1. Endocrine Physiology THYROID GLAND
Dr. Meg-angela Christi Amores

2. Where is your thyroid gland located?
located immediately below the larynx on each side of and anterior to the trachea
normally weighing 15 to 20 grams in adults

3. What are the hormones of the thyroid gland?
two major hormones:
Thyroxine(T4) and triiodothyronine(T3)
increase the metabolic rate of the body
Thyroid secretion is controlled primarily by thyroid-stimulating hormone (TSH) secreted by the anterior pituitary gland
also secretes calcitonin

4. Synthesis and Secretion
93% of metabolically active hormones secreted by the thyroid gland = THYROXINE (T4)
7% = TRIIODOTHYRONINE (T3)
Triiodothyronine is about four times as potent as thyroxine

5. Synthesis and Secretion
Physiologic Anatomy
Composed of large numbers of closed follicles
filled with a secretory substance called colloid and lined with cuboidal epithelial cells that secrete into the interior of the follicles

6. Synthesis and Secretion
Thyroglobulin
major constituent of the colloid
contains the thyroid hormones within its molecule
Iodine
Required for formation of thyroxine
50 milligrams of ingested iodine in the form of iodides are required each year, or about 1 mg/week

8. Transport of iodides into follicles (iodide pumping)
conversion to an oxidized form of iodine
Each molecule of thyroglogulin contains 70 tyrosine amino acids
Oxidized Iodine (I3)is capable of combining directly with the amino acid tyrosine
Oxidation is promoted by enzyme PEROXIDASE and accompanied with HYDROGEN PEROXIDE

9. binding of iodine with the thyroglobulin molecule is called organification of the thyroglobulin
successive stages of iodination of tyrosine and final formation of the two important thyroid hormones, thyroxine and triiodothyronine

10. Tyrosine is first iodized to monoiodotyrosine
and then to diiodotyrosine
Then, during the next few minutes, hours, and even days, more and more of the iodotyrosine residues become coupled with one another

11. Transport of thyroid hormones
Thyroxine and Triiodothyronine Are Bound to Plasma Proteins
99% of thyroid hormones are bound to:
thyroxine-binding globulin
thyroxine-binding prealbumin and albumin
Thyroid Hormones Have Slow Onset and Long Duration of Action
T4: long latency >2-3 days, maximumum in 10 – 12 days
T3: latent: 6 to 12 hours , maximum in 2 – 3 days

12. Physiologic Function

13. Physiologic Function
Thyroid Hormones Increase the Transcription of Large Numbers of Genes
Thyroid Hormones Increase Cellular Metabolic Activity
Effect on growth:
thyroid hormone is essential for the metamorphic change of the tadpole into the frog
promote growth and development of the brain during fetal life and for the first few years of postnatal life

14. Physiologic Function Effects on specific bodily mechanisms
Stimulation of Carbohydrate Metabolism
Stimulation of Fat Metabolism
Increased Requirement for Vitamins
Increased Basal Metabolic Rate
Decreased Body Weight

15. Regulation of Thyroid hormone