Thyroid gland

M.PRASAD NAIDUMSC MEDICAL BIOCHEMISTRY, PH.D,.

THYROID GLAND

Thyroid gland

Thyroid tissue is present in all vertebratesTG consists of 2 lobes, one on each side of

trachea H- shape25 gmsSeason, climate, geographical location, food

Thyroid gland

Thyroglobulin : glyco protein – storage form of thyroid glands

TGb on hydrolysis – MIT & DITTGb on hydrolysis also yields non-iodinated

compounds which ↓serum Ca2+

Biosynthesis & secretion

Entry of iodide ions from the bloodAgainst the conc. Gradient (Active tpt)↑TSH↓Thiocyanate, perchlorateOxidation of I- to I+/ HIO- (iodide peroxidase)Iodination first at 3rd & 5th

MITDITSynthesis of T2,T3 and T4

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

Regulation

TSHGrowth of TG, iodide uptake, oxidation,

iodination, coupling & release of thyroid hormones

Clinical importance

T3 & T4 are synthesized only when sufficient iodine is supplied in the diet

Goiter – Iodine deficiency hypothyroidism:Myxedema in adultsCretinism in childrenHyper thyroidism: Graves disease

Parathyroid gland

In humans , usually 4 2 are superior poles & 2 are in inferior poles

of thyroid gland4 glands weigh about 0.3gm2 hormones namelyParathormone (PTH)Calcitonin

PTH

Linear PP84 aa8500N- Ala & C- glutamineChief cells of parathyroid glands

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

Regulation

PTH is not stored in the glandSynthesized & secreted continuouslyPTH requires Vit D for its functioningWhen Ca conc is low , PTH secretion is ↑

Calcitonin

Thyroid and parathyroidsSynthesized from C-cells or parafollicular

cellsSingle PP32 aa3600N- Cys & C- prolinamide

Functions

Causes rapid & brief ↓ Ca level in bloodInfluences the tpt of ions in the kidneyRegulation:Blood Ca levels↑ in serum Ca ↑ calcitonin - hypocalcimia

THANK YOU