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

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

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