Digestive System Of Insect :
- It is a Long tube-like structure runs from the mouth to the anus.
- Centrally located within the body cavity, or hemocoel.
- Divided into three regions : Foregut, midgut and hindgut.
- Ectodermal in origin.
- Internal cuticular lining is present
- mouth cavity have – labrum – upper lip,labium – lower lip with mandibles and maxillae laterally and hypopharynx at the centre.
- At the base of the hypopharynx, salivary glands open into the mouth cavity.
Foregut consists of :
- Pharynx: Region between the mouth and esophagus.
- Oesophagus: Narrow part by help of this food get transported from pharynx into the crop.
- Crop : sac like structure which is a dilated form and storage of food material.
- Gizzard (Proventriculus) : small constricted part which consists of the cuticular intima layer modified in to a teeth like denticles that help for grinding the food material.
The internal cuticle of gizzard is variously modified as follows.
i.Teeth like in cockroach to grind and strain food.
ii. Plate like in honey bee to separate pollen grains from nectar
iii.Spine like in flea to break the blood corpuscles.
Function: Begin the breakdown of food Particles & transport to the next region.
After gizzard the foregut forms into a stomodeal valve which is surrounded by gastric (or) hepatic caecae, which may vary from 5-6 in number .
- Endodermal origin
- Foregut opens in to midgut through stomodael / cardiac valve.
- Midgut is a short, straight tube in case of primitive insects or a sac or may be Pyriform or fusiform in shape in caterpillars.
- This part contains no cuticular lining.
Midgut is made up of three types of epithelial cells.
(i) Secretory cells (Columnar cells)
(ii) Goblet cells (aged secretory cells),
(iii) Regenerative cells which replaces secretory cells.
Structurally midgut consists of :
(i)Gastric caecae: (Enteric caecae or Hepatic caecae) :
- Finger like outgrowths found in anterior or posterior ends of midgut.
- structure increases the functional area of midgut and shelter symbiotic bacteria in some insect.
ii) Peritrophic membrane:
- Secreted by entire layer of midgut epithelial cells. Present in solid feeders and absent in sap feeders.
- Layer Semipermeable in nature to digestive enzymes and digestion products. It lubricate food and facilitate food movement. Envelops the food and protects the midgut epithelial cells against harder food particles.
iii) Pyloric valve: (Proctodeal valve )
- Midgut opens into hindgut through pyloric valve, which regulate food flow. In honey bee grub midgut is not connected to hindgut pupation.
(iv) Filter chamber:
- Found in midgut in hemipteran insects (fluid feeders).
- Anterior part of midgut forms a thin-walled bladder
- Which is closely bound to either posterior part of hindgut and Malpighian tubules.
- Enables the excess fluids including sugar in the food to pass directly from the anterior part of the midgut to the hindgut without passing through the middle portion of midgut.
- Preventing excessive dilution of haemolymph, enzymes for facilitate better enzyme activity.
- In aphids, the honey dew (rich in sugars) excreted.
Function : Major area of digestion & Absorption and Undigested food particles then pass into the third region
- Ectodermal in origin .
- Internal cuticular lining is present, which is permeable to salts, ions, aminoacids and water.
- Seprated into ileum, colon and rectum.
- In the larva of scarabids and termites, illeum is pouch like for housing symbionts and acts as fermentation chamber.
- Colon may (or) may not be present and if present, it leads to rectum
- Rectum contains rectal pads which are involved in reabsorption of water, salts from the faecal matter and it opens out through anus.
Functions : Reabsorption of water, salt and other useful substances from the faeces and urine.
Available YouTube video Lecture on this topic Please click on this link : https://youtu.be/iaRfiKqTkbU