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.
If the right substance comes along that fits into the receptor â like a key fitting into a lock â the switch is turned on and a particular activity in the cell begins. One type of receptor found in normal breast cells is the hormone receptor. By attaching to hormone receptors, estrogen and/or progesterone contribute to the growth and function of breast cells.