DIGESTIVE SYSTEM
Alimentary canal
The alimentary canal or gut of insects can be divided into 3 sections
- Foregut (stomodeam)
- Midgut (mesenteron)
- Hindgut (proctodeam)
FOREGUT
The foregut consists of the
- mouth (oral cavity) The salivary glands provide fluids and enzymes to the mouth for lubrication and to begin food breakdown.
- throat (pharynx)
- oesophagus
- crop, for storage of food
- proventriculus, (or gizzard) where present, sometimes armed with teeth for grinding
MIDGUT
The midgut consists of the
- ventriculus, where most digestion is carried out
- gastric caeca (sing. caecum) which , if present provide greater area for digestion
HINDGUT
The hindgut consists of the
- anterior hindgut
- rectum
Both these areas reabsorb water and salts.
Valves are present to prevent back-flow of material within the gut
- cardiac (stomodeal) valve between fore and midgut
- pyloric valve between mid and hindgut
In insects the products of excretion are emptied from the Malpighian tubules into the alimentary canal at the beginning of the hindgut.
Specialisation: The FILTER CHAMBER
The most obvious specialisation in gut structure occurs in many of the Hemiptera or true bugs. These insects ingest large quantities of often dilute fluid and have an unusual arrangement of the gut called a filter chamber whereby the gut is looped upon itself. This allows contact of the anterior and hind guts so that water can be absorbed across the hind gut and gut contents concentrated by passing through several loops before major absorbsion of nutrients.
FAT BODY
The fat body is diffuse tissue lying usually in the abdomen.
It is important in the storage of fat, protein and glycogen and as such, grows in size in larvae, and is reduced during pupation and metamorphosis. It is quite small in the adult when reserves are used for egg production.
The fat body is also involved in intermediate metabolism and in this way, resembles the vertebrate liver. The fat body is rich in enzymes. Fats may be synthesised, released by the fat body into the haemocoel or be broken down. It is also important in detoxification and symbiotics are present in some insect fat bodies and aid in the synthesis of various vitamins and amino acids for protein synthesis.
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