Scientific Classification

Common Name :- Cockroach
Phylum :- Arthropoda
Class :- Insecta
Order :- Blattodea
Genus :- Periplaneta
Species :- americana

Introduction

The digestive system of cockroach is a well-developed system that helps in ingestion, digestion, absorption, and egestion of food
The cockroach digestive system is a long, coiled tube of uneven diameter. It includes a mouth cavity, a long alimentary canal and digestive enzymes
It is divided into three main regions: Foregut, Midgut and Hindgut.
Foregut and Hindgut are ectodermal and lined with a thin cuticle Midgut is endodermal and lacks a cuticular lining which helps in absorbing digested food in the digestive system of cockroach.

Embryological Origins

Foregut and Hindgut: These regions are ectodermal in origin. A defining characteristic is that they are lined internally with a thin cuticle secreted by the ectodermal layer.
Midgut: This central region is endodermal in origin. Crucially, it is devoid of any cuticular lining, which is a feature that facilitates its primary role in absorbing digested food.

A. Foregut (Stomodaeum)

The foregut is the anterior part of the digestive system and consists of several specialized sections designed for receiving and initially processing food. The components are:

Foregut includes: Mouth Cavity → Pharynx → Oesophagus → Crop → Gizzard

1. Mouth Cavity (Pre-oral Chamber)

The mouth cavity, also called pre-oral chamber, is a small ill-defined space located outside the mouth. It is surrounded by mouthparts on all sides. In the digestive system;

Hypopharynx divides it into two parts:

Salivarium - It is posterior part into which common salivary duct opens here
Cibarium - It is anterior part, acts as narrow food passage towards mouth

Food is crushed and acted upon by saliva here.

2. Mouth (True Mouth)

It is the small opening situated at the base of preoral cavity which leads directly into the pharynx acting as the entry point of the digestive tract.

The mouth itself performs no digestion— it simply allows food to pass from the preoral caviy into the pharynx

3. Pharynx

The pharynx is the short and tubular in structure.Its cuticular lining(lumen) is more folded posteriorly in cockroach digestive system which helps in gripping and pushing food downward.
The pharynx works like a muscular pump — it sucks food in from the mouth and pushes it into the oesophagus through muscular contractions.

4. Oesophagus

The Oesophagus is long, straight, narrow and laterally compressed tube arises from pharynx.
It passes through the nerve collar.It runs through the neck and enters the thorax which merges with the crop in the digestive system
The oesophagus does not digest food — it transports the food from the pharynx to the crop by peristaltic movement.

5. Crop

The crop is a large, thin-walled, pear-shaped sac. It extends up to the 3rd or 4th abdominal segment and the largest part of the foregut.
Internal epithelial and cuticular lining is highly folded in this part and Outer surface is covered by a network of tracheae that supply oxygen.
The primary function of the crop is to act as a reservoir for storing food — it holds ingested food temporarily before passing it to the gizzard for mechanical grinding.
Some preliminary digestion by salivary enzymes also occurs here while food is being stored.

EXAM POINT: Crop absorbs large quantities of fat through its epithelial cells — important for absorption.

6. Gizzard (Proventriculus)

Crop leads behind into a small, cone-shaped, muscular and thick-walled chamber. It is also known as proventriculus. It marks the end of the foregut.

It Consists of two parts:

(a) Armarium

The anterior part of the gizzard is known as armarium. It possesses 6 longitudinal folds internally and these folds greatly reduce the lumen.longitudinal folds alternate with 6 longitudinal grooves which also bear small secondary folds
These longitudinal folds alternate with six longitudinal grooves bearing small secondary folds.

Cuticular lining of each fold forms:

Anterior part: A thick plate produced centrally into strong sharp teeth called denticles that grind and crush food particles.
Posterior part: thin plate behind each fold the cuticular lining forms soft cushion lobe like a pad called pulvillus which has long backwardly directed hairs
These hairs act as strainers - allow only fine food particles into midgut,Grinds food particles and blocking larger unground particles.

