When You're the One Canceling a Flight. In defense of Spirit, most airlines operate on razor thin margins and refund dollars do add up. Even airlines that allow refunds-generally only under very special circumstances-may make you jump through hoops and even pay a fee.
Medical Definition of receptor. 1  1: a cell or group of cells that receives stimuli : sense organ. 2  2: a chemical group or molecule (as a protein) on the cell surface or in the cell interior that has an affinity for a specific chemical group, molecule, or virus.
1 Not all cells have a hormoneâs compatible receptor. The ones that do are called target cells.  Once inside a target cell, the hormone (pink) binds to a receptor (purple) - similar to a hand sliding in a glove or mitten - and forms what is known as a hormone-receptor complex between the ligand and receptor.