👉 In biology and medicine, a ligand is an agent that binds to a receptor on a cell or other cell type. Ligands can be small molecules, ions, enzymes, hormones, or proteins. When a ligand binds to its target, it activates a signaling pathway and triggers the release of a signal molecule (such as a hormone) that regulates the activity of the receptor. This signaling cascade is essential for maintaining cellular homeostasis by regulating various physiological processes such as cell division, gene expression