In biology , tissue is an assembly of similar cells and their extracellular matrix from the same embryonic origin that together carry out a specific function. Tissues occupy a biological organizational level between cells and a complete organ . Accordingly, organs are formed by the functional grouping together of multiple tissues.
128-882: An infection is the invasion of tissues by pathogens , their multiplication, and the reaction of host tissues to the infectious agent and the toxins they produce. An infectious disease , also known as a transmissible disease or communicable disease , is an illness resulting from an infection. Infections can be caused by a wide range of pathogens , most prominently bacteria and viruses . Hosts can fight infections using their immune systems . Mammalian hosts react to infections with an innate response, often involving inflammation , followed by an adaptive response. Specific medications used to treat infections include antibiotics , antivirals , antifungals , antiprotozoals , and antihelminthics . Infectious diseases resulted in 9.2 million deaths in 2013 (about 17% of all deaths). The branch of medicine that focuses on infections
256-454: A prion . The benefits of identification, however, are often greatly outweighed by the cost, as often there is no specific treatment, the cause is obvious, or the outcome of an infection is likely to be benign . The diagnosis is aided by the presenting symptoms in any individual with an infectious disease, yet it usually needs additional diagnostic techniques to confirm the suspicion. Some signs are specifically characteristic and indicative of
384-421: A runny nose . In certain cases, infectious diseases may be asymptomatic for much or even all of their course in a given host. In the latter case, the disease may only be defined as a "disease" (which by definition means an illness) in hosts who secondarily become ill after contact with an asymptomatic carrier . An infection is not synonymous with an infectious disease, as some infections do not cause illness in
512-425: A colonization is often only a matter of circumstance. Non-pathogenic organisms can become pathogenic given specific conditions, and even the most virulent organism requires certain circumstances to cause a compromising infection. Some colonizing bacteria, such as Corynebacteria sp. and Viridans streptococci , prevent the adhesion and colonization of pathogenic bacteria and thus have a symbiotic relationship with
640-442: A critical point. This simultaneous collapse occurs, because pollinator species depend on each other when surviving under difficult conditions. Such a community-wide collapse, involving many pollinator species, can occur suddenly when increasingly harsh conditions pass a critical point and recovery from such a collapse might not be easy. The improvement in conditions needed for pollinators to recover could be substantially larger than
768-466: A disease and are called pathognomonic signs; but these are rare. Not all infections are symptomatic. In children the presence of cyanosis , rapid breathing, poor peripheral perfusion, or a petechial rash increases the risk of a serious infection by greater than 5 fold. Other important indicators include parental concern, clinical instinct, and temperature greater than 40 °C. Many diagnostic approaches depend on microbiological culture to isolate
896-454: A disease. This amplification of nucleic acid in infected tissue offers an opportunity to detect the infectious agent by using PCR. Third, the essential tools for directing PCR, primers , are derived from the genomes of infectious agents, and with time those genomes will be known if they are not already. Thus, the technological ability to detect any infectious agent rapidly and specifically is currently available. The only remaining blockades to
1024-743: A function is called cellular differentiation . Cells of meristematic tissue differentiate to form different types of permanent tissues. There are 2 types of permanent tissues: Simple permanent tissue is a group of cells which are similar in origin, structure, and function. They are of three types: Parenchyma (Greek, para – 'beside'; enchyma– infusion – 'tissue') is the bulk of a substance. In plants, it consists of relatively unspecialized living cells with thin cell walls that are usually loosely packed so that intercellular spaces are found between cells of this tissue. These are generally isodiametric, in shape. They contain small number of vacuoles or sometimes they even may not contain any vacuole. Even if they do so
1152-604: A function of providing mechanical support. They do not have inter-cellular spaces between them. Lignin deposition is so thick that the cell walls become stronger, rigid and impermeable to water, which are also known as a stone cells or sclereids. These tissues are mainly of two types: sclerenchyma fiber and sclereids. Sclerenchyma fiber cells have a narrow lumen and are long, narrow and unicellular. Fibers are elongated cells that are strong and flexible, often used in ropes. Sclereids have extremely thick cell walls and are brittle, and are found in nutshells and legumes. The entire surface of
1280-452: A further term in the formula, representing a saturation mechanism, to avoid this occurring. In 1989, David Hamilton Wright modified the above Lotka–Volterra equations by adding a new term, βM / K , to represent a mutualistic relationship. Wright also considered the concept of saturation, which means that with higher densities, there is a decrease in the benefits of further increases of the mutualist population. Without saturation, depending on
1408-422: A hospital stay. Lastly, a community-acquired infection is one in which the infection is acquired from a whole community. One manner of proving that a given disease is infectious, is to satisfy Koch's postulates (first proposed by Robert Koch ), which require that first, the infectious agent be identifiable only in patients who have the disease, and not in healthy controls, and second, that patients who contract
