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What is the circulatory system of cockroach?

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Circulatory system of cockroach consists of the following organs:

Heart and Aorta:

The heart of cockroach is an elongated contractile, narrow tube lying along the mid-dorsal line of thorax and abdomen just beneath the terga. The heart is enclosed in a pericardial sinus, the wall of which has segmented bundles of alary mus­cles and a dorsal fenestrated diaphragm.

The wall of the heart is composed of outer con­nective tissue and median muscle cells. The cavity of the heart is lined by the sarcolemma of median muscle cells. The heart consists of thirteen funnel-shaped and segmentally arranged chambers, each communicating by a valvular opening with that lying in front of it.

The hinder end of each chamber has a pair of minute, lateral and valvular openings called ostia, which allows the flow of blood from the pericardium into the heart only and not in reverse direction. In each seg­ment, heart sends a pair of ex-current arteries.

The heart is closed behind but is continued forward as a short and narrow tube without ostia called the aorta. This aorta and segmen­tal arteries finally open within the haemocoelic spaces.


The body cavity of cock­roach is not a true coelom but a haemocoel containing blood (haemolymph).

Circulating Fluid in Cockroach:


In cockroach, the circu­lating fluid does not always flow through the vessels, rather comes in direct contact with the tissues while flowing in the haemo­coel.

So the ‘blood’ of cockroach is both blood as well as lymph and is therefore, called haemolymph. It is colourless, as it lacks the respiratory pigment haemoglobin and does not take part in respiration. It con­sists of a clear fluid plasma in which are sus­pended nucleated cells or haemocytes.

The plasma contains various inorganic ions like sodium, potassium, calcium; organic com­pounds like, citrate; amino acids viz. ala­nine, cystine, glycine, tyrosine, valine etc.; enzymes like chitinase and glucosidase; car­bohydrates; lipids and uric acid.


The structure and function of the haemocytes of different insects inclu­ding cockroach have been reviewed by different workers. However, the following haemocytes are most commonly present in cockroach haemolymph.

1. Prohaemocytes:

Small round cells with large nucleus and thin agranular cyto­plasm. These cells divide to give rise to other kinds of haemocytes.

2. Plasmocytes:

Large amoeboid cells with pseudopodia, large nucleus and large mass of a granular cytoplasm.

3. Granulocytes:

Small to large cells with granular cytoplasm.

4. Cystocytes/Coagulocytes:

Cells with small nucleus and a pale hyaline cyto­plasm with black granules. The total number of cells in the haemolymph of adult Periplaneta is about 15,00,000 though the number obviously depends on the volume of haemolymph which is about 15.7-17.5 per cent of body weight. Haemo­cytes play significant role in the physiology and survival of cockroaches.

Mechanism of Circulation in Cockroach:

The contrac­tion of alary muscles enlarges the pericardial space so that the haemolymph flows into it from the underlying perivisceral sinus. When the alary muscles relax, the haemolymph is forced through the ostia into the heart. As the heart relaxes during diastole the tension of the ligament stretches out the walls of heart so that the haemolymph flows into the organs; anteriorly into the head.

It then passes back from the haemocoel of head into that of the thorax and abdomen and enters the pericardium. In addition to alary muscles, contraction of dorsal diaphragm also helps in rapid circulation of haemo­lymph. The heart beats at a rate of 100-200 per minute at 27°C. A complete cycle of circulation of haemolymph through the body takes 20-30 minutes.

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