TSH on surface receptor uses second messenger as
**Core Concept**
The thyroid-stimulating hormone (TSH) receptor is a G protein-coupled receptor that plays a crucial role in regulating thyroid function. When TSH binds to its surface receptor, it activates a signaling cascade that ultimately leads to increased production of thyroid hormones.
**Why the Correct Answer is Right**
TSH binding to its surface receptor activates the Gs protein, leading to the stimulation of adenylate cyclase. This enzyme catalyzes the conversion of ATP to cyclic adenosine monophosphate (cAMP), which acts as the second messenger. cAMP then activates protein kinase A (PKA), which phosphorylates and activates various downstream targets, ultimately leading to increased production of thyroid hormones.
**Why Each Wrong Option is Incorrect**
**Option A:** This option is not relevant to the TSH receptor signaling pathway.
**Option B:** This option is incorrect because the TSH receptor does not use calcium as a second messenger.
**Option C:** This option is incorrect because the TSH receptor uses cAMP as a second messenger, not inositol trisphosphate (IP3).
**Clinical Pearl / High-Yield Fact**
It's essential to remember that the TSH receptor is a G protein-coupled receptor that activates the Gs protein, leading to increased production of thyroid hormones. This is a critical concept in understanding the pathophysiology of thyroid disorders, such as Graves' disease.
**Correct Answer:** C. cAMP.