Peritrophic matrix
Encyclopedia
The peritrophic matrix or peritrophic membrane is a semi-permeable, non-cellular structure which surrounds the food bolus
in an organism’s midgut
. Although they are often found in insect
s, peritrophic matrixes are found in seven different phyla
. The peritrophic matrix serves several functions, including improvement of digestion
, protection against mechanical and chemical damage and serving as a barrier to infection by pathogen
s.
microfibrils, (3–13% of matrix mass), and species specific proteins (20–55%) embedded in a proteoglycan
matrix. The peritrophic matrix also includes very small pores which allow for passage of small molecules into and out of the matrix. Thus, due to size limitations (pores reach a maximum size of 10 nm) larger, unwanted materials taken in while feeding are trapped and excreted
along with the matrix.
s that produce a peritrophic matrix. In type I formation, the peritrophic matrix is secreted by the entire midgut, and is formed simply by delamination from the surface of the midgut epithelium
. Type I formation usually occurs as a response to feeding
, but can also be produced continually. When formed in response to feeding, a single matrix is secreted by the midgut epithelium. This matrix surrounds the food bolus and is later excreted along with unwanted materials present in the food bolus after digestion. When formed continually, as in the insect family Acrididae
(locusts), multiple peritrophic matrixes are secreted and surround the food bolus, creating a peritrophic envelope. When no food bolus is present, peritrophic matrixes that are secreted are rapidly passed in excrement.
technique, and is found only in some families of the diptera
, dermaptera, embioptera
and lepidoptera
orders of insects. In type II formation, the peritrophic matrix is produced by a specialized group of cells present on the proventriculus
of the anterior midgut. Type II formation is a continuous process which is carried out regardless of the presence or absence of a food bolus. Thus, the peritrophic matrix is secreted as an unbroken, concentric, “sleeve like” structure. Although the peritrophic matrix is secreted continually, the presence of a food bolus significantly increases the rate of production. In addition, the presence of a food bolus stimulates the production of multiple matrixes which surround the bolus. Following the secretion of a primary peritrophic matrix, subsequent matrixes are secreted underneath the first matrix to create a layered peritrophic envelope.
. Following feeding, the food bolus is surrounded by the peritrophic matrix, effectively isolating it from the midgut
epithelium
. This isolation creates two distinct compartments within the midgut, the endoperitrophic space and ectoperitrophic space. This compartmentalization of the midgut provides three general advantages: prevention of non-specific binding of undigested material to the epithelium wall, conservation and concentration of enzyme
s and substrates
and rapid removal of indigestible molecules.
Prevention of non-specific binding is particularly important, as it increases the efficiency of the absorption process by filtering out undigested material which would otherwise block access to the midgut epithelium
. Due to the small pore size of the matrix, only small molecules which have been broken down by enzymes or can already be effectively absorbed come in contact with the midgut epithelium. The remaining materials, undigested food and unwanted molecules, are kept within the matrix until they can be broken down by enzyme
s or excreted.
Concentrating enzymes and food substrate within the endoperitrophic space significantly decreases the time required for digestion in the midgut. In addition, since enzymes are small enough to easily move into and out of the peritrophic matrix, they are rarely lost when the matrix, along with its contents still in the endoperitrophic space, is excreted. A counterflow of fluid in the ecoperitrophic space also helps recycle enzymes, thus maximizing their efficacy.
The presence of a peritrophic matrix significantly simplifies the excretion process. Rather than having to continually sift through a mixture of digestible and unwanted molecules, digestible molecules are quickly broken down by enzymes, removed from the matrix and absorbed. Once the digestive process is completed, unwanted molecules are kept confined within the endoperitrophic space and excreted along with the matrix.
strains up to 500 mmH2O. This capacity to expand prevents the food bolus from rupturing the delicate epithelial layer while assisting the passage of food through the gut.
s are too large to pass through the small pores of the peritrophic matrix. For example, some insects that are resistant to the insecticide
DDT
shed large amounts of the toxin in the peritrophic matrix. In addition, some smaller toxins bind with specific surface proteins present in the peritrophic matrix. This binding is particularly important for blood-feeding insects. Heme groups, which are components of hemoglobin
, an oxygen carrying protein present in vertebrate blood, act as strong oxidizers
in insects. Although this oxidizing agent
is safe in vertebrates, it is very damaging to insects. However, heme
groups ingested in a blood meal bind to proteins on the peritrophic matrix, enabling insects to safely feed on blood.
