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Endocrine System Part 2 Thyroid Gland Saddle bag shaped gland Largest endocrine gland in the body 3 hormones Throxin Triiodothyronine Calcitonin Thyroid hormone Pineal gland Hypothalamus Pituitary gland Thyroid gland Parathyroid glands (on dorsal aspect of thyroid gland) Thymus Adrenal glands Pancreas Ovary (female) Testis (male) Copyright © 2010 Pearson Education, Inc. Figure 16.1 Figure 16.8 Thyroid Hormone (TH) Actually two related compounds T4 (thyroxin) 2 tyrosine molecules + 4 bound iodine atoms T3 (triiodothyronine) 2 tyrosines + 3 bound iodine atoms Thyroid Hormone (TH) 1) 2) 3) 4) 5) 6) 7) Iodide enters body Converted to iodine by thyroid gland Iodine binds to thyroglobulin Tyrosine added to iodized thyroglobulin, combined in vacuole with lysosomes Thyroglobulin freed and recycled while T3/T4 diffuses into blood T3/T4 bind to thyroxin-binding globulin in blood At tissue receptor T4 converted to active T3 by tissue enzymes Thyroid follicle cells Colloid 1 Thyroglobulin is synthesized and discharged into the follicle lumen. Tyrosines (part of thyroglobulin molecule) Capillary 4 Iodine is attached to tyrosine in colloid, forming DIT and MIT. Golgi apparatus Rough ER Iodine 3 Iodide is oxidized to iodine. 2 Iodide (I–) is trapped (actively transported in). Iodide (I–) Lysosome T4 T3 DIT (T2) MIT (T1) Thyroglobulin colloid 5 Iodinated tyrosines are linked together to form T3 and T4. T4 T3 T4 T3 6 Thyroglobulin colloid is endocytosed and combined with a lysosome. 7 Lysosomal enzymes cleave T4 and T3 from thyroglobulin colloid and hormones diffuse into bloodstream. Colloid in lumen of follicle To peripheral tissues Figure 16.9 Thyroid Hormone (TH) Major metabolic hormone (catabolism) Regulates tissue growth and development Increases reactivity of mature nerve cells Regulates heart rate Regulates movement of gastrointestinal tract Hypothalamus TRH Anterior pituitary TSH Thyroid gland Thyroid hormones Target cells Stimulates Inhibits Copyright © 2010 Pearson Education, Inc. Figure 16.7 Imbalances of Thyroid Hormone Goiter Cretinism Myxedema Graves’ disease Copyright © 2010 Pearson Education, Inc. Figure 16.10 Calcitonin Lowers serum calcium Inhibits bone resorption Stimulates uptake by the bone matrix Antagonist to parathyroid hormone (PTH) Regulated by Ca2+ concentration in the blood Negative feedback mechanism Parathyroid Glands Four tiny glands embedded in the posterior aspect of the thyroid Parathyroid hormone (PTH) Most important hormone in Ca2+ homeostasis Pharynx (posterior aspect) Thyroid gland Parathyroid glands Chief cells (secrete parathyroid hormone) Oxyphil cells Esophagus Trachea (a) Copyright © 2010 Pearson Education, Inc. Capillary (b) Figure 16.11 Parathyroid Hormone Functions Stimulates osteoclasts to digest bone matrix Enhances reabsorption of Ca2+ by the kidneys Increases absorption of Ca2+ by intestinal mucosa Negative feedback Rising Ca2+ in the blood inhibits PTH release Hypocalcemia (low blood Ca2+) stimulates parathyroid glands to release PTH. Rising Ca2+ in blood inhibits PTH release. Bone 1 PTH activates osteoclasts: Ca2+ and PO43S released into blood. Kidney 2 PTH increases 2+ Ca reabsorption in kidney tubules. 3 PTH promotes kidney’s activation of vitamin D, which increases Ca2+ absorption from food. Intestine Ca2+ ions PTH Molecules Copyright © 2010 Pearson Education, Inc. Bloodstream Figure 16.12 Adrenal Glands Paired, pyramid-shaped glands atop the kidneys Essentially two glands in one Adrenal medulla Nervous tissue: part of the sympathetic nervous system NE and Epinephrine Adrenal cortex Three layers of glandular tissue Synthesize and secrete steroid hormones Pineal gland Hypothalamus Pituitary gland Thyroid gland Parathyroid glands (on dorsal aspect of thyroid gland) Thymus Adrenal glands Pancreas Ovary (female) Testis (male) Figure 16.1 Adrenal Cortex Three layers that produce corticosteroids Outer layer = mineralocorticoids Middle layer = glucocorticoids Inner layer = sex hormones, or gonadocorticoids Capsule Zona glomerulosa • Medulla • Cortex Cortex Adrenal gland Zona fasciculata Zona reticularis Medulla Kidney Adrenal medulla (a) Drawing of the histology of the adrenal cortex and a portion of the adrenal medulla Figure 16.13a Mineralocorticoids Regulate extracellular Na+ and K+ Na+: affects ECF volume, blood volume, blood pressure K+: sets resting membrane potential of cells Aldosterone is most important Stimulates Na+ reabsorption (and water retention) by kidneys Stimulates K+ secretion Primary regulators Secretion mainly controlled by blood pressure and potassium levels Blood volume and/or blood pressure Other factors K+ in blood Stress Blood pressure and/or blood volume Hypothalamus Kidney Heart CRH Renin Initiates cascade that produces Direct stimulating effect Anterior pituitary Atrial natriuretic peptide (ANP) ACTH Angiotensin II Inhibitory effect Zona glomerulosa of adrenal cortex Enhanced secretion of aldosterone Targets kidney tubules Absorption of Na+ and water; increased K+ excretion Blood volume and/or blood pressure Figure 16.14 Glucocorticoids Regulate carbohydrate metabolism Keep blood sugar levels relatively constant Gluconeogenesis Suppress inflammation Vasoconstriction