The circulator system of spiders
* Spiders are arthropods and they have an open circulatory system. * The open circulatory system is a system in which the organs are directly bathed with nutrients and oxygen. The blood flow is not restricted as much as a closed circulatory system. * The spider’s heart is a simple heart, a tube surrounded by muscle with a one-way valve at each end. * It is located in the abdomen a short distance within the middle line of the dorsal body-wall, and above the intestine. * A thin-walled sac, known as the pericardium, completely surrounds the heart. This sac contains muscles that contract the heart to allow the flow of blood. * The heart is not dependent on the brain to function, but they are connected. It receives messages from the brain to adjust heart rate if needed. * The lack of structure(veins) means a spider’s blood travels slowly unless there is an increase in blood pressure. * Their bodies are filled with haemolymph, which is pumped through arteries by a heart. * Hemolymph is composed of water, inorganic salts (mostly Na+, Cl-, K+, Mg2+, and Ca2+), and organic compounds (mostly carbohydrates, proteins, and lipids). * The haemolymph contains hemocyanin, a respiratory protein similar in function to hemoglobin (human blood). * Hemocyanin contains two copper atoms, tinting the haemolymph with a faint blue color when combined with oxygen. * Hemocyanin binds oxygen but only releases it after it receives the right chemical signal. * The blood also serves another purpose. It is used locally to raise the blood pressure during moulting (shedding of old skin) and stretching the legs.
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