(b) Stomodaeal Valve

It is located at the posterior end of gizzard which extends into the lumen of midgut as a spout-like narrow tube. It is also known as stomodaeal valve.
The latter folds back on itself - making it double-walled

Main function:Its critical function is to prevent regurgitation — it stops food from flowing back from the midgut into the gizzard, ensuring one-way passage of food.

🔗 Read detailed notes on T.S. of Cockroach Gizzard

B. Midgut (Mesenteron)

It is short and narrow tube-like middle region of alimentary canal also known as ventriculus or mesenteron.
Internally lined by glandular epithelium which forms the true stomach.

Main function: digestion and absorption of food

1. Hepatic Caeca

There are 7 to 8 short, narrow, blindly ending hollow tubes which open into the anterior end of midgut also known as enteric or hepatic caeca.It is internally lined by epithelium.

Function: secrete digestive enzymes

2. Malpighian Tubules

Malpighian tubules are 80 to 90 very narrow, thread-like, yellow-coloured blind tubules which arise from the junction of midgut and hindgut and it is project freely into the haemocoel which is named after Italian anatomist Malpighi. Actually arise from hindgut.

Function: excretory in nature
In Periplaneta, shown to contain certain intracellular enzymes also(E. Schlottke 1937)

C. Hindgut (Proctodaeum)

It forms the posterior 1/3 part of the alimentary canal

Divided into three regions: Ileum, Colon and Rectum

1. Ileum

Ileum is narrow and short tube and posterior end has 6 tiny triangular lobes internally.These lobes bear spicules

Acts as a sort of sphincter in digestive system of cockroach

2. Colon

It is the longer and wider than ileum. It has an irregular shape.

3. Rectum

The rectum is oval or spindle-shaped sac.It has external ridges alternating with internal longitudinal thickenings.
Internal thickenings called rectal pads or rectal papillae

Rectal pads are 6 in number and also known as rectal glands
Rectum opens to the outside by anus

Note: The lining of hindgut is also cuticular but more permeable to water than that of foregut..

EXAM POINT: Rectal pads = 6 in number = rectal papillae = rectal glands. All four names refer to the same structure. Commonly asked!

Digestive Enzymes

Salivary Enzyme — Zymase
🔹 Source — Zymogen cells of the salivary glands located in the thorax.
🔹 Site of Action — Salivarium of the preoral cavity.
🔹 Function — Hydrolyses starchy food material. Saliva also contains mucus which lubricates the food and binds food particles together for smooth passage into the alimentary canal.
Enzymes of Hepatic Caeca and Midgut Epithelium
These secretory cells produce four major digestive enzymes. These are the most important enzymes for proper digestion.

i) Trypsin-like Enzyme

Substrate — Proteins
Function — it breaks down proteins into smaller peptide units and amino acids.

ii) Peptidases

Substrate — Polypeptides
Function — It further breaks down peptides into free amino acids. Works alongside the trypsin-like enzyme for complete protein digestion.

iii) Amylase

Substrate — Starch and complex carbohydrates
Function — It completes the breaking down of starches into simple sugars.

iv) Lipase

Substrate — Fats and lipids
Function — It breaks down fats into fatty acids and glycerol.

EXAM POINT: Zymase ≠ Amylase. Zymase is the salivary enzyme from salivary glands. Amylase is secreted by hepatic caeca and midgut. Do not confuse these two!

Conclusion

The digestive system of cockroach is well-developed and efficient for ingestion, digestion, absorption, and egestion of food. It consists of foregut, midgut, and hindgut, which work together for proper digestion.

Did You Know .?

The cockroach can survive for several days to weeks without food because its digestive system is highly efficient at storing and extracting nutrients from available food sources..

Reference :-

A Textbook of Invertebrates — R. L. Kotpal
Jordan & Verma — Invertebrate Zoology
Modern Textbook of Zoology: Invertebrates
A Manual of Practical Zoology: Invertebrates

Digestive System Of Cockroach—Easy Explanation with Diagram, Structure, Functions & Enzymes | BSc Zoology Notes