STRUCTURE AND FUNCTIONS OF DIGESTIVE SYSTEM
The alimentary canal of insects is a long, muscular, and tubular structure extending from mouth to
anus. It is differentiated into three regions viz., Foregut, Midgut and Hindgut.
Foregut is ectodermal in origin. Anterior invagination of ectoderm forms foregut (
Internal cuticular lining is present. Terminal mouth parts leads into a
between epipharynx and hypopharynx is called as
. Preoralcavity between hypopharynx
and salivary duct is
. Behind the mouth a well musculated organ called
present which pushes the food into oesophagous. Pharynx acts as a
is a narrow tube which conducts food into crop.
is the dilated distal
part of oesophagus acting as food reservoir. In bees crop is called as honey stomach where
nectar conversion occurs.
Proventriculus or Gizzard
is the posterior part of foregut and is
musculated. It is found in solid feeders and absent in fluid feeders or sap feeders. The internal
cuticle of gizzard is variously modified as follows.
Teeth like in cockroach to grind and strain food.
Plate like in honey bee to separate pollen grains from nectar
Spine like in flea to break the blood corpuscles
Food flow from foregut to midgut is regulated through
Cardiac valve or Oesophageal valve
Midgut is endodermal in origin and also called as
. 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.
Insect Morphology and Systematics
Important structures present in midgut are as follows:
It is the internal lining of midgut, secreted by anterior or entire layer of midgut epithelial cells.
Present in solid feeders and absent in sap feeders. This layer is semipermeable in nature to
digestive juices and digestion products. Its functions are
Lubricate and facilitate food movement
Envelops the food and protects the midgut epithelial cells against harder food
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