, also depend on the peritrophic matrix to filter out the disease agents, which are often too large to fit through the matrix pores. This benefit in particular is thought to be an important driving force in the evolution of peritrophic matrixes, as many insects feeding on foods with low pathogen levels lack the ability to produce a peritrophic matrix. This trend is highlighted by mosquitoes, as blood-feeding female mosquitoes produce a peritrophic matrix while nectar-feeding males do not. A significant trend can also be observed in the type of peritrophic matrix produced by blood-feeding insects that are capable of transmitting disease. The majority of blood-feeding insects that are good disease vectors produce a type I matrix. In comparison, blood-feeding insects that produce a type II matrix, which provides a more impenetrable barrier to pathogens, are rarely disease vectors.
and arbovirus
es (arthropod borne viruses) are transmitted to the mosquito in their infective form and are able to immediately invade mosquito tissue. However, other pathogens such as the malaria protozoan must first develop into an infective stage within the midgut before invading other tissues. These pathogens secrete chitinase
and proteinase enzymes which dissolve the chitin microfibrils and proteins present in the peritrophic matrix. These enzymes open large holes in the membrane, allowing the pathogen to infect the epithelium and other tissues in the insect.
Bolus (digestion)
In digestion, a bolus is a mass of food that has been chewed at the point of swallowing. Once a bolus reaches the stomach, digestion begins....
in an organism’s midgut
Midgut
The midgut is the portion of the embryo from which most of the intestines develop. After it bends around the superior mesenteric artery, it is called the "midgut loop"...
. Although they are often found in insect
Insect
Insects are a class of living creatures within the arthropods that have a chitinous exoskeleton, a three-part body , three pairs of jointed legs, compound eyes, and two antennae...
s, peritrophic matrixes are found in seven different phyla
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....
. The peritrophic matrix serves several functions, including improvement of digestion
Digestion
Digestion is the mechanical and chemical breakdown of food into smaller components that are more easily absorbed into a blood stream, for instance. Digestion is a form of catabolism: a breakdown of large food molecules to smaller ones....
, protection against mechanical and chemical damage and serving as a barrier to infection by pathogen
Pathogen
A pathogen gignomai "I give birth to") or infectious agent — colloquially, a germ — is a microbe or microorganism such as a virus, bacterium, prion, or fungus that causes disease in its animal or plant host...
s.
Chemical composition and structure
The peritrophic matrix is composed of regularly arranged chitinChitin
Chitin n is a long-chain polymer of a N-acetylglucosamine, a derivative of glucose, and is found in many places throughout the natural world...
microfibrils, (3–13% of matrix mass), and species specific proteins (20–55%) embedded in a proteoglycan
Proteoglycan
Proteoglycans are proteins that are heavily glycosylated. The basic proteoglycan unit consists of a "core protein" with one or more covalently attached glycosaminoglycan chain. The point of attachment is a Ser residue to which the glycosaminoglycan is joined through a tetrasaccharide bridge...
matrix. The peritrophic matrix also includes very small pores which allow for passage of small molecules into and out of the matrix. Thus, due to size limitations (pores reach a maximum size of 10 nm) larger, unwanted materials taken in while feeding are trapped and excreted
Excretion
Excretion is the process by which waste products of metabolism and other non-useful materials are eliminated from an organism. This is primarily carried out by the lungs, kidneys and skin. This is in contrast with secretion, where the substance may have specific tasks after leaving the cell...
along with the matrix.
