Tegument (Helminth)
Encyclopedia
Tegument ˈtɛɡjəmənt is a terminology in helminthology
for the name of the outer body covering among members of the phylum
Platyhelminthes. The name is derived from a Latin
word tegumentum or tegere, meaning "to cover". It is characteristic of all flatworms including the broad groups of tapeworms 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, carbohydrates and RNA
. It forms the protective layer and the host
-parasite interface of the worms, serving both secretive
and absorptive functions.
consisting of multinucleated tissues with no distinct 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 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
.
A large number of important enzymes has been detected in the tegument. Glutathione S-transferase
, ATP diphosphorylase, alkaline and acid phosphatases
, β-glucorunidase, amino peptidase, acetylcholine esterase, phosphofructokinase
, 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
", 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
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 turned inside out.
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 "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.
is responsible for inhibition of the host digestive enzymes, absorption of cations and bile
salts, and enhancement of the host amylase
activity. The acidic glycosaminoglycans
of the glycocalyx are specific for inhibiting a number of digestive enzymes of the host. The microtriches in cestodes, and pits and spines in trematodes increase the surface area of the teguments for enhanced absorption of nutrients. It is well supported by a lot studies in cestodes and trematode. 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
.
Helminthology
Helminthology is the study of worms, especially parasitic worms. This field deals with the study of their taxonomy and the effect on their hosts....
for the name of the outer body covering among members of the phylum
Phylum
In biology, a phylum The term was coined by Georges Cuvier from Greek φῦλον phylon, "race, stock," related to φυλή phyle, "tribe, clan." is a taxonomic rank below kingdom and above class. "Phylum" is equivalent to the botanical term division....
Platyhelminthes. The name is derived from a Latin
Latin
Latin is an Italic language originally spoken in Latium and Ancient Rome. It, along with most European languages, is a descendant of the ancient Proto-Indo-European language. Although it is considered a dead language, a number of scholars and members of the Christian clergy speak it fluently, and...
word tegumentum or tegere, meaning "to cover". It is characteristic of all flatworms including the broad groups of tapeworms and flukes
Trematoda
Trematoda is a class within the phylum Platyhelminthes that contains two groups of parasitic flatworms, commonly referred to as "flukes".-Taxonomy and biodiversity:...
. Once considered to be a non-living component, it is now known to be a dynamic cellular structure
Cell (biology)
The cell is the basic structural and functional unit of all known living organisms. It is the smallest unit of life that is classified as a living thing, and is often called the building block of life. The Alberts text discusses how the "cellular building blocks" move to shape developing embryos....
. In fact it is a living structure consisting of proteins, lipids, carbohydrates and RNA
RNA
Ribonucleic acid , or RNA, is one of the three major macromolecules that are essential for all known forms of life....
. It forms the protective layer and the host
Host (biology)
In biology, a host is an organism that harbors a parasite, or a mutual or commensal symbiont, typically providing nourishment and shelter. In botany, a host plant is one that supplies food resources and substrate for certain insects or other fauna...
-parasite interface of the worms, serving both secretive
Secretion
Secretion is the process of elaborating, releasing, and oozing chemicals, or a secreted chemical substance from a cell or gland. In contrast to excretion, the substance may have a certain function, rather than being a waste product...
and absorptive functions.
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 syncytiumSyncytium
In biology, a syncytium is a large cell-like structure; filled with cytoplasm and containing many nuclei. Most cells in eukaryotic organisms have a single nucleus; syncytia are specialized forms used by various organisms.The term may also refer to cells that are connected by specialized membrane...
consisting of multinucleated tissues with no distinct cell
Cell (biology)
The cell is the basic structural and functional unit of all known living organisms. It is the smallest unit of life that is classified as a living thing, and is often called the building block of life. The Alberts text discusses how the "cellular building blocks" move to shape developing embryos....
