located on anterior surface of trachea, inferior to larynx only endocrine gland that stores its hormones in large quantities (up to 3 mo. worth) Thyroid follicle cells utilize iodine from the diet to produce the thyroid hormones : thyroxine (T 4 ) and triiodothyronine (T 3 ) o Production and release of these hormones controlled by TSH from anterior pituitary o Function: stimulates cellular metabolism and is referred to as the body’s major metabolic hormone because of its widespread effects C cells or parafollicular cells of thyroid gland produce calcitonin o Function: reduces Ca 2+ concentration in blood o Mechanisms: Stimulates osteoblasts (bone making cells) inhibits osteoclasts (breakdown of bone) 5
Increases the kidney’s excretion of Ca 2+ o Calcitonin released in response to Ca 2+ concentration of blood ↑ Ca 2+ concentration stimulates calcitonin release from C cells ↓ Ca 2+ inhibits calcitonin release Parathyroid Glands 2-4 glands located on the posterior surface of the thyroid gland chief cells produce parathyroid hormone (PTH) o Function: increase Ca 2+ concentration of blood o Mechanisms: Stimulates osteoclasts bone resorption increased blood Ca 2+ Inhibits osteoblasts Increases Ca 2+ reabsorption in kidneys Converts Vitamin D to active form (calcitriol) increases Ca 2+ absorption by small intestine Adrenal Glands On superior aspect of each kidney Each gland is two endocrine glands in one Adrenal Medulla o Directly stimulated by the sympathetic nervous system (i.e., cells are innervated by sympathetic preganglionic fibers) o releases the hormones Norepinephrine (NE) and Epinephrine (Epi) , which are called catecholamines o catecholamines produce effects similar to those of the SNS (i.e., fight or flight response) increased respiration rate increased diameter of airway increased HR and force of contraction mobilization of energy reserves redistribution of blood flow vasoconstriction to nonessential organs (e.g., urinary, digestive) vasodilation to essential organs increased blood flow (skeletal muscle, lungs, brain, heart) Adrenal Cortex o Divided into 3 layers that produce hormones that are collectively called corticosteroids o each layer produces a particular type of corticosteroid 1. Mineralcorticoids (outer region) Primary hormone is aldosterone Function: maintains H 2 O and electrolyte (Na + and K + ) balance mechanisms: ↓ Na + and/or ↑ K + directly stimulates aldosterone release net result: ↑ Na + reabsorption and ↑ K + secretion at kidney ↑ Na + reabsorption = ↑ H 2 O reabsorption ↓ blood volume triggers the release of aldosterone via rennin-angiotensin system 2. Glucocorticoids (middle layer) Most abundant hormone is cortisol Function: effects nutrient metabolism 6
o (+) synthesis of new glucose molecules from non-glucose substrates (gluconeogenesis) o (+) lipolysis (Fat fatty acids) o (+) proteolysis (Protein amino acids) 7
Control of secretion: o
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