1. Dr. Omary Chillo (MD, PhD)
The Thyroid Hormones
17/09/2018
Dr. Omary Chillo (MD, PhD)

2. Dr. Omary Chillo (MD, PhD)
17/09/2018
Dr. Omary Chillo (MD, PhD)

3. Follicular Cells of the Thyroid Gland
Colloid
Capillaries
Thyroid Follicle
17/09/2018
Dr. Omary Chillo (MD, PhD)

4. Dr. Omary Chillo (MD, PhD)
17/09/2018
Dr. Omary Chillo (MD, PhD)

5. Dr. Omary Chillo (MD, PhD)
TSH
Gs Protein
Enzyme
Adenyl Cyclase
ATP
Activated cAMP
Thyroxine
17/09/2018
Dr. Omary Chillo (MD, PhD)

6. Follicular Cells Hormones Secreted by the Thyroid Gland
Follicular cells/Cuboidal epithelial cells
Colloid
Thyroid Follicle
93%
Thyroxine/ Tetraiodothyronine (T4)
T3 is 4 times more potent than T4
Follicular Cells 7%
Triiodothyronine (T3)
Para follicular cells
Calcitonin
17/09/2018
Dr. Omary Chillo (MD, PhD)

7. Synthesis and secretion of Thyroid Hormones
Colloid contains thyroglobulin
17/09/2018
Dr. Omary Chillo (MD, PhD)

8. Dr. Omary Chillo (MD, PhD)
Colloid
Na+/I- symporter
Na+ I-
Capillaries
17/09/2018
Dr. Omary Chillo (MD, PhD)

9. Dr. Omary Chillo (MD, PhD)
MIT
DIT
Iodinated Thyroglobulin I2
Peroxidase I-
17/09/2018
Dr. Omary Chillo (MD, PhD)

10. Dr. Omary Chillo (MD, PhD)
Iodinated Thyroglobulin I I
MIT
DIT
DIT I I I I I I T3
Thyroxine T4
17/09/2018
Dr. Omary Chillo (MD, PhD)

11. Dr. Omary Chillo (MD, PhD)
Thyroid Follicles
17/09/2018
Dr. Omary Chillo (MD, PhD)

12. Why is Iodine Important in Thyroid Hormone Production?
Thyroid hormones are unique biological molecules in that they incorporate iodine in their structure.
Thus, adequate iodine intake (diet, water) is required for normal thyroid hormone production.
Major sources of iodine:
- iodized salt
- iodated bread
- dairy products
- shellfish
Minimum requirement: 75 micrograms/day
17/09/2018
Dr. Omary Chillo (MD, PhD)

13. Transport of Thyroid Hormones
Thyroid hormones are lipid-soluble
Thus, they are found in the circulation associated with binding proteins:
- Thyroid Hormone-Binding Globulin (~70% of hormone)
- Pre-albumin (transthyretin), (~15%)
- Albumin (~15%)
Less than 1% of thyroid hormone is found free in the circulation.
17/09/2018
Dr. Omary Chillo (MD, PhD)

14. One Major Advantage of this System
The thyroid gland is capable of storing many weeks worth of thyroid hormone (coupled to thyroglobulin).
If no iodine is available for this period (about 3 months), thyroid hormone secretion will be maintained.
17/09/2018
Dr. Omary Chillo (MD, PhD)

15. Autoregulation of Thyroid Hormone Production
The rate of iodine uptake and incorporation into thyroglobulin is influenced by the amount of iodide available:
- low iodide levels increase iodine transport into follicular cells
- high iodide levels decrease iodine transport into follicular cells
Thus, there is negative feedback regulation of iodide transport by iodide.
17/09/2018
Dr. Omary Chillo (MD, PhD)

16. Action of TSH on the Thyroid
TSH acts on follicular cells of the thyroid.
increases iodide transport into follicular cells
increases production and iodination of thyroglobulin
increases endocytosis of colloid from lumen into follicular cells

17. Regulation of TSH Release from the Anterior Pituitary
TSH release is influenced by hypothalamic TRH, and by thyroid hormones themselves.
Thyroid hormones exert negative feedback on TSH release at the level of the anterior pituitary.
- inhibition of TSH synthesis
- decrease in pituitary receptors for TRH
17/09/2018
Dr. Omary Chillo (MD, PhD)

18. Actions of Thyroid Hormone
Required for GH action
Increases intestinal glucose reabsorption (glucose transporter)
Increases mitochondrial oxidative phosphorylation (ATP production)
Induces enzyme synthesis
Result: stimulation of growth of tissues and increased metabolic rate. Increased heat production (calorigenic effect)
17/09/2018
Dr. Omary Chillo (MD, PhD)

19. Effects of Thyroid Hormone on Nutrient Sources
Effects on protein synthesis and degradation:
-increased protein degradation at high thyroid hormone levels (high metabolic rate; energy)
Effects on carbohydrates:
- high doses increase glycogen breakdown (high metabolic rate; glucose production)
17/09/2018
Dr. Omary Chillo (MD, PhD)

20. 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
17/09/2018
Dr. Omary Chillo (MD, PhD)

21. Effects of Thyroid Hormones on the Respiratory System
Increase resting respiratory rate
Increase minute ventilation
Increase ventilatory response to hypercapnia and hypoxia
17/09/2018
Dr. Omary Chillo (MD, PhD)

22. Effects of Thyroid Hormones on the Renal System
Increase blood flow
Increase glomerular filtration rate
17/09/2018
Dr. Omary Chillo (MD, PhD)

23. Effects of 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
17/09/2018
Dr. Omary Chillo (MD, PhD)

24. Effects 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
17/09/2018
Dr. Omary Chillo (MD, PhD)

25. Effects of 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
17/09/2018
Dr. Omary Chillo (MD, PhD)

26. Effects of 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
17/09/2018
Dr. Omary Chillo (MD, PhD)

27. Diseases of the thyroid
Hyperthyroidism
Secret times of normal Thyroxine hormone
Thyroid gland increases in size
Increases BMR > %
The most common cause is an autoimmune disease called Graves’ disease
Exophthalmos
17/09/2018
Dr. Omary Chillo (MD, PhD)

28. Diseases of the thyroid
Hypothyroidism
Reduced Thyroxine hormone production
Thyroid gland increases in size
Decreases BMR
The most common cause is insufficient Iodine, lack of TH receptors, and lack of TH transport proteins
Thyroid Goitre
17/09/2018
Dr. Omary Chillo (MD, PhD)

29. How is Goiter Related to Hyperthyroidism?
Due to excessive stimulation by TSH (thyroglobulin production, enlarged follicles…).
In this case, excessive stimulation of the thyroid gland by TSH DOES result in thyroid hormone secretion, since iodine is available.
17/09/2018
Dr. Omary Chillo (MD, PhD)

30. Dr. Omary Chillo (MD, PhD)
Thanks
17/09/2018
Dr. Omary Chillo (MD, PhD)