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
Macromolecule
A macromolecule is a very large molecule commonly created by some form of polymerization. In biochemistry, the term is applied to the four conventional biopolymers , as well as non-polymeric molecules with large molecular mass such as macrocycles...
s known as the glycocalyx
Glycocalyx
Glycocalyx is a general term referring to extracellular polymeric material produced by some bacteria, epithelia and other cells. The slime on the outside of a fish is considered a glycocalyx. The term was initially applied to the polysaccharide matrix excreted by epithelial cells forming a...
, that varies in thickness from one species
Species
In biology, a species is one of the basic units of biological classification and a taxonomic rank. A species is often defined as a group of organisms capable of interbreeding and producing fertile offspring. While in many cases this definition is adequate, more precise or differing measures are...
to another. The distal cytoplasm
Cytoplasm
The cytoplasm is a small gel-like substance residing between the cell membrane holding all the cell's internal sub-structures , except for the nucleus. All the contents of the cells of prokaryote organisms are contained within the 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
Microtubule
Microtubules are a component of the cytoskeleton. These rope-like polymers of tubulin can grow as long as 25 micrometers and are highly dynamic. The outer diameter of microtubule is about 25 nm. Microtubules are important for maintaining cell structure, providing platforms for intracellular...
s. The proximal cytoplasm contains nuclei
Cell nucleus
In cell biology, the nucleus is a membrane-enclosed organelle found in eukaryotic cells. It contains most of the cell's genetic material, organized as multiple long linear DNA molecules in complex with a large variety of proteins, such as histones, to form chromosomes. The genes within these...
, endoplasmic reticulum
Endoplasmic reticulum
The endoplasmic reticulum is an organelle of cells in eukaryotic organisms that forms an interconnected network of tubules, vesicles, and cisternae...
, Golgi complex, mitochondria, ribosomes, glycogen deposits
Glycogen
Glycogen is a molecule that serves as the secondary long-term energy storage in animal and fungal cells, with the primary energy stores being held in adipose tissue...
, and numerous vesicles
Vesicle (biology)
A vesicle is a bubble of liquid within another liquid, a supramolecular assembly made up of many different molecules. More technically, a vesicle is a small membrane-enclosed sack that can store or transport substances. Vesicles can form naturally because of the properties of lipid membranes , or...
. The internal most layer is bounded by a layer of connective tissue
Connective tissue
"Connective tissue" is a fibrous tissue. It is one of the four traditional classes of tissues . Connective Tissue is found throughout the body.In fact the whole framework of the skeleton and the different specialized connective tissues from the crown of the head to the toes determine the form of...
known as the "basal lamina
Basal lamina
The basal lamina is a layer of extracellular matrix secreted by the epithelial cells, on which the epithelium sits. It is often confused with the basement membrane, and sometimes used inconsistently in the literature, see below....
". The basal lamina is followed by a thick layer of muscle
Muscle
Muscle is a contractile tissue of animals and is derived from the mesodermal layer of embryonic germ cells. Muscle cells contain contractile filaments that move past each other and change the size of the cell. They are classified as skeletal, cardiac, or smooth muscles. Their function is to...
.
A large number of important enzymes has been detected in the tegument. Glutathione S-transferase
Glutathione S-transferase
Enzymes of the glutathione S-transferase family are composed of many cytosolic, mitochondrial, and microsomal proteins. GSTs are present in eukaryotes and in prokaryotes, where they catalyze a variety of reactions and accept endogenous and xenobiotic substrates.GSTs can constitute up to 10% of...
, ATP diphosphorylase, alkaline and acid phosphatases
Phosphatase
A phosphatase is an enzyme that removes a phosphate group from its substrate by hydrolysing phosphoric acid monoesters into a phosphate ion and a molecule with a free hydroxyl group . This action is directly opposite to that of phosphorylases and kinases, which attach phosphate groups to their...
