## **Core Concept**
FSH (Follicle-Stimulating Hormone), LH (Luteinizing Hormone), and TSH (Thyroid-Stimulating Hormone) are all glycoprotein hormones that exert their effects through specific cell surface receptors. These hormones play critical roles in reproductive and thyroid functions.

## **Why the Correct Answer is Right**
These hormones act through **G protein-coupled receptors (GPCRs)**, specifically through receptors that are coupled to **Gs proteins**. When FSH, LH, or TSH binds to their respective receptors, it activates the Gs protein, which in turn stimulates **adenylyl cyclase**. This activation leads to an increase in intracellular **cAMP (cyclic adenosine monophosphate)**, acting as a second messenger to trigger downstream signaling pathways that ultimately result in the physiological effects of these hormones.

## **Why Each Wrong Option is Incorrect**
- **Option A:** This option is incorrect because it does not accurately describe the receptor type through which FSH, LH, and TSH act.
- **Option B:** This option is incorrect as it does not correctly represent the signaling pathway used by these hormones.
- **Option C:** While some hormones act through intracellular receptors (e.g., steroid hormones), FSH, LH, and TSH do not; they act through cell surface receptors.

## **Clinical Pearl / High-Yield Fact**
A key point to remember is that defects or abnormalities in the signaling pathways of these hormones can lead to various endocrine disorders. For example, mutations in the TSH receptor can lead to hyperthyroidism or hypothyroidism, depending on the nature of the mutation.

## **Correct Answer:** .