Introduction
T S of cockroach gizzard (proventriculus) is an important part of digestive system.
The transverse section (T.S.) of the cockroach gizzard, also called the proventriculus, is a small, cone-shaped, muscular and thick-walled chamber located at the posterior end of the foregut. The gizzard performs mechanical grinding of food, filters food particles and regulates the passage of finely processed food into the midgut.
Parts of T.S. of Cockroach Gizzard
The transverse section of the cockroach gizzard shows two main parts:
➤ Armarium — anterior grinding region
➤ Stomodaeal Valve — posterior valve region
Armarium — Anterior Part
The armarium is the anterior grinding and filtering region of the gizzard. It is structurally complex and contains the following parts:
1.Six Longitudinal Folds
- The armarium possesses six longitudinal folds that project inward from the inner wall of the gizzard. These folds reduce the lumen into a narrow star-shaped cavity visible in the T.S. diagram.
- The six longitudinal folds alternate with six longitudinal grooves, each bearing small secondary folds. Their main function is to create pressure for effective crushing and grinding of food particles.
2.Denticles (Teeth)
- The cuticular lining of the anterior part of each fold forms a thick plate that projects inward as strong, sharp denticles or teeth.
- These denticles are made of hard, sclerotised chitin and act as the primary grinding structures of the gizzard. Their function is to crush and grind food particles into fine pieces during muscular contractions.
3.Posterior Thin Plate
- Behind the denticles, the cuticular lining becomes thin and flat, forming the posterior thin plate.
- This thin plate does not take part in grinding. It mainly forms the protective base of the lining and guides ground food toward the filtering region of the pulvilli.
4.Pulvillus (Pad) — Biological Filter
- Behind each longitudinal fold lies a soft, cushion-like lobe called the pulvillus or pad. There are six pulvilli in total.
- Each pulvillus bears long backwardly directed hairs that act as a biological strainer. These hairs allow only finely ground food particles to pass into the midgut while blocking larger particles for further grinding.
5.Thick Inner Cuticular Lining
- The entire inner surface of the gizzard is lined by a thick cuticular lining made of heavily sclerotised chitin.
- This lining protects the inner wall of the gizzard from damage caused by continuous grinding and mechanical pressure.
6.Epithelium
- Beneath the cuticular lining lies a thin layer of epithelial cells.
- These cells secrete and maintain the cuticular lining. Since the cuticle undergoes wear during grinding, the epithelium continuously replaces it.
7.Thick Circular Muscle Layer
- Outside the epithelium lies a thick circular muscle layer composed of smooth muscle fibres arranged in rings around the gizzard.
- Its strong contractions compress the lumen and press the denticles together to grind food effectively.
8.Longitudinal Muscle Fibres
- The outermost layer of the gizzard wall consists of longitudinal muscle fibres running parallel to the long axis of the gizzard.
- These fibres work together with the circular muscles to produce powerful grinding and forward movement of food.
Stomodaeal Valve — Posterior Part
- The stomodaeal valve is the posterior part of the gizzard that projects into the lumen of the midgut.
- It forms a narrow, spout-like, double-walled tube. Its main function is to prevent regurgitation of food from the midgut back into the gizzard. Thus, it ensures one-way movement of food through the alimentary canal.
Conclusion
Thus, the cockroach gizzard is a specialised muscular grinding organ that crushes, filters and regulates the passage of food before it enters the midgut.
Referrence :-
- A Textbook of Invertebrates — R. L. Kotpal
- Jordan & Verma — Invertebrate Zoology
- Modern Textbook of Zoology: Invertebrates
- A Manual of Practical Zoology: Invertebrates
Suggested reading :-
- Digestive System of Cockroach
- Mouthparts of Cockroach