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The Thyroid Notes

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This is an extract of our The Thyroid document, which we sell as part of our Endocrinology Notes collection written by the top tier of University Of Leicester students.

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The Thyroid Tyrosine Iodination Monoiodotyrosine Iodination Diiodotyrosine Triiodotyrosine T3 - active)

Thyroxine (T4)

Monodeiodination T3 acts via nuclear receptors to
- Increase cell metabolism o Stimulate glucose uptake and metabolism o Stimulate protein breakdown Effects are usually catabolic e.g increased BMR, heat production + O2 consumption
- Increase catecholamine effects o Vital for normal growth and development o Absence causes physical and mental retardation (cretinism) Anatomy
- The thyroid consists of two lobes connected by an isthmus
- Moves on swallowing
- Palpable in normal women
- Embriologically originates from base of tounge and descends to middle of neck
- Blood supply o Superior and inferior thyroid arteries

- One of the most common endocrine conditions with UK prevalence of 1%
- Usually primary from underactive thyroid
- May be secondary to hypothalamic-pituitary disease (reduced TSH drive) Causes
- Autoimmune o Hashimotos thyroiditis
? Lymphocytic and plasma cell infiltration
? Goitre
? V. High antibody titres o Primary atrophic hypothyroidism
? Common
? Diffuse lymphocytic infiltration of thyroid = atrophy (no goiter)
- Acquired o Iodine deficiency o Destructive therapy (radioiodine, surgery) for cancer/hyperthyroidism o Drug induced Clinical features Symptoms Tiredness Weight gain Cold intolerance Depression Poor appetite Goitre Dry skin Constipation

Signs Mental slowless
- ataxia Deep voice Goitre Thin, dry hair Dry skin Overweight/obese Bradycardia

- TFTs o High level serum TSH indicates primary hypothyroidism o Low free T4 confirms hypothyroid state
- FBC o Anaemia due to menorrhagia, or associated pernicious anaemia
- LFT o Increased aspartate transferase levels from muscle/liver
- Lipids o Hypercholesterolaemia
- U+E o Hyponatraemia due to increase in ADH and impaired free water clearance Management
- Replacement therapy with levothyroxine (T4) for life

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