, β-glucorunidase, amino peptidase, acetylcholine esterase, phosphofructokinase
Phosphofructokinase
Phosphofructokinase-1 is the most important regulatory enzyme of glycolysis. It is an allosteric enzyme made of 4 subunits and controlled by many activators and inhibitors...
, glucose transporters, serine hydrolases and several glycolytic enzymes
Glycolysis
Glycolysis is the metabolic pathway that converts glucose C6H12O6, into pyruvate, CH3COCOO− + H+...
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
Microtriches 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 cestodes, giving the body surface a smooth and silky appearance...
", 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
Excretory system
The excretory system is a passive biological system that removes excess, unnecessary or dangerous materials from an organism, so as to help maintain homeostasis within the organism and prevent damage to the body. It is responsible for the elimination of the waste products of metabolism as well as...
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
Gut (zoology)
In zoology, the gut, also known as the alimentary canal or alimentary tract, is a tube by which bilaterian animals transfer food to the digestion organs. In large bilaterians the gut generally also has an exit, the anus, by which the animal disposes of solid wastes...
of animals turned inside out.
In trematodes the tegument contains a number of invaginations or surface pits, and is externally lined with minute tubercle
Tubercle
A tubercle is generally a wart-like projection, but it has slightly different meaning depending on which family of plants or animals it is used to refer to....
s among which are dispersed bristle-like projections called "spines
Spine (zoology)
A spine is a hard, thorny or needle-like structure which occurs on various animals. Animals such as porcupines and sea urchins grow spines as a self-defense mechanism. Spines are often formed of keratin...
". Spines are embedded in the basal lamina and the tip is finely pointed to the external surface. They are made up of paracrystalline
Paracrystalline
Paracrystalline materials are defined as having short and medium range ordering in their lattice but lacking long-range ordering at least in one direction....
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 glycocalyxGlycocalyx
Glycocalyx is a general term referring to extracellular polymeric material produced by some bacteria, epithelia and other cells. The slime on the outside of a fish is considered a glycocalyx. The term was initially applied to the polysaccharide matrix excreted by epithelial cells forming a...
is responsible for inhibition of the host digestive enzymes, absorption of cations and bile
Bile
Bile or gall is a bitter-tasting, dark green to yellowish brown fluid, produced by the liver of most vertebrates, that aids the process of digestion of lipids in the small intestine. In many species, bile is stored in the gallbladder and upon eating is discharged into the duodenum...
salts, and enhancement of the host amylase
Amylase
Amylase is an enzyme that catalyses the breakdown of starch into sugars. Amylase is present in human saliva, where it begins the chemical process of digestion. Food that contains much starch but little sugar, such as rice and potato, taste slightly sweet as they are chewed because amylase turns...
activity. The acidic glycosaminoglycans
Glycosaminoglycan
Glycosaminoglycans or mucopolysaccharides are long unbranched polysaccharides consisting of a repeating disaccharide unit. The repeating unit consists of a hexose or a hexuronic acid, linked to a hexosamine .-Production:Protein cores made in the rough endoplasmic reticulum are posttranslationally...
of the glycocalyx are specific for inhibiting a number of digestive enzymes of the host. The microtriches in cestodes, and pits and spines in trematodes increase the surface area of the teguments for enhanced absorption of nutrients. It is well supported by a lot studies in cestodes and trematode. In addition, they act as sensory organs for detecting the surrounding environmental cues. The capacity of the tegument to absorb exogenous
Exogenous
Exogenous refers to an action or object coming from outside a system. It is the opposite of endogenous, something generated from within the system....
materials is proportional to the number and extent of pits or microtriches
Microtriches
Microtriches 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 cestodes, giving the body surface a smooth and silky appearance...
and the number of mitochondria in the distal cytoplasm
Cytoplasm
The cytoplasm is a small gel-like substance residing between the cell membrane holding all the cell's internal sub-structures , except for the nucleus. All the contents of the cells of prokaryote organisms are contained within the cytoplasm...
.