Insect Integumentary System PDF

THE INTEGUMENTARY SYSTEM CPROT4205MDSLABE:DCPCAgCLSU1STSEM20242025 INTEGUMENT OR BODY WALL  Outer covering of the living tissues of insects; sclerotized for protection from abrasion as well as water proofing  Composed of a single layer of cells called EPIDERMIS bounded on th...

THE INTEGUMENTARY SYSTEM CPROT4205MDSLABE:DCPCAgCLSU1STSEM20242025 INTEGUMENT OR BODY WALL  Outer covering of the living tissues of insects; sclerotized for protection from abrasion as well as water proofing  Composed of a single layer of cells called EPIDERMIS bounded on the inside by a BASEMENT MEMBRANE and on the outside by the CUTICLE epicuticle exocuticle endocuticle ------------------ CUTICLE ------------------ EPIDERMIS ------------------ BASEMENT MEMBRANE INTEGUMENTARY SYSTEM The CUTICLE  Produced by the epidermis  Covers the entire body surface = restricts water loss  Lines the insect’s air tubes, salivary glands and parts of the alimentary tract (fore- & hindgut) PRIMARY LAYERS OF THE CUTICLE  EPICUTICLE  thin outer layer, 3 mµ to 0.1 mµ thick; permeable to chemicals and nutrients for growth but impermeable to enzymes that breakdown parts of the old cuticle before it is shed  When first laid on the surface, it is deeply folded and later, straighten after ecdysis (insect swallow air)  Layers:  Homogenous layer - innermost layer  Layers of cuticulin (lipoprotein) = critical in the growth process  Wax ( long hydrocarbon chain)  Cement ( tanned protein with lipids serving as a varnish-like covering of the wax or maybe in the form of an open meshwork providing a reservoir of lipids to replace lost surface lipids) LAYERS OF THE CUTICLE  EXOCUTICLE  Thicker layer  Forms the exuvium at molting  Gives the cuticle its characteristic strength and resilience  Formed of chitin (C18H13NO5) complexed with protein Chitin is a polymerized compound, a nitrogenous polysaccharide linked to a protein. This is common in nature as a base for materials like wood, hair, horn  ENDOCUTICLE  Still a thicker layer Basement membrane - composed of mucopolysaccharide secreted by hemocytes. Along it run the nerves, tracheaoles the integument of an insect seta pore canal oil gland epicuticle exocuticle endocuticle epidermis basement membrane INTEGUMENTARY SYSTEM CUTICULAR EXTENSIONS 1. SPINES - multicellular with undifferentiated epidermal cells 2. SETAE OR HAIRS OR MACROTRICHIA OR TRICHOID SENSILLA - multicellular with specialized cells 3. ACANTHAE that are unicellular in origin 4. MICROTRICHIA - subcellular, from several to many extensions per cell INTEGUMENTARY SYSTEM SETAE sense much of the insect’s tactile environment  Bristles/chaetae = large setae  Scales on Lepidoptera are flattened setae 3 separate cells form each seta 1. Trichogen cell = for hair formation 2. Tormogen cell = for socket formation 3. Sensory cell INTEGUMENTARY SYSTEM PORE CANALS are passageways of secretions by the epidermis from inside to outside. Epidermal secretions make possible the repair of cuticle, secretion of wax and release tanning agents. [THE INSECT STRUCTURES ARE FORMED FROM THE BODY WALL], THE BODY WALL SUPPLIES A SUPPORT SYTEM KNOWN AS EXOSKELETON INTEGUMENTARY SYSTEM Functions of the exoskeleton 1. Provides a rigid foundation of the body 2. Serves as a point of attachment of muscles 3. Serves as a covering to protect internal organs 4. Helps prevent desiccation MOLTING (casting of the old cuticle) IS TRIGGERED BY HORMONES RELEASED WHEN AN INSECT’S GROWTH REACHES PHYSICAL LIMITS OF ITS EXOSKELETON  What happens during molting? PHYSIOLOGY OF MOLTING/DISTINCT SEQUENCE OF EVENTS 2 processes : Apolysis –separation of cuticle from the epidermis Ecdysis - actual process of shedding off of the old skin 1.Changes in epidermal cells EPIDERMAL CELLS RESPOND TO HORMONAL CHANGES BY INCREASING RATE OF PROTEIN SYNTHESIS THAT QUICKLY LEADING TO APOLYSIS (physical separation of epidermis from old endocuticle) MOLTING 2.Secretion of molting fluid EPIDERMAL CELLS(EC) FILL THE RESULTING GAP WITH AN INACTIVE MOLTING FLUID 3.Secretion of cuticulin layer SECRETE A SPECIAL LIPOPROTEIN (CUTICULIN LAYER) THAT INSULATES AND PROTECTS THE EC FROM MOLTING FLUID’S (MF) DIGESTIVE ACTION. THE CUTICULIN LAYER BECOMES PART OF THE NEW EXOSKELETON’S EPICUTICLE MOLTING 4. Activation of molting fluid AFTER FORMATION OF CUTICULIN LAYER, MF BECOMES ACTIVATED AND CHEMICALLY “DIGESTS” THE ENDOCUTICLE OF THE OLD EXOSKELETON. MOLTING 5.Absorption of the digested remains of old cuticle and start of secretion of new procuticle BREAKDOWN PRODUCTS (AA AND CHITIN MICROFIBRILS) PASS