span
the cell membrane
2. Bound receptor activates a
second-messenger that
alters cellular processes

Steroid Hormones:
1. Pass through the cell
membrane
2. Bind to receptors inside the
cell
3. Steroid-receptor complex
binds to specific regions of
DNA & controls gene
expression

• NEUROENDOCRINE CELLS: specialized
neurons that release hormones into the blood

• NEGATIVE FEEDBACK:
output feeds back and
inhibits signals for further
secretion

• PITUITARY GLAND: releases
hormones and regulates
other endocrine glands
• PITUITARY STALK: connects
the pituitary to the
hypothalamus
PITUITARY GLAND

Posterior pituitary gland
• Releases:
–OXYTOCIN
–VASOPRESSIN (AVP)
• Hormones produced in
the hypothalamus
PITUITARY GLAND

Posterior pituitary gland
• OXYTOCIN:
– uterine contraction, nursing
– reproduction and parenting
• VASOPRESSIN:
– water regulation
– pair bonding
PITUITARY GLAND

Figure 8.9 The Milk Letdown Reflex
PITUITARY GLAND

Anterior Pituitary Gland
• RELEASING HORMONES: control the
release of tropic hormones
• HYPOTHALAMIC-PITUITARY PORTAL
SYSTEM: blood vessels leading from
hypothalamus to anterior pituitary
• TROPIC HORMONES: pituitary
hormones that affect secretion by
other endocrine glands
PITUITARY GLAND

Steps in Anterior Pituitary Action
1. Hypothalamus triggers the neuroendocrine cells to release
their releasing hormones into the portal system
2. The portal systems carries the releasing hormones in local
circulation to the anterior pituitary
3. Releasing hormone activates neuroendocrine cells in the
anterior pituitary, causing them to release tropic hormones
4. Tropic hormones move through general circulation activating
receptors on target endocrine glands
5. Target endocrine glands release hormones into general
circulation.

• NEGATIVE FEEDBACK:
output feeds back and
inhibits signals for further
secretion
PITUITARY GLAND

• NEGATIVE
FEEDBACK: output
feeds back and
inhibits signals for
further secretion
PITUITARY GLAND

Hypothalamic neurons that synthesize releasing
hormones are sensitive to two influences:
1. Circulating messages such as other hormones,
which contribute to negative feedback
1. Synaptic input from other brain regions, which
can be inhibitory or excitatory
PITUITARY GLAND

• GONADOTROPIN RELEASING-HORMONE (GnRH) :
released by the hypothalamus into the portal system
• GONADOTROPINS: released by the anterior pituitary in
response to GnRH
PITUITARY GLAND
Follicle-Stimulating Hormone
Luteinizing
Hormone
Males Sperm production Testosterone production
Females Follicle development & estrogen
release
Corpus luteum development &
progesterone release

• Gonads regulate reproduction
• Gonads have specialized
compartments that produce:
–Hormones
–Gametes
• Testes produce and secrete
testosterone.
PITUITARY GLAND

• Ovaries produce:
– Progestins
– Estrogens
• FSH stimulates ovarian
follicles to grow and secrete
estrogens, beginning the
ovulatory cycle
• LH triggers ovulation and
forms the corpus luteum,
PITUITARY GLAND

SEXUAL DIFFERENTIATION
• SEXUAL DIFFERENTIATION: the process of
developing male/female bodies and behaviors
• SEX DETERMINATION: early developmental
events that determines sex

Definition Criteria
1. Genetic Males = XY
Females = XX
2. Gonadal
(Internal Anatomy)
Males = testes, prostate, seminal vesicles, vas deferens
Females = ovaries, Fallopian tubes, uterus, upper vagina
3. Phenotypic
(External Anatomy)
Males = penis, scrotum
Females = clitoris, labia, vaginal opening
4. Secondary Sex
Characteristics
Males = facial hair, enlarged larynx, broader shoulders +
narrow hips, increased muscle mass, larger bodies, heavier
bones
Females = breasts, narrow shoulders + wider hips, higher
proportion of body fat

1. GENETIC SEX
• Chromosomes are arranged in 23
pairs.
• 22 pairs of autosomes (matched
pairs).
• 1 pair of sex chromosomes (XX =
female; XY = male)

1. GENETIC SEX
• GAMETES:
– Sperm, Eggs/Ova
– 23 chromosomes
• ZYGOTE:
– Sperm & ovum united
– 46 chromosomes

1. GENETIC SEX
• Each gamete contains one sex chromosome
– Each egg contains an X
– Sperm contain either an X or a Y
X
X Y
X
XY
XX

2. GONADAL SEX
Both XX & XY embryos have an
indifferent gonad
• Cortex – potential to be ovary
• Medulla – potential to be a
testis

3. PHENOTYPIC SEX
• Both XX & XY embryos can
develop…
– Female Reproductive Ducts
(Müllerian)
– Male Reproductive Ducts
(Wolffian)

Figure 8.24 Sexual Differentiation
in Humans (Part 2)
3. PHENOTYPIC SEX
• Masculinizing Hormones:
– Testosterone promotes the
wolffian system
– ANTI-MÜLLERIAN HORMONE
(AMH): causes the müllerian
system to regress
• 5 ALPHA-REDUCTASE: enzyme that
converts T into a more powerful form

3. PHENOTYPIC SEX
• In the absence of masculinizing
hormones:
• Wolffian ducts regress
• Müllerian ducts develop

Figure 8.24 Sexual Differentiation
in Humans (Part 3)

