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Published byAlison Skinner Modified over 9 years ago
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THE THYROID GLAND
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Anatomical Structure
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Gross Anatomy Located in neck –lobes –isthmus Relations –Larynx –Trachea –Recurrent laryngeal nerves –Parathyroid glands –Carotid sheath Blood supply –Sup. thyroidal a. –Inf. thyroidal a.
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Embryology Thyroglossal duct Foramen caecum Thyroid cysts
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Histology Thyroid follicles –Simple cuboidal- columnar Colloid – Thyroglobulin Rich vascularization Parafollicular cells
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Thyroid Hormone 3-Monoiodotyrosine (MIT) 3,5-Diiodotyrosine (DIT) 3,5,3’-Triiodothyronine (T 3 ) Tyrosine 3,5,3’,5’-Tetraiodothyronine (T 4 ) 3,3’,5’-Triiodothyronine (Reverse T 3, rT 3 )
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Thyroid Hormone Synthesis Tyrosine in Thyroglobulin CH 3 CH N C=O RC C=O RC OH-
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Thyroid Hormone Synthesis Thyroperoxidase attaches Iodine to 3 position---MIT CH 3 CH N C=O RC C=O RC I OH-
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Thyroid Hormone Synthesis Thyroperoxidase attaches Iodine to 5 position---DIT CH 3 CH N C=O RC C=O RC I I OH-
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Thyroid Hormone Synthesis Thyroperoxidase attaches ring from one DIT to adjacent DIT = Thyroxine (T 4 ) CH 3 CH N C=O RC C=O RC I I O I I OH-
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Thyroid Hormone Synthesis Thyroperoxidase attaches ring from one MIT to adjacent DIT = Triiodothyronine (T 3 ) CH 3 CH N C=O RC C=O RC I I O I OH-
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Thyroid Hormone Synthesis Thyroperoxidase attaches ring from one DIT to adjacent MIT = Reverse T 3 CH 3 CH N C=O RC C=O RC I O I I OH-
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Thyroid Hormone Biosynthesis Iodine pump/trap Thyroglobulin Iodination Thyronine Thyroglobulin pinocytosis Hormone release
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Thyroid hormone transport Thyroid binding globulin (TBG) –Highest affinity Thyroid binding prealbumin –Intermediate affinity Albumin –Low affinity, High capacity
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Thyroid Hormone T 3 is 3-8X more active than T 4 Thyroid Gland produces 10X T 4 to T 3 5’-deiodinase –Converts T 4 to T 3 in Target Tissues –Primarily responsible for circulating levels of T 3 T 4 probably a pro-hormone Thyroid hormone receptor –Nuclear
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Physiological effects of thyroid hormone Increases oxygen consumption and heat production Positive chronotropic and inotropic effects on heart Increase sensitivity to adrenergic effectors –Up-regulates -adrenergic receptors Increase gut motility Increase bone turnover
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Physiological effects of thyroid hormone Increases reflex response Increase hepatic glycogenolysis and gluconeogenesis Stimulates lipolysis Developmental effects –Growth –Brain development
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REGULATION OF THE THYROID GLAND THYROID GLAND ANTERIOR PITUITARY HYPOTHALAMUS TRH TSH T4T4 LONG-LOOP FEEDBACK T 3 & T 4 TSH SHORT-LOOP FEEDBACK BODY TEMP. EXPOSURE TO COLD STARVATION TSH- RECEPTOR ANTIBODIES THYROID AUTO REGULATION HIGH SERUM IODIDE HIGHER BRAIN CENTERS GOITROGENS
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Endocrinopathies
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Hyperthyroidism Level of the defect (1 , 2 , 3 ) Thyrotoxicosis Graves’ disease Toxic Adenoma Toxic Multinodular Goiter Chronic Thyroiditis
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Hyperthyroidism Symptoms Tachycardia/arrhythmia Muscle tremors Hyperreflexia Increased core & skin temp./ Heat Intolerant Exophthalmos Muscle wasting Loose stool Osteoporosis Hair loss Oligo-/amenorrhea Irritability, Restlessness
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Hypothyroidism 1 , 2 , 3 Newborn –Cretinism –Lack of myelination Children –Retarded Growth –Disproportionate
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Hypothyroidism Adult –Muscle weakness –Mental slowness –Tired/fatigued –Cold –Slowed intestinal peristalsis –Impaired renal function –Anemia –Myxedema
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Myxedema
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Causes of Hypothyroidism Iodine deficiency Hashimoto’s Disease –Initially hyperthyroid Post-ablative 5’-Deiodinase Deficiency
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Thyroid hormone resistance Mutation of the receptor. Characterized by high blood levels of both TSH and Thyroid hormones
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Non-toxic goiter Iodine deficiency
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Thyroiditis Subacute thyroiditis Chronic thyroiditis (Hashimoto’s Disease) –Autoimmune
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Euthyroid Syndrome Patient presents and complains of hypothyroid type symptoms Levels of Thyroid hormones (free & total), & TSH in low normal range. May be due to a 5’-deiodinase deficiency
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Allopathic treatments for thyroid disorders Hyperthyroidism –Goitrogens –Partial thyroidectomy –Radiothyroidectomy Hypothyroidism –Hormone Replacement
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