18-1 Thyroid Gland On each side of trachea is lobe of thyroid Weighs 1 oz & has rich blood supply

18-2 Photomicrograph of Thyroid Gland

Copyright 2009, John Wiley & Sons, Inc.

Thyroid Gland Located inferior to larynx 2 lobes connected by isthmus Thyroid follicles produce thyroid hormones  Thyroxine or tetraiodothyronine (T 4 )  Triiodothyronine (T 3 ) Both increase BMR, stimulate protein synthesis, increase use of glucose and fatty acids for ATP production,and growth increases sympathetic activity Parafollicular cells or C cells produce calcitonin  Lowers blood Ca 2+ by inhibiting bone resorption

18-5 Actions of Thyroid Hormones T3 & T4 = thyroid hormones responsible for our metabolic rate, synthesis of protein, breakdown of fats, use of glucose for ATP production

Copyright 2009, John Wiley & Sons, Inc. Control of thyroid hormone secretion  Thyrotropin-releasing hormone (TRH) from hypothalamus  Thyroid-stimulating hormone (TSH) from anterior pituitary  Situations that increase ATP demand also increase secretion of thyroid hormones

Low blood levels of T 3 and T 3 or low metabolic rate stimulate release of Hypothalamus TRH Actions of Thyroid Hormones: Increase basal metabolic rate Stimulate synthesis of Na + /K + ATPase Increase body temperature (calorigenic effect) Stimulate protein synthesis Increase the use of glucose and fatty acids for ATP production Stimulate lipolysis Enhance some actions of catecholamines Regulate development and growth of nervous tissue and bones 1 Anterior pituitary TRH, carried by hypophyseal portal veins to anterior pituitary, stimulates release of TSH by thyrotrophs Low blood levels of T 3 and T 3 or low metabolic rate stimulate release of Hypothalamus TSH TRH Actions of Thyroid Hormones: Increase basal metabolic rate Stimulate synthesis of Na + /K + ATPase Increase body temperature (calorigenic effect) Stimulate protein synthesis Increase the use of glucose and fatty acids for ATP production Stimulate lipolysis Enhance some actions of catecholamines Regulate development and growth of nervous tissue and bones 1 2 Anterior pituitary TRH, carried by hypophyseal portal veins to anterior pituitary, stimulates release of TSH by thyrotrophs TSH released into blood stimulates thyroid follicular cells Thyroid follicle Low blood levels of T 3 and T 3 or low metabolic rate stimulate release of Hypothalamus Anterior pituitary TSH TRH Actions of Thyroid Hormones: Increase basal metabolic rate Stimulate synthesis of Na + /K + ATPase Increase body temperature (calorigenic effect) Stimulate protein synthesis Increase the use of glucose and fatty acids for ATP production Stimulate lipolysis Enhance some actions of catecholamines Regulate development and growth of nervous tissue and bones T 3 and T 4 released into blood by follicular cells TRH, carried by hypophyseal portal veins to anterior pituitary, stimulates release of TSH by thyrotrophs TSH released into blood stimulates thyroid follicular cells Thyroid follicle Low blood levels of T 3 and T 3 or low metabolic rate stimulate release of Hypothalamus Anterior pituitary TSH TRH Actions of Thyroid Hormones: Increase basal metabolic rate Stimulate synthesis of Na + /K + ATPase Increase body temperature (calorigenic effect) Stimulate protein synthesis Increase the use of glucose and fatty acids for ATP production Stimulate lipolysis Enhance some actions of catecholamines Regulate development and growth of nervous tissue and bones T 3 and T 4 released into blood by follicular cells Elevated T 3 inhibits release of TRH and TSH (negative feedback) TRH, carried by hypophyseal portal veins to anterior pituitary, stimulates release of TSH by thyrotrophs TSH released into blood stimulates thyroid follicular cells Thyroid follicle Low blood levels of T 3 and T 3 or low metabolic rate stimulate release of Hypothalamus Anterior pituitary TSH TRH Actions of Thyroid Hormones: Increase basal metabolic rate Stimulate synthesis of Na + /K + ATPase Increase body temperature (calorigenic effect) Stimulate protein synthesis Increase the use of glucose and fatty acids for ATP production Stimulate lipolysis Enhance some actions of catecholamines Regulate development and growth of nervous tissue and bones

Copyright 2009, John Wiley & Sons, Inc. Thyroid Gland Located inferior to larynx 2 lobes connected by isthmus Thyroid follicles produce thyroid hormones  Thyroxine or tetraiodothyronine (T 4 )  Triiodothyronine (T 3 ) Both increase BMR, stimulate protein synthesis, increase use of glucose and fatty acids for ATP production increases sympathetic activity Parafollicular cells or C cells produce calcitonin  Lowers blood Ca 2+ by inhibiting bone resorption

18-9 Actions of Thyroid Hormones T3 & T4 = thyroid hormones responsible for our metabolic rate, synthesis of protein, breakdown of fats, use of glucose for ATP production Calcitonin = responsible for building of bone & stops reabsorption of bone (lower blood levels of Calcium)

