Exocytosis: Constitutive vs. Regulated Secretory Pathways

Exocytosis: The Constitutive and Regulated Secretory Pathways

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  • Exocytosis Definition

    • Exocytosis is a cellular process where substances are expelled from a cell by vesicles that fuse with the plasma membrane. This mechanism is crucial for various physiological functions, including secretion of hormones, neurotransmitters, and other molecules.
  • Constitutive Secretory Pathway

    • This pathway is responsible for the continuous delivery of proteins and lipids to the plasma membrane and extracellular space.
    • Key Characteristics:
      • Unregulated membrane fusion means that vesicles continuously release substances without the need for specific signals.
      • It operates in various cell types for maintaining the extracellular environment and membrane composition.
      • Includes the delivery of newly synthesized plasma membrane proteins and lipids.
  • Regulated Secretory Pathway

    • Unlike the constitutive pathway, this pathway is activated by specific signals (e.g., hormones or neurotransmitters).
    • Key Characteristics:
      • Performed by secretory vesicles that store proteins, which are only released upon receiving a signal.
      • The process involves an intracellular signaling pathway that triggers the vesicles to fuse with the plasma membrane.
      • Essential in processes such as the release of insulin by pancreatic cells or neurotransmitters by nerve cells.
  • Golgi Apparatus Role

    • The Golgi apparatus plays a crucial role in processing and packaging proteins for both secretory pathways.
    • Proteins synthesized in the endoplasmic reticulum are transported to the Golgi apparatus, where they undergo modifications before being sorted for exocytosis.
  • Signaling Molecules

    • The regulated pathway is often activated by signaling molecules, illustrating the importance of external cues in cellular processes.
    • Understanding these signaling pathways can provide insights into various biological functions and the development of certain diseases where exocytosis is impaired.

Extended readings:

www.ncbi.nlm.nih.gov
Transport from the Trans Golgi Network to the Cell Exterior: Exocytosis
www.sciencedirect.com
Secretory Pathway - an overview | ScienceDirect Topics
www.sciencedirect.com
Exocytosis - an overview | ScienceDirect Topics