PERITROPHIC MATRIX STRUCTURE AND FUNCTION

Formed of proteins, glycoproteins, and chitin microfibrils in a proteo glycan matrix, the peritrophic matrix (PM) separates the food from the midgut epithelium in most but not all insects. A PM occurs in two for ms. A type I PM is delaminated from the entire midgut epithelium and, in some cases, may only be formed in response to feeding and the type of meal ingested. A type II PM is produced by a specialized region of the anterior midgut called the cardia and forms a continuous sleeve (o r sleeves) that is always present. As it is positioned between food an d midgut epithelium, the PM plays key roles in the intestinal biology of the insect. The PM may protect the midgut epithelium from mechanica l damage and insult from pathogens and toxins; it must act as a semipe rmeable membrane regulating passage of molecules between the different midgut compartments; and it may separate the midgut lumen into differ ent, physiologically significant compartments.