thyroid gland, structure, function, effects, disorders, regulation, mode of action

1. Thyroid Gland
By:
Khuram Aziz
M.Phill Biochemistry
Scientist by IBC Life sciences
Member of Pakistan Young Scientist Association

2. Outline
• Location
• Structure
• Synthesis
• Mode of action
• Effects
• Regulation
• Disorders

3. Thyroid gland
• Largest gland in the body
• Location : in the neck inferior the larynx and
spanning over the ventral surface of trachea
• Function:
– Secretion of thyroxin and triiodothyronine
– Secretion of calcitonin

4. Fig 19-7
Thyroid Gland
 Anterior surface of trachea just
inferior of thyroid cartilage (or
Adam’s apple)
 Two lobes connected by isthmus
 Microscopic thyroid follicles
produce thyroid hormone
 C Cells - produce calcitonin
( Ca2+)

5. Structures and Functions of Endocrine
System
Fig. 48-10. Thyroid and parathyroid glands. Note the surrounding structures.
5
Copyright © 2011, 2007 by Mosby, Inc., an
affiliate of Elsevier Inc.

6. Thyroid Gland: Hormones and Iodine
Metabolism

8. Synthesis of Thyroid Hormone
Blood Follicle Epithelium Colloid MIT+DIT
Thyroid Peroxidase
I- I- I2 I2 T3
Pump
+
Na+
TG TG DIT+DIT
MIT
+ Tyrosine
DIT
-T3
-T4 -T3
T4
T3 -MIT -T4
+
T4 TG -DIT TG -MIT
-DIT
Thyroid hormone synthesis and secretion involves processes that occur within follicular
epithelial cells and in colloid.
I-: iodide ions; I2: iodine; TG: thyroglobulin; MIT: monoiodotyrosine; DIT: diiodotyrosine.

9. Releases of Thyroid Hormone

10. Synthesis of thyroid hormones
1. Iodide trapping
– By sodium iodide symporter
– Blocked by:
• Thiocyanate SCN-
• Perchlorate ClO4-
• Pertechnetate TcO4-
2. Oxidation of iodide
– By thyroid peroxidase
– Inhibited by:
1. large intake of iodide >150mcgday
2. Thioamides(refer to hyperthyroidism therapy)

11. Synthesis of thyroid hormones
3. Organification
– Tyrosine residues of thyroglobulin is iodinated
1. Inhibited by large intake of
iodide >150mcgday
2. Thioamides(refer to
hyperthyroidism therapy)
– Produce monoiodotyrosine residues MITnd
diiodotyrosine residues DIT

12. Thyroxine and its precursors: Structure &
Synthesis
Figure 1-1: Thyroid hormones are made from tyrosine and iodine

14. Synthesis of thyroid hormones
4. Coupling
– DIT+MIT=T3
– DIT+MIT=T4
5. Storage :
– Along with thyroglobulin
6. Exocytosis and proteolysis
– Release of T4 & T3
7. Conversion of T4 to T3 in peripheral tissue

16. Drugs that inhibit 5’deiodenase
• Steroids
• Amiodarone
• Beta blockers
• Thioamides

17. T4 vs T3
T4 T3
• Thyroid gland synthesize • Thyroid gland synthesize 9%
90% • 0.4% fr
• 0.04%free • active
• Not active
• Long T12

18. Mechanism of action of thyroid
hormones

20. Thyroid Gland
 Thyroid hormones target almost every body cell
 Can enter cells & bind to intracellular receptors on
mitochondria & in nucleus
 Effects include:
 increased ATP production
 increased cellular metabolism, energy utilization &
oxygen consumption
 increased body temperature
 growth & development of skeletal, muscular &
nervous system in fetus & children

21. Effects Of Thyroid Hormones On The
Cardiovascular System
• Increase heart rate
• Increase force of cardiac contractions
• Increase stroke volume
• Increase Cardiac output
• Up-regulate catecholamine receptors

22. Effects Of Thyroid Hormones On The
Respiratory System
• Increase resting respiratory rate
• Increase minute ventilation
• Increase ventilatory response to hypercapnia
and hypoxia

23. Effects Of The Thyroid Hormones On
The Renal System
• Increase blood flow
• Increase glomerular filtration rate

24. Effects Of The Thyroid Hormones On
Oxygen Carrying Capacity
• Increase RBC mass
• Increase oxygen dissociation from
hemoglobin

25. Thyroid Hormone Actions Which
Increase Oxygen Consumption
• Increase mitochondrial Size,Number and Key
Enzymes
• Increase Plasma membrane Na-K ATPase
Activity
• Increase Futile Thermogenic Energy Cycles
• Decrease Superoxide Dimutase Activity

26. Effects Of The Thyroid Hormones On
Intermediary Metabolism
• Increase glucose absorption from the GI
tract
• Increase carbohydrate,lipid and protein
turnover
• Down-regulate insulin receptors
• Increase substrate availability

27. Effects Of The Thyroid Hormones In
Growth And Tissue Development
• Increase growth and maturation of bone
• Increase tooth development and eruption
• Increase growth and maturation of epidermis,hair
follicles and nails
• Increase rate and force of skeletal muscle
contraction
• Inhibits synthesis and increases degradation of
mucopolysaccharides in subcutaneous tissue

28. Effects Of The Thyroid Hormones On
The Nervous System
• Critical for normal CNS neuronal
development
• Enhances wakefulness and alertness
• Enhances memory and learning capacity
• Required for normal emotional tone
• Increase speed and amplitude of peripheral
nerve reflexes

29. Effects Of The Thyroid Hormones On
The Reproductive System
• Required for normal follicular development
and ovulation in the female
• Required for the normal maintenance of
pregnancy
• Required for normal spermatogenesis in
the male

30. Regulation of Thyroid Hormones

31. Thyroid Gland Function
 Thyroxin (T4) and
triiodothyronine (T3)
speed up metabolic rate
Goiter
 Calcitonin lowers
blood Ca2+ levels
 Thyroid pathologies: Exophthalmus
Hyper- and
Hypothyroidism

32. Goiter Formation
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• Lack of iodine
• Interferes with
negative feedback
control of TSH
• Results in abnormal
enlargement of the
thyroid gland

33. Hypothyroidism
Hyperthyroidism
Slowing of mind
and body

34. Disease of thyroid gland
Hypothyroidism Hyperthyroidism
• Hashimoto thyroiditis • Graves disease
(autoimmune disorder) (autoimmune disease)
• Iodine deficiency • Toxic multinodular goiter
• Drugs (amiodarone) • Drugs (amiodarone)
• Radiation exposure • Thyroid storm(life
• Pituitary tumors threatening condition of
• Myxedema (life threatening hyperthyroidism)
condition of
hypothyroidism)

35. 6. Clinic connection
Hyperthyroidism

36. Hypothyroidism
Cretinism

37. Apply Your Knowledge
True or False: ANSWER:
T Thyroid hormones stimulate protein synthesis.
__
Thyroid follicles store
F The thyroid gland does not store hormones. some hormones.
__
PTH activates osteoclasts.
__ PTH activates osteoblasts.
F
Thyroid hormone
F Calcitonin increases cellular energy production.
__ increases cellular
energy production.
T The four parathyroid glands are located on the thyroid gland.
__
T Calcitonin lowers blood calcium levels.
__
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