MANOJ KUMAR (SHELFORD)

Saturday, October 1, 2011

the integuments of insect: generalised study (part 1)

Integuments (part 1)

The integuments of insects like that of other animals are an outer dermo-skeletal covering of the body and are derived from the embryonic ectoderm. It is functionally a composite structure that serves as a skin, skeleton, food reservoir, and switches on post-embryonic development by undergoing moulting repeatedly.

A. Structure and chemistry:

It is basically composed of three layers; the inner basement membrane, middle epidermis, and the outer cuticle. The epidermis is commonly called as the hypodermis as it lies below the cuticle. It is thin layer of integument that is cellular, while the inner basement membrane as well as the outer cuticle, both is a cellular structure. The epidermis secretes the cuticle and the cuticle is modified; later on into various skeletal sclerities, appendages, and sensory organs and internal linings of the fore a hind gut, the tracheal system, some organs of reproduction and the exocrine glands:

1. The basement membrane: it is formed from the degenerated epidermal cells, and appears as a non living, amorphous, granular, inner lining of the integument. It separates the epidermis from the hemocoel. It is about 0.5 micron thick. The histochemical studies reveal that it is composed primarily of the neutral mucopolysaccharides. On inner surface of the basement membrane, are attached the muscles, hemocytes and oenocytes. Sometimes, the stellate tracheal cells, collagen fibrils and connective tissue fibrils are imbedded in the basement membrane.

2. The epidermis: it is a unicellular layer formed from the polygonal cells. The polygonal cells are polyploidy, possessing a large number of nucleoli. The cytoplasm is characterized by containing various types of pigment granules. The adjacent epidermal cells are held with one another by means of cytoplasmic process, the desmosomes. Each epidermal cell produces a large number of cytoplasmic processes apically, the pore canals traversing the cuticle and opening above a cuticulin layer. The epidermal cells differentiate in some regions of the integument and constitute various types of mechano and chemoreceptor organs, the dermal glands and particularly in dipteran larvae, the peristigmatic glands around the spiracles. Each dermal gland is formed by a group of three cells; the medial cell constituting the body of gland is formed by a group of three cells, the medial cell constituting the body of the gland and is termed as tormogen cells. During moulting, some epidermal cells modify in to the so called moulting glands which secretes the moulting fluid that digests the old endocuticle to ensure further growth of the new cuticle.

Sometimes, the myofibrils penetrate the epidermis from the site of muscle attachment.

3. The cuticle: the cuticle is secretory product of epidermis. It forms an outermost thick layer of the integument and determines surface pattern and physio-chemical properties of integuments.

clip_image001clip_image003It is differentiated into three major regions; outer epicuticle, middle exocuticle and inner endocuticle. The epicuticle is non-chitinous while the exo and the endocuticle are chitinous regions. The exo- and the endocuticles are differentiated from the initially secreted procuticle due to sclerotization or tanning that takes place on the upper region. The exocuticle, therefore represents the sclerotized or tanned and the endocuticle nonsclerotized or untanned, undifferentiated regions of the cuticle.

Besides these three static regions, two more non-static regions develop at the time of moulting. I.e. between the exo- and endocuticles as a transitional semi hard and little darkened region commonly known as the mesocuticle. The other region arises in between the endocuticle and the epidermis in the form of a membrane and is called as the ecdysial membrane or the subcuticle. These structures can be seen only during the larval and pupal moults and are completely absent from the cuticle of the adult insects. The functional significance of these regions is still obscure.

a. The epicuticle: the epicuticle is a very thin outermost layer and varies in thickness from 0.03 to 0.04 micron. It is composed of three or four superimposed layers; outer cement layer, second wax layer, third polyphenol layer and inner one cuticulin. The polyphenol layer is reported only in some insects.

1. The cement layer: it is secreted by the dermal glands or so called verson’s gland in Lepidoptera. It is composed of the lipoprotein complex resembling the natural product, shellac secreted by the lac insect, laccifer lacca. It also contains the carbohydrates like al laccose. It functions as a varnish and provides protective external surface to the integuments. It absorbs the mobile lipids that are used for sealing over the surface abrations in order to prevent water loss from the body. It serves as reservoirs for the lipids too.

2. Wax layer: prominent layer about 0.35 micron thick layer containing partially oriented wax molecules.

Composition:

Hydrocarbons: 48 t0 58 %

Fatty acids: 25 to 18 %

Esters: 9 to 11 %

Cholesterol: 2 to 3 %

Polymers: 12 to 15 %

Note: unlike the plant wax the insect wax lacks the alcohol.

It is a mono layer in solid or liquid phase and hydrophilic groups of molecules are adsorbed on cuticulin layer. It serves as a water proof layer of integument.

3. the polyphenol layer:

It is most commonly described in the blood sucking bugs. Often appears in liquid state containing various types of polyhydric phenols-homocatechol, protocatechol, dopacatechol etc...

The polyphenols are transported above the cuticulin layer by the pore canals, Secreted by the epidermal cells. At the time of sclerotization the phenols are converted into the quinone in the presence of the phenol oxidase. Quinone gets tanned first. The protein of cuticulin layer and protein of outer procuticle together forms the exocuticle.

4. The cuticulin layer: refractile amber coloured layer formed of a lipoprotein-cuticulin. It is a highly resistant to mineral acids of and most of the organic solvents. It also serves as a growth barrier and determines the surface properties of the integuments.

b. THE CHITINOUS CUTICLE:

It is composed of the exo- and the endocuticle. It is a stratified structure differentiated as an exocuticle and endocuticle. The exocuticle is darkly pigmented, hard, and sclerotized. It provides strong mechanical support to the body size due to its toughness and inelastic properties.

