Question

Explain the digestive system in cockroaches.

Answer 1

Hint: The combination of various organs that help in the mechanical and chemical breakdown of food. In cockroaches, it consists of the alimentary canal and digestive glands.

Complete answer:
As we know the alimentary canal of cockroach is divided into three main parts as follows:
Foregut: It is starting part of the alimentary canal which begins with the mouth.
-The buccal cavity of cockroaches has a mouth at one end and it further leads to the pharynx.
-Pharynx leads to a narrow tubular canal known as the oesophagus.
-Oesophagus opens into a structure known as a crop which is a sac-like structure used to store the food.
-Crop opens into a gizzard which is also known as proventriculus. The outer layer of the gizzard is made up of thick muscular fibres. While the inner layer of thick cuticle forms six highly chitinous plates called teeth.
-Gizzard helps in grinding of food particles.
Midgut: It is also called mesenteron.
-A ring of 6-8 blind tubules is present at the junction of foregut and midgut.
-These tubules are known as gastric caeca or hepatic caeca.
-Gastric or hepatic caeca secret digestive juices which contain enzymes like invertase, amylase, lipase and protease. These enzymes digest the remaining carbohydrates, fats and proteins in food.
-The midgut is not lined by cuticle rather it is lined by a peritrophic membrane.
-Absorption of digested food majorly takes place in the midgut.
Hindgut: It is the last part of the digestive tract.
-At the junction of midgut and hindgut, another set of tubules is present. These are thin yellow and around 150 in number. These tubules are called Malpighian tubules.
-They help in removal of excretory products, that is they absorb nitrogenous products from haemolymph and convert them into uric acid for excretion.
- Malpighian tubules also secrete fluids in the posterior intestine which are reabsorbed again here and certain substances and transported into the haemolymph.
-The hindgut is divided into 3 parts :
Proximal – ileum: it is the small narrow tubular part which absorbs remaining nutrients.
Middle – colon: reabsorption of contents in juices secreted by Malpighian tubules.
Distal – rectum: it stores the undigested food.
Rectum opens to the exterior via the anus.
Digestive glands:
Unlike in humans salivary glands play a major part in the digestive system of cockroaches. These are situated on each side of the oesophagus and crop. The glands secrete digestive enzymes as well as lubricate the food with the help of mucous. The starch is digested by an enzyme known as hydrolyses. It also includes amylase, chitinase and cellulose.

Note:
-Hepatic caeca secret digestive juices containing enzymes which help in the digestion.
-Malpighian tubules contain different ion channels that help in excretion.
-Haemolymph is a circulating fluid in the bodies of insects that is the equivalent of blood.
-The peritrophic membrane is a mesh-like structure that protects the midgut from abrasion produced by hard contents in food.