Thyroid Gland. Chapter 18 Part 2. Thyroid gland. Thyroid Gland. Thyroid Gland. Parathyroid Gland. Adrenal Gland. Pancreas

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1 Thyroid Gland Chapter 18 Part 2 Synthesis and function of Thyroid hormone Calcitonin and Calcium regulation Parathyroid Gland PTH and Calcium regulation Adrenal Gland The corticosteroids Pancreas Regulation of blood glucose Covers anterior surface of trachea 2 lobes with isthmus Thyroid Gland Trachea lobe of thyroid Hyoid Bone lobe of thyroid Isthmus Tissue consists of follicles Follicles are hollow spheres lined with epithelial cells (follicle cells) Follicular cells take up Iodine from circulation and produce thryoglobulin (the precursor to thyroid hormone) Thyroglobulin is stored in the colloid of follicle Thyroid gland Thyroid Gland An elusive C-cell is indicated C cells produce calcitonin (CT) Here thyroglobulin, a glycoprotein, is stained hot pink 1

2 Synthesis of thyroid hormone Synthesis of thyroid hormone A funky, multistep process Iodine selectively pumped into the membrane of follicular cells Iodine bound to tyrosine molecules, forming thyroid hormone, incorporated into thyroglobulin Thyroglobulin is stored in follicle Upon TSH stimulation, thyroglobulin is endocytosed back into follicle cell, diffuses across cell, and released into bloodstream T4 versus T3 What is the difference? The thyroid releases 90% T4, 10% T3 T3 is the active form! Functions of Thyroid Hormone Actively transported into all cells of body Binds mitochondria, increases rate of mitochondrial ATP production Binds nuclear receptors and increases transcription of Na+/K+ ATPase Also activates genes that code for enzymes involved in glycolysis and ATP production PUNCHLINE: Thyroid hormone increases basal metabolic rate 2

3 Thyroid Hormone Regulation TSH causes thyroid hormone release AND growth of thyroid tissue Misregulation and Goiters C cells and Calcitonin C cells respond directly to high levels of Ca2+ in body fluids Release Calcitonin (CT), works to reduce Ca2+ concentration in body fluids How?? Calcitonin and Ca2+ regulation Inhibition of osteoclasts (the bone breaker-downer cells) Stimulation of Ca2+ excretion at kidneys CT osteoclast 3

4 Parathyroid Glands Located on the posterior aspect of the thyroid gland Chief cells produce and release parathyroid hormone (PTH) directly in response to low circulating Ca2+ levels PTH works to increase Ca2+ levels Parathyroid Glands Stimulates osteoclasts Inhibit osteoblasts (decreases rate of Ca2+ deposition) Increases Ca2+ resorption at kidnes Stimulates formation of calcitriol at kidneys (works at gut) PTH osteoclast Chomp, chomp! PTH and Calcitonin regulate Ca2+ levels Adrenal Gland cortex medulla The cortex has three cellular regions (zones), each that makes specific hormones Zona glomerulosa (outermost) Zona fasciculata (middle) Zona reticularis (innermost) 4

5 Adrenal Gland Adrenal Cortex medulla Endocrine tissue that produces a variety of corticosteroids (general term for steroids from the cortex) All affect gene transcription This collection of steroids are vital to life The cortex has three cellular regions (zones), each that makes specific hormones Zona glomerulosa: Mineralocorticoids Zona fasciculata: Glucocorticoids Zona reticularis: Androgens 250uM Adrenal Cortex Zona glomerulosa -Mineralocorticoids Aldosterone, the Na+ saver Its release is triggered by a drop in blood Na+, blood volume or blood pressure Aldosterone works at: kidneys, sweat glands, salivary glands and pancreas to decrease Na+ secretion/release Effect: water follows Na+, so water is saved, as well Adrenal Cortex Zona fasciculata Glucocorticoids When stimulated by ACTH, cortisol and corticosterone secreted (and cortisone is converted from cortisol by the liver) Glucocorticoids exhibit negative feedback at both the hypothalamus and anterior pituitary 5

6 Effects of Glucocorticoids Accelerate rates of glucose synthesis and glycogen formation, especially at liver Adipose breaks down TG into Fas Anti-inflammatory effects Inhibit WBC and other immune system fuction Slow migration of phagocytic cells into injury site, and decrease activity Negative effects on wound healing Zona Reticularis Produces androgens Adrenal cortex Adrenal Medulla Sympathetic division Adrenal Medulla Parasympathetic division What is the composition of this part of the gland? What triggers the release? What hormones are produced? 6

7 Effects of Adrenal Medulla skeletal muscles: mobilize glycogen reserves, increase beakdown of glucose into adipose tissue: stored fats are broken down, fatty acids into glycogen breakdown (the brain needs heart, β1 receptors stimulated, increase in cardiac force and rate Pancreas A unique gland with both exocrine and endocrine functions Exocrine: produces enzymes for digestion Endocrine: produces hormones for blood glucose regulation Histology of the Pancreas Regulation of Blood Glucose α cells release glucagon A single islet containing α and β cells β cells release insulin Endocrine Islets in a sea of exocrine cells (acinar cells) Nutshell version: Normal blood glucose levels = mg/dl --When blood glucose is low, glucagon stimulates glycogen breakdown and glucose release from liver --When glucose levels are elevated, insulin encourages the uptake use, and storage of glucose 7

8 Regulation of blood glucose One example in detail How does insulin actually increase glucose uptake by cells? This process is not totally understood and is an area of intensive research. Glucose transporter discovered in mid 1980 s gluconeogenesis Diabetes 17 million Americans have Type 2 (adultonset) diabetes, a disorder in which cells lose their ability to absorb glucose from the blood stream. This is different from Type 1 (juvenile onset) diabetes, in which the immune system attacks insulin-producing, β cells. What tissues, organs suffer in diabetic state? Why? 8