Thyroid Hormone Production and Biosynthesis

What is the result of the peroxidation of iodide into iodine?

During the organification process, how many iodine atoms can bind to a single tyrosine residue?

What is the final product of the coupling step involving monoiodotyrosine (MIT) and diiodotyrosine (DIT)?

Which of the following statements about DIT in the coupling phase is true?

What role does thyroid peroxidase play in the processes described?

What is the primary function of triiodothyronine (T3) and thyroxine (T4) in the body?

What effect do thyroid hormones have on cholesterol levels in the body?

Which enzyme is crucial for the peroxidase-mediated steps in thyroid hormone biosynthesis?

How does high iodine concentration affect thyroid hormone production?

Which cells in the thyroid gland are responsible for the biosynthesis of calcitonin?

What is the role of thyroid-stimulating hormone (TSH) in thyroid hormone production?

What is the effect of thyroid hormones on cardiovascular function?

What mechanism does iodide uptake into follicular cells primarily utilize?

Thyroid Hormone Production

Calorigenesis: Thyroid hormones increase heat production in the body.
Cholesterol Reduction: Thyroid hormones decrease hepatic LDL receptors, leading to lower total cholesterol.
Cardiovascular Effects: Thyroid hormones have an inotropic effect, increasing beta receptor activity. This leads to increased heart rate, cardiac output, and blood pressure.
Fluid Retention: Thyroid hormones promote fluid retention.

Thyroid Hormone Biosynthesis

Location: Biosynthesis of T3 and T4 occurs in follicular cells of the thyroid gland. Calcitonin is produced in parafollicular (C) cells.
Iodide Uptake: Iodide enters follicular cells via the sodium/iodide symporter (NIS). High levels of iodide inhibit this process and overall thyroid hormone synthesis. Other anions, like thiocyanate (SCN-), pertechnetate (TcO4-), and perchlorate (ClO4-) can also inhibit iodide uptake.

Peroxidase-Mediated Steps

Enzyme: Thyroid peroxidase (TPO) is the key enzyme. TSH from the anterior pituitary increases TPO production, stimulating thyroid hormone release.
Peroxidation: Iodide is oxidized to iodine by thyroid peroxidase, a critical step in thyroid hormone synthesis. High iodide levels and thioamide drugs can block this peroxidation (and other steps that depend on TPO).
Organification: Iodine is incorporated into tyrosine residues within the thyroglobulin protein molecule. This results in monoiodotyrosine (MIT) and diiodotyrosine (DIT).
Coupling: MIT and DIT combine, forming T3 (triiodothyronine). Two DITs combine to form T4 (thyroxine). T3 and T4 are still bound to thyroglobulin at this point.

This quiz covers key concepts related to thyroid hormone production and biosynthesis. It explores the functions of thyroid hormones, their effects on the body, and the biosynthesis process within the thyroid gland. Understand the mechanisms behind calorigenesis, cholesterol reduction, and other physiological impacts of thyroid hormones.