Digestive System of Cockroch: With Related Important QnA

Digestive System of Cockroach: With Related Important QnA

           

Explain the digestive system of a Cockroach with a labelled diagram.

                       Or

Give an account of the digestive system of Periplaneta Americana.

Cockroaches are omnivorous and they consume any kind of organic molecule as food.

The digestive system of cockroach comprises of,

• Mouthparts
• Alimentary Canal

Digestive System of Cockroach: Diagram 

1. Mouth parts: 

Mouth comprises of

• Labrum or upper lip
• A pair of mandibles 
• A pair of maxilla 
• Labium or lower lip
• Hypopharynx

Labrum: 

It is slightly rectangular and hangs from the frontal edge of the head on the lower side. It covers the mouth and mandibles.

Mandibles:

Mandibles are made of hard dark-coloured large triangular structures on either side. They move side by side horizontally, to crush the food.

Maxillae:

Maxilla is a paired structure outside and behind mandibles. It consists of three parts,

•  Protopodite: Has stipes and cardo.
• Exopodite: Has 5 segments and is related to taste. 
• Endopodite: Made of inner lacinia and outer galea.

Maxillae helps manipulate the food before it enters the mouth.

Labium:

Labium, forming the broad median of the lower lip. It has three pairs of segmented labial parts on either side. They are sensory in function. It is formed by the fusion of 2nd pair of Maxillae.

Hypopharynx:

It lies between the maxilla and above the labium, inside the mouth cavity. The common salivary duct opens at its front end.

Alimentary canal of Cockroach:

The Alimentary canal is complete and divided into three parts, i.e., Foregut, Midgut and Hindgut.

I. Foregut or stomodaeum: 

• a. Ectodermal in origin.
• b. Internally lined with cuticle.

It consists of,

 i. Pre-oral cavity or mouth cavity, bounded by mouthparts. Tongue-like hypopharynx hangs in it. The hypopharynx divides the oral cavity posteriorly as a salivarium, where common salivary ducts open and anteriorly as a cibarium, which leads towards the mouth as a narrow food passage. 

* The saliva acts on the food in the mouth cavity.

 ii. Mouth: It is a small opening at the base of the mouth cavity leading to the pharynx.

iii. Pharynx: It is a short and tubular extension, reaching the next part, the oesophagus.

iv. Oesophagus: It passes through the nerve collar and neck, entering the thorax to merge with the crop.

v. Crop or ingluvius: It is large, pear-shaped, thin-walled and extends up to the third or fourth abdominal segment. Anatomically, its internal epithelial and cuticular lining shows folds and the outer covering shows a network of tracheae. 

Function:The crop acts as a reservoir and stores the food.

vi. Gizzard or proventriculus:

The end of the foregut is marked by a gizzard, which is a small cone-shaped, muscular, thick-walled chamber. It consists of two parts. 

1. Armarium: Internally it possesses six longitudinal folds forming six grooves which in turn bear secondary folds. Its cuticular lining forms,

• Anteriorly a thick plate produces, in the centre, six sharp chitinous teeth or denticles.
• Posteriorly a thin plate produces six cushion-like pads or pulvilli, with long backwardly directed hairs Function: These act as strainers, allowing only finer food particles to reach the midgut

 2. Stomodaeal valve: Posteriorly the gizzard extends as a spout-like narrow tube, the Stomodaeal valve, into the lumen of the midgut. 

Stomodaeal valve folds back on itself and thus it is double walled. 

Function:

It secretes a protective peritrophic membrane around the food and also prevents the regurgitation of food back to the gizzard.

II.Mid gut or Mesenteron or Ventriculus:

It is endodermal in origin, short and tube-like middle portion of the digestive system of cockroaches. 

Internally lined by glandular epithelium forming true stomach to serve in digestion and absorption.

It comprises,

i. Hepatic caeca:

There are 7 or 8  narrow, hollow hepatic or enteric caeca in the anterior end of the midgut. They are internally lined by epithelium.

Function: Secrete digestive enzymes.

ii. Malpighian tubules:

Posteriorly, at the junction of midgut and hindgut, 60- 150 narrow, yellow-coloured, thread-like blind tubules project outward in the haemocoel. These are called Malpighian tubules. They are secretory.

* Named after the great Italian Anatomist Malpighi.

III.Hindgut or Proctodaeum:

Ectodermal in origin, lined with cuticle, like foregut but is more pervious to water than the latter. 

It makes the posterior 1/3 part of the alimentary canal. It comprises of ileum, colon and rectum.

i. Ileum: 

The ileum is a narrow and short tube which at its posterior end possesses internally, six tiny triangular lobes bearing spicules.

Function: It acts like a sphincter. 

ii. Colon: 

It is longer, wider with an irregular shape.

iii. Rectum:

The rectum is an oval or spindle-shaped sac showing six external ridges alternating internally with longitudinal thickenings called rectal pads, rectal papillae or rectal glands.

It finally opens out by a slit-like aperture, the anus at the end of the abdomen below the 10th tergum.

Digestive Glands:

i. Salivary glands:

A pair is present in the thorax. One on either side of the crop. Made up of bipartite and lobulated glandular parts and a long sac-like reservoir or receptacle. Saliva is secreted by the glandular part and contains starch-splitting amylase enzyme.

II. Hepatic caeca

III. Midgut lining

Digestion is completed by the enzymatic secretion of hepatic caeca and midgut lining which possess Trypsin and Erepsin (to hydrolyse protein into amino acids); lipase (to digest fats into fatty acids and glycerol); and invertase, maltase and lactase ( to digest the carbohydrates like sucrose, maltose and lactose).

