Process of digestion
Digestion mainly takes place in 5 steps.
- Ingestion:
- Food is partially digested in the oral cavity with the help of salivary enzymes. In insects like fluid feeders, carnivorous hemiptera, blowfly larvae etc, digestion occurs outside the intestine by a process called extra intestinal (or) extra oral digestion.
- Transportation:
- The food material entered in to the oesophagus is transported in to the crop by muscular activity i.e. by peristatic movements.
- Food moves continuously from oesophagus in to the crop where it is stored.
- From the crop, food enter in to the gizzard where it is still broken in to very minute particles with the help of denticles or the cuticular teeth.
- Digestion:
- From the gizzard through the stomodeal valve, food passes in to the midgut where actually digestion starts.
- The epithelial cells produce enzymes i.e. proteases which break proteins in to aminoacids, carbohydrases breaking carbohydrates in to mono & disaccharides, lipases breaking lipids in to fatty acids and glycerol.
- Absorption:
- Midgut epithelial cells absorb the nutrients from the digested food and pass on the faecal matter and undigested food material into the hindgut.
- The Malpighian tubules maintain ionic balance by absorbing Na and K salts from the blood.
- The cells of the hindgut are also involved in the reabsorption of water, salts and other metabolites from the faecal matter.
- Egestion:
- The waste food material is discharged through the anus due to the action of the anal muscles.