the ppt is on thyroid hormone- physiologic aspect

1. PHYSIOLOGY
THYROID HORMONE
by
Karishma R. Pandey
Dept. of Basic and Clinical Physiology

2. OBJECTIVES
1. Introduction-an anatomical consideration
2. Bio-synthesis and Secretion of thyroid hormone
3. Transport
4. Activation and degradation at target organ
5. Physiological activities at target organs
6. Control/ regulation of thyroid hormone
7. Pathophysiology & pharmacology-A snapshot
8. Tests of thyroid function

3. Introduction

4. Uniqueness
• Easily seen and palpated
• Iodine
• Stored in an extracellular site
• Peptide hormones - no cell-membrane
receptors
• Nuclear receptors.

5. Bio-synthesis and Secretion of Thyroid Hormone
1. Iodide Transport
2. Thyroglobulin
Synthesis
3. Oxidation o f
Iodide
4. Organification
(lodination)
5. Coupling
6. Storage
7. Secretion

6. Structures of Thyroid
Hormone

7. Secretion of thyroid hormone

8. ALB
T4,T3
TRANSTHYRETIN
T4,T3
TBG
T4,T3,
rT3
Transport of thyroid hormones

9. T4 T3
Total conc. in
plasma
8 µg/dl 0.15 µg/dl
% of bound
form
99.98% 99.8%
Free form 2 ng/dl 0.3 ng/dl
% of free form 0.02% 0.2%
Biological half-
life
Long (6-7days)
Shorter average 2
days

10. Thyroxine (T4)
T3 rT3
Thyronine
Deiodinase
1 & 2
Deiodinase 3
DeiodinaseDeiodinase
Thyroxine Catabolism
DIT
MIT
Deiodinase
Conjugated in liver
Hydrolysed/
reabsorbed/
excreted

11. Action at target organ

12. Mechanism of T3
4 functional intranuclear T3 receptors: α1, α2, β1 and β 2;
nonfunctional receptor: α2.
The different forms of thyroid receptors have patterns of expression
that vary by tissue and by developmental stage.
The presence of multiple forms of the thyroid hormone receptor, with
tissue and stage-dependent differences in their expression, suggests
an extraordinary level of complexity in the physiologic effects of
thyroid hormone.

14. 1. Effect of thyroid hormones on BMR
• Extreme excess of thyroid secretion increases BMR to 60-100%
above normal
• Complete lack of thyroid secretion causes BMR to fall 40-50%
below normal
Mechanism of increasing metabolic rate and
temperature
by increasing number, size and activity of mitochondria
By increasing plasma membrane Na+-K+ ATPase Activity
By stimulating both catabolic and anabolic reactions in pathways
affecting fats ,carbohydrates, and proteins

15. Effects secondary to increased metabolism
Increased O2 consumption in almost all the cells
exceptions are the adult brain,testes,uterus,lymph nodes,spleen,and
anterior pituitary.
Nitrogen excretion is increased
Weight loss due to catabolism of endogenous protein and fat stores
Increased urinary excretion of K+, uric acid
Precipitation of vitamin deficiency syndrome due to increased need
for vitamins resulting from increased metabolic rate

16. Control and regulation of thyroid hormones

17. Thyroid Disease States
• Disease is associated with both inadequate
production and overproduction of thyroid hormones.

18. Hyperthyroidism
Effects and
symptoms

21. Effects and
symptoms
Hypothyroidism

24. Sick Euthyroid Syndrome
 The relative activity of the deiodinase changes in response to
physiological and pathological stimuli
 The decrease in T3 production with fasting is an important
adaptive response, increase in rT3 and normal TSH
 Non thyroidal illness
• Burns
• Trauma, advanced cancers,
• Cirrhosis
• Renal failure.
• Fasting
• Glucocorticoids
• Fetus
• Certain drugs

26. Thyroid Function Tests
 TSH
 FT4, (T4)
 T3, FT3
 Thyroid stimulating immunoglobulin (TSI) or
TSHR antibody
 Antithyroid peroxidase antibodies (Anti TPO)

27. Thioamides:
propylthiouracil,
Methimazole,
Carbimazole
Thiocyanate (SCN– )
Perchlorate (ClO4– ),
Site of Action of Different Antithyroid Agents

30. Thank you