hormones & the endocrine system. i. the effects of prenatal hormones on sexual development xx...
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Hormones & the Endocrine System
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I. The Effects of Prenatal Hormones on Sexual Development XX & XY – first 6 weeks of life all embryos are female1. 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
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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**
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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
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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
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An interesting wrinkle based on animal research:
Aromatization hypothesis – for masculinizing the brain (testosterone
estradiol): see diagram
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Aromatization of Testosterone
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Male disorders (too little or ineffective testosterone) – androgenic insensitivity 1. XY: X chromosome is responsible for
the testosterone receptorsi. These receptors become insensitive
to testosteroneii. Child is born with appearance of female genitalia
**Mullerian inhibiting system is okay; so internal organs are not female**
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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
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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.
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Hormones are Extremely Powerful
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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)
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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
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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
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Major Glands of the Endocrine System
• Hypothalamus
• Pituitary
• Thyroid
• Adrenal
• Gonads: Ovaries & Testes
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Six Highlighted Endocrine Glands
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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
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• Posterior Pituitary - derived from nervous tissue - two protein hormones released: oxytocin &
vasopressin _________________________________
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.
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Hypothalamus
Anterior Pituitary Posterior Pituitary
Target Organs Target Organs
RF
SH
Hormone
Hormone
RF = Releasing Factor SH = Stimulating Hormone
Pituitary & all Hormones are Under the Control of the Hypothalamus
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Hypothalamic Hormones:
Gondotropin RF Corticotropin RF
(CRF)
Thyrotropin RF Growth Hor RF Prolactin RF
Pituitary Hormones:
Follicle SH &
Lutenizing Hor.
Thyrotropin SHAdrenocorticoptropin
Hormone (ACTH)
ProlactinGrowth
Hormone
Target Gland or Structure:
Ovaries & Testes
(androgens, estrogen)
Adrenal Gland
(cortisol)
Cells of bodyThyroid Gland
(thyroxine)
Bones, breasts & cells of body
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Adrenal Glandi. 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
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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
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Gonads & Hormones
LH & FSH
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Growth Hormone
Cells of body in response to growth hormonei. During childhood GH is at maximum
1. Too little and we have a small person2. 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
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Oxytocin
• The hormone involved in inducing labor during childbirth
• Hormone involved in bonding
• Hormone involved in relationships
• Might be deficient in Autism
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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
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Feedback Mechanisms
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Hormones are Extremely Powerful
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Ultimately,what controls the endocrine system?
• Our emotions• Our perceptions• Our cognitions• Our experiences• Our behavior• Our response to the environment
Higher Brain Areas
Hypothalamus
Pituitary
Endocrine Glands