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Goiter. Thyroid Gland. Thyroid Hormones: Functions. PERMISSIVE ACTIONS Growth and development Reproduction DIRECT EFFECTS Metabolic/thermogenic. What makes thyroid hormones different from every other class of hormones?. IODINE. Thyroid Gland. Thyroid Gland. OH. OH. CH2. CH2.
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Thyroid Hormones: Functions • PERMISSIVE ACTIONS • Growth and development • Reproduction • DIRECT EFFECTS • Metabolic/thermogenic
What makes thyroid hormones different from every other class of hormones? IODINE
OH OH CH2 CH2 thyroglobulin OH OH I I I I O O I I I CH2 CH2 Synthesis of Thyroid Hormones • Alter tyrosine residues to create thyroxine and tri-iodothyronine • 3 main steps: • Synthesize thyrogobulin
OH OH CH2 CH2 thyroglobulin OH OH I I I I O O I I I CH2 CH2
OH OH CH2 CH2 OH OH I I I I enzymes O O I I I I CH2 CH2 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 thyroglobulin
1. Synthesis of thyrogolulin 2. Alteration of tyrosine 3. Enzymatic breakdown of thyroglobulin Follicular Cells colloid • What does TSH do? • Stimulates I- uptake • Stimulates thyroglobulin synthesis • Stimulates re-uptake of thyroglobulin into the cell • Stimulates breakdown of thyroglobulin • Follicle cell enlargement and cell division
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
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)