1. Goiter

2. Thyroid Gland

3. Thyroid Hormones: Functions PERMISSIVE ACTIONS –Growth and development –Reproduction DIRECT EFFECTS –Metabolic/thermogenic

4. What makes thyroid hormones different from every other class of hormones? IODINE

5. Thyroid Gland

7. Synthesis of Thyroid Hormones 3 main steps: –Synthesize thyrogobulin OH I I CH2 O I OH I I CH2 O I I OH CH2 OH thyroglobulin –Alter tyrosine residues to create thyroxine and tri- iodothyronine

8. CH2 OH CH2 OH thyroglobulin OH I I CH2 O I OH I I CH2 O I I

9. Synthesis of Thyroid Hormones 3 main steps: –Synthesize thyrogobulin –Alter tyrosine residues to create thyroxine and tri- iodothyronine –Use enzymes to cleave T3+4 from thyroglobulin CH2 OH CH2 OH thyroglobulin OH I I CH2 O I I enzymes OH I I CH2 O I I

10. Follicular Cells colloid 2. Alteration of tyrosine 1. Synthesis of thyrogolulin 3. Enzymatic breakdown of thyroglobulin What does TSH do? 1.Stimulates I- uptake 2.Stimulates thyroglobulin synthesis 3.Stimulates re-uptake of thyroglobulin into the cell 4.Stimulates breakdown of thyroglobulin 5.Follicle cell enlargement and cell division

11. There is 50X more T4 than T3 in the blood More T4 is produced in the thyroid gland Binding globulin: –T4 has a much higher affinity for Thyroid-binding- globulin than T3 –So a higher proportion of T4 will be bound, less will be free –More of T3 will be free to enter cells In fact, it is thought that T3 is the ‘active’ form of thyroid hormone –Thyroid hormone receptors in cells have higher affinity for T3 –Most cells contain an enzyme to remove one of the iodines off of T4 –The liver converts T4 to T3

12. Thyroid Hormone Receptors Can be nuclear: –Regulate gene transcription Can be in the mitochondria: –Can regulate gene transcription of mitochondrial DNA Effects on Metabolism –Thyroid hormones increase ATP production in the mitochondria –Increases oxygen consumption, and therefore basal metabolic rate Effects on Thermoregulation: –Decreases the efficiency of ATP production Less ATP produced, more heat let off Increases Na+ transport pumps in cells (pumps produce heat)

13. Clinical Aspects of Thyroid Hormones

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