thyroid hormone

Thyroid Hormones

Presenter: Dr Anurag Yadav

Thyroid Hormone

• Secreted by the thyroid gland• Gland secret major hormone;– Thyroxine (T4)– Triiodothyronine (T3)

• Controlled by the primarily TSH (Thyroid stimulating hormone) secreted by the ant Pituitary gland.

• Gland also secrete calcitonin (imp hormone in calcium metabolism).

Transport of thyroid hormone

• Both T3 & T4 are bound to plasma proteins– Thyroxine binding globin (TBG)– Transthyretin (TTR – formerly known as Thyroxine

binding prealbumin [TBPA])– Albumin

• T4 is secreted 20fold excess over T3.• TBG carry 80% of bound hormone (T4>T3),

10% by albumin, 10% TTR

• Approximately

– 99.98% T4 bound

– 99.7% T3 bound

• fT4 is higher conc than fT3.

• Unbound hormone is available for the

biologically action/activity.

Hormone synthesis

• About 93% is secreted as thyroxine & 7% as

T3.

• However eventually converted to T3 in tissue.

• T3 is 4 times potent than T4.

Iodine metabolism

• Iodine is required for the formation of thyroid

(150-200μg/day) (sr 5-10 μg/dL)

• About 80% is stored in Thyroid gland.

• Ingredients which prevent the utilization of

Iodine are called as Goitrogens.

Synthesis & secretion of Thyroxin

Uptake of Iodine

Oxidation of Iodine Iodination

CouplingStorage

Utilization Hydrolysis Release

Salvaging of Iodine

Transport of Thyroid

Hormones

Catabolism of thyroid

Hormones

Mechanism of action

• Action mediated by

– TSH = cAMP (secondary messenger)mediated

– Thyroxine = intracellular receptor mediated

Growth & DevelopmentIntermediary

Metabolism

Calorigenesis

CNS

CVSSkeletal Muscle

GIT

Kidney

Hemopoiesis

Reproduction

Effect of Thyroid Hormones


•Fat mobilization.•Oxidation of FA•Inversely related to hormone levels.

Lipid metabolism

•Enhance insulin dependent glucose entry•Increased gluconeogenesis & glycogenolysis.

Carbohydrate metabolism

•For normal growth.

Growth

•Physical and mental development in fetal, neonatal, young and adult.

Development

•Cardiovascular•Central nervous system•Reproductive system•Hemopoiesis•Skeletal, GIT, Kidney

Other effect

Thyroid Function test

• Assay of Hormone– T3, T4, TSH, FT4, FT3,rT3, Anti-TPO, Anti-Tg– Assay by ELISA/CLIA/ECLIA– Normal reference interval

• T3 – 0.8-2.0ng/ml• T4 – 5.1-14.1μg/dl• fT4 – 0.93-1.7ng/dl• fT3 - 3.5-7.8pmol/L• TSH – 0.27-4.1μIU/ml• Anti-TPO - <34.0IU/ml• Tg - 3-40 ng/mL

Thyroid DisordersCretinism

Hyperthyroidism

Hypothyroidism

Euthyroid Goiter

Drugs for thyroid dysfunction

Thyroid supplement : Thyroxine Thyroid inhibitors

Antithyroid drugs

Propylthiouracil,

Methimazole,

Carbimazole

Ionic inhibitors

Thiocynates,

perchlorates, Nitrates

Inhibit hormone

relase

Iodine, iodides of

Na & K, Organic Iodide

Destroy thyroid tissue

Radioactive Iodine (131I, 125I,

123I)

• Reference– Vasudevan-Textbook of Biochemistry– Harper’s-Illustrated Biochemistry – Gyton-Human Physiology– KD Tripathi- Essential of medical Pharmacology– Internet sources

thyroid hormone

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