Tegument is a term in

helminthology Helminthology is the study of parasitic worms (helminths). The field studies the Taxonomy (biology), taxonomy of helminths and their effects on their host (biology), hosts. The origin of the first compound of the word is the Greek ''wikt:ἕλ� ...

for the outer body covering of members of the phylum

Platyhelminthes The flatworms, flat worms, Platyhelminthes, or platyhelminths (from the Greek πλατύ, ''platy'', meaning "flat" and ἕλμινς (root: ἑλμινθ-), ''helminth-'', meaning "worm") are a phylum of relatively simple bilaterian, unsegme ...

. The name is derived from a

Latin Latin (, or , ) is a classical language belonging to the Italic branch of the Indo-European languages. Latin was originally a dialect spoken in the lower Tiber area (then known as Latium) around present-day Rome, but through the power of the ...

word ''tegumentum'' or ''tegere'', meaning "to cover". It is characteristic of

flatworms The flatworms, flat worms, Platyhelminthes, or platyhelminths (from the Greek πλατύ, ''platy'', meaning "flat" and ἕλμινς (root: ἑλμινθ-), ''helminth-'', meaning "worm") are a phylum of relatively simple bilaterian, unsegment ...

including the broad groups of

tapeworms Cestoda is a class of parasitic worms in the flatworm phylum (Platyhelminthes). Most of the species—and the best-known—are those in the subclass Eucestoda; they are ribbon-like worms as adults, known as tapeworms. Their bodies consist of ...

and flukes. Once considered to be a non-living component, it is now known to be a dynamic cellular structure. In fact it is a living structure consisting of proteins,

lipids Lipids are a broad group of naturally-occurring molecules which includes fats, waxes, sterols, fat-soluble vitamins (such as vitamins A, D, E and K), monoglycerides, diglycerides, phospholipids, and others. The functions of lipids include ...

, carbohydrates and RNA. It forms the protective layer and the host-

parasite Parasitism is a close relationship between species, where one organism, the parasite, lives on or inside another organism, the host, causing it some harm, and is adapted structurally to this way of life. The entomologist E. O. Wilson has ...

interface of the

worms Worms may refer to: *Worm, an invertebrate animal with a tube-like body and no limbs Places *Worms, Germany Worms () is a city in Rhineland-Palatinate, Germany, situated on the Upper Rhine about south-southwest of Frankfurt am Main. It had ...

, serving both secretory and absorptive functions.Cheng TC (1986). ''General Parasitology, 2nd edn''. Academic Press, Division of Hardcourt Brace & Company, USA, pp. 253-2546.

Structure and composition

The fine structure of tegument is essentially the same in both the

cestodes Cestoda is a class of parasitic worms in the flatworm phylum (Platyhelminthes). Most of the species—and the best-known—are those in the subclass Eucestoda; they are ribbon-like worms as adults, known as tapeworms. Their bodies consist of man ...

and

trematodes Trematoda is a class of flatworms known as flukes. They are obligate internal parasites with a complex life cycle requiring at least two hosts. The intermediate host, in which asexual reproduction occurs, is usually a snail. The definitive host ...

. A typical tegument is 7-16 μm thick, with distinct layers. It is a

syncytium A syncytium (; plural syncytia; from Greek: σύν ''syn'' "together" and κύτος ''kytos'' "box, i.e. cell") or symplasm is a multinucleate cell which can result from multiple cell fusions of uninuclear cells (i.e., cells with a single nucleu ...

consisting of multinucleated tissues with no distinct

cell Cell most often refers to: * Cell (biology), the functional basic unit of life Cell may also refer to: Locations * Monastic cell, a small room, hut, or cave in which a religious recluse lives, alternatively the small precursor of a monastery ...

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 macromolecules known as the

glycocalyx The glycocalyx, also known as the pericellular matrix, is a glycoprotein and glycolipid covering that surrounds the cell membranes of bacteria, epithelial cells, and other cells. In 1970, Martinez-Palomo discovered the cell coating in animal c ...

, that varies in thickness from one

species In biology, a species is the basic unit of classification and a taxonomic rank of an organism, as well as a unit of biodiversity. A species is often defined as the largest group of organisms in which any two individuals of the appropriate s ...

to another. The distal

cytoplasm In cell biology, the cytoplasm is all of the material within a eukaryotic cell, enclosed by the cell membrane, except for the cell nucleus. The material inside the nucleus and contained within the nuclear membrane is termed the nucleoplasm. ...

