Thyroid gland

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THYROID GLAND

• M.Prasad Naidu
• MSc Medical Biochemistry, Ph.D,.

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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

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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

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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

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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

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Regulation

• TSH
• Growth of TG, iodide uptake, oxidation,
  iodination, coupling release of thyroid
  hormones

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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

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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

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PTH

• Linear PP
• 84 aa
• 8500
• N- Ala C- glutamine
• Chief cells of parathyroid glands

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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

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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 ?

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Calcitonin

• Thyroid and parathyroids
• Synthesized from C-cells or parafollicular cells
• Single PP
• 32 aa
• 3600
• N- Cys C- prolinamide

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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

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