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

2. By 12 weeks after conception a process of masculinization is occurs 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 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

1. Estrogen, progesterone, androgens ii. Adrenal hormones 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.

Pituitary & all Hormones are Under the Control of the Hypothalamus RF Hormone Anterior Pituitary Posterior Pituitary Hormone SH Target Organs Target Organs RF = Releasing Factor SH = Stimulating Hormone

Hypothalamic Hormones: Gondotropin RF Corticotropin RF (CRF) Thyrotropin RF Growth Hor RF Prolactin RF Pituitary Hormones: Growth Hormone Prolactin Adrenocorticoptropin Hormone (ACTH) Thyrotropin SH Follicle SH & Lutenizing Hor. Target Gland or Structure: Bones, breasts & cells of body Cells of body Ovaries & Testes (androgens, estrogen) Adrenal Gland (cortisol) Thyroid Gland (thyroxine)

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? Higher Brain Areas Hypothalamus Pituitary Endocrine Glands Our emotions Our perceptions Our cognitions Our experiences Our behavior Our response to the environment