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 microtubules. The proximal cytoplasm contains nuclei, endoplasmic reticulum, Golgi complex, mitochondria, ribosomes, glycogen deposits, and numerous vesicles. 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.Bogitsh BJ, Carter CE, Oeltman TN (2005).
Human Parasitology, 3rd Edition
'. Academic Press, pp. 177-179. A large number of important enzymes has been detected in the tegument.

Glutathione S-transferase Glutathione ''S''-transferases (GSTs), previously known as ligandins, are a family of eukaryotic and prokaryotic phase II metabolic isozymes best known for their ability to catalyze the conjugation of the reduced form of glutathione (GSH) ...

, ATP diphosphorylase, alkaline and acid phosphatases, β-glucuronidase, amino

peptidase A protease (also called a peptidase, proteinase, or proteolytic enzyme) is an enzyme that catalyzes (increases reaction rate or "speeds up") proteolysis, breaking down proteins into smaller polypeptides or single amino acids, and spurring the for ...

acetylcholine esterase Acetylcholinesterase (HGNC symbol ACHE; EC 3.1.1.7; systematic name acetylcholine acetylhydrolase), also known as AChE, AChase or acetylhydrolase, is the primary cholinesterase in the body. It is an enzyme that catalyzes the breakdown of acet ...

phosphofructokinase Phosphofructokinase (PFK) is a kinase enzyme that phosphorylates fructose 6-phosphate in glycolysis. Function The enzyme-catalysed transfer of a phosphoryl group from ATP is an important reaction in a wide variety of biological processes. ...

, glucose transporters, serine hydrolases and several glycolytic enzymes have been detected with their biological roles. 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 Microtriches (singular microtrix) are the highly specialized microvilli covering the entire surface of the tegument of cestodes. They are fine hair-like filaments distributed throughout the surface of the body, both unique to and ubiquitous among ...

", 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 and

excretory system The excretory system is a passive biological system that removes excess, unnecessary materials from the body fluids of an organism, so as to help maintain internal chemical homeostasis and prevent damage to the body. The dual function of excreto ...

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 of

animals Animals are multicellular, eukaryotic organisms in the biological kingdom Animalia. With few exceptions, animals consume organic material, breathe oxygen, are able to move, can reproduce sexually, and go through an ontogenetic stage in ...

turned inside out. In trematodes the tegument contains a number of invaginations or surface pits, and is externally lined with minute

tubercle In anatomy, a tubercle (literally 'small tuber', Latin for 'lump') is any round nodule, small eminence, or warty outgrowth found on external or internal organs of a plant or an animal. In plants A tubercle is generally a wart-like projection ...

s among which are dispersed bristle-like projections called " spines". Spines are embedded in the basal lamina and the tip is finely pointed to the external surface. They are made up of

paracrystalline In materials science, paracrystalline materials are defined as having short- and medium-range ordering in their lattice (similar to the liquid crystal phases) but lacking crystal-like long-range ordering at least in one direction. Origin and ...

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

is responsible for inhibition of the host

digestive enzymes Digestive enzymes are a group of enzymes that break down polymeric macromolecules into their smaller building blocks, in order to facilitate their absorption into the cells of the body. Digestive enzymes are found in the digestive tracts of anima ...

, absorption of

cations An ion () is an atom or molecule with a net electrical charge. The charge of an electron is considered to be negative by convention and this charge is equal and opposite to the charge of a proton, which is considered to be positive by con ...

and bile salts, and enhancement of the host

amylase An amylase () is an enzyme that catalyses the hydrolysis of starch (Latin ') into sugars. Amylase is present in the saliva of humans and some other mammals, where it begins the chemical process of digestion. Foods that contain large amounts of ...

activity. The acidic glycosaminoglycans of the glycocalyx are specific for inhibiting a number of digestive enzymes of the host. The microtriches in

, and pits and spines in

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

and the number of mitochondria in the distal

.Smyth JD, Halton DW (1983).
The Physiology of Trematodes
'. Cambridge University Press, UK, pp.

References

{{Reflist

External links

Schistosomiasis Research Group at University of Cambridge

Platyhelminth anatomy

Structure and composition

Functions

See also

References

External links