Type I
Type I formation of a peritrophic matrix is thought to be the ancestral method, and is found in the majority of organismOrganism
In biology, an organism is any contiguous living system . In at least some form, all organisms are capable of response to stimuli, reproduction, growth and development, and maintenance of homoeostasis as a stable whole.An organism may either be unicellular or, as in the case of humans, comprise...
s that produce a peritrophic matrix. In type I formation, the peritrophic matrix is secreted by the entire midgut, and is formed simply by delamination from the surface of the midgut epithelium
Epithelium
Epithelium is one of the four basic types of animal tissue, along with connective tissue, muscle tissue and nervous tissue. Epithelial tissues line the cavities and surfaces of structures throughout the body, and also form many glands. Functions of epithelial cells include secretion, selective...
. Type I formation usually occurs as a response to feeding
Feeding
Feeding is the process by which organisms, typically animals, obtain food. Terminology often uses either the suffix -vore from Latin vorare, meaning 'to devour', or phagy, from Greek φαγειν, meaning 'to eat'.-Evolutionary history:...
, but can also be produced continually. When formed in response to feeding, a single matrix is secreted by the midgut epithelium. This matrix surrounds the food bolus and is later excreted along with unwanted materials present in the food bolus after digestion. When formed continually, as in the insect family Acrididae
Acrididae
The Acrididae are the predominant family of grasshoppers, comprising some 10,000 of the 11,000 species of the entire suborder Caelifera. The Acrididae are best known because all locusts are of the Acrididae. The subfamily Oedipodinae is sometimes classified as a distinct family Oedipodidae in the...
(locusts), multiple peritrophic matrixes are secreted and surround the food bolus, creating a peritrophic envelope. When no food bolus is present, peritrophic matrixes that are secreted are rapidly passed in excrement.
Type II
Type II formation of a peritrophic matrix is considered to be a derivedDerived
In phylogenetics, a derived trait is a trait that is present in an organism, but was absent in the last common ancestor of the group being considered. This may also refer to structures that are not present in an organism, but were present in its ancestors, i.e. traits that have undergone secondary...
technique, and is found only in some families of the diptera
Diptera
Diptera , or true flies, is the order of insects possessing only a single pair of wings on the mesothorax; the metathorax bears a pair of drumstick like structures called the halteres, the remnants of the hind wings. It is a large order, containing an estimated 240,000 species, although under half...
, dermaptera, embioptera
Embioptera
The order Embioptera, commonly known as webspinners, are a small group of mostly tropical and subtropical insects, classified under the subclass Pterygota. The order has also been referred to as Embiodea or Embiidina...
and lepidoptera
Lepidoptera
Lepidoptera is a large order of insects that includes moths and butterflies . It is one of the most widespread and widely recognizable insect orders in the world, encompassing moths and the three superfamilies of butterflies, skipper butterflies, and moth-butterflies...
orders of insects. In type II formation, the peritrophic matrix is produced by a specialized group of cells present on the proventriculus
Proventriculus
The proventriculus is part of the digestive system of birds, invertebrates and insects.-Birds:The proventriculus is a standard part of avian anatomy...
of the anterior midgut. Type II formation is a continuous process which is carried out regardless of the presence or absence of a food bolus. Thus, the peritrophic matrix is secreted as an unbroken, concentric, “sleeve like” structure. Although the peritrophic matrix is secreted continually, the presence of a food bolus significantly increases the rate of production. In addition, the presence of a food bolus stimulates the production of multiple matrixes which surround the bolus. Following the secretion of a primary peritrophic matrix, subsequent matrixes are secreted underneath the first matrix to create a layered peritrophic envelope.
Improve digestion
In many organisms the primary function of the peritrophic matrix is to improve digestionDigestion
Digestion is the mechanical and chemical breakdown of food into smaller components that are more easily absorbed into a blood stream, for instance. Digestion is a form of catabolism: a breakdown of large food molecules to smaller ones....
