The circulatory system of a cockroach is quite different from that of humans and other vertebrates. Unlike humans, cockroaches do not have a closed circulatory system, meaning their blood (or hemolymph) is not confined to vessels like veins and arteries. Instead, it flows freely within the body cavity. Despite its simplicity, the cockroach’s circulatory system is efficient enough to support its active lifestyle. Let’s dive deeper into the structure and function of the cockroach circulatory system.
The circulatory system of a cockroach is open, meaning that the blood or hemolymph does not circulate through closed blood vessels. Instead, it bathes the organs directly in the hemocoel (body cavity), providing nutrients and removing waste. The system includes a dorsal heart, aorta, and several other components that help in the circulation of hemolymph.
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1. Hemolymph
The cockroach’s circulatory fluid is called hemolymph, a fluid that serves as both the blood and the lymph. It is a colorless fluid, containing a mixture of water, salts, proteins, and other substances. Hemolymph functions to transport nutrients, hormones, and waste products and is also involved in the immune response.
2. Dorsal Heart
The cockroach has a dorsal heart that runs along the length of the body and is located just beneath the thorax and abdomen. The heart is a long, tubular structure with ostia (small openings) that allow the entry of hemolymph. The heart is divided into several chambers, and each chamber has valves to regulate the flow of hemolymph.
3. Aorta
The aorta is a continuation of the dorsal heart and extends from the head region. It carries hemolymph toward the head and is responsible for distributing the fluid throughout the body cavity.
4. Hemocoel
The hemocoel is the body cavity in which hemolymph circulates. It acts as a space for internal organs like the gut, reproductive organs, and muscles. The organs are not encased in separate blood vessels but are bathed in hemolymph.
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The circulatory system of the cockroach operates in a pulsatile manner, with the heart contracting and relaxing to push the hemolymph forward. The movement of hemolymph is not continuous but happens in pulses.
Cockroaches are the orderly Blattodea insect, sometimes called Blattaria, about 30 of the 4,600 species associated with human habitats. They have six legs. About four species are best known as insects. Cockroaches live in various parts of the world. Insect species adapt to a wide range of conditions but prefer warmer climates. Many tropical species prefer even the warmer climate. The cockroaches mostly fly at night and will flee when exposed to light.
Cockroaches have long horns that help them detect odors and vibrations. The horns are attached to the head, which includes the brain, strong oral components for scrubbing and chewing food, and mixed eyes. They do not see well and do not like the light. Behind the head comes the thorax. It includes three pairs of legs - cockroaches with six legs in total - and two pairs of wings. There is a plate behind the head called the pronotum. Older cockroaches have wings. The abdomen contains the reproductive organs. At the back of the abdomen are two short sections called the cerci. They act as hind limbs and are attached to the roach's legs by the abdominal nerve ganglia. This allows their legs to start moving when a vibration is heard, usually before their brains process a threat.
The whole body is divided into three stages: the head, thoracic, and abdomen. The head has compact eyes, horns, and parts of the mouth. The thorax has moving legs and wings. The stomach has anal cerci.