How are proteins destined for secretion sorted and packaged. This cartoon shows the sorting of proteins destined for secretion into vacuoles in the trans Golgi Complex. Note that lysosomal enzymes are sorted into another compartment, thanks to the mannose 6 phosphate receptor. The above cartoon also shows the process of exocytosis. We defined regulated secretion initially when we talked about the Golgi complex .
Regulated secretion requires a stimulus, usually from the outside.
The process may begin by the binding of a ligand to a specific receptor. Therefore, the process of receptor mediated endocytosis and exocytosis can and does occur simultaneously. One should be able to recognize the cytological signs of both processes in the same cell. Click this link to see an electron micrograph of exocytosis. They are not exclusive to the plasma membrane.