In an insect like the grasshopper, the body cavity or haemocoel consists of a network of blood filled spaces. The internal organs of the insect are immersed in the blood in these spaces.
The blood flows through a dorsal tubular heart with the several chambers which stretches from the thorax into the abdomen. The heart extends towards the head as a single blood vessel, the aorta, which opens into the haemocoel. Each chamber of the heart has a pair of slit like openings at its side. These have valves which allow blood to enter the heart.
Muscles attached to the heart chambers make the heart contracts, these slits close and blood is pushed forward into the aorta and out into the haemocoel. When the heart relaxes, the slits open and blood that has passed through various parts of the body enters the heart. Valves between the heart chambers ensure that the blood floes towards the head.
The haemocoel is partitioned By thin walls which make sure that the blood flows in a definite backward direction in the spaced in the thorax and abdomen. The movements of the abdominal walls helps help to make the blood flow into the heart.
The blood moves slowly into his system. Its main function is to transport digested food from the gut to the various body cells and to collect wastes from the these cells to the malpighian tubules for excretion. Oxygen is not transported by the blood but by a network of air tubes. as a result, the blood is colourless, as it does not contain haemoglobin, the red pigment needed to transport oxygen.
The open circulatory system is an in efficient transport system. It is adequate in an insect simply because an insect has a well developer system of air tubes for transporting oxygen to all parts of its body.
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