What are some examples of things the body has receptors for?

• A. Neurotransmitters and hormones only
• B. Growth factors and enzymes only
• C. Neurotransmitters, hormones, growth factors, transporters, structural proteins, and enzymes
• D. Lipids and nucleic acids

Answer: (C)

Receptors are binding sites that detect signals and convert them into a cellular response. They aren’t limited to just neurotransmitters and hormones; many other kinds of molecules can act as ligands for receptors, triggering specific pathways.

Growth factors bind to their own receptor types (like tyrosine kinase receptors) to drive growth and survival signals. Signaling cascades activated by receptors can regulate transporters at the cell surface, changing how substances are taken up or released. Receptors also influence enzymes by modulating their activity through signaling networks, and they can affect structural proteins by altering cytoskeletal dynamics or protein interactions. This wide range of potential ligands explains why the best answer lists neurotransmitters, hormones, growth factors, transporters, structural proteins, and enzymes.

The other options miss large parts of this picture: one limits targets to just neurotransmitters and hormones, another to growth factors and enzymes, and another to lipids and nucleic acids, which doesn’t capture the breadth of receptors involved in normal signaling.