Receptors can be classified into two main categories:
1. Cell surface receptors: These include G protein-coupled receptors (GPCRs), ion channel receptors, and enzyme-linked receptors. They are embedded in the plasma membrane and interact with extracellular ligands. 2. Intracellular receptors: These are located within the cell, usually in the cytoplasm or nucleus, and bind to lipophilic ligands that can easily cross the cell membrane.