• Most of the absorption takes place in the midgut. The lining cells of the caeca absorb the glucose only. 
• Water and minerals are absorbed in the hindgut.
• The undigested food or faeces is finally expelled out through the anus in the form of almost solid pellets.

Related important questions:

Question: Describe the mouthparts of cockroaches and add a note on the feeding mechanism.

 Answer: 

Mouthparts of cockroach:

Cockroaches are omnivorous and their food includes any kind of animal or vegetable matter or wood, cloth, leather, paper, paste, glue, hair and even cast cuticles. It usually feeds at night.

Mouthparts of Cockroach: Diagram 

Mouth comprises of

• Labrum or upper lip
• A pair of mandibles 
• A pair of maxilla 
• Labium or lower lip
• Hypopharynx

Labrum: It is an appendage of the third head segment. It is plate-like and attached to the lower margin the of clypeus forming the interior margin of the mouth cavity. A small sclerite called torma is present at the junction the of labrum with clypeus, on each inner side. 

Furthermore, the inner surface bears two rows of sensory or gustatory setae on each side. 

The labrum overlaps the toothed portions of mandibles.

Mandibles: 

It is an appendage of the 4th head segment. They are small triangular highly sclerotised structures.

Mandibles are attached to the sides of the head capsules which are articulated by the condyle with the gena of the same side.

The inner margin of each mandible has two small cutting or serrated lobes, i.e. distal incisor and proximal molar. Each bearing three tooth-like denticles of thickened cuticle.

On the proximal end of the molar lobe, is the membranous prostheca that bears sensory hairs.

Function: Mandible work as Jaws. The denticles in it act as the interlocking structures.

The smooth Molar areas help in mastication.

The sideways movement of both mandibles is done by the adductor and abductor muscles.

Maxillae:

These are paired appendages of the 5th head segment and are known as the first pair of Maxillae.

They lie beneath the mandibles and articulate with the posterior surface of the head capsule one on either side.

They are biramous in structure.

At the base, the protopodite distally consists of cylindrical stipes hinged to the proximal cardo at an obtuse angle.

Stipes show three processes

i. inner lacinia bearing sclerotised sharp denticles and blunt lacinula.

ii. Middle Galea acting as a hood.

iii. Maxillary palp on the outer side with  5 

segment. It is sensory.

The maxillary palp is born out of a small basal sclerite called the palpifer.

Maxillary palp represents exopodite while the lacinia and galea represent endopodite.

Function:

1. The pair of maxilla act as accessory Jaws. Move sideways to masticate the food and help them reach the oral cavity.

2. They also help to clean antennae and forelegs.

Libium: 

The labium or lower lip is the appendage of the 6th head segment. It is at the posterior-most end of all mouthparts. It is formed by the fusion of two maxilla-like embryonic appendages or a second pair of Maxillae.

It represents protopodite and is of 3 segments.

i. The large proximal submentum.

ii. A small middle mentum.

iii. The distal prementum.

Submentum:

The partially fused endopodite forms a tongue-like ligula consisting of inner glossa and outer paraglossa on each half, corresponding with lacinia and galea respectively.

The distal prementum:

The premium bears three jointed sensory labial palps on each side. The labial palp is born on basal projection, the palpiger.

At the terminal end, the palp is covered with sensory setae.

 Hypopharynx:

The hypopharynx is situated between the maxillae and above the labium, in the mouth cavity. It is somewhat cylindrical in structure and is also called Lingua.

 

Distally two comb-like plates, the superlingua are present. 

Its front end opens to the common duct of the salivary gland.

Feeding mechanism in cockroach

The mouth parts of the cockroach are the biting and chewing type, also called the mandibulate type.

Cockroaches are omnivorous so their mouth parts are unspecialised.

The Cockroach bites and chews hard stuff, consumes soft stuff and laps up liquids.

Sweep their antenna to search for food. The maxillae and labial pulp help to taste food and the foreleg, labrum and labium help to seize the food. 

The food when taken in, the mandible and maxilla move sideways to masticate and cut the food into finer particles. This action is done with the help of the adductor and abductor muscles of the mandibles.

Question: Write a short note on the Salivary apparatus of Cockroach.

Answer:

The Salivary apparatus: 

In the thorax region of the cockroach, is present a pair of bipartite, diffused and whitish salivary glands on the dorsolateral sides of the oesophagus.

Salivary apparatus of cockroach: Diagram 

In each gland, there are several clusters of grape-like
secreting lobules or acini interconnected by fine tubules.

Acini contains two types  of cells,

1. Zymogenic cells

2. Ductule-containing cells

These cells secrete saliva. Saliva consists of an enzyme zymase and a mucoid substance.

Ductule-containing cells give out ductules which open into intercalary ducts. All such ducts from the numerous acini join similar ducts to form a larger duct.

Also associated with each gland is a sac-like thin-walled reservoir or receptacle to store the saliva.

The ducts from two salivary glands unite to form a single common glandular duct. In the same way, ducts from each reservoir unite forming a common reservoir duct.

Both of these common ducts then join to form a common efferent salivary duct which opens at the base of the hypopharynx in the salivarium of the pre-oral cavity.

Functions of salivary glands of cockroaches:

1. They moisten the mouth parts and serve as lubricant.
2. The act is food solvent.
3. They serve as a medium for digestive enzymes and various anticoagulants and agglutinins.

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