When a molecule binds to a receptor on a cell surface, it means that a signal has been received by that cell. In this case, the cell that sent the signal is the same cell that is receiving the signal. Autocrine signaling is the term that describes a cell sending a signal to itself ("auto" in this context means self). Exocrine signaling occurs when a substance is secreted through a gland or duct. Endocrine signaling occurs when a substance is secreted into the bloodstream. Paracrine signaling occurs when a cell sends a signal to nearby cells (often to change the behavior or properties of those cells).