. Following feeding, the food bolus is surrounded by the peritrophic matrix, effectively isolating it from the midgut
Midgut
The midgut is the portion of the embryo from which most of the intestines develop. After it bends around the superior mesenteric artery, it is called the "midgut loop"...
epithelium
Epithelium
Epithelium is one of the four basic types of animal tissue, along with connective tissue, muscle tissue and nervous tissue. Epithelial tissues line the cavities and surfaces of structures throughout the body, and also form many glands. Functions of epithelial cells include secretion, selective...
. This isolation creates two distinct compartments within the midgut, the endoperitrophic space and ectoperitrophic space. This compartmentalization of the midgut provides three general advantages: prevention of non-specific binding of undigested material to the epithelium wall, conservation and concentration of enzyme
Enzyme
Enzymes are proteins that catalyze chemical reactions. In enzymatic reactions, the molecules at the beginning of the process, called substrates, are converted into different molecules, called products. Almost all chemical reactions in a biological cell need enzymes in order to occur at rates...
s and substrates
Substrate (biochemistry)
In biochemistry, a substrate is a molecule upon which an enzyme acts. Enzymes catalyze chemical reactions involving the substrate. In the case of a single substrate, the substrate binds with the enzyme active site, and an enzyme-substrate complex is formed. The substrate is transformed into one or...
and rapid removal of indigestible molecules.
Prevention of non-specific binding is particularly important, as it increases the efficiency of the absorption process by filtering out undigested material which would otherwise block access to the midgut epithelium
Epithelium
Epithelium is one of the four basic types of animal tissue, along with connective tissue, muscle tissue and nervous tissue. Epithelial tissues line the cavities and surfaces of structures throughout the body, and also form many glands. Functions of epithelial cells include secretion, selective...
. Due to the small pore size of the matrix, only small molecules which have been broken down by enzymes or can already be effectively absorbed come in contact with the midgut epithelium. The remaining materials, undigested food and unwanted molecules, are kept within the matrix until they can be broken down by enzyme
Enzyme
Enzymes are proteins that catalyze chemical reactions. In enzymatic reactions, the molecules at the beginning of the process, called substrates, are converted into different molecules, called products. Almost all chemical reactions in a biological cell need enzymes in order to occur at rates...
s or excreted.
Concentrating enzymes and food substrate within the endoperitrophic space significantly decreases the time required for digestion in the midgut. In addition, since enzymes are small enough to easily move into and out of the peritrophic matrix, they are rarely lost when the matrix, along with its contents still in the endoperitrophic space, is excreted. A counterflow of fluid in the ecoperitrophic space also helps recycle enzymes, thus maximizing their efficacy.
The presence of a peritrophic matrix significantly simplifies the excretion process. Rather than having to continually sift through a mixture of digestible and unwanted molecules, digestible molecules are quickly broken down by enzymes, removed from the matrix and absorbed. Once the digestive process is completed, unwanted molecules are kept confined within the endoperitrophic space and excreted along with the matrix.
Mechanical protection
Although the peritrophic matrix is a very thin layer of compounds (type I matrixes reach a maximum thickness of 20 µm, type II matrixes reach a maximum thickness of 2 µm), it can withstand mechanical pressurePressure
Pressure is the force per unit area applied in a direction perpendicular to the surface of an object. Gauge pressure is the pressure relative to the local atmospheric or ambient pressure.- Definition :...
strains up to 500 mmH2O. This capacity to expand prevents the food bolus from rupturing the delicate epithelial layer while assisting the passage of food through the gut.
Chemical protection
Much like indigestible molecules present in the food bolus, many toxinToxin
A toxin is a poisonous substance produced within living cells or organisms; man-made substances created by artificial processes are thus excluded...
s are too large to pass through the small pores of the peritrophic matrix. For example, some insects that are resistant to the insecticide
Insecticide
An insecticide is a pesticide used against insects. They include ovicides and larvicides used against the eggs and larvae of insects respectively. Insecticides are used in agriculture, medicine, industry and the household. The use of insecticides is believed to be one of the major factors behind...
