extracelular

Extracelular, or extracellular, refers to anything located outside the cells of an organism. In multicellular life, the extracellular milieu consists mainly of the extracellular fluid and the extracellular matrix, which together surround cells and organize tissues. The extracellular fluid (ECF) includes interstitial fluid that bathes tissues and plasma, the liquid component of blood. The composition of the ECF is tightly regulated, providing nutrients and ions while removing wastes.

The extracellular matrix is a network of macromolecules secreted by cells, forming a scaffold that supports cells and tissues. Major components include fibrous proteins such as collagen and elastin; polysaccharide-rich proteoglycans and glycosaminoglycans such as hyaluronan; and adhesive glycoproteins such as fibronectin and laminin. The basement membrane is a specialized ECM underlying epithelial and endothelial layers.

ECF and ECM provide mechanical stability, regulate tissue permeability, and create biochemical niches that influence cell behavior through signaling molecules and receptors. ECM remodeling during development and wound healing alters architecture; dysregulation can contribute to fibrotic disease, cancer invasion, edema, or defective tissue regeneration.

Cells communicate with their exterior via secreted factors (hormones, cytokines) and surface receptors; extracellular proteins regulate diffusion gradients and morphogen signaling during development.