Download Topic #7 -- introduction to the endocrine system

BIOS 472, Spring 2001
Introduction to Endocrinology
Hormone: specialized, specific chemical substances synthesized by specialized tissues that are secreted into
and carried by the blood stream to target organs and cells where they produce specific biological effects.
How to study the endocrine system: Where appropriate, understand the following points with respect to each
of the major hormones:
1. The origin within a gland
2. The synthesis and structure of the hormone
3. Storage
4. Secretion and its control (i.e., feedback loops)
5. Transport
6. Primary sites of action
7. Metabolism and secretion
8. Pathophysiology – hyposecretion, hypersecretion, dysfunction
Hormone categories
1. Amino acid derivatives
2. Peptide/protein hormones
3. Steroid hormones
Glucocorticoids
Mineralcorticoids
Androgens
Estrogens
Progestins
Calciferols
The thyroid gland -- Maintains the optimal level of metabolism for tissues
 Stimulate the O2 consumption for most of the cells of the body
 Helps regulate lipid and carbohydrate metabolism
 Necessary for growth and maturation
The thyroid is regulated by thyroid stimulating hormone (TSH) from the anterior pituitary. TSH is, in turn,
regulated by thyrotropin releasing hormone from the hypothalamus
The principle hormones secreted by the thyroid are thyroxin (T4) and triiodothyronine (T3).
The thyroid hormones enter cells and bind to thyroid receptors in the nuclei (T 3 binds much more avidly than
T4)
Specific effects
Calorigenic
Nervous system
Cardiac tissue
Skeletal muscle
Carbohydrate metabolism
The pituitary and growth
The posterior pituitary is made up lagely of the endings on blood vessels of axons from the supraoptic and
paraventricular nuclei of the hypothalamus.
ADH (anti-diuretic hormone)
Oxytocin
The anterior pituitary has a special vascular connection with the hypothalamus
Thyroid stimulating hormone (TSH)
Adrenocorticotropic hormone (ACTH)
Luteinizing hormone (LH)
Follicle-stimulating hormone (FSH)
Prolactin
Growth hormone (GH, somatotropin)
Growth hormone
Chondrogenesis is accelerated
Viscera growth
Increase protein mass/decrease fat mass
Somatomedins – polypeptide growth factors secreted by the liver and other tissues in response to
stimulation by GH
Insulin-like growth factor I (IGF- I)
Insulin-like growth factor II (IGF-II)
In general, GH doesn’t directly affect growth, but rather sets cells up to respond to IGF. For
example, GH acts on cartilage to convert stem cells into cells that respond to IFG-I, that promotes
chondrogenesis
GH is regulated through the hypothalamus. GHRH from hypothalamus triggers GH release.
 GHRH =  GH =  IGF-I = GH release
Of course, growth is a complex phenomena that is affected by not only GH and Somatomedins, but thryoid
hormones, androgens and estrogens, glucocorticoids, insulin, and proper nutrition.