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Introduction

The circulatory system of any organism forms the core function of the body. It is responsible for transportation of respiratory gases, food and metabolic waste of body. The circulatory system of a human being comprises of various organs and blood vessels such as veins, arteries, and capillaries. The circulatory system of cockroaches is different from that of humans.

 Cockroach has an open circulatory system. Open means that blood does not flow through closed blood vessels.  So, let us take a look at the working of this system.

Anatomy and Function

The system is not adequately developed. Some of the organs that are present are as follows:

Circulatory Organs

Heart and Aorta

The heart of cockroach is a narrow, elongated and contractile tube-like structure. It lies in the middle of the thoracic cavity, runs along the whole mid-dorsal line. It is enveloped within a pericardial sinus. The heart’s outer lining comprises of connective tissues on the outside and median muscle cells on the inside. The heart has 13 chambers in the shape of a systematically arranged funnels.

Each chamber has an opening called the Ostia at its rear end. This allows the inflow of blood into the heart. The heart is tapered into the Aorta. The aorta and the segmental arteries open into the haemocoelic cavity.

Haemocoel

The word hemocoel comes from the coelom, which means the body’s general cavity, including all the other cavities. Haemocoel is divided into three parts horizontally. These three parts are as follows:

  1. The pericardial sinus that, as the name suggests, encloses the tube-like heart, aorta, and the alary muscles.
  2. The alimentary canal is enclosed within the perivisceral cavity.
  3. The most significant and outermost cavity is the perineural cavity, which extends into the legs as septa. Inside the cockroaches’ body is a perforated diaphragm that allows blood to flow through the three sinuses.

Circulatory Fluids

  • Haemolymph

The circulatory system of cockroaches is an open circulatory system because the circulatory fluid does not flow through blood vessels but reaches the tissues directly. The circulatory fluid inside cockroaches is colorless, as it does not contain hemoglobin. It cannot be classified into the blood as it is also lymph, so the name hemolymph. The hemolymph consists of:

  1.     Clear Plasma
  2.     Nucleated Cells called haemocytes

  • Haemocytes

There are different hemocytes present in the circulatory fluid of cockroaches. These are as follows:

  • Prohaemocytes

These are the primal hemocytes. These produce the other thymocytes by dividing a single thymocyte into more. Prohaemocytes are round and have a large nucleus surrounded by a granular cytoplasm, which is considerably thin in consistency.

  • Plasmocytes

These hemocytes have small projections on their surfaces, called pseudopodia. It is because of these projections they are considered to be amoeboid cells. Like prohaemocytes, these also have a large nucleus suspended in a rich cytoplasm.

  • Granulocytes 

These vary in size. They have a granular cytoplasm.

Coagulocytes or Cystocytes

The cells which perform the function similar to white blood cells of the human body are called granulocytes. These cells have a small nucleus and a cloudy, hyaline cytoplasm. There are black dot-like granules suspended in the cytoplasm.

The alary muscle contracts to expand the pericardial spaces so that the hemolymph flows inside the expanded space through the perivisceral sinus. When the alary muscle expand it forces the blood into the Ostia and finally into the heart.

Functions of the Circulatory System of Cockroaches

  •     This process helps the fluid reach all the parts of the body providing the necessary nutrients to all the parts
  •     Unlike the respiratory system of other organisms, oxygen is not transported to the other parts of the body through blood
  •     The circulatory system helps maintain the temperature of 27 degrees Celsius
  •     The plasma in the haemolymph helps transport nutrients from food and waste through the length of the body
  •     The haemolymph also acts as a store of dissolved food
  •     Plasma also helps to form eggs, expand wings, and molting
  •     The plasma also contains the haemocytes that help remove pathogens, like debris, from the body
  •     Detoxifying the body from various poisons
  •     Helps synthesise carbohydrates and protein in the body
  •     Helps heal injuries

Conclusion

The circulatory system of cockroaches is described as one of the most straightforward systems present. This system is an open circulatory system. The heartbeat rate of a cockroach is 100-200 per minute. Even though the insect cockroach is small, it takes about 20 to 30 minutes for a whole haemolymph circulation.