11. Study of Animal Type - Cockroach - part 02 - Digestive system of cockroach

 

11. Study of Animal Type - Cockroach - part 02 - Digestive system of cockroach


Body cavity : 

  • A body cavity or true coelom is present around the viscera.
  • Because of the open type of circulation, the body cavity is filled up with blood. Hence, it is called haemocoel. 
  • In the haemocoel, fat bodies are seen.
  • It is in the form of loose, whitish massof tissue. 
  • The fat body is made up of large, polygonal cells which contain 
  1. fat globules
  2. proteins and
  3. sometimes glycogen.


Digestive system of cockroach :


  • Digestive system of cockroach consists of -
  1. mouth parts
  2. alimentary canal and
  3. a pair of salivary glands.


  • Alimentary canal is a long (6-7 cm) tube of different diameters and two openings.
  • Alimentary canal is divisible into three regions as -
  1. Foregut (stomodaeum)
  2. Mid-gut (mesenteron) and 
  3. Hindgut (proctodaeum).

Mouth : 

  • Mouth / pre-oral chamber is a narrow space bounded by mouth parts. 
  • Hypopharynx is present at the centre of mouth. 
  • Salivary duct opens at the base of hypopharynx. Mouth opens into foregut.

Fore-gut (Stomodaeum) :

  • Foregut consists of -
  1. pharynx,
  2. oesophagus
  3. crop and
  4.  gizzard. 

pharynx
  • Pharynx is very short, narrow but muscular tube. 
  • It contains taste sensillae. 
  • It leads to oesophagus.
Oesophagus 

  • Oesophagus  is slightly long and narrow tube. 
  • It opens in crop. 
Crop

  • Crop is large, pear shaped sac like organ. 
  • It temporarily stores the food and then sends it to gizzard.

Gizzard


  • Gizzard (Proventriculus) is small, spherical organ. 
  • Internally, it is provided with a circlet of six chitinous teeth and backwardly directed bristles. 
  • Teeth are responsible for crushing the food. 
  • Bristles help in filtering the food. 
  • Foregut ends with gizzard.



Mid-gut (Mesenteron) : 

  • Midgut consists of -
  1.  stomach and 
  2. hepatic caecae. 
Stomach

  • Stomach (ventriculus) is straight, short and narrow. 
  • It is lined by glandular epithelium. Which secretes digestive enzymes. 
  • Hence, stomach is mainly responsible for digestion and absorption.

Hepatic caecae 

  • Hepatic caecae are thin, transparent, short, blind (closed) and hollow tubules. 
  • Hepatic caecae secrete digestive enzymes and thus help in digestion of food.



Hind-gut (Proctodaeum) :

  • Hindgut consists of -
  1. ileum
  2. colon and 
  3. rectum. 
Ileum

  • Ileum is short and narrow part of hind-gut. 
  • Malpighian tubules open in the anterior lumen of ileum, near the junction of mid-gut with hind-gut. 
  • Posterior region of ileum contains sphincter. 
  • Ileum sends nitrogenous wastes and undigested food towards colon.

Colon

  • Colon is longer and wider part of hind-gut.
  • It sends the waste material towards rectum.
  • It reabsorbs water from wastes as per need.

Rectum

  • Rectum is oval or spindle-shaped, terminal part of hind-gut. 
  • It contains six rectal pads along internal surface for absorption of water.
  • Rectum opens outside by anus. 
  • Anus is present on ventral side of 10th segment. 
  • Anus is last/ posterior opening of digestive system. It gives out undigested food.

Salivary Glands :


  •  Cockroach has a pair of salivary glands which secrete saliva. 
  • Each gland consists of - 
  1. two glandular lobes and 
  2. one receptacle or reservoir. 
Glandular lobes 

  • Glandular lobes consists of many irregular-shaped and white lobules.
  • These lobules secrete saliva. Each gland has a salivary duct. 
  • Both ducts unite together to form a common salivary duct. 
Receptacle
  • Receptacle of each gland is thin-walled, elongated, sac-like structure. 
  • Each receptacle has a duct. 
  • These ducts unite to form common reservoir duct.
  • Both common ducts i.e. common salivary duct and common reservoir duct unite together toform common efferent salivary duct. 
  • Efferent salivary duct opens at the base of tongue or hypopharynx.




Food and digestion : 

  • Cockroach is omnivorous.
  • It feeds upon plant and animal material. 
  • It has chewing and biting type of mouth parts, that chew the food and push it into alimentary canal. 
  • As food passes through the alimentary canal, it is digested and finally undigested food is eliminated through anus.

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