DDT
DDT
DDT is one of the most well-known synthetic insecticides. It is a chemical with a long, unique, and controversial history....
shed large amounts of the toxin in the peritrophic matrix. In addition, some smaller toxins bind with specific surface proteins present in the peritrophic matrix. This binding is particularly important for blood-feeding insects. Heme groups, which are components of hemoglobin
Hemoglobin
Hemoglobin is the iron-containing oxygen-transport metalloprotein in the red blood cells of all vertebrates, with the exception of the fish family Channichthyidae, as well as the tissues of some invertebrates...
, an oxygen carrying protein present in vertebrate blood, act as strong oxidizers
Oxidizing agent
An oxidizing agent can be defined as a substance that removes electrons from another reactant in a redox chemical reaction...
in insects. Although this oxidizing agent
Oxidizing agent
An oxidizing agent can be defined as a substance that removes electrons from another reactant in a redox chemical reaction...
is safe in vertebrates, it is very damaging to insects. However, heme
Heme
A heme or haem is a prosthetic group that consists of an iron atom contained in the center of a large heterocyclic organic ring called a porphyrin. Not all porphyrins contain iron, but a substantial fraction of porphyrin-containing metalloproteins have heme as their prosthetic group; these are...
groups ingested in a blood meal bind to proteins on the peritrophic matrix, enabling insects to safely feed on blood.
Infection barrier
Organisms that take in food often infected with pathogens, such as blood-feeding insectsHematophagy
Hematophagy is the practice of certain animals of feeding on blood...
, also depend on the peritrophic matrix to filter out the disease agents, which are often too large to fit through the matrix pores. This benefit in particular is thought to be an important driving force in the evolution of peritrophic matrixes, as many insects feeding on foods with low pathogen levels lack the ability to produce a peritrophic matrix. This trend is highlighted by mosquitoes, as blood-feeding female mosquitoes produce a peritrophic matrix while nectar-feeding males do not. A significant trend can also be observed in the type of peritrophic matrix produced by blood-feeding insects that are capable of transmitting disease. The majority of blood-feeding insects that are good disease vectors produce a type I matrix. In comparison, blood-feeding insects that produce a type II matrix, which provides a more impenetrable barrier to pathogens, are rarely disease vectors.
Pathogen interference of the peritrophic matrix
Many pathogens are too large to fit through the small pores of the peritrophic matrix, and thus have evolved specialized mechanisms of evading being filtered out by the matrix. Since type I peritrophic matrixes are secreted in response to the presence of a food bolus in the midgut, some pathogens simply invade the epithelial cells before the matrix is excreted. Many helminth microfilariaMicrofilaria
The microfilaria is a stage in the life cycle of certain parasitic nematodes in the family Onchocercidae. In these species, the adults live in the circulatory system of vertebrates while the early larval stages develop in blood-feeding arthropod vectors...
and arbovirus
Arbovirus
Arbovirus is a term used to refer to a group of viruses that are transmitted by arthropod vectors. The word arbovirus is an acronym . Some arboviruses are able to cause emergent disease.-Transmission:...
es (arthropod borne viruses) are transmitted to the mosquito in their infective form and are able to immediately invade mosquito tissue. However, other pathogens such as the malaria protozoan must first develop into an infective stage within the midgut before invading other tissues. These pathogens secrete chitinase
Chitinase
Chitinases are hydrolytic enzymes that break down glycosidic bonds in chitin. As chitin is a component of the cell walls of fungi and exoskeletal elements of some animals , chitinases are generally found in organisms that either need to reshape their own chitin or dissolve and digest the chitin of...
and proteinase enzymes which dissolve the chitin microfibrils and proteins present in the peritrophic matrix. These enzymes open large holes in the membrane, allowing the pathogen to infect the epithelium and other tissues in the insect.