Chemical Classification Of Hormones

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Chemical Classification Of Hormones

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Endocrine System
-Endocrine glands (ductless) secrete hormones  
intercellular chemical messengers that are secreted into the blood and each target cells thru circulation
Chemical classes of hormones
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
Thyroid Gland
-anterior neck -circular arrangement of epithelial cells surround thyroid follicle; no blood within follicle
Synthesis of T3 and T4 in Thyroid Gland
-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
Storage of T3 and T4 in Thyroid Gland
-Thyroglobulin is the colloid in follicular lumen -Thyrogloblin = storage form of T3 and T4
Release of T3 and T4 from Thyroid Gland
-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)
Transport of T4 and T3 in Blood
-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  
Intracellular Actions of T4 and T3 in Target Cells
-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
Actions of Thyroid Hormone on Target Tissues
-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)
Symptoms of Hypothyroidism
-Low BMR -Cold intolerance -Weight gain -Lethargy -Slow reflexes
Symptoms of Hyperthyroidism
-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
Catecholamine Receptors
Types: -Adrenergic- NE and Epi -Dopaminergic- Dop   Location: plasma membrane   Receptors: act as ion channels, enzymes, or allosteric activation of G proteins
Actions of NE and Epi
Heart: stim HR and force of contraction (CO, BP)   Vascular smooth muscle: stimulates contraction and/or relaxation (BP)   Liver and skeletal muscle: carb metabolism (stim glycogenolysis and gluconeogenesis (blood glucose))   Adipose tissue: fat metabolism (stim lipolysis (energy, blood glucose))   Pancreatic islets: hormone secretion (inhibit insulin sec, stim glucagon secretion)
Actions of Dopamine
Ant Pit Gland: inhibits prolaction secretion
Snthesis of proteins
Preprohormone Prohormone Hormone Hormone
Protein/Peptide hormones
-Most hormones -Hypothalamus: most -Post and Ant Pit: all -GI system: all -Pancreas: important ones for metabolism
Protein/Peptide Receptors
-Many types -Location: plasma membranes (polar) -Receptors: act as ion channels, enzymes, or allosteric activation of G proteins
Steroid Hormones
-derived from cholesterol -highly nonpolar --> not stored
Adrenal Gland
Medulla = inner Cortex = outer   1. Zona Glomerulosa- aldosterone 2. Zona Fasiculata- cortisol, androgens 3. Zona Reticularis- Epi and NE
Major Steroid Hormones of Adrenal Cortex
1. Corticosterone 2. Aldosterone 3. Cholesterol 4. Cortisol 5. Androgens = Dehydroepiandrosterone and Androsternedione
Types of Adrenocortical Steroids
1. Mineralcorticoids -Actions on renal handling of minerals (Na and K) -Aldosterone and Corticosterone   2. Glucocorticoids -Actions on carb metabolism -Actions in stress responses -Cortisol and Corticosterone   3. Androgens -Actions similar to those of testosterone, but weaker -Dehydroepiandrosterone (DHEA) -Androstenedione (ASD)
Transport of Adrenal Corticosteroids in Blood
-Binding to corticosteroid binding globulin (CBG) -Most in blood are bound -Only free form are active
Intracellular Actions of Adrenal Corticosteroids in Target Cells
-Diffuse into target cells -Receptors for corticosteroids are intracellular -Hormone-receptor complexes act as transcription factors
Actions of Normal Basal Concentrations of Cortisol on Target Tissues
-Permissive for catecholamine actions on vascular smooth muscle (bp) -Permissive for enzyme levels that mediate gluconeogenesis (liver) and lipolysis (adipose) -Permissive for normal fetal and neonatal dev
Actions of Stress Levels (Inc conc) of Cortisol on Target Tissues
-Enhanced vascular reactivity to catecholamines (bp) -Enhanced actions on metabolism to provide extra fuel sources and to maintain blood glucose: inc. protein catabolism. gluconeogensis, lipolysis dec. glucose uptake by skeletal muscle and adipose tissue
Gonadal Steroid Hormones
Males: Androgens    Testosterone   Females: Estrogens    Estradiol Progesterone   *estrogen is generic term that included estrone, estradiol, etic.
Testes = testosterone
Ovaries = predominant steroid varies w/ phase of menstrual cycle Follicular phase (1st 2 wks) = Estradiol Luteal phase (2nd 2 wks) = Progesterone
Transport of Gondal Steroids in Blood
-Binding to sex hormone binding globulin (SHBG) -Most are bound form -Free form is active
Intracellular Actions of Gonadal Steroids on Target Tissues
-Diffuse into target cells -Location = intracellular -Hormone-receptor complexes act as transcription factors
Conversion of Gonadal Steroids to Active Forms in Some Target Cells in Male
Testosterone -> 5-alpha-Dihydrotestosterone   Testosterone -> Estradiol
Mechanism of Action of Hormones with Intracelullular Receptors
-Free hormone diffuses through cell (nonpolar) -Receptors in nucleus -Function as transcription factor
Mechanism of Action of Hormones with Plasma Membrane Receptors
-Polar -Receptors on plasma membranes
Regulation of Hormone Receptors
-By natural hormonal ligands: up and down reg -By other hormones: permissive effects, whereby presence of one hormone is necessary for action of another hormone
Permissive Action of Thyroid Hormone on Epinephrine-Induced Lipolysis
Thyroid hormone = little effect   Epinephrine = min effect   TH and Epi = large effect