DIGESTIVE SYSTEM: structure and function.
Mouthparts: - these structures are located anterior to the mouth.
- review the sketches.
- you will see an array of different mouthparts in the laboratory; ask yourself why different insect species have such different mouthparts - the answer is probably obvious. However, the great variation in the structure of digestive system associated with each different set of mouth parts may be less obvious. Modifications in the digestive system reflect the processing requirements, that is, insect which feed on plant foliage require a different set of modifications than those feeding on plant sap.
All insects have a digestive system that consists of
FOREGUT (Stomodeum)
- mouth - mouthparts.
- pharynx - pumps.
- esophagus.
- crop - storage.
- stomodeal/cardiac valve.MIDGUT (Mesenteron)
- columnar epithelium.
- gastric caeca (if present).
- peritrophic membraneHINDGUT (Proctodeum)
- pyloric valve.
- openings of Malpighian tubules.
- anterior intestine.
- rectum (colon) - water absorption from urine and faeces.
- anus.
Developmentally foregut and hindgut derived from ectoderm as is the integument. As a consequence these parts of the digestive system are lined with cuticle although it has some different properties than the cuticle of the integument.
In most insects the majority of the "food processing" (digestion and absorption of nutrients) occurs in the midgut. Can you guess why this is the case?
EXCRETORY SYSTEM
Malpighian tubules
- nitrogenous wastes.
- blind-ending tubules; free-floating in haemocoel.
- variable number 2-250 or more.
- missing in some insects.
- numerous types; all act as filtration devices, but reabsorb material.question: How else can insects remove metabolic wastes?