THRU THE CUTICULIN LAYER WHERE THEY ARE RECYCLED BY THE EPIDERMAL CELLS AND SECRETED UNDER THE CUTICULIN LAYER AS A NEW PROCUTICLE =EXO AND ENDOCUTICLE (SOFT AND WRINKLED) MOLTING 6. Formation of wax and cement layer Wax line the pore canals for the water retention and water loss mechanism PORE CANALS WITHIN THE PROCUTICLE ALLOW MOVEMENT OF LIPIDS AND PROTEIN TOWARD THE NEW EPICUTICLE WHERE WAX AND CEMENT LAYER FORM. MOLTING 7. Ecdysis and expansion of the new cuticle WHEN THE NEW EXOSKELETON IS READY, MUSCULAR CONTRACTIONS AND INTAKE OF AIR CAUSE THE INSECT’S BODY TO SWELL AND THE OLD E SPLITS OPEN ALONG LINES OF WEAKNESS (ECDYSIAL SUTURES) AND THE INSECT SHEDS OLD SKIN QUICKLY (ECDYSIS) AND CONTINUES TO FULLY EXPAND THE MOLTING 8. Sclerotization /Tanning –processes by which the new cuticle are made more resistant to degradation, stiffer, less soluble. Processes by which cuticular proteins are cross-linked by the action of quinones, and therefore change the cuticle into dark, hard, insoluble material. QUINONES= tanning subst for the cuticle coming from tyrosine or para-OH phenylalanine in the hemolymph OVER THE NEXT FEW HRS, SCLERITES HARDEN AND DARKEN AS QUINONE CROSS-LINKAGES FORM WITHIN THE EXOCUTICLE. THIS PROCES CALLED SCLEROTIZATION OR TANNING GIVES THE E ITS FINAL TEXTURE AND APPEARANCE. THIS PROCESS IS COMPLETED IN A DAY OR TWO. Sclerotization is controlled by bursicon Β – sclerotization = for hardening without development of new color Quinone sclerotization = hardening with colors MOLTING 9. Start of wax secretion WAX STARTS TO BE SECRETED MOLTING PHARATE CONDITION = INSECT ACTIVELY CONSTRUCTING NEW EXOSKELETON TAKES DAYS OR WEEKS WITH VERY LITTLE EVIDENCE OF CHANGE TENERAL CONDITION = NEWLY MOLTED INSECT, SOFT UNPIGMENTED (WHITE OR IVORY), UNTIL THE TANNING PROCESS IS COMPLETED (A DAY OR TWO) PHYSIOLOGY OF MOLTING/DISTINCT SEQUENCE OF EVENTS 1. Changes in epidermal cells 2. Secretion of molting fluid 3. Secretion of outer layer of cuticulin 4. Secretion of homogenous layer of cuticulin 5. Activation of molting fliid 6. Absorption of the digested remains of old cuticle 7. Start of secretion of new procuticle (exo/endocuticle) 8. Ecdysis and expansion of the new cuticle 9. Sclerotization 10. Start of wax secretion CONTROL OF MOLTING AND ASSOCIATED PROCESSES 1.Ecdysone – play a vital role in controlling the events of molting; triggers the epidermal cells to change in number and size (MOLTING HORMONE) 2.Bursicon – controls sclerotization = necessary for cuticle tanning and endocuticle formation in flies and other insects 3.A hormone released from the corpora allata-corpora cardiaca complex with ecdysone to control wax secretion … continuation: Control 4. A hormone with ecdysone controlling endocuticle production 5. Ecdepteroids induce sclerotization in ligated abdomen of blowfly larvae resulting to the induction of de novo synthesis of enzyme dopa-decarboxylase in the epidermal cells DIFFERENT TYPES OF CUTICLE The cuticle varies in nature in the different parts of the insect’s body RIGID CUTICLE  Produced as a result of tanning in the outer part of the procuticle to form the exocuticle, but the extent of tanning, and hence the hardness of the cuticle varies The chitinous cuticle as it is 1st secreted is known as procuticle, but subsequently the outer part become tanned/sclerotized to form exocuticle while the inner undifferentiated part is called endocuticle. e.g. nymphs of Schistocerca (grasshopper) = the exocuticle of the sclerites is sharply differentiated from the endocuticle which never tans. DIFFERENT TYPES OF CUTICLE MEMBRANOUS CUTICLE The sclerites are joined by flexible arthrodial membranes and in these the procuticle remains untanned but it also differs quantitatively from the cuticle of the sclerites in containing proteins with a different amino acid composition [arthrodial=permitting motion in any direction in articulations] e.g. Membrane between 2 adjacent sclerites resulting to unrestricted movement exocuticle also absent along ecdysial lines of larval holometabolous insects. The cuticle along these lines consists only of undifferentiated pro and epicuticle so that they constitute lines of weakness along which the cuticle splits at ecdysis DIFFERENT TYPES OF CUTICLE ELASTIC AND EXTENSIBLE CUTICLE Some parts of the cuticle contains a colorless, rubber-like protein called resilin e.g. those found in elastic hinges such as wing-hinge ligament lying between the pleural process and the 2nd maxillary sclerite also in clypeo-labral spring keeping the labrum pressed against the mandibles -END-