Thyroid Hormone Synthesis Pathway

Overview

• Video explains thyroid hormone synthesis pathway step-by-step.
• Important for diagnosing and treating thyroid conditions.
• Three main structures: Hypothalamus, Anterior Pituitary Gland, Thyroid Gland.
• Collectively known as the Hypothalamic-Pituitary-Thyroid (HPT) axis.
• Self-regulatory circuit maintaining thyroid hormone levels.

Sequence of Structures

1. Hypothalamus
   • Located in the brain, below the thalamus.
   • Secretes Thyrotropin-Releasing Hormone (TRH) from neurons in the paraventricular nucleus.
2. Anterior Pituitary Gland
   • Located below the hypothalamus.
   • TRH travels via the hypophyseal portal system to stimulate thyrotropes.
   • Thyrotropes release Thyroid Stimulating Hormone (TSH).
3. Thyroid Gland
   • Located in the neck, butterfly-shaped.
   • TSH stimulates the production of thyroid hormones: Triiodothyronine (T3) and Thyroxine (T4).

Hormone Synthesis Process

• TRH: Stimulates anterior pituitary to release TSH.
• TSH: Enters the bloodstream, travels to the thyroid gland.

Thyroid Gland Detail

• Composed of follicles lined by follicular cells (thyrocytes).
• Colloid (center of follicle) is rich in thyroglobulin.
• Thyroglobulin: Precursor for thyroid hormones.
• Iodide: Absorbed from diet, travels to thyroid via bloodstream.

Synthesis Steps

1. Iodide Uptake
   • TSH enhances uptake of iodide into follicular cells using Sodium Iodide Symporter.
2. Iodide to Iodine Conversion
   • Enzyme: Thyroid Peroxidase (TPO).
   • Converts iodide into iodine (iodide oxidation).
3. Organification
   • Iodine attaches to tyrosine on thyroglobulin.
   • Forms Monoiodotyrosine (MIT) and Diiodotyrosine (DIT).
4. Coupling
   • TPO enzyme combines MIT and DIT to form T3 and T4.
   • T3 (Triiodothyronine): One MIT + One DIT.
   • T4 (Thyroxine): Two DITs.
5. Release into Bloodstream
   • T3 and T4 cleaved from thyroglobulin by protease enzyme.
   • Bound to Thyroxine Binding Globulin (TBG) in blood.

Enzyme Function

• Thyroid Peroxidase (TPO):
  • Involved in oxidation, iodination, and coupling steps.
  • Activity enhanced by TSH.

Summary

• Understanding of hormone synthesis critical for diagnosing and treating thyroid conditions.
• Step-by-step guide and charts available in lecture notes and study guides.

Additional Resources

• Detailed lecture notes available on the website.
• Future videos will cover thyroid conditions and the role of TRH, TSH, T3, T4, thyroglobulin, and thyroid peroxidase in diagnosis and treatment.

Remember to check the lecture notes for a detailed step-by-step explanation.