The first stage of regulated secretion involved collecting large amounts of a specialized protein into secretory vesicles docked at the cell membrane awaiting a specific release signal. Clicking on each of the thumbnail images will bring up a larger, labeled version of the described scene.

To see the Flash movie for the following sequence of images, click here.

	An example of a polarized cell type that engages in the regulated secretion of a specialized protein is the beta cell, a type of cell found in the pancreas that secretes insulin.
	Insulin travels from the endoplasmic reticulum into the Golgi apparatus where it is packaged into transport vesicles.
	Insulin-containing transport vesicles from the trans Golgi-network fuse at the cell membrane to form large secretory vesicles.

NEXT --> 2.) EXOCYTOSIS