Lecture 8-Insect digestive system, modification, physiology of digestion-1.pptx

Insect digestive system details ppt easy. To understand

1. AEN 201 FUNDAMENTALS OF ENTOMOLOGY (2+1) Lec: No. Lecture title 8. Insect digestive system, modification, digestive enzymes, physiology of digestion Dr. V.G. Mathirajan , Ph.D. Professor ( Agrl.Entomology ) Department of Entomology Dr. MSS Agricultural College and Research Institute Eachangkottai , Thanjavur

2. Digestive system Divided into three regions Foregut or stomodaeum Midgut or mesenteron or ventriculus Hindgut or proctodaeum

3. Digestive system Divided into three regions Foregut or stomodaeum Midgut or mesenteron or ventriculus Hindgut or proctodaeum

4. Anatomy of Digestive system

5. Gut FOREGUT MIDGUT HINDGUT

6. Foregut ( Stoemodium ) Ectodermal origin Intima : Cuticular lining Mouth (pre-oral cavity) leads into pharynx Pharynx leads immediately into a narrow tube oesophagus Salivary apparatus consists of two pairs of salivary glands and a pair of salivary reservoirs (digestive gland) Distal end of oesophagus enlarges into a large sac-like structure – crop- useful to store food prior to digestion Posterior part of crop narrows down to a small sac- gizzard or proventriculus Inside gizzard, six chitinous cuticular teeth -help in pulverizing food

7. Head (Cross Section)

8. Foregut Preoral cavity and Pharynx Salivary glands Cibarium: Cavity between epipharynx & hypopharynx Salivarium: Cavity between hypopharynx and salivary duct Pharynx: Well musculated organ that pushes food into oesophagous in solid feeders Pharynx acts as sucking pump in sap feeders Foregut - lateral view Head- cross section

9. Pharyngeal pump Lepidoptera Homoptera

10. Foregut Oesophagous, Crop & Proventriculus Oesophagous: A narrow tube that conducts food into crop Crop: Sac-like at distal, acts as reservoir of food modified as honey stomach in bees and sucking stomach in sucking insects Proventruclus or Gizzard: Musculated and hard Found in solid feeders Teeth-like in cockroach & grasshopper to grind and strain food Plate-like in honeybee to separate pollen grains from nectar Spine-like in flea to break blood corpuscles Absent in blister beetles and caterpillars

11. Crop Lepidoptera and Diptera have permanent sac The capacity of crop in honey pot ants -enarmous

12. Midgut (mesentron) Endodermal origin Intima- absent Site of digestion & assimilation Parts: Gastric caecum –digestive gland- finger-like projections at the junction of foregut and midgut, -serve as enzyme source for digestion Ventriculus Peritrophic membrane

13. Gastric caecae Also called as entric caecae or hepatic caecae Finger-like outgrowth Increases functional area of midgut Shelters symbiotic microbes

14. Midgut Ventriculus (not lined with cuticle) Internal lining secreted by epithelial cells: Peritrophic membrane Present in solid feeder and absent in liquid feeder Semi permeable Lubricate and facilitate food movement Protect midgut epithelium Acts as barrier to microbes

15. Midgut Cross Section

16. Midgut Malpighian Tubules: Mesodermal in origin At the joint between midgut and hindgut Excretory in function- eliminates nitrogenous waste from insect blood

17. Midgut modification - Filter chamber Anterior and posterior midgut regions-in close contact so that water can be diverted directly to hindgut without diluting contents of midgut Potassium is actively secreted into Malpighian tubules and posterior midgut drawing water from anterior Much of this fluid containing dilute concentrations of amino acids and sugars: HONEYDEW

18. Midgut modification - Filter chamber Anterior and posterior midgut regions-in close contact so that water can be diverted directly to hindgut without diluting contents of midgut Potassium is actively secreted into Malpighian tubules and posterior midgut drawing water from anterior Much of this fluid containing dilute concentrations of amino acids and sugars: HONEYDEW

19. Hindgut (Proctodeum) Ectodermal in origin Pyloric valve between hindgut and midgut Malpighian tubules attach below valve Internal cuticular lining- present-permeable to salts, ions, amino acids and water Narrow Ileum, wider colon and sac-like rectum

20. Physiology of Digestion Process of digestion Conversion of food into a form capable of assimilation by blood Providing nourishment by action of digestive chemicals Extra-intestinal digestion

21. Extra-intestinal digestion Digestives juices- secreted from mouth onto food before their intake into alimentary canal Portion of food digested e.g. predaceous beetles and bugs

22. Intra-intestinal digestion Steps: Salivary gland secret saliva-mixes with food Partial digestion and no absorption in crop Solid food -crushed and broken in gizzard Cells of mesentron or midgut secret digestive enzymes and do absorption of nutrients Lipid absorption by midgut caecae Sugars and proteins absorption by microvilli of midgut epithelium Salts and water absorption by proctodaeum or hindgut and also partial digestion by microorganism

23. Roles Salivary glands Digestive enzymes

24. Salivary Gland Glands: Labial glands in cockraoch Mandibular glands in caterpillars Two –lie ventral to foregut-varied size and shape Often described as acinar (cluster of grapes) Saliva-secretary product-clear product Functions: Food solvent, lubricate mouthparts, transport flavour to gustatory receptors Saliva contains: Anticoagulins in mosquitos Amylase to digest starch in cockroach Invertase to digest sucrose in honeybee Lipase and protease to digest lipids and protein in leafhopper Toxins, which produces tissue necrosis and phytotoxemia, by planthopper Pectinase in stylet penetration in plant bugs Pectinase for partial digestion by predaceous insects Indole acetic acid produce galls by gall insects Saliva useful in: Pathogens transmission by insect vectors Gluing of puparial cages to substrate in flies

25. Digestive Juices or Enzymes Insect group Enzymes Phytophagous larvae Amylase, Maltase, Invertase Omnivorous Protease, Lipase Nectar feeders Invertase Wood boring cerambycid grubs and termites Cellulase Meat eating maggots Collagenase Wool feeders (bird lice) Keratinase

26. Microbes in digestion Symbiotic microorganisms -called MYCETOCYTE : protozoa, bacteria, fungi They aggregate to form an organ: MYCETOME Microbes provide: Vitamins and amino acids in bed bugs & cockroach Cellulase for cellulose digestion in wood termites Bacterial enzymes to digest wax in wax moth Microbes transmission: Mouth-to-mouth food exchange (trophallaxis)

27. Absorption of nutrients In many insects absorption of nutrients occurs through microvilli of midgut epithelial cells by diffusion Absorption of water and ions occur through rectum in hind gut In cockroach, lipid absorption occurs through crop In termites and scarabaeids, absorption occurs through ileum In solid feeders, re-absorption of water from faeces occurs in rectum and faeces -expelled as pellets In sap feeders (liquid feeders)- faeces liquid like- Liquid faeces of Homopteran bugs (aphids, mealy bugs, scales and psyllids) with soluble sugars and amino acids-Honey dew- which attracts ants for feeding