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17 & 18-thyroid disorder.white & blue

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

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Thyroid Disorders In Children Abdulmoein E Al-Agha; MBBS,DCH,CABP,MRCP(UK) Pediatric Endocrinologist
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Anatomy Over Trachea Two Lobes connected together by an isthmus 15 to 20 g
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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)
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Sites of normal & ectopic thyroid tissue
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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
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FUNCTIONAL UNIT IS THE FOLLICLE
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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 μ g/kg/day in infancy with gradual decrement to 1.5 μ g/kg/day in adult
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Thyroid Regulation Somatostatin, Glucocorticoid Dopamine
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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
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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
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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
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Production of Thyroid Hormones NIS (Na+/I- Sympoter) TPO
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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
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Increase BMR ( Basal Metabolic Rate )
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