1. M.Prasad Naidu MSc Medical Biochemistry, Ph.D,.
Thyroid hormones
M.Prasad Naidu
MSc Medical Biochemistry, Ph.D,.

2. Thyroid gland produces two principal hormones … thyroxine & tri iodo thyronine which regulate the metabolic rate of the body.
Iodine is essential for the synthesis of thyroid hormones
More than half of the body’s total content is found in the thyroid gland

10. Hypothalamo pituitary axis
The hypothalamo-pituitary axis is a classical negative feedback regulatory mechanism in which secretion of TSH is modulated by thyroid hormones. Release of TSH from the pituitary gland is stimulated by thyrotropin releasing hormone (TRH) from the hypothalamus.

11. Hypothalamo pituitary axis
A small increase in T3 and T4 produces a diminished TSH response to TRH at the pituitary level.
T3 and T4 act at the hypothalamic level by inhibiting mRNA for TRH synthesis.
Only unbound fractions of hormone are metabolically active and only this free hormone has an inhibitory effect on the secretory activity of the thyroid.
dopamine physiologically inhibits TSH secretion
glucocorticoids have been shown to dull the response of the pituitary to TRH
oestrogens increase the sensitivity of thyrotrophs to TRH

12. Mechanism of thyroid hormone receptor action

13. Actions of thyroid hormones
Brain----growth&development of nervous system
Bone&tissue growth– linear growth & maturation of bones
CVS-- increased contractility,heart rate &cardiac output
GUT—increased absorption of nutrients, increased motility
Liver -increased gluconeogenesis&glyco genolysis
Adipose tissue –increased lipolysis
Muscle –increased protein catabolism in skeletal muscle
Kidney -increased erythropoietin synthesis
Respiration- increased central stimulation of respiration
Energy metabolism -increased BMR,increased oxygen consumption,increased heat production stimulation of Na-K-ATP ase

14. Wolff-chaikoff effect
Iodine deficiency increases thyroid blood flow & upregulates the NIS , stimulating more efficient uptake.
Excess iodide transiently inhibits thyroid iodide organification ,a phenomenon known as the wolff- chaikoff effect

15. The functional unit of thyroid is thyroid follicle. Normal follicle

16. Thyroid follicle with high TSH stimulation
Thyroid follicle with out TSH

18. High T3 or T4 gives decreased TSH subunit synthesis
inactive thyrotrophs may lose the capacity to respond to reduced T3 or T4 levels

19. derives from the median eminence of the hypothalamus
somatostatin
TRH
inhibits TSH release
potentiates the effect of thyroid hormones on thyrotrophs, ie thyroid hormone has inhibitory effects on TSH release
derives from the median eminence of the hypothalamus
thyrotropin releasing hormone, ie stimulates TSH release

20. Primary hypo thyroidism
Secondary hypotyroidism
Iodine deficiency
Hasimoto’s thyroiditis
Thyroidectomy
Radiation therapy
Drugs-lithium,antithyroid drugs and PAS
Absent or ectopic thyroid gland
Dyshormonogenesis
TSH receptor mutation
Hypopituitarism
Tumors,pituitary surgery, irradiation/infiltration, sheehan’s syndrome & isolated TSH deficiency
Hypothalamic disease
Trauma & infiltration

21. cretinism
congential absence of T3 and T4 or chronic iodine deficiency during childhood
retarded growth
sluggish movements
mental deficiencies

22. Interesting, right?
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