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1. M . P R A S A D N A I D U
M S C M E D I C A L B I O C H E M I S T R Y , P H . D , .
THYROID GLAND

2. Thyroid gland
 Thyroid tissue is present in all vertebrates
 TG consists of 2 lobes, one on each side of trachea
 H- shape
 25 gms
 Season, climate, geographical location, food

3. Thyroid gland
 Thyroglobulin : glyco protein – storage form of
thyroid glands
 TGb on hydrolysis – MIT & DIT
 TGb on hydrolysis also yields non-iodinated
compounds which ↓serum Ca2+

4. Biosynthesis & secretion
 Entry of iodide ions from the blood
 Against the conc. Gradient (Active tpt)
 ↑TSH
 ↓Thiocyanate, perchlorate
 Oxidation of I- to I+/ HIO- (iodide peroxidase)
 Iodination first at 3rd & 5th
 MIT
 DIT
 Synthesis of T2,T3 and T4

5. Functions
 T3 is the most reactive
 5-10 time more active than T4
 ↑ Protein synthesis
 ↑ blood sugar ( Hyperglycemia)
 ↑ utilization of glucose
 ↑ glycolysis, TCA cycle, HMP shunt
 ↑ lipolysis & lipogenesis
 ↑ degradation of cholesterol – bile acids
 ↑ rate of energy exchange & O2 consumption (calorigenic effect)
 ↑ requirement of certain B complex vitamins
 ↑normal growth & skeletal maturation
 ↑ heart beat rate (T4)
 Partly effects calcium levels

6. Regulation
 TSH
 Growth of TG, iodide
uptake, oxidation, iodination, coupling & release of
thyroid hormones

7. Clinical importance
 T3 & T4 are synthesized only when sufficient iodine
is supplied in the diet
 Goiter – Iodine deficiency
 hypothyroidism:
 Myxedema in adults
 Cretinism in children
 Hyper thyroidism: Graves disease

8. Parathyroid gland
 In humans , usually 4
 2 are superior poles & 2 are in inferior poles of
thyroid gland
 4 glands weigh about 0.3gm
 2 hormones namely
 Parathormone (PTH)
 Calcitonin

9. PTH
 Linear PP
 84 aa
 8500
 N- Ala & C- glutamine
 Chief cells of parathyroid glands

10. functions
 ↑ Ca conc in serum by
 i) ↑ absorption of Ca from the intestine
 ii) ↑ rate of mobilization of Ca from bones
 iii) ↑ renal tubular reabsorption
 Thus PTH produces Hypercalcimia
 ↓ P conc in serum
 ↑ elimination of Ca & P in urine
 ↑ citrate content of blood, kidney & bones
 ↑ alkaline phospatase & acidphosphatase in blood plasma
 Depolymerization of skeletal mucopolysaccharides
 Acts on kidney through ↑ cAMP

11. Regulation
 PTH is not stored in the gland
 Synthesized & secreted continuously
 PTH requires Vit D for its functioning
 When Ca conc is low , PTH secretion is ↑

12. Calcitonin
 Thyroid and parathyroids
 Synthesized from C-cells or parafollicular cells
 Single PP
 32 aa
 3600
 N- Cys & C- prolinamide

13. Functions
 Causes rapid & brief ↓ Ca level in blood
 Influences the tpt of ions in the kidney
 Regulation:
 Blood Ca levels
 ↑ in serum Ca ↑ calcitonin - hypocalcimia

14. THANK YOU