Question

Answer the following question.

Describe the digestive system of cockroach.

Answer the following question.

With help of neat labelled diagram, describe the digestive system of cockroach.

Answer 1

• Digestive system of cockroach consists of mouthparts, alimentary canal and salivary glands.
• Mouthparts: Pre-oral cavity present in front of the mouth receives food. It is bounded by chewing and biting type of mouth parts. These are movable, segmented appendages that help in the ingestion of food. The mouthparts of cockroach comprises of:
  
  Mouthparts of cockroach

1. Labrum: It forms the upper lip. It is a single flap-like movable part which covers the mouth from upper side. It forms an anterior wall of preoral cavity.
   Function: It is useful in holding the food during feeding.
2. Mandibles: These are two dark, hard, chitinous structures with serrated median margins. They are true jaws present on either side, behind the labrum.
   Function: They perform co-ordinated side-wise movements with the help of adductor and abductor muscles to cut and crush the food.
3. Maxillae: These are the accesssory jaws. They are also called as first pair of maxillae. These are situated on either side of the mouth behind the mandibles. Each maxilla consists of sclerites like cardo, stipes, galea, lacinia and maxillary palps.
   Functions: Maxillae hold food, help mandibles for mastication. They are also used for cleaning the antennae and front legs. Maxillary palps act as tactile organs.
4. Labium: It forms the lower lip. Labium is also known as the second maxilla which covers the pre-oral cavity from the ventral side. It is firmly attached to the posterior part of the head. It has three jointed labial palps which are sensory in function.
   Function: It is useful in pushing the chewed food in the pre-oral cavity. It prevents the loss of food falling from the mandibles, while chewing.
5. Hypopharynx: Hypopharynx is also known as a lingua. It is a somewhat cylindrical single structure, located in front of the labium and between the first maxillae. The salivary duct opens at the base of the hypopharynx. Hypopharynx bears comb-like plates called super-lingua on either side. Hypopharynx is present at the center of the mouth.
   Function: It is useful in the process of feeding and mixing saliva with food.

• Alimentary canal: It is long a (6 - 7cm) tube of different diameters with two openings.
• The alimentary canal is divisible into three parts: foregut, midgut and hindgut.
  

1. Foregut or stomodaeum: It consists of pharynx, oesophagus, crop and gizzard.
   a. Pharynx: It is a very short, narrow but muscular tube that opens into oesophagus.
   Function: Conduction of food into the oesophagus.
   b. Oesophagus: It is a slightly long and narrow tube which opens into crop.
   c. Crop: Crop is a large, pear shaped and saclike organ.
   Function: It temporarily stores the food and then sends it to gizzard.
   d. Gizzard: Gizzard or proventriculus is a small spherical organ. It is provided internally with a circlet of six chitinous teeth and backwardly directed bristles.The foregut ends with gizzard.
   Function: The chitinous teeth present in gizzard are responsible for crushing the food and the bristles help to filter the food.
2. Midgut or mesenteron: It consists of stomach and hepatic caeca.
   a. Ventriculus or stomach: It is straight, short and narrow. Stomach is lined by glandular epithelium which secretes digestive enzymes.
   Function: It is mainly responsible for digestion and absorption.
   b. Hepatic caeca: These are thin, transparent, short, blind (closed) and hollow tubules.
   Function: They secrete digestive enzymes.
3. Hindgut or proctodaeum: It consists of ileum, colon and rectum.
   a. Ileum: It is short and narrow part of hindgut. Malpighian tubules open in the anterior lumen of ileum, near the junction of midgut and hindgut. Posterior region of ileum contains sphincter. Ileum directs the nitrogenous wastes and undigested food towards colon.
   b. Colon: It is a longer and wider part of the hindgut. It directs waste material towards the rectum. It reabsorbs water from wastes as per the need.
   c. Rectum: It is oval or spindle-shaped, terminal part of the hindgut. It contains six rectal pads along the internal surface for absorption of water. Rectum opens into anus. Anus is present on the ventral side of the 10th segment. It is the last or posterior opening of the digestive system. The undigested food is released out of the body through the anus.

• Salivary glands:

1. Cockroach has a pair of salivary glands which secrete saliva.
2. Each salivary gland has two glandular lobes and a receptacle or reservoir.
3. The glandular lobes consist of several irregular-shaped white coloured lobules which secrete saliva.
4. Each gland has a salivary duct. Both the ducts unite to form a common salivary duct.
5. The receptacle of each salivary gland is thin-walled, elongated, sac-like structure. Each receptacle has a duct. These ducts unite to form a common reservoir duct.
6. Common salivary duct and common reservoir duct unite together to form a common efferent salivary duct. The efferent salivary duct opens at the base of tongue or hypopharynx.