Spider 2020-07-29

Blood

• The spider's blood, called hemolymph, circulates oxygen, nutrients and hormones to the different organs in the body. Unlike humans, spiders have an open circulatory system.
• Spiders have a very different vascular system. Firstly, it is an open network which means its arteries carry haemolymph, the arthropod equivalent of mammalian blood, out into the tissue spaces where it diffuses past individual cells before being collected back into the heart. There are few, if any, veins in this system and definitely no capillaries.
• The heart pumps much of its haemolymph forward through the pedicel and into the cephalothorax using a large artery that some authors refer to as the anterior aorta. There is also the equivalent of a posterior aorta that delivers oxygenated haemolymph to those abdominal organs that need it. To ensure one-way fluid flow a simple valve may be present at the beginning of each of these major arteries. In those spiders that have been studied so far the heart rate seems to be somewhere in the range 30 - 200 beats per minute, depending on the species involved and on the extent to which it is active.
• Spider 'blood' is just as different from its mammalian equivalent as the circulatory apparatus is. A more correct name for it is haemolymph because it has many features in common with the lymph that diffuses through human tissue spaces before being returned to the circulatory system. It is not red because it does not contain the oxygen-carrying pigment, haemoglobin. Instead, it is a pale blue colour due to the presence in it of haemocyanin, an oxygen-carrying molecule that is blue because it contains copper rather than iron as found in haemoglobin. Both are proteins but haemoblobin is packed into cells called erythrocytes whereas haemocyanin is simply dissolved in the haemolymph despite its large molecular size (1,700,000 daltons compared with 66,000 daltons for haemoglobin). In addition, haemoglobin can carry about 17 times as much oxygen as haemocyanin. The haemolymph of a typical spider also contains some cells but it is much less cellular than human blood, which is about 45 percent cells by volume.

• The available evidence indicates that some of them help minimize bleeding from small injuries such as a lost leg and thereby also promote healing. In this respect they probably work in a manner similar to that of the platelets in our blood or the thrombocytes of vertebrates other than mammals. It is for this reason spiders can lose a leg or two without dying, although damage to the more fragile abdomen is almost always rapidly lethal.

  
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• They only have one or two openings called spiracles, these being located on the underside of the abdomen between the spinnerets and the book lungs. Although the air in the tracheal system of spiders is not exchanged in a cyclic fashion there may be some incidental replacement of the tracheal air by other movements the spider makes.

  
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• Tracheae allow better direction of oxygenated haemolymph to those structures that need it most. Hence, tracheae that extend forwards through the pedicel provide an efficient oxygen supply for the spider brain and those species that have them in the cephalothorax tend to have significantly reduced maximum heart rates. Surprisingly, it appears that not more than ten percent of a spider's tracheal tubes are in the cephalothorax and they do not penetrate the muscles that allow cyclic compression of it although in web-monitoring spiders such as the uloborids they do enter the first segments of the legs. There are two other advantages that tracheoles have over book lungs: they are better for water conservation in spiders such as the salticids that are active during the daylight hours, and they also can store a small but significant amount of air when the spiracles are closed.
• There is no convincing evidence that air flow in either the book lungs or the tracheae is regulated by deliberate neuromuscular activity but some passive air exchange undoubtedly does occur and the spider may be able to vary the amount of haemolymph perfusing them when necessary. On the other hand, there is research data that suggests there is a circulatory centre within the brain, at least in tarantulas. This centre exerts neural control over a cardiac ganglion located in the first segment of the spider heart. Stimulation of the nerves to this ganglion sometimes leads to either an increase or a decrease in heart rate, suggesting the circulatory centre may have both cardioaccerator and cardioinhibitor areas.

Please note this information source from (http://www.findaspider.org.au/info/spiderblood.htm)

Breathing

• Spiders have two different types of respiratory systems -- trachea and book lungs (most species have both, but some have one or the other)