Vessel permeability Stabilizing lysosomes Imbalances of Glucocorticoids Cushing’s disease Addison’s disease Also involves deficits in mineralocorticoids Figure 16.15 Gonadocorticoids (Sex Hormones) Most are androgens (male sex hormones) Converted to testosterone in tissue cells or estrogens in females Supplement hormones secreted by gonads May contribute to Onset of puberty Secondary sex characteristics Sex drive Adrenal Medulla Epinephrine Affects the metabolic rate of all cells Bronchial dilation Increased blood flow to skeletal muscles and heart Norepinephrine Increased blood pressure Increased heart rate Increased stroke volume Short-term stress More prolonged stress Stress Nerve impulses Hypothalamus CRH (corticotropinreleasing hormone) Spinal cord Corticotroph cells of anterior pituitary To target in blood Preganglionic sympathetic fibers Adrenal medulla (secretes amino acidbased hormones) Catecholamines (epinephrine and norepinephrine) Short-term stress response 1. Increased heart rate 2. Increased blood pressure 3. Liver converts glycogen to glucose and releases glucose to blood 4. Dilation of bronchioles 5. Changes in blood flow patterns leading to decreased digestive system activity and reduced urine output 6. Increased metabolic rate Adrenal cortex (secretes steroid hormones) ACTH Mineralocorticoids Glucocorticoids Long-term stress response 1. Retention of sodium and water by kidneys 2. Increased blood volume and blood pressure 1. Proteins and fats converted to glucose or broken down for energy 2. Increased blood glucose 3. Suppression of immune system Figure 16.16 Imbalances in Adrenal Medulla Adrenal medullary hormones not essential for life Pheochromocytoma Pancreas Long, flat gland near stomach Exocrine function Produces enzyme-rich juice for digestion Endocrine function Pancreatic islets (islets of Langerhans) Alpha () cells = glucagon Hyperglycemic hormone Beta () cells = insulin Hypoglycemic hormone Pineal gland Hypothalamus Pituitary gland Thyroid gland Parathyroid glands (on dorsal aspect of thyroid gland) Thymus Adrenal glands Pancreas Ovary (female) Testis (male) Figure 16.1 Glucagon Major target is the liver Release of glucose to the blood Hyperglycemic factor Insulin Effects Lowers blood glucose levels Enhances membrane transport of glucose Inhibits glycogenolysis and gluconeogenesis Stimulates glucose uptake by cells Tissue cells Insulin Pancreas Stimulates glycogen formation Glucose Glycogen Blood glucose falls to normal range. Liver Stimulus Blood glucose level Stimulus Blood glucose level Blood glucose rises to normal range. Pancreas Liver Glucose Glycogen Stimulates glycogen Glucagon breakdown Figure 16.18 Imbalances of Insulin Diabetes mellitus (DM) Due to hyposecretion or hypoactivity of insulin Vascular component Three cardinal signs of DM Polyuria = copious urine output Polydipsia = excessive thirst Polyphagia = excessive hunger and food consumption Table 16.4 Diabetes Mellitus Type I Type II Gestational Insulin cont. Other hormones affecting insulin levels Growth hormone (GH) Adrenocorticotropic hormone (ACTH) Minor Endocrine Glands Thymus Pineal gland Thymus 2 lobed organ high in chest Thymosins = lymphocytes Active during fetal development and for first two years after birth Pineal Gland Small gland hanging from the roof of the third ventricle Melatonin Timing of sexual maturation and puberty Photoperios Physiological processes that show rhythmic variations Body temperature, sleep, appetite Not well understood in humans Stress Physical Psychological Strong emotional reactions Individual reactions vary The Stress Response Changes largely mediated by hypothalamus Three stages Alarm (acute, sympathetic) Resistance (chronic, endocrine) Exhaustion Temporary change in homeostasis = General Adaptation Syndrome (GAS) Alarm Reaction Immediate Hypothalamus Sympathetic nervous system Adrenal medulla Increased serum glucose Increased circulation Resistance Reaction Long-term modification Hypothalamus Pituitary gland Many effects… Increases energy availability Produces new proteins Improves circulation Short-term stress More prolonged stress Stress Fight or Flight Nerve impulses Resistance Hypothalamus CRH (corticotropinreleasing hormone) Spinal cord Corticotroph cells of anterior pituitary To target in blood Preganglionic sympathetic fibers Adrenal medulla (secretes amino acidbased hormones) Catecholamines (epinephrine and norepinephrine) Short-term stress response 1. Increased heart rate 2. Increased blood pressure 3. Liver converts glycogen to glucose and releases glucose to blood 4. Dilation of bronchioles 5. Changes in blood flow patterns leading to decreased digestive system activity and reduced urine output 6. Increased metabolic rate Adrenal cortex (secretes steroid hormones) ACTH Mineralocorticoids Glucocorticoids Long-term stress response 1. Retention of sodium and water by kidneys 2. Increased blood volume and blood pressure 1. Proteins and fats converted to glucose or broken down for energy 2. Increased blood glucose 3. Suppression of immune system Figure 16.16 Exhaustion Stressor too strong K+ loss = cell death Glucocorticoid depletion = cell starvation Immune system failure General Adaptation Syndrome (or Stress Response) Questions?