Figure 8.25 The Sequence of
Sexual Differentiation

4. SECONDARY SEX
CHARACTERISTICS
• PUBERTY: Hormonal
changes
– Body growth
– Sexual maturation
• Determined by relative
levels of androgens &
estrogens

• INTERSEX: a person with atypical genital
development and sexual differentiation
– 17/1000 infants are intersex
– NIH Intersex Categories…

61
Intersex Categories
1. XX INTERSEX: genetically female but with ambiguous male
external genitalia
• Congenital Adrenal Hyperplasia (CAH): exposure to excess
androgens

62
Intersex Categories
2. XY INTERSEX: genetically male, but with
ambiguous female external genitals
• 5-Alpha-Reductase Deficiency (5-ARD):
infants appear female until puberty, when
bodies become masculinized
• Androgen Insensitivity Syndrome (AIS): a
person has XY chromosomes, but androgen
receptors do not function

64
Intersex Categories
3. TRUE GONADAL INTERSEX: has both ovarian and testicular
tissue
• Cause: unknown

65
Intersex Categories
4. COMPLEX OR
UNDETERMINED INTERSEX:
atypical chromosome
configurations
• Turner Syndrome:
only one X (X0)
• Klinefelter Syndrome:
extra X chromosome (XXY)

The “Social Emergency” of Intersexuality

SEXUAL DIMORPHISM:
physical differences
between males and
females
SEXUAL DIMORPHISM

• The same steroids that masculinize the developing
genitalia also masculinize the brain
• This ORGANIZATIONAL EFFECT permanently alters
behavior, in contrast to a temporary activational effect
• Steroids have an organizational effect only when
present during a SENSITIVE PERIOD in early
development
• Depending on the species and the behavior, this period
may be before birth or just afterward, in the
NEONATAL period
SEXUAL DIMORPHISM

Figure 8.29 Organizational Effects
of Testosterone on Rodent
Behavior (Part 1)
SEXUAL DIMORPHISM

Behavior (Part 2)
SEXUAL DIMORPHISM

Behavior (Part 3)
SEXUAL DIMORPHISM

• The organizational hypothesis explains sexual
differentiation:
–A single steroid signal (androgen) masculinizes the
body, the brain, and behavior
–If the nervous system does not receive an androgen
signal, the body will organize itself as a female
–This explains many rat behaviors. If exposed to
androgens early in life, they behave as males; if not, as
females
SEXUAL DIMORPHISM

SEXUAL DIMORPHISM
• In rats, a nucleus in the preoptic
area (POA) of the hypothalamus is
larger in males than in females
• The nucleus is known as the
SEXUALLY DIMORPHIC NUCLEUS
OF THE POA (SDN-POA)—lesions in
this area disrupt ovulatory and
copulatory behaviors

Figure 8.31 Organization of the
SDN-POA
SEXUAL DIFFERENTIATION & ORIENTATION

• In rats, the bulbocavernosus
(BC) muscles that surround the
base of the penis are innervated
by neurons in the SPINAL
NUCLEUS OF THE
BULBOCAVERNOSUS (SNB)
• The SNB is larger in males than
in females.

• Before birth the muscles in both
sexes are nearly equal. Near
birth, in females many SNB cells
and the BC muscles die—
androgen injections can prevent
this.
• ONUF’S NUCLEUS is the human
region similar to the SNB

Figure 8.33 Sexual Dimorphism in
the Human Brain
• Some parts of the human brain are
sexually dimorphic.
• Are these dimorphisms caused by
prenatal hormone exposure or by
social influence?
• Two classes of possible influence :
– The biological factor (very strong in
animal models) - varying levels of fetal
androgen direct future behavior
– Society’s instruction on how one should
behave when grown up

What Determines Sexual Orientation?
1. Genetics
2. Hormones
3. Birth Order
4. Physiology
SEXUAL ORIENTATION

1. Genetics
• Homosexual Males:
– 52% of identical twins and
– 22% of fraternal twins were also gay.
• Homosexual Females:
– 48% of identical twins and
– 16% of fraternal twins were also lesbian.
SEXUAL ORIENTATION

2. Hormones
• Prenatal Factors:
– Hormone injections in pregnancy can result in
homosexual behavior
– Women exposed to DES (synthetic estrogen) are
less likely to be heterosexual
• Adult Hormone Levels: no significant
difference in blood androgen levels
SEXUAL ORIENTATION

3. Birth Order
• FRATERNAL BIRTH ORDER EFFECT:
– Each older brother increases a man’s chance of being
gay by 33%
• MATERNAL IMMUNE HYPOTHESIS:
– Mothers may develop an immune response to
masculinizing hormones
– “Anti-male” antibodies may affect the sexual
differentiation of successive sons
SEXUAL ORIENTATION

4. Physiology
• Areas of the hypothalamus
– Straight men & lesbian women may be more alike
– Straight women and gay men may be more alike
• Gay men are more likely to use both sides of
their brain (similar to heterosexual women)
SEXUAL ORIENTATION

4. Physiology
• Gay men & lesbians are more likely to be left-
handed than heterosexual people
– Lesbians are 91% more likely to be left handed
than heterosexual women
– Gay men are 34% more likely
SEXUAL ORIENTATION

4. Physiology
• Finger length:
SEXUAL ORIENTATION
Female-Type Finger Pattern Male-Type Finger Pattern

SEXUAL ORIENTATION
• May result in more acceptance
• Potential for scary genetic engineering
• Should it really matter whether homosexuality is
biologically based for people to receive equal rights?

PSY-2 Ch08 Hormones & Sex

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PSY-2 Ch08 Hormones & Sex