View source for Tegument (helminth)

'''Tegument''' {{IPAc-en|ˈ|t|ɛ|ɡ|j|ʊ|m|ə|n|t}} is a term in [[helminthology]] for the outer body covering of members of the [[phylum]] [[Platyhelminthes]]. The name is derived from a [[Latin]] word ''tegumentum'' or ''tegere'', meaning "to cover".<ref>{{cite web|title=tegument|url=http://dictionary.reference.com/browse/tegumental|website=Dictionary.com|accessdate=5 February 2016}}</ref><ref>{{cite web|title=tegument (n.)|url=http://www.etymonline.com/index.php?term=tegument|website=Online Etymology Dictionary|accessdate=5 February 2016}}</ref> It is characteristic of [[platyhelminthes|flatworms]] including the broad groups of [[tapeworms]] and [[trematoda|flukes]]. Once considered to be a non-living component, it is now known to be a dynamic [[cell (biology)|cellular structure]]. In fact it is a living structure consisting of [[proteins]], [[lipids]], [[carbohydrates]] and [[RNA]]. It forms the protective layer and the [[Host (biology)|host]]-[[parasite]] interface of the [[platyhelminthes|worms]], serving both [[secretion|secretory]] and [[absorption (digestive)|absorptive]] functions.<ref name="ch">Cheng TC (1986). ''General Parasitology, 2nd edn''. Academic Press, Division of Hardcourt Brace & Company, USA, pp. 253-2546. {{ISBN|0-12-170755-5}}</ref>
==Structure and composition==
The fine structure of tegument is essentially the same in both the [[cestodes]] and [[trematodes]]. A typical tegument is 7-16 μm thick, with distinct layers. It is a [[syncytium]] consisting of multinucleated tissues with no distinct [[cell (biology)|cell]] boundaries. The outer zone of the syncytium, called the "distal cytoplasm," is lined with a [[plasma membrane]]. This plasma membrane is in turn associated with a layer of carbohydrate-containing [[macromolecule]]s known as the [[glycocalyx]], that varies in thickness from one [[species]] to another. The distal [[cytoplasm]] is connected to the inner layer called the "proximal cytoplasm", which is the "cellular region or cyton or perikarya" through cytoplasmic tubes that are composed of [[microtubule]]s. The proximal cytoplasm contains [[cell nucleus|nuclei]], [[endoplasmic reticulum]], [[Golgi complex]], [[mitochondria]], [[ribosomes]], [[glycogen| glycogen deposits]], and numerous [[vesicle (biology)|vesicles]].<ref>{{cite journal |vauthors=Gobert GN, Stenzel DJ, McManus DP, Jones MK |title=The ultrastructural architecture of the adult ''Schistosoma japonicum'' tegument |journal=Int J Parasitol  |volume=33 |issue=14 |pages=1561–1575 |year=2003 |pmid=14636672 |doi=10.1016/s0020-7519(03)00255-8}}</ref>  The internal most layer is bounded by a layer of [[connective tissue]] known as the "[[basal lamina]]". The basal lamina is followed by a thick layer of [[muscle]].<ref name="Bog">Bogitsh BJ, Carter CE, Oeltman TN (2005). ''[https://books.google.com/books?id=gOTjnL7tWxsC&dq=tegument&pg=PA177 Human Parasitology, 3rd Edition]''.  Academic Press, pp. 177-179. {{ISBN|0-12-088468-2}}</ref>
A large number of important [[enzymes]] has been detected in the tegument. [[Glutathione S-transferase]], ATP diphosphorylase, [[phosphatase|alkaline and acid phosphatases]], β-glucuronidase, amino [[peptidase]], [[acetylcholine esterase]], [[phosphofructokinase]], [[glucose transporters]], [[hydrolases|serine hydrolases]] and several [[glycolysis|glycolytic enzymes]] have been detected with their biological roles.<ref>Mansour TE, mansour JM (2002). ''[https://books.google.com/books?id=a20hDtdyUA4C&dq=tegument&pg=PA193 Chemotherapeutic Targets in Parasites]''. Cambridge University Press, UK, pp. 192-297. {{ISBN|0-521-62065-1}}</ref>
The external surface of tegument is associated with unique defining structures in cestodes and trematodes. In cestodes the tegument is further covered with highly specialized [[microvilli]], called "[[microtriches]]", projecting from the outer limiting membrane of the tegument. These microtriches are fine hair-like filaments distributed throughout the surface of the body, and give the body surface a smooth and silky appearance. Since cestodes are devoid of any [[digestive system|digestive]] and [[excretory system]]s, the tegument with its microtriches constitute the principal site of absorption of [[nutrients]] and elimination of waste materials. In fact the tegument highly resembles the [[gut (zoology)|gut]] of [[animals]] turned inside out.<ref>Smyth JD, McManus DP (1989). ''[https://books.google.com/books?id=wv1lZoQtI48C&dq=tegument&pg=PA5 The Physiology and Biochemistry of Cestodes]''. Academic Press, pp. 5-8. {{ISBN|0-521-35557-5}}</ref>
In trematodes the tegument contains a number of invaginations or surface pits, and is externally lined with minute [[tubercle]]s among which are dispersed bristle-like projections called "[[spine (zoology)|spines]]". Spines are embedded in the basal lamina and the tip is finely pointed to the external surface. They are made up of [[paracrystalline]] arrays of [[actin filaments]]. Tubercles are numerous, fairly regularly arranged, rounded protuberances.
==Functions==
The tegument is the host-parasite interface, and metabolically active body covering performing all the vital activities such as protection, absorption and secretion. The [[glycocalyx]] is responsible for inhibition of the host [[digestive enzymes]], absorption of [[cations]] and [[bile]] salts, and enhancement of the host [[amylase]] activity.<ref name="ch"/> The [[glycosaminoglycan|acidic glycosaminoglycans]] of the glycocalyx are specific for inhibiting a number of digestive enzymes of the host.<ref name="Bog"/> The microtriches in [[cestodes]], and pits and spines in [[trematodes]] increase the surface area of the teguments for enhanced absorption of nutrients. In addition, they act as [[sensory organs]] for detecting the surrounding environmental cues. The capacity of the tegument to absorb [[exogenous]] materials is proportional to the number and extent of pits or [[microtriches]] and the number of [[mitochondria]] in the distal [[cytoplasm]].<ref>Smyth JD, Halton DW (1983). ''[https://books.google.com/books?id=WyM4AAAAIAAJ&dq=tegument&pg=PA8 The Physiology of Trematodes]''. Cambridge University Press, UK, pp. {{ISBN|0-521-22283-4}}</ref>
== See also ==
* [[Platyhelminthes]]
* [[Trematoda]]
* [[Cestoda]]
== References ==
{{Reflist}}
== External links ==
* [https://web.archive.org/web/20100405014627/http://www.path.cam.ac.uk/~schisto/general_parasitology/parasitology_cestodes_tegument.html Schistosomiasis Research Group at University of Cambridge]
* [https://web.archive.org/web/20090312071406/http://parasitology.informatik.uni-wuerzburg.de/login/n/h/1111.html Parasitology Informatik]
* [https://web.archive.org/web/20100109230055/http://www.aber.ac.uk/~mpgwww/Edu/Cestodes/CestTxt.html The Parasitology Group at Aberystwyth University]
* [https://web.archive.org/web/20100719163209/http://bioweb.uwlax.edu/zoolab/Lab-4a/Class-Trematoda-1.htm Bioweb]
[[Category:Platyhelminth anatomy]]