I. The lamellar organisation: the chitin microfibrills lie parallel to each other to form a group of layers about 20 to 25 Å thick. The orientation of the micro fibrils differs from one lamella to the other; hence they can be easily distinguished and counted in the sections. Observations of the locusts have shown that lamellar cuticle is formed during the night and the non lamellar cuticle is formed during the day time. Thus a fully formed cuticle will have alternate bands of the lamellar and non lamellar cuticle. The lamellar regions are elastic in nature hence facilitate the elasticity to the endocuticle for flexibility and stretching properties

II. The pore canals: they run throughout the cuticle. They are about 0.15 to 1.0 micron in diameter. They encase the cytoplasmic fin processes of epidermal cells. In newly synthesised cuticle the pore canals are arranged in a spiral course and contain he cytoplasmic filaments. But in the mature cuticle they become straight and contain cubicula substances. After penetrating the cuticulin layer the pore canals divide. Sometimes the site of division is separated from the pore canal by a plate called the pore plate. The pore plate separates the wax fluid-filled region from the chitin filled region. There are about 15000 canals per square mm in endocuticle of sacrophaga. And about 200000 per cuticle per square mm in periplaneta. Functions: the pore canals transport the secretions of the epidermal cells to the upper surface of the procuticle to facilitate its growth and sclerotization.

(To be continued.................)

No comments:

Post a Comment

Blog Archive

Labels

2012 4TH LARVAL AND PUPAL STAGES. manoj kumar adaptations ADHATODA VASICA agarose agarose gel electrophoresis. agaros gel electrophoresis theory allergic reactions allergy amino acids anopheles ANSWER KEYS CSIR antheraea mylitta ANTI-HEMOLYTIC anti-typhoid antibacterial antibody anurans aquatic aquatic mammals arthropoda autotrophs BACTERIAL DISEASES BAT BEHAVIOUR benedict reagent benedict's reagent benedict's test benedicts reagent biochemistry bioscan biotechnology BIRDS bis bizzare phenomena blood blood sucking blood sucking bugs bruce effect bugs carbohydrate carbon dioxide CARNIVORUS. CAT CBSE CBSE 2014 CBSE EXAM CBSE SEMESTER II SCIENCE cbsex census 2011 centepede central board of secondary education chapter chapter 2 chapter2 class class 6 CLASS 7 class x class6 CLASS7 classical genetics CLASSIFICATION classification of amino acids cloning vectors COMMON DISEASES conference india CSIR WEB LINKS cuscuta dav dempster department of zoology Digestive System DNA RECOMBINANT TECHNOLOGY DOG domestic domestic levels. india DOWNLOAD NET ANSWER KEYS DOWNLOAD NET QUESTION PAPERS drury haemocytes drury hemocytes ecology ecoscan electrophoresis elements of innate immune system energy entomology environmental biology. exam extraction farmers fat father female anopheles fertilisers fine structure of antibody FMD food food chain FOOT AND MOUTH DISEASE Franz frog vocal FUNCTIONS fut content analysis GE02 gel genetic engineering genetics giardia giardiasis glucose test gorakhpur conference 2013 gram stain harmony - 2013 harmony 2-13 HARMONY 2014 harmony-2013 harmony2013 hemiptera heteroptera heterotrophs house centipede hypersensitivity immune system immunology in in plants India inheritance innate inportance INSECT ENDOCRINOLOGY isotypes Jhakrhand kwashiorkor lamblia larval stage law of minimum leibig levels limiting factors M. P. SINHA M. P. SINHA. malaria malarial malnutrition mammals mammals. manoj kumar manoj kumar shelford manoj kumar zoology manoj kumar zoology ranchi marasmus MATING microbiology MINERAL CONTENTS minerals MODE OF ACTION OF RABIES VIRUSE molecular genetics Mp sinha national environmentalists association ncert nea NEA CONFERENCE nea conference 2013 NEST nutrition nutrition in NUTRITIVE VALUE origin and evolution of reptiles oxygen parasite PARENTAL CARE IN BIRDS pcr pharmacological photosynthesis physical barriers PHYTOCHEMICALS PLACENTA PLACENTA VERA plants plasmids plasmodium polyadenylation. polymerase chain reaction potable potable water precipitaion test pregnancy block proper growth protein protein energy malnutrition proteins PROTOZOAN DISEASE purification qpcr qualitative test RABIES RANCHI UNIVERSITY RANCHI. revesion test RHEOCIRUSE SA -b 1SCIENCE SA CBSE SCIENCE SA-II SCIENCE SAMPLE PAPER CLASS X saprotrophs science SCIENCE CBSE science class x Scoliodon Scoliodong ppt scutigera sex linked inheritance shelford significance of foood chain soxhlet soxhlet extraction soxhlet. soxlet extraction stanley cohen STUDIES ON ANTHERAEA MYLITTA DRURY HEMOCYTES DURING 3RD sucking sucking bugs Sukumar Dandapat summative assesment summative assesment - II summative assesment 2012 synce ten trap cropping TYPES TYPHOID UDAIPUR UMBILICAL CORD use of radioactive isotopes vectors VIRUS. VIRUSE vitamins VITEX NEGUNDO vocalisation in amphibia vocalization in amphibians Von water web