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

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

Effect of Thyroid Hormones

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