Insect integument

                     INSECT INTEGUMENT

The integument or the body wall consists of a layer of cells known as the epidermis. Outside, there is a non-cellular chitinous layer secreted by the epidermis-the cuticle, which forms the outer layer of the exoskeleton. Typically, the cuticle is composed of two parts: an outer chitin-free epicuticle and an inner chitionous procuticle

 a.     Epicuticle is a complex of minutes layers less than 4 microns thick and is credited with so many functions as to verge on the magical. It is the ultimate morphogenetic determinant of the shape of an insect. It controls surface properties of the integument with regard to permeability. It can withstand variation in seasonal and habitat temperature and humidity; it’s is also reasonably adapt at resisting pathogenic attack. Starting from outside, it consists of a cement layer, a wax layer, an outer epicuticle and an inner epicuticle.                         

b.    The procuticle constitutes the bulk of the integument and is composed mostly of chitin and protein, and is particularly prominent in hard-bodied insect. It may be undifferentiated or may become differentiated by sclerotization into an sclertized hard portion called exocuticle and an inner soft endocuticle. Procuticle may vary from 1micron to several mm in thickness. Chitin is the structural component of the insect cuticle and is a helicle polymer.It is generally present in the cuticle as a chitin- protein complex.                                                                                                     The cuticle is resistant to alkalis and dilute mineral acids. The surface of the cuticle bears two types of process: the one rigid ,which included spines and minute hair-like structure; and the other ,articulate or movable ,such as spurs , general clothing hair , sensory setae and glandular satae. Important functions of the cuticle are support for muscle attachment, protection from environment factors and permeability barrier against loss of the water from the body and against the entry of foreign materials like microorganism, toxicants, etc. into the body. Beneath the cuticle lies a single layer of epithelial cells known as epidermis. Aside from performing normal cellular activities, the epidermis is a major regulator both of cuticular properties and of itself.