Exoskeleton
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An exoskeleton, in contrast to an endoskeleton, is an external anatomical feature that supports and protects an animal's body. All arthropods (such as insects, spiders and crustaceans) and many other invertebrate animals (such as shelled mollusks) have exoskeletons. Lobsters, for example, have tough outer shell systems which provide rigidity and shape to their bodies, in addition to an endoskeleton. The endoskeleton of arthropods is continuous with and an extension of the exoskeleton and is shed at the same time as the exoskeleton.
An insect's exoskeleton (integument) serves not only as a protective covering (armour) over the body but also as a surface for muscle attachment, a water-tight barrier against desiccation and a sensory interface with the environment. It is a multi-layered structure with four functional regions: epicuticle, procuticle, epidermis and basement membrane.[1] Note that, while the arthropod exoskeleton is chitin-based, it is not composed entirely of chitin. In fact, the membranous portions of the exoskeleton and endoskeleton are closer to pure chitin than the hardened external sclerites.
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[edit] Human equivalents
Humans have long used armour as an artificial exoskeleton for protection, especially in combat. Exoskeletal machines are also starting to be used for medical and industrial purposes, while Powered human exoskeletons are a feature of science fiction writing, but are currently moving into prototype stage. Orthoses are a limited, medical form of exoskeleton.
[edit] Natural exoskeletons
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[edit] Types
- Bone and cartilage
- Ostracoderms (extinct armoured fish)
- Turtles, Terrapins and Tortoises
- Chitin
- Arthropods
- some Bacteria
- Calcium compounds
- Silicate
[edit] Ecdysis
An exoskeleton may interfere with an animal's growth. To overcome this, arthropods go through a process called ecdysis in which they shed their exoskeleton and replace it with a new, larger one. The shedding of the exoskeleton, commonly known as molting, starts with a process called apolysis where the cuticular layers separate from the epidermis due to the secretion of hormones. Ecdysis is the process at the end stages of molting where the arthropod casts off the exoskeleton. Insects usually appear white following the molting process. Sclerotization is the process by which the new cuticle hardens and darkens. It occurs right after molting in adults.
Excellent as a principle of defence, exoskeletons may nevertheless cause problems where entities carry an excessive weight to surface-area ratio or whenever organism growth requires an enlargement of the exoskeleton. Exoskeletons are found on shellfish, and insects.
[edit] Artificial human exoskeletons
[edit] In history
Medieval armour (in the case of mounted knights) is not load-bearing, but furnishes the appearance of an artificial human exoskeleton.
[edit] In medicine
An orthosis (plural orthoses) is a device which attaches to a limb, or the torso, to support the function or correct the shape of that limb or the spine. Orthotics is the field dealing with orthoses, their use, and their manufacture. An orthotist is a person who designs and fits orthoses.
A limb prosthesis (plural prostheses) is a device that substitutes for a missing part of a limb. If the prosthesis is a hollow shell and self-carrying, it is exoskeletal. If internal tubes are used in the device and the cover (cosmesis) to create the outside shape is made of a soft, non-carrying material, it is endoskeletal. Prosthetics is the field that deals with prostheses, use, and their manufacture. A prosthetist is a person who designs and fits prostheses.
[edit] In modern and near-future technology
[edit] References
[edit] See also
- Mechatronics
- Spiracle - Small openings in the exoskeleton that allow insects to breathe
