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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
Synthesis of Thyroid Hormones
• 3 main steps:– Synthesize thyrogobulin
OH
II
CH2
O
I
OH
II
CH2
O
II
CH2
OH
CH2
OH
thyroglobulin
– Alter tyrosine residues to create thyroxine and tri-iodothyronine
CH2
OH
CH2
OH
thyroglobulin
OH
II
CH2
O
I
OH
II
CH2
O
II
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
II
CH2
O
IIenzymesOH
II
CH2
O
II
Follicular Cells
colloid
2. Alteration of tyrosine
1. Synthesis of thyrogolulin
3. Enzymatic breakdown of thyroglobulinWhat does TSH do?
1. Stimulates I- uptake2. Stimulates thyroglobulin synthesis3. Stimulates re-uptake of thyroglobulin
into the cell4. Stimulates breakdown of thyroglobulin5. 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)
Clinical Aspects of Thyroid Hormones
Clinical Aspects of Thyroid Hormones
Clinical Aspects of Thyroid Hormones
Clinical Aspects of Thyroid Hormones
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Clinical Aspects of Thyroid Hormones
