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Hormones & the Endocrine
System
I. The Effects of Prenatal Hormones on
Sexual Development
XX & XY – first 6 weeks of life all
embryos are female
1. Primordial gonads
a. Mullerian system – Female, destined to
form female internal organs & female
external genitalia
b. Wolffian system – Male equivalent,
destined to form male internal organs &
male external genitalia
1. All children are born with both, there is an active
process that allows Wolffian system to take over and
make males.
2. By 12 weeks after conception a process of
masculinization is occurs
i. Synthesis of H-Y antigen (about 6 weeks) leads to
the synthesis of testosterone, which activates the
Wolffian system & Mullierian Inhibiting Substance
which blocks further development of the female
system
**Maternal estrogen does not cross the blood-placental barrier**
**Testosterone can cross the blood-placental barrier**
In the body of the of the developing fetus:
Testosterone: Responsible for
masculinizing male genitalia
(testosterone binds to androgen receptor
for masculine genitalia)
Female disorders (too much testosterone)
1. For triplets with 1 female and 2 males
the female will have enlarged
external genitalia
2. Adrenal congenital hyperplasia –
There is a balance between
testosterone & corticosteroids, in this
disorder there is too little
corticosteroids which results in
increased testosterone
i. Testosterone crosses blood – placental
barrier and masculinizes female
genitalia in female fetus’s,
“intersexed appearance”
ii. Testosterone is undergoing
aromatization to masculinize the brain
An interesting wrinkle based on animal
research:
Aromatization hypothesis – for
masculinizing the brain (testosterone 
estradiol): see diagram
Aromatization of Testosterone
Male disorders (too little or ineffective testosterone) –
androgenic insensitivity
1. XY: X chromosome is responsible for
the testosterone receptors
i. These receptors become insensitive to
testosterone
ii. Child is born with appearance of
female genitalia
**Mullerian inhibiting system is okay; so
internal organs are not female**
II. Endocrine System vs Neuronal System
1. Neural & Hormonal communication
a. Similarities
i. Chemicals are stored and released
ii. Release of chemicals is due to stimulation
iii. Many different hormones &
neurotransmitters
iv. Both systems react w/specific receptors
v. Second messenger involved in both
(The first messenger reacts to the
initial signal - like an ionotropic
receptor, found in CNS only)
2. Second messenger reacts to a signal
from a first messenger (like a
metabotropic receptor) and affects
intracellular functioning; it is a
complex intracellular response that
affects functioning.
Hormones are Extremely Powerful
b. Differences
i. In nervous system, neurons communicate with
adjacent neurons; in hormones messages are sent
long distances
ii. Neural messages induce rapid response
compared to hormones which have slower messages
iii. Neural messages follow the all or none
principle; hormonal messages are graded in strength
iv. Neural messages can be directed as observed in
behavior; hormonal messages are primarily
involuntary (cannot be directed)
2. Three types of hormones
a. Protein hormones – effect is on receptors
within the membrane, binds to the receptors on
the outside of membrane; its effects are the
most rapid of all the hormones
i. Oxytocin – involved in development of
relationships
ii. Adrenocorticotrophin – protein hormone;
chains of amino acids
b. Amine hormones – same relatively fast
receptor response as protein hormones
i. Epinepherine
ii. Norepinepherine
iii. Thyroid hormones
iv. Melatonin
c. Steroid hormones – binds to the
intercellular receptors; slow actions
i. Gonadal hormones
1. Estrogen, progesterone, androgens
ii. Adrenal hormones
1. Glucocorticoids, mineralocorticoids
Major Glands of the Endocrine
System
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Hypothalamus
Pituitary
Thyroid
Adrenal
Gonads: Ovaries & Testes
Six Highlighted Endocrine Glands
Pituitary
• Anterior Pituitary
- derived during embryological
development from the roof of the mouth
- connected to the hypothalamus by a portal
system (hypothalamic-pituitary portal
system)
- most of the hormones are released from
the anterior pituitary
• Posterior Pituitary
- derived from nervous tissue
- two protein hormones released: oxytocin &
vasopressin
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Two Important Points:
Hormones released from the posterior pituitary are
synthesized in the hypothalamus.
Hormones released from the anterior pituitary are
dormant unless directed to be released by the
hypothalamus via Releasing Factors.
Pituitary & all Hormones are Under the
Control of the Hypothalamus
Hypothalamus
RF
Anterior Pituitary
SH
Target Organs
Hormone
Posterior Pituitary
Hormone
Target Organs
RF = Releasing Factor SH = Stimulating Hormone
Hypothalamic Hormones:
Gondotropin RF
Corticotropin RF
Thyrotropin RF
Growth Hor RF
Prolactin RF
(CRF)
Pituitary Hormones:
Follicle SH &
Lutenizing Hor.
Adrenocorticoptropin Thyrotropin SH Growth
Hormone
Hormone (ACTH)
Prolactin
Target Gland or Structure:
Ovaries & Testes
(androgens, estrogen)
Adrenal Gland
Thyroid Gland
(cortisol)
(thyroxine)
Cells of body
Bones, breasts
& cells of body
Adrenal Gland
i. Adrenal cortex (outer) produces about 50 different
chemicals including…
1. Mineralocorticoids (outer layer)
2. Glucocorticoids, cortisol (middle layer)
3. Sex hormones (inner most layer)
a. Estrogen, progesterone androgens
note: Congenital adrenal hyperplasia – too much testosterone
produced by mother. This comes from dysfunction in adrenal gland.
ii. Adrenal medulla (inner)
1. Dopamine  Norepinepherine/Epinepherine
Thyroid Gland
1. Too little thyroxin – hypothyroidism
a. Depression (clinical or subclinical),
attention & memory problems
2. Too much thyroxin – hyperthyroidism
a. Agitation, irritability, & weight loss
*Goiters – Growths on thyroid gland
Gonads & Hormones
LH & FSH
Growth Hormone
Cells of body in response to growth hormone
i. During childhood GH is at maximum
1. Too little and we have a small person
2. Too much and we have gigantism,
often accompanied by acromegaly
(continued growth of extremities of
bones)
a. Makes hands, feet, jaw, nose, and
eye sockets (orbits) enlarged
Oxytocin
• The hormone involved in inducing labor
during childbirth
• Hormone involved in bonding
• Hormone involved in relationships
• Might be deficient in Autism
All hormones utilize feedback loops:
Autocrine response – Same as the
autoreceptors, both communicate and
terminate release
Note similarity to the CNS:
Autoreceptors – in the CNS the receptors on
presynaptic cell that are sensitive to its own
NT
Feedback Mechanisms
Hormones are Extremely Powerful
Ultimately,what controls the
endocrine system?
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Higher Brain Areas
Our emotions
Our perceptions
Our cognitions
Our experiences
Our behavior
Our response to
the environment
Hypothalamus
Pituitary
Endocrine Glands