18-10 Parathyroid Glands 4 pea-sized glands found on back of thyroid gland

Copyright 2009, John Wiley & Sons, Inc. Parathyroid Glands Embedded in lobes of thyroid gland Usually 4 Parathyroid hormone (PTH) or parathormone  Major regulator of calcium, magnesium, and phosphate ions in the blood  Increases number and activity of osteoclasts  Elevates bone resorption Blood calcium level directly controls secretion of both calcitonin and PTH via negative feedback

18-12 Parathyroid Hormone Raise blood calcium and Mg levels (decrease HPO4) -2 )  increase activity of osteoclasts  increases reabsorption of Ca+2 by kidney  increase loss of phosphate (HPO4) -2 in urine  promote formation of calcitriol (vitamin D3) by kidney which increases absorption of Ca+2, HPO4 and Mg+2 by intestinal tract Opposite function of calcitonin

1 High level of Ca 2+ in blood stimulates thyroid gland parafollicular cells to release more CT. 1 High level of Ca 2+ in blood stimulates thyroid gland parafollicular cells to release more CT. CALCITONIN inhibits osteoclasts, thus decreasing blood Ca 2+ level. 2 1 High level of Ca 2+ in blood stimulates thyroid gland parafollicular cells to release more CT. Low level of Ca 2+ in blood stimulates parathyroid gland chief cells to release more PTH. CALCITONIN inhibits osteoclasts, thus decreasing blood Ca 2+ level High level of Ca 2+ in blood stimulates thyroid gland parafollicular cells to release more CT. Low level of Ca 2+ in blood stimulates parathyroid gland chief cells to release more PTH. CALCITONIN inhibits osteoclasts, thus decreasing blood Ca 2+ level. PARATHYROID HORMONE (PTH) promotes release of Ca 2+ from bone extracellular matrix into blood and slows loss of Ca 2+ in urine, thus increasing blood Ca 2+ level PTH also stimulates the kidneys to release CALCITRIOL. High level of Ca 2+ in blood stimulates thyroid gland parafollicular cells to release more CT. Low level of Ca 2+ in blood stimulates parathyroid gland chief cells to release more PTH. CALCITONIN inhibits osteoclasts, thus decreasing blood Ca 2+ level. PARATHYROID HORMONE (PTH) promotes release of Ca 2+ from bone extracellular matrix into blood and slows loss of Ca 2+ in urine, thus increasing blood Ca 2+ level CALCITRIOL stimulates increased absorption of Ca 2+ from foods, which increases blood Ca 2+ level. PTH also stimulates the kidneys to release CALCITRIOL. High level of Ca 2+ in blood stimulates thyroid gland parafollicular cells to release more CT. Low level of Ca 2+ in blood stimulates parathyroid gland chief cells to release more PTH. CALCITONIN inhibits osteoclasts, thus decreasing blood Ca 2+ level. PARATHYROID HORMONE (PTH) promotes release of Ca 2+ from bone extracellular matrix into blood and slows loss of Ca 2+ in urine, thus increasing blood Ca 2+ level

18-14 Adrenal Glands One on top of each kidney 3 x 3 x 1 cm in size and weighs 5 grams Cortex produces 3 different types of hormones from 3 zones of cortex Medulla produces epinephrine & norepinephrine

18-15 Structure of Adrenal Gland Cortex derived from mesoderm Medulla derived from ectoderm

Copyright 2009, John Wiley & Sons, Inc. Adrenal Glands 2 structurally and functionally distinct regions  Adrenal cortex Mineralocorticoids affect mineral homeostasis Glucocorticoids affect glucose homeostasis  Cortisol “hydrocortisone”, corticosterone and cortisone Androgens have masculinzing effects  Dehydroepiandrosterone (DHEA) only important in females  Adrenal medulla Modified sympathetic ganglion of autonomic nervous system Intensifies sympathetic responses Epinephrine and norepinephrine

18-17 Mineralocorticoids 95% of hormonal activity due to aldosterone Functions  increase reabsorption of Na+ with Cl-, bicarbonate and water following it  promotes excretion of K+ and H+ Hypersecretion = tumor producing aldosteronism  high blood pressure caused by retention of Na+ and water in blood

18-18 Regulation of Aldosterone

18-19 Glucocorticoids 95% of hormonal activity is due to cortisol Functions = help regulate metabolism  increase rate of protein catabolism & lipolysis  conversion of amino acids to glucose  stimulate lipolysis  provide resistance to stress by making nutrients available for ATP production  raise BP by vasoconstriction  anti-inflammatory effects reduced reduce release of histamine from mast cells decrease capillary permeability depress phagocytosis Decrease tissue repair

18-20 Adrenal Medulla Chromaffin cells receive direct innervation from sympathetic nervous system  develop from same tissue as postganglionic neurons Produce epinephrine & norepinephrine Hormones are sympathomimetic  effects mimic those of sympathetic NS  cause fight-flight behavior Acetylcholine increase hormone secretion by adrenal medulla