Intracellular receptors are used by ?
**Core Concept**
Intracellular receptors are a class of receptors that are located inside the cell, as opposed to cell surface receptors. They play a crucial role in the regulation of gene expression and cellular metabolism in response to various hormones and signaling molecules.
**Why the Correct Answer is Right**
Intracellular receptors are used by steroid hormones, thyroid hormones, and retinoids to regulate gene expression. These hormones can diffuse through the cell membrane and bind to specific intracellular receptors, which then form a complex with other proteins and translocate to the nucleus to regulate gene transcription. This process is crucial for the regulation of various physiological processes, including growth and development, metabolism, and immune responses.
**Why Each Wrong Option is Incorrect**
**Option A:**
This option is incorrect because intracellular receptors are not used by neurotransmitters, which primarily interact with cell surface receptors to regulate synaptic transmission.
**Option B:**
This option is incorrect because G-protein coupled receptors (GPCRs) are a class of cell surface receptors that are used by various hormones, neurotransmitters, and sensory stimuli to regulate cellular signaling pathways.
**Option C:**
This option is incorrect because ion channels are a class of proteins that regulate the flow of ions across the cell membrane, but they do not interact with intracellular receptors.
**Clinical Pearl / High-Yield Fact**
Intracellular receptors are involved in the regulation of gene expression, and their dysfunction can lead to various diseases, including cancer, metabolic disorders, and developmental abnormalities. For example, the androgen receptor is a type of intracellular receptor that plays a crucial role in the development and progression of prostate cancer.
**Correct Answer: D. Steroid hormones**