17 & 18-thyroid disorder.white & blue

17 & 18-thyroid disorder.white & blue -...

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Unformatted text preview: Thyroid Disorders In Children Abdulmoein E Al-Agha; MBBS,DCH,CABP,MRCP(UK) Pediatric Endocrinologist Anatomy Over Trachea Two Lobes connected together by an isthmus 15 to 20 g Thyroid gland Thyroid gland derives from the floor of embryonic pharynx Begins to develop around 4 weeks of gestation Moves down the neck while forming its characteristic bilobular structure Thyroid development is largely completed between 10-20 weeks of gestation Thyroid gland size increase gradually by 1g/year until age of 15 years were it achieves adult size (15-25 g) Sites of normal & ectopic thyroid tissue Thyroid gland Thyroid gland is composed over a million cluster of follicles Follicles are spherical & consists of epithelial cells surrounding a central mass (colloid) Thyroglobulin is storage room Two main hormones: Tetraiodothyronine (Thyroxin) Triiodothyronine FUNCTIONAL UNIT IS THE FOLLICLE Thyroid gland Thyroid gland normally secretes mainly T4 70 % of T3 derived from T4 in peripheral tissues T4 is converted to T3 by 5-deiodinase enzyme Both T4 and T3 are in bound form (TBG, pre albumin and albumin) Only 0.025% of T4 and 0.35% of T3 are free Free hormone concentration best correlates with thyroid status T4 production is 5-6 g/kg/day in infancy with gradual decrement to 1.5 g/kg/day in adult Thyroid Regulation Somatostatin, Glucocorticoid Dopamine Thyroid hormone synthesis 1) Iodide pump Rate limiting step in thyroid hormone synthesis which needs energy Follicles have in their basement membrane an iodide trapping mechanism which pumps dietary I - into the cell Normal thyroid: serum iodine is 30-40:1 Iodide uptake enhancers: TSH Iodine deficiency TSH receptors antibody Iodide uptake inhibitors Iodide ion Drugs Digoxin Thiocynate perchlorate Thyroid hormone synthesis 2) Iodide oxidation to iodine and Organification Inside the cells, iodide is oxidized by peroxidase system to more reactive iodine Iodine immediately reacts with tyrosine residue on a thyroid glycoprotein called thyroglobulin to form : T1= mono-iodotyrosyl thyroglobulin T2= di-iodotyrosyl thyroglobulin Both processes are catalyzed by thyroid peroxidase enzyme Thyroid hormone synthesis 3) Coupling T1& T2 couple together to form T3&T4 MIT +DIT = T3 (Tri-iodothyronine) DIT + DIT = T4 (Thyroxin) All attached to thyroglobulin and stored in the colloid Thyroglobulin molecule This process is stimulated by TSH Production of Thyroid Hormones NIS (Na+/I- Sympoter) TPO Effects of thyroid hormones Fetal brain & skeletal maturation Increase in basal metabolic rate Inotropic & chronotropic effects on heart Increases sensitivity to catecholamines Stimulates gut motility Increase bone turnover Increase in serum glucose, decrease in serum cholesterol Conversion of carotene to vitamin A Play role in thermal regulation Increase BMR ( Basal Metabolic Rate )...
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This note was uploaded on 12/21/2011 for the course STEP 1 taught by Professor Dr.aslam during the Fall '11 term at Montgomery College.

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17 & 18-thyroid disorder.white & blue -...

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