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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
OH
OH
• 3 main steps:
CH2
– Synthesize thyrogobulin
CH2
thyroglobulin
– Alter tyrosine residues to create thyroxine and triiodothyronine
OH
OH
I
I
I
O
O
I
CH2
I
I
I
CH2
OH
OH
CH2
CH2
thyroglobulin
OH
OH
I
I
I
O
O
I
CH2
I
I
I
CH2
Synthesis of Thyroid Hormones
OH
• 3 main steps:
– Synthesize thyrogobulin
OH
CH2
CH2
thyroglobulin
– Alter tyrosine residues to create thyroxine and triiodothyronine
– Use enzymes to cleave T3+4 from thyroglobulin I
OH
I
I
O
I
I
CH2
enzymes
OH
I
O
I
I
CH2
Follicular
Cells
1. Synthesis of thyrogolulin
2. Alteration of tyrosine
colloid
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
3. Enzymatic breakdown of
thyroglobulin
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-bindingglobulin 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
?
Clinical Aspects of Thyroid
Hormones