Microtriches
Encyclopedia
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. They are different from typical microvilli in that they contain conspicuous electron dense materials at the tip. Due to their morphological variation they make up unique defining structures in cestodes. Since cestodes are devoid of any digestive and excretory system
s, the tegument with its microtriches is the principal site of absorption and secretion. In fact the tegument highly resembles the gut
of animals turned inside out.
in different species
of tapeworms, and serve as an identifying character among the members of Eucestoda
. They are also of special interest in pharmacology as they are the basic interface of the tapeworm with its surrounding, thus serve as the primary site of absorption of nutrients and the target site of anthelmintics.
Though microtriches have been described for several decades, the consensus terminology for the structure was made only at the turn of 21st century. Standardised terms were resolved based on discussions that occurred at the International Workshops on Cestode Systematics in Storrs
, Connecticut
, USA in 2002, in Ceské Budejovice
, Czech Republic
in 2005 and in Smolenice
, Slovakia
in 2008. The following terms were endorsed for the components of each microtrix: the distal, electron-dense portion is the "cap", the proximal more electron-lucent region is the "base", and these two parts are separated from one another by the "baseplate". The base is composed of, among other elements, microfilaments, while the cap is composed of cap tubules. The electron-lucent central portion of the base is referred to as the "core". The core may be surrounded by an electron-dense tunic. The entire microthrix is enveloped by a plasma membrane, the external layer of which is referred to as the glycocalyx
. Two distinct sizes of microtriches are recognised: those < or = 200 nm in basal width, termed "filitriches", and those >200 nm in basal width, termed "spinitriches". Filitriches are considered to occur in three lengths: papilliform (< or = 2 times as long as wide), acicular (2-6 times as long as wide), and capilliform (>6 times as long as wide). Spinitriches are much more variable in form.
s, therefore, the tegument with its microtriches constitute the principal site of absorption of nutrients and elimination of waste materials. Moreover the microtriches are the primary structures for host
-parasite interface, and are metabolically active
performing all the vital activities such as sensory, absorptive and secretory functions. Thus their structural significance is clearly to amplify the total surface area of the tegument. The surface carbohydrate
complex called glycocalyx
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 nutrient
s. In addition, they act as sensory organs for detecting the surrounding environmental cues and primary target site of anthelmintic drugs
. 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.
Tegument (Helminth)
Tegument 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...
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. They are different from typical microvilli in that they contain conspicuous electron dense materials at the tip. Due to their morphological variation they make up unique defining structures in cestodes. 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 is the principal site of absorption and secretion. 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.
Structure
The microtriches are fine cylindrical tubular filaments, with smooth rounded ends, and arranged in rows corresponding to the regular ridges of the tegument. Microtriches are documented to exhibit wide range of morphologyMorphology (biology)
In biology, morphology is a branch of bioscience dealing with the study of the form and structure of organisms and their specific structural features....
in different 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...
of tapeworms, and serve as an identifying character among the members of Eucestoda
Eucestoda
Eucestoda is the larger of the two subclasses of flatworms in the class Cestoda. Its larvae are hexacanth in contrast to the decacanth Cestodaria. All species of the Eucestoda are parasites...
. They are also of special interest in pharmacology as they are the basic interface of the tapeworm with its surrounding, thus serve as the primary site of absorption of nutrients and the target site of anthelmintics.
Though microtriches have been described for several decades, the consensus terminology for the structure was made only at the turn of 21st century. Standardised terms were resolved based on discussions that occurred at the International Workshops on Cestode Systematics in Storrs
Storrs, Connecticut
Storrs is a census-designated place and part of the town of Mansfield, Connecticut located in eastern Tolland County. The population was 10,996 at the 2000 census...
, Connecticut
Connecticut
Connecticut is a state in the New England region of the northeastern United States. It is bordered by Rhode Island to the east, Massachusetts to the north, and the state of New York to the west and the south .Connecticut is named for the Connecticut River, the major U.S. river that approximately...
, USA in 2002, in Ceské Budejovice
Ceské Budejovice
České Budějovice is a city in the Czech Republic. It is the largest city in the South Bohemian Region and is the political and commercial capital of the region and centre of the Roman Catholic Diocese of České Budějovice and of the University of South Bohemia and the Academy of Sciences...
, Czech Republic
Czech Republic
The Czech Republic is a landlocked country in Central Europe. The country is bordered by Poland to the northeast, Slovakia to the east, Austria to the south, and Germany to the west and northwest....
in 2005 and in Smolenice
Smolenice
Smolenice is a village and municipality of Trnava District in the Trnava Region of Slovakia, on the foothills of the Little Carpathians. It is 60 km northeast of Bratislava and 25 km northwest of Trnava...
, Slovakia
Slovakia
The Slovak Republic is a landlocked state in Central Europe. It has a population of over five million and an area of about . Slovakia is bordered by the Czech Republic and Austria to the west, Poland to the north, Ukraine to the east and Hungary to the south...
in 2008. The following terms were endorsed for the components of each microtrix: the distal, electron-dense portion is the "cap", the proximal more electron-lucent region is the "base", and these two parts are separated from one another by the "baseplate". The base is composed of, among other elements, microfilaments, while the cap is composed of cap tubules. The electron-lucent central portion of the base is referred to as the "core". The core may be surrounded by an electron-dense tunic. The entire microthrix is enveloped by a plasma membrane, the external layer of which is referred to 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...
. Two distinct sizes of microtriches are recognised: those < or = 200 nm in basal width, termed "filitriches", and those >200 nm in basal width, termed "spinitriches". Filitriches are considered to occur in three lengths: papilliform (< or = 2 times as long as wide), acicular (2-6 times as long as wide), and capilliform (>6 times as long as wide). Spinitriches are much more variable in form.
Functions
All cestodes lack digestive and excretory systemExcretory 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, therefore, the tegument with its microtriches constitute the principal site of absorption of nutrients and elimination of waste materials. Moreover the microtriches are the primary structures for 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, and are metabolically active
Metabolism
Metabolism is the set of chemical reactions that happen in the cells of living organisms to sustain life. These processes allow organisms to grow and reproduce, maintain their structures, and respond to their environments. Metabolism is usually divided into two categories...
performing all the vital activities such as sensory, absorptive and secretory functions. Thus their structural significance is clearly to amplify the total surface area of the tegument. The surface carbohydrate
Carbohydrate
A carbohydrate is an organic compound with the empirical formula ; that is, consists only of carbon, hydrogen, and oxygen, with a hydrogen:oxygen atom ratio of 2:1 . However, there are exceptions to this. One common example would be deoxyribose, a component of DNA, which has the empirical...
complex called 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...
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
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...
are specific for inhibiting a number of digestive enzymes of the host. The microtriches in cestodes, and pits and 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...
in trematodes increase the surface area of the teguments for enhanced absorption of nutrient
Nutrient
A nutrient is a chemical that an organism needs to live and grow or a substance used in an organism's metabolism which must be taken in from its environment. They are used to build and repair tissues, regulate body processes and are converted to and used as energy...
s. In addition, they act as sensory organs for detecting the surrounding environmental cues and primary target site of anthelmintic drugs
Anthelmintic
Anthelmintics or antihelminthics are drugs that expel parasitic worms from the body, by either stunning or killing them. They may also be called vermifuges or vermicides .-Pharmaceutical classes:...
. 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.