Exocytosis

EXOCYTOSIS

1) Proteins synthesized in the endoplasmic reticulum and trafficked to the Golgi apparatus

2) From the Golgi, the proteins are sorted and can follow different paths:

3a) Constitutive secretory pathway

Also called default pathway as it does not require a signal for cargo to enter this pathway
Can transport soluble proteins or plasma membrane proteins
Transport vesicles fuse with the plasma membrane and release their contents (plasma membrane proteins become accessible to the extracellular space)

3b) Regulated secretory pathway

Found mainly in specialized cells that release molecules like hormones, neurotransmitters, etc.
Secretory vesicles are blocked from fusing with the plasma membrane without a proper signal
An extracellular ligand binds a cellular receptor which causes an intracellular signal that releases the block on the secretory vesicles
Secretory vesicles then fuse with the plasma membrane and release their cargo