====== Extracellular Space ======

The **extracellular space** refers to the **area outside of cells**, filled with **extracellular fluid (ECF)** and various molecules. It is a key component of all tissues and plays critical roles in communication, transport, and structural support.

===== 🔬 Key Characteristics =====

  * **Contents:**
    * Water and electrolytes (e.g., Na⁺, Cl⁻, Ca²⁺)
    * Proteins (e.g., albumin, cytokines, enzymes)
    * Lipids and metabolites
    * **Extracellular matrix (ECM)** components:
      * Collagen, fibronectin, laminin
    * Extracellular vesicles (e.g., exosomes, microvesicles)

  * **Functions:**
    * Facilitates **cell-to-cell communication**
    * Enables **transport** of nutrients, oxygen, and waste
    * Provides **mechanical and biochemical support**
    * Maintains **tissue homeostasis**
    * Participates in **signal transduction** (e.g., hormones, neurotransmitters)

===== 🧠 Examples =====

  * **Brain:** tightly regulated extracellular space crucial for synaptic transmission
  * **Connective tissue:** ECM-rich, provides mechanical support and elasticity
  * **Tumor microenvironment:** altered extracellular space affects invasion, angiogenesis, and therapy resistance

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''Note:'' The composition and regulation of the extracellular space are central to many physiological and pathological processes, including inflammation, cancer, neurodegeneration, and tissue repair.