Introduction
The cockroach salivary apparatus (Periplaneta americana) is an important accessory digestive system in insects responsible for the secretion, storing and transporting saliva. In Periplaneta americana, saliva helps in lubrication and the initial digestion of food before it enters the alimentary canal.
The salivary apparatus consists mainly of a pair of salivary glands, salivary reservoirs and a duct system that opens into the pre-oral cavity
Location
- It is present in the thoracic region of the body.
- Located on the dorso-lateral sides of the oesophagus
- It occurs as a pair, one on each side
Structure of Salivary Glands
Each salivary gland is:
- Bipartite (divided into two parts)
- Diffuse and irregular in appearance
- It is whitish in colour
Each gland is made up of several small secreting units called acini or lobules arranged in grape-like clusters. These acini are connected by fine tubules which form the duct system.
Diagram: Salivary Apparatus of Cockroach
Structure of a Salivary Acinus
Each acinus contains the following parts:
1. Zymogenic Cells
- These are outer secretory cells
- Present in different stages of secretory activity
- Secrete the digestive enzyme zymase
Function
Helps in the chemical digestion of starchy food material.
2. Ductule-Containing Cells
- Inner cells containing fine intracellular ductules
- Ductules open into the intercalary duct
- Secrete a mucoid substance
Function
The mucus lubricates food and helps in smooth swallowing.
3. Intercalary Duct
- Collects secretion from ductule-containing cells
- Leaves the acinus and joins ducts of neighbouring acini
- Forms progressively larger ducts
4. Nuclei
- Present inside the secretory cells
- Control the secretory activity of the gland
5. Nerve Supply
- Salivary acini are richly supplied with nerves
- Regulates secretion of saliva
Both zymogenic cells and ductule-containing cells contribute to saliva formation. Cockroach saliva contains zymase enzyme and mucus.
Salivary Reservoir (Receptacle)
Each salivary gland is associated with a salivary reservoir.
Features
- Thin-walled
- Elongated and sac-like
- Acts as a storage chamber for saliva
Function
Stores saliva temporarily and releases it during feeding.
Complete Duct System of Salivary Apparatus
The pathway of saliva is as follows:
The duct system shows bilateral symmetry because both glands and reservoirs unite into a single common efferent duct.
Composition of Cockroach Saliva
| Component | Secreted By | Function |
|---|---|---|
| Zymase | Zymogenic cells | Digestion of starchy food |
| Mucoid substance. | Ductule-containing cells. | Lubrication of food |
Functions of Salivary Apparatus of Cockroach
Produce saliva
Stores saliva temporarily
Lubricates food particles
Initiates digestion of starch
Helps in swallowing food smoothly
Conclusion
Thus, the salivary apparatus of cockroach is a well-developed accessory digestive system composed of salivary glands, reservoirs and ducts. It plays an important role in lubrication and the initial digestion of food before ingestion into the alimentary canal.
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
- Gizzard of cockroach