Hormones & the Endocrine System

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

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 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**

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

• 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 _________________________________

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.

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

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

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

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 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

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?

• Our emotions• Our perceptions• Our cognitions• Our experiences• Our behavior• Our response to the environment

Higher Brain Areas

Hypothalamus

Pituitary

Endocrine Glands