The thyroid gland secretes the major hormones thyroxine (T4) and triiodothyronine (T3), which are controlled by thyroid stimulating hormone (TSH) from the pituitary gland. T4 and T3 are bound to plasma proteins and transported throughout the body, where a small unbound fraction exerts biological effects. The thyroid hormones regulate growth, development, metabolism, and other physiological processes. Thyroid function is tested by measuring T3, T4, TSH, and other markers. Disorders like hypothyroidism and hyperthyroidism can be treated with thyroid hormone supplements or inhibitors.

1. Thyroid Hormones
Presenter: Dr Anurag Yadav

2. 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).

3. 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

4. • Approximately
– 99.98% T4 bound
– 99.7% T3 bound
• fT4 is higher conc than fT3.
• Unbound hormone is available for the
biologically action/activity.

5. 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.

6. 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.

7. Synthesis & secretion of Thyroxin
Uptake of
Iodine
Oxidation of
Iodine
Iodination
Coupling Storage
Utilization
Hydrolysis
Release
Salvaging of
Iodine
Transport of
Thyroid
Hormones
Catabolism of
thyroid
Hormones

9. Mechanism of action
• Action mediated by
– TSH = cAMP (secondary messenger)mediated
– Thyroxine = intracellular receptor mediated

16. Growth &
Development Intermediary
Metabolism
Calorigenesis
CNS
CVS
Skeletal
Muscle
GIT
Kidney
Hemopoiesis
Reproduction
Effect of Thyroid Hormones

17. 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

18. Effect of Thyroid Hormones

19. 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

20. Thyroid Disorders
Cretinism
Hyperthyroidism
Hypothyroidism
Euthyroid Goiter

21. 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)

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