What Type of Circulatory System Does Cockroach Have?
Cockroach has an open or lacunar circulatory system. In this system, blood — also called haemolymph — flows freely within the body cavity known as the haemocoel. Unlike the closed system in vertebrates, there are no capillaries and no veins. Only a heart and an aorta are present.
1. Haemocoel — The Body Cavity
The body cavity of the cockroach is called haemocoel (Greek: haima = blood + koila = cavity) because it is filled with blood or haemolymph.
(a) Pericardial Sinus
(b) Perivisceral Sinus
(c) Perineural Sinus
(a) Diaphragms and Sinuses
The haemocoel is divided by a dorsal diaphragm and a ventral diaphragm into three sinuses:
- Dorsal pericardial sinus — encloses the heart, aorta, and paired fan-shaped (triangular) alary muscles; one pair in each segment, on either side of the heart; apices of alary muscles attach to the terga and their broad bases to the dorsal diaphragm
- Middle perivisceral sinus — Middle or perivisceral sinus contains the alimentary canal. It is mostly occupied by a whitish mass of tissue called the fat body. It consists of several types of cells. Trophocytes stores reserve food in the form of fat globules, protein globules and glycogen. The latter is used during starvation.Urate cells are excretory in nature. Oenocytes produce wax while myocytes contains intracellular symbiotic bacteria
- Ventral perineural (sternal) sinus — encloses the ventral nerve cord
2. Heart and Aorta
- The heart is enclosed by the dorsal pericardial sinus
- It lies mid-dorsally beneath the terga of the thorax and abdomen
- It is a long, narrow tube with the anterior end open and posterior end closed
- Consists of 13 funnel-shaped chambers (segments), each communicating with the one in front by a valvular opening
- Each chamber has a pair of minute lateral openings called ostia — these allow haemolymph to flow from the pericardial sinus into the heart only (not in reverse)
- The anterior narrow tubular part of the heart is called the anterior aorta — it has no ostia and opens forwards into the head sinuses
3. Haemolymph In Cockroach
- Haemolymph consists of a clear, colourless plasma rich in amino acids, uric acid, and various cells
- These cells are called haemocytes
- According to Wigglesworth (1965), there are seven types of haemocytes
Types of Haemocytes and Their Functions:
| Cell Type | Function |
|---|---|
| Trophocytes | Store reserve food — fat globules, protein globules, glycogen |
| Urate cells | Excretory in nature |
| Oenocytes | Produce wax |
| Myocytes | Contain intracellular symbiotic bacteria |
| Phagocytic cells | Remove metabolic wastes from tissues |
| Transfer cells | Transfer food material from blood to tissues |
Important: Haemolymph is devoid of a respiratory pigment and hence does not assist in respiration. This is why cockroaches have a separate tracheal system for gas exchange.4. Blood Circulation — How Does It Work?
Blood circulation in cockroach occurs by the contraction and relaxation of the heart, assisted by the paired fan-shaped alary muscles.
Step-by-Step Mechanism:
Diastole (Relaxation): Alary muscles contract → pericardial sinus enlarges → blood flows into pericardial sinus from the perivisceral sinus belowSystole (Contraction): Alary muscles relax → blood is forced through ostia into the heart
Heart and aorta contract peristaltically from behind forwards → blood is driven into head sinuses
From head sinuses, blood flows backwards into the perivisceral and sternal sinuses
Rate of heartbeat in Periplaneta: 49 beats/min
5. Accessory Pumping Organs
- From the head sinuses, haemolymph is also pumped into the antennae by two small ampullae located in the head
- In the case of wings, small pulsatile organs at the base of each wing cause haemolymph to flow through the veins of the fore and hindwings.
6. Functions of Haemolymph in cockroach
Haemolymph, though it does not carry oxygen, performs several vital functions in the cockroach body:
- Transport of Nutrients — It carries digested food materials such as amino acids, sugars, and fatty acids from the alimentary canal to body tissues
- Transport of Hormones — It distributes hormones secreted by various endocrine glands to their target organs
- Removal of Metabolic Wastes — It collects nitrogenous and other metabolic wastes from tissues and carries them to excretory organs for elimination
- Protection by Phagocytic Cells — Haemocytes act as phagocytes, engulfing and destroying foreign particles, bacteria, and dead cells — providing innate immunity
- Maintenance of Internal Pressure (Hydrostatic Pressure) — Haemolymph helps maintain internal body pressure (turgor), which is important during moulting and in the movement of appendages like legs, wings, and antennae
Note: Since haemolymph lacks a respiratory pigment like haemoglobin, gaseous exchange is not a function of haemolymph in cockroach — this role is performed entirely by the tracheal system.
Conclusion
Thus, the circulatory system of cockroach is an open type (lacunar) circulatory system in which haemolymph flows freely within the haemocoel without being confined to vessels. The heart, haemocoel, three sinuses (pericardial, perivisceral, and perineural), alary muscles, and accessory pumping organs (ampullae and pulsatile organs) together ensure efficient circulation throughout the body. Although haemolymph does not participate in respiration, it plays a critical role in the transport of nutrients and hormones, removal of wastes, immune defence, and maintenance of body pressure in Periplaneta americana. This system is a characteristic feature of all insects and most other arthropods.
Referrence :-
- A Textbook of Invertebrates — R. L. Kotpal
- Jordan & Verma — Invertebrate Zoology
- Modern Textbook of Zoology: Invertebrates
- A Manual of Practical Zoology: Invertebrates