Thyroid hormones belong to which class of hormone?
**Core Concept**
Thyroid hormones, including triiodothyronine (T3) and thyroxine (T4), are complex hormones produced by the thyroid gland. They play a crucial role in regulating metabolism, growth, and development.
**Why the Correct Answer is Right**
Thyroid hormones belong to the class of steroid hormones, but more specifically, they are classified as iodothyronines. This classification is due to the presence of iodine atoms in their molecular structure. Steroid hormones are derived from cholesterol, whereas thyroid hormones are synthesized from tyrosine residues on thyroglobulin. The thyroid gland produces T3 and T4 through a series of enzymatic reactions, including iodination, oxidation, and coupling of tyrosine residues.
**Why Each Wrong Option is Incorrect**
**Option A:** Thyroid hormones are not peptide hormones, as they do not consist of short chains of amino acids linked by peptide bonds.
**Option B:** While thyroid hormones are lipophilic and can diffuse through cell membranes, they are not classified as local hormones, which are hormones that act on adjacent cells.
**Option C:** Thyroid hormones are not classified as catecholamines, which are a class of hormones derived from the amino acid tyrosine but are structurally and functionally distinct from thyroid hormones.
**Clinical Pearl / High-Yield Fact**
It's essential to remember that the thyroid gland produces two primary hormones, T3 and T4, which have different biological activities. T4 is the primary hormone produced by the thyroid gland, and T3 is produced through peripheral conversion of T4.
**Correct Answer: C. Iodothyronines.