[6] Type II formation of a peritrophic matrix is considered to be a derived technique, and is found only in some families of the diptera, dermaptera, embioptera and lepidoptera orders of insects.
[3] In type II formation, the peritrophic matrix is produced by a specialized group of cells present on the proventriculus of the anterior midgut.
Although the peritrophic matrix is secreted continually, the presence of a food bolus significantly increases the rate of production.
This compartmentalization of the midgut provides three general advantages: prevention of non-specific binding of undigested material to the epithelium wall, conservation and concentration of enzymes and substrates and rapid removal of indigestible molecules.
[7] Prevention of non-specific binding is particularly important, as it increases the efficiency of the absorption process by filtering out undigested material which would otherwise block access to the midgut epithelium.
[7] Concentrating enzymes and food substrate within the endoperitrophic space significantly decreases the time required for digestion in the midgut.
Much like indigestible molecules present in the food bolus, many toxins are too large to pass through the small pores of the peritrophic matrix.
Heme groups, which are components of hemoglobin, an oxygen carrying protein present in vertebrate blood, act as strong oxidizers in insects.
[9] A significant trend can also be observed in the type of peritrophic matrix produced by blood-feeding insects that are capable of transmitting disease.
In comparison, blood-feeding insects that produce a type II matrix, which provides a more impenetrable barrier to pathogens, are rarely disease vectors.
These pathogens secrete chitinase and proteinase enzymes which dissolve the chitin microfibrils and proteins present in the peritrophic matrix.