Chemical Classification of Hormones

-Endocrine glands (ductless) secrete hormones

Intercellular chemical messengers that are secreted into the blood and each target cells thru circulation

1. Amines 2. Proteins and Peptides 3. Steroids

-derivative of tyrosine * Thyroid Hormones -T3 and T4 (secretes more T4, but T3 has higher activity) * Catecholamines -Norepinephrine, Epinephrine, and Dopamine

-anterior neck -circular arrangement of epithelial cells surround thyroid follicle; no blood within follicle

-Uptake of I- from blood and transport thru epithelial cells of thyroid follicles into follicular lumen -Secretion of Thyroglobulin into follicular lumen -Oxidation of I- to I and incorporation into thyroid hormone molecules that are part of Thyroglobulin

-Thyroglobulin is the colloid in follicular lumen -Thyrogloblin = storage form of T3 and T4

-Endocytosis of thyroglobulin by thyroid follicular cells -Intracellular hydrolysis of thyroglobulin, which yields 3 thyroid hormone molecules -Release of T4 and T3 into blood (most is T4)

-Binding to thyroxine-binding globulin (TBG) -Most T3 and T4 in blood are in bound form -Only free form is active (can be taken into target) *T3 and T4 - nonpolar so can bind to TBG

-Carrier-mediated uptake of T3 and T4 into target cells -T4 converted to T3 by intracellular deiodinase -T3 enters nucleus and binds to thyroid hormone receptors -Hormone-receptor complex acts as transcription factor

-Target tissues = all tissues in body, except RBCs (no nucleus) Actions: - stimulation of MR (calorigenic effect) -increased activity of Na/K-ATPase -Permissive for catecholamine effects (permissive = presence of one hormone is necessary for action of another)- upregulation of beta adrenergic receptors -Tissue growth- synthesis and growth-promoting actions of growth hormone from ant pit. -Nervous system development and function- fetal brain dev and postnatal nervous system func (reflex, cognition)

-Low BMR -Cold intolerance -Weight gain -Lethargy -Slow reflexes

-High BMR -Heat intolerance -Weight loss -Hyperactivity -Rapid reflexes

Sources: Adrenal medulla- norepinephrine (20%) and epinephrine (80%) Hypothalamus- dopamine -Transported thru circulation w/o binding protein - very water soluble

Types: -Adrenergic- NE and Epi -Dopaminergic- Dop Location: plasma membrane Receptors: act as ion channels, enzymes, or allosteric activation of G proteins