Glycocalyx is a general term referring to extracellular polymeric material (glycoprotein) produced by some bacteria, epithelia and other cells. The slime on the outside of a fish is considered a glycocalyx. The term was initially applied to the polysaccharide matrix excreted by epithelial cells forming a coating on the surface of epithelial tissue. External to the plasma membrane, all animal cells have a fuzzy coat called the glycocalyx. This coat consists of the carbohydrate moieties of membrane glycolipids and glycoproteins. Only identical twins have chemically identical glycocalices; everyone else is unique. The glycocalyx is a type of identification that the body uses to distinguish between its own healthy cells and transplanted tissues, diseased cells, and invading organisms.

Image from The Cell, by Fawcet (link)

“The glycocalyx is exceptionally well developed on the brush border of intestinal absorptive cells. Each microvillus bears a tuft of fine, branching filaments. Those of neighboring microvilli intermingle to form a continuous mat over the villous tips of the brush border. Similar filaments are found on the sides of the microvilli but these are only a fraction the length of those at the tip. This surface layer acts as a barrier to penetration of large particles while allowing emulsified lipid, colloidal particles, and substances in solution to pass freely through its meshes and into the intervillous clefts. It is resistant to a variety of proteolytic and potent mucolytic agents. The prevailing radial orientation of the filaments and their continuity with the outer dense lamina of the underlying membrane indicates that they are an integral part of the cell surface and not merely an adherent layer of mucus.”  From Fawcett’s The Cell

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