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Explain Digestive system in cockroach.

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Digestive system :

The digestive system includes alimentary canal & salivary glands.

Alimentary canal :

It is a simple tubular structure which is divisible into three parts-

  1. Foregut or Stoinodaeum : It orgmates from the ectoderm & it is lined by the cuticle. It includes mouth, oesophagus, crop & gizzard.
  2. Mid gut or Mesenterone : It originates from the endoderm.
  3. Hind gut or Proctodaeum : It originates from the ectoderm & lined by the cuticle. It includes ileum, colon, rectum & anus.
    The various parts of the alimentary canal are as follows –
  • Mouth : It is situated at the base of the preoral cavity & it leads directly in to the oesophagus.
  • Oesophagus : It is a narrow & simple tube which is found in the neck & the prothorx. It is folded internally.
  • Crop : It is a bag-like structure which is thin-walled & elastic. It is found in the mcsothorax, metathorax & first 3 or 4 abdominal segments. It’s wall is renewable or breakable.

  • Gizzard : It is also called as proventncuius. It is a small, thick walled, hard & conical structure which is found in the abdomen. It is surrounded by a thick layer of circular muscles.
    It’s cavity is lines by the cuticle. Its anterior part is called as armarium which bears 6 chitinous & cuticular teeth. There are six longitudinal grooves alternate to the teeth which are provided with longitudinal muscles & bristles. These grooves function as strainer. The posterior part of the gizzard is funnel shaped. It has pads bearing bristles.
    The posterior part extends into the mid-gut to form a stomodael valve. This valve prevents reverse entry of the food.
  • Mesenterone : It is the soft & delicate part of the alimentary canal which is 1/3 of the alimentary canal. Its anterior part is called as cardia which receives 6 to 8 hepatic caecae. The hepatic caecae are attached at the junction between the fore gut & mid gut.

  • The hepatic caecae are thin & blind tubes which are yellowish in color. The hepatic caecae secretes the digestive enzymes. The anterior half of the mid-gut is called as secretory part and the posterior half part as absorptive part.
  • Ileum : It is a small & narrow tube. It receives malpighian tubules which are attached at the joint between the mid gut & the hind gut. It is lined by the cuticle & internally it has many spines.
  • Colon : It is a long & broad tube which is coiled. It is without spines.
  • Rectum : It is the last part which opens outside through the anus It is small, broad & provided withe 6 longitudinal rectal papillae. The rectal papillae are padlike structures bounded by thin cuticle.

Salivary glands :

There is a pair of salivary glands which are situated in the thorax on both the sides of the crop. Each salivary gland is bipartite i.e. it’s anterior 1/3 part is bilobed. The salivary gland gives out a salivary duct. Both the salivary ducts joins to form a common salivary duct. The salivary glands secrete saliva.

There is pair of reservoirs which are called as receptacles. The reservoirs are the thin-walled & transparent bag-like structure which store the saliva. Each reservoir gives out a reservoir duct. Both the reservoir ducts join to form a common reservoir duct. The common salivary duct & the common reservoir duct join to from an efferent salivary duct which open into the pre-oral cavity.

Digestion :

It is an omnivorus animal which feeds with the help of biting & chewing mouth parts. In the pre-oral cavity, the food receives saliva with contains mucous and enzymes (amylase, chitinase & cellulase). The mucous makes the food slimy & soil.

The amylase, the chitinase & the cellulase perform part digestion of various carbohydrates. The partly digested food in the crop receives the hydrolases secreted by the hepatic caecae viz.—invertase. maltase lactase, trypsin, proteiase, lipase etc. They perform semi-digestion of the food. The semi-digested food enters into the gizzard where it is subjected to the grinding. The gizzard also filters the semi-digested fine food particles which enter into the mid-gut.

The stomodael valve secretes a peritrophic membrane around the semi-digested fine food particles. The peritrophic membrane is made up of protein & chitin. It is permeable to the digested food & the hydrolases. The peritrophic membrane protects the soft mid-gut from the hard food particles.

The secretory part of the mid-gut secretes the various hydrolases which complete the digestion of the food. Most of the digested food is absorbed by the secretory part of the mid gut. In the ileum, the spines tear the peritrophic membrane and absorbs the remaining digested food. The colon absorbs the water but most of the water is absorbed by the rectal papellae in the rectum. The fecal matter is digested in the form of small dry pellets.

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