The midgut of insects plays an important role in digestion, nutrient uptake, detoxification, and responding to oxidative stress. It produces and secretes digestive enzymes like proteases, lipases, and carbohydrases to break down food. Cytochrome P450 monooxygenases in the midgut help detoxify xenobiotics through oxidation-reduction reactions. The foregut and hindgut also aid in digestion. The foregut contains structures like a pharynx, esophagus, crop, and gizzard. The hindgut absorbs water, salts, and other substances from waste before it exits through the anus.

1. Digestive Enzymes in Cockroach-An
Overview
BY Dr. S.SREEREMYA
FACULTY OF BIOLOGY

2.  The insect mid gut plays critical and pivotal roles in digestion and
nutrient uptake as well as detoxification and oxidative stress
responses (Xu et al., 2013). These roles are essential for
environmental adaptation. In most insects, digestion occurs majorly
in the mid gut, where a large portion of the insect’s digestive
enzymes are produced and secreted, including proteases, lipases,
and carbohy drases (Hakim et al., 2010). The insect midgut is
considered to be the centre of detoxification metabolism and stress
response, which include three major interrelated pathways:
oxidation-reduction, conjugation and hydrolysis (Daborn et al.,
2007). Cytochrome P450 monooxy genases (P450s) are the most
important catalysts of oxidation-reduction reactions and able to
detoxify many types of xenobiotics

3.  FOREGUT Foregut is ectodermal in origin. Anterior in vagination of ectoderm forms
the foregut (Stomodeum). Internal cuticular lining is present. Terminal mouth parts
paves into a preoralcavity (Cruden et al., 1987). Preoralcavity between epipharynx and
hypopharynx is called as Cibarium. Preoralcavity between the hypopharynx and
salivary duct is Salivarium. Behind the mouth a well musculated organ termed Pharynx
is present which pushes the food into oesophagous (Downer, 1978). Pharynx acts as a
sucking pump in sap feeders. Oesophagous is a narrow tube which mainly conducts
food into crop. Crop is the dilated distal part of oesophagus majorly acting as food
reservoir (Ferenz, 1985). In bees crop is called as honey stomach where nectar
conversion occurs (Fuwa, 1954). Proventriculus or Gizzard is the posterior part of
foregut and is very much musculated. It is found in solid feeders and absent in fluid
feeders or the sap feeders (Genta et al., 2003). The internal cuticle of gizzard is
variously modified as follows (Hivrale et al., 2005).
 i

4.  . Teeth like in cockroach to grind and strain the food.
 ii. Plate like in honey bee to separate pollen grains from the nectar
 iii. Spine like in flea to break the blood corpuscles
 Food flow from foregut to midgut is regulated through Cardiac
valve or Oesophageal valve. MIDGUT Midgut is endodermal in origin
and also teremd as mesentron(Kawooya et al.,1988). This part
comprses 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(Klowden et al.,2007).

5.  Gastric caecae: (Enteric caecae or Hepatic caecae) Finger like outgrowths
found in anterior or posterior ends of midgut(Lubzens et al.,1981). This
structure aggrandizes the functional area of midgut and shelter symbiotic
bacteria in some insects (Mouille et al., 1966). Pyloric valve: (Proctodeal
valve) Midgut opens into the hindgut through pyloric valve, which regulate
food flow. In certain immature stages of insects midgut is not connected to
hindgut till pupation(Morihara et al.,1977). e.g. Honey bee grub. Filter
chamber: Filter chamber is a complex organ in which two ends of ventriculus
and the begining of hind gut are enclosed in a sac. This is useful to short
circuit typically excess water found in liquid food in homopteran insects.
This process avoids the dilution of digestive enzymes and concentrates food
for efficient digestion. Also aids in osmoregulation by preventing dilution of
haemolymph.

6.  HINDGUT Hindgut is ectodermal in origin and produced by
posterior invagination of ectoderm(Nation et al.2008).
Internal cuticular lining is present, which is permeable to
salts, ions, aminoacids and water. The main functions of
hindgut are absorption of water, salt and other useful
substances typically from the faeces and urine(Rust et
al.,1991). Hindgut is much differentiated into three regions
viz., ileum, colon and rectum. In the larva of scarabids and
termites, illeum is pouch like for housing symbionts and
acts as fermentation chamber. Rectum comprises rectal
pads helping in dehydration of faeces and it opens out
through anus.

7.  Journal of Research in Microbiology and Immunology,
Digestive Enzymes in Cockroach-An Overview ,
Dr.S.Sreeremya , 2019.Vol 1(1):1-10.
REFERNCE