What are the types of exocytosis?

There are three pathways of exocytosis - constitutive, regulated, and fusion of vesicles with lysosomes.

Constitutive exocytosis – This pathway serves to transfer molecules from the Golgi network to the cell’s outer surface and to eliminate substances to the cell’s exterior. Constitutive exocytosis is performed by all cells and is the default pathway for most membrane proteins.

Regulated exocytosis – Regulated exocytosis is performed only by secretory cells. It serves to release hormones, cytokines, neurotransmitters and other small signaling molecules such as histamine that are stored in secretory cells. The expulsion of materials occurs in response to specific extracellular signals, conditions or biochemical triggers.

Fusion of vesicles with lysosomes – In this pathway, microbes, cellular debris and waste materials are broken down by acid hydrolase enzymes present in the vesicles. The digested material is then transported to the cell membrane by lysosomes where they dock and fuse with the membrane. The contents are then released into the extracellular matrix.