Total Iodine content of body is 20-30 mg (20% of which is contained in the thyroid gland) Thyroid Iodine occurs in the following forms: 1) 1% iodide ions (I-) 2) 20-25% incorporated in T3 and T4 3) Rest as thyroglobulin sources Sea foods / Cod liver oil Small amounts of iodide added to table salts prevents iodine deficiency Dietary iodine is converted to iodide and absorbed t3 t4 T3 – Triiodothyronine T4 – Tetraiodothyronine/Thyroxine 1) Trapping of iodide (I-) by Thyroid gland by Iodide Pump (Na+K+ ATPase Pump) 2) Oxidation of Iodide By Iodide peroxidase (thyroperoxidase) 3) Iodination of tyrosine forming 3-monoiodotyrosine  (MIT) and 3,5-diiodotyrosine (DIT): 1) Trapping of iodide (I-) by Thyroid gland: by Iodide Pump (Na+K+ ATPase Pump) Na+ pumped out of cells. Na+ reenters along with iodide ions Na+ I- transporter Iodide uptake paralyzed by inhibitor of this pump i.e. oubain Anoxia and substances like cyanide/dinitrophenol which inhibit ATP synthesis also inhibit iodide uptake Enables thyroid gland to concentrate iodide 10-100 times more than the serum on wt. basis oxidation of iodide By Iodide peroxidase (thyroperoxidase) which contains heme; H2O2 utilized in this reaction Iodide oxidized to nascent iodine (Io) or (I3-) which are highly unstable and reactive Storage: T3 and T4 stored in follicles within the molecules of thyroglobulin of colloid material Release: Thyroid cells take up colloid material from the follicles by pinocytosis Ingested colloid material fuses with lysosomes to form phagolysosomes MIT, DIT, T3 and T4 released Only T3 and T4 enter blood stream MIT and DIT are acted upon by enzyme iodotyrosine deiodinase present in thyroid cells resulting in release of I2 from these compounds The I2 liberated is stored and reused for hormone synthesis 30% of T4 is converted to T3 in liver and kidneys hyperthyroidism Graves’ Disease – Most Common Autoimmune Autoantibodies bind to TSH receptors and stimulate the gland to hyperfunction Graves’ Disease – Most Common Autoimmune Autoantibodies bind to TSH receptors and stimulate the gland to hyperfunction

1. MINERALS
Iodine
Maryam Fida (o-1827)
Source: Biochemistry – Lippincott’s
Illustrated Reviews
World Wide Web

2. IODINE
• Total Iodine content of body is 20-30 mg (20% of
which is contained in the thyroid gland)
• Thyroid Iodine occurs in the following forms:
1) 1% iodide ions (I-)
2) 20-25% incorporated in T3 and T4
3) Rest as thyroglobulin

3. DIETARY SOURCES/ABSORPTION
• Sea foods / Cod liver oil
• Small amounts of iodide added to table salts
prevents iodine deficiency
• Dietary iodine is converted to iodide and absorbed

5. BIOSYNTHESIS OF THYROID
HORMONES (T3 AND T4)
T3 – Triiodothyronine
T4 – Tetraiodothyronine/Thyroxine
1) Trapping of iodide (I-) by Thyroid gland by Iodide Pump
(Na+K+ ATPase Pump)
2) Oxidation of Iodide By Iodide peroxidase (thyroperoxidase)
3) Iodination of tyrosine forming 3-monoiodotyrosine
(MIT) and 3,5-diiodotyrosine (DIT):

6. BIOSYNTHESIS OF THYROID
HORMONES (T3 AND T4)
1) Trapping of iodide (I-) by Thyroid gland:
• by Iodide Pump (Na+K+ ATPase Pump)
• Na+ pumped out of cells. Na+ reenters along
with iodide ions
• Na+ I- transporter

7. • Iodide uptake paralyzed by inhibitor of this pump i.e.
oubain
• Anoxia and substances like cyanide/dinitrophenol which
inhibit ATP synthesis also inhibit iodide uptake
• Enables thyroid gland to concentrate iodide 10-100
times more than the serum on wt. basis

8. 2) Oxidation of Iodide
• By Iodide peroxidase (thyroperoxidase) which
contains heme; H2O2 utilized in this reaction
• Iodide oxidized to nascent iodine (Io) or (I3
-) which
are highly unstable and reactive

9. 3) Iodination of tyrosine forming 3-
monoiodotyrosine (MIT) and 3,5-diiodotyrosine
(DIT):
• Tyrosine + ½ I2 MIT
• Tyrosine + I2 DIT
Nascent IodineThyroglobulin
Thyroperoxidase
Thyroperoxidase

10. 4)Coupling Reactions – Formation of Thyroid Hormones
MIT + DIT T3 + Alanine
DIT + DIT T4 + Alanine
Note: Only a small amount of plasma T3 comes
from this reaction. The remaining comes from
conversion of T4 to T3

11. S

12. Storage:
• T3 and T4 stored in follicles within the molecules of thyroglobulin
of colloid material
Release:
• Thyroid cells take up colloid material from the follicles by
pinocytosis
• Ingested colloid material fuses with lysosomes to form
phagolysosomes
• MIT, DIT, T3 and T4 released

13. • Only T3 and T4 enter blood stream
• MIT and DIT are acted upon by enzyme
iodotyrosine deiodinase present in thyroid cells
resulting in release of I2 from these compounds
• The I2 liberated is stored and reused for hormone
synthesis
• 30% of T4 is converted to T3 in liver and kidneys

14. REGULATION

15. HYPERTHYROIDISM/THYR
OTOXICOSIS
• Graves’ Disease – Most Common
• Autoimmune
• Autoantibodies bind to TSH receptors and stimulate the gland
to hyperfunction

16. • An autoantibody is an antibody (a type of protein)
produced by the immune system that is directed against
one or more of the individual's own proteins. Many
autoimmune diseases (notably lupus erythematosus) are
caused by such autoantibodies
• Autoimmunity is the system of immune responses of an
organism against its own healthy cells and tissues

18. Signs & Symptoms of Hyperthyroidism:
• Intolerance to heat
• Tolerance to cold
• Excessive sweating
• Tachycardia
• Fine tremors of the outstretched hand
• Brisk tendon reflexes
• Exophthalmos
• Pretibial Myxedema (infiltration by hydrophilic
mucopolysaccharides)

19. Rx:
• Surgical Removal
• Radioactive iodine I131
• Antithyroid drugs – Thiourea
• Propranolol – Beta Blocker

20. HYPOTHYROIDISM
• In Infants – Cretinism
• In adults - Myxedema

21. CRETINISM
• Faiure to grow in wt. and length
• Somnolence, low body temp., severe constipation
• Mental retardation, enlarged protruding tongue

23. MYXEDEMA
Signs & Symptoms:
• Lethargic, somnolent, husky low pitched voice
• Intolerance to cold
• Hair coarse , brittle and scanty
• Deposition of mucoprotein in the dermis

24. Periorbital
Swelling

25. TPO = Thyroid peroxidase antibody

26. ASSIGNMENT 16-12-2016
DUE DATE 26-12-2016
• Sources, RDA, Biochemical Functions, Effects of Deficiency:
• Zn
• Selenium
• Fluoride
• Copper
• Na
• K
• Chloride