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#17327732280961536-531: A host with depressed resistance ( immunodeficiency ) or if they have unusual access to the inside of the body (for example, via trauma ). Opportunistic infection may be caused by microbes ordinarily in contact with the host, such as pathogenic bacteria or fungi in the gastrointestinal or the upper respiratory tract , and they may also result from (otherwise innocuous) microbes acquired from other hosts (as in Clostridioides difficile colitis ) or from
1664-498: A host. As bacterial and viral infections can both cause the same kinds of symptoms, it can be difficult to distinguish which is the cause of a specific infection. Distinguishing the two is important, since viral infections cannot be cured by antibiotics whereas bacterial infections can. There is a general chain of events that applies to infections, sometimes called the chain of infection or transmission chain . The chain of events involves several steps – which include
1792-430: A link between virulence and transmissibility. Diagnosis of infectious disease sometimes involves identifying an infectious agent either directly or indirectly. In practice most minor infectious diseases such as warts , cutaneous abscesses , respiratory system infections and diarrheal diseases are diagnosed by their clinical presentation and treated without knowledge of the specific causative agent. Conclusions about
1920-445: A net benefit. Mutualism is a common type of ecological interaction. Prominent examples are: Mutualism can be contrasted with interspecific competition , in which each species experiences reduced fitness, and exploitation , and with parasitism , in which one species benefits at the expense of the other. However, mutualism may evolve from interactions that began with imbalanced benefits, such as parasitism . The term mutualism
2048-518: A number of basic dyes due to the electrostatic attraction between negatively charged cellular molecules and the positive charge on the dye. A cell is normally transparent under a microscope, and using a stain increases the contrast of a cell with its background. Staining a cell with a dye such as Giemsa stain or crystal violet allows a microscopist to describe its size, shape, internal and external components and its associations with other cells. The response of bacteria to different staining procedures
2176-404: A particular pathogen at all (no matter how little) but also is often used in a sense implying a clinically apparent infection (in other words, a case of infectious disease). This fact occasionally creates some ambiguity or prompts some usage discussion; to get around this it is common for health professionals to speak of colonization (rather than infection ) when they mean that some of
2304-492: A pathogen from the appropriate clinical specimen. In a microbial culture, a growth medium is provided for a specific agent. A sample taken from potentially diseased tissue or fluid is then tested for the presence of an infectious agent able to grow within that medium. Many pathogenic bacteria are easily grown on nutrient agar , a form of solid medium that supplies carbohydrates and proteins necessary for growth, along with copious amounts of water. A single bacterium will grow into
2432-428: A pathogen. A fluorescence microscope is then used to detect fluorescently labeled antibodies bound to internalized antigens within clinical samples or cultured cells. This technique is especially useful in the diagnosis of viral diseases, where the light microscope is incapable of identifying a virus directly. Other microscopic procedures may also aid in identifying infectious agents. Almost all cells readily stain with
2560-431: A patient's blood or other body fluids for antigens or antibodies that indicate presence of a specific pathogen that the doctor suspects. Other techniques (such as X-rays , CAT scans , PET scans or NMR ) are used to produce images of internal abnormalities resulting from the growth of an infectious agent. The images are useful in detection of, for example, a bone abscess or a spongiform encephalopathy produced by
2688-466: A persistent infection by infecting different cells of the body. Some viruses once acquired never leave the body. A typical example is the herpes virus, which tends to hide in nerves and become reactivated when specific circumstances arise. Persistent infections cause millions of deaths globally each year. Chronic infections by parasites account for a high morbidity and mortality in many underdeveloped countries. For infecting organisms to survive and repeat
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#17327732280962816-476: A phenomenon that is used in Three Sisters farming . One researcher has proposed that the key advantage Homo sapiens had over Neanderthals in competing over similar habitats was the former's mutualism with dogs. The microbiota in the human intestine coevolved with the human species, and this relationship is considered to be a mutualism that is beneficial both to the human host and the bacteria in
2944-595: A plant trades food resources in the form of nectar or pollen for the service of pollen dispersal. However, daciniphilous Bulbophyllum orchid species trade sex pheromone precursor or booster components via floral synomones /attractants in a true mutualistic interactions with males of Dacini fruit flies (Diptera: Tephritidae: Dacinae). Phagophiles feed (resource) on ectoparasites , thereby providing anti-pest service, as in cleaning symbiosis . Elacatinus and Gobiosoma , genera of gobies , feed on ectoparasites of their clients while cleaning them. Zoochory
3072-402: A result of an infectious disease with immunosuppressive activity (such as with measles , malaria or HIV disease ). Primary pathogens may also cause more severe disease in a host with depressed resistance than would normally occur in an immunosufficient host. While a primary infection can practically be viewed as the root cause of an individual's current health problem, a secondary infection
3200-470: A result of their presence or activity within the normal, healthy host, and their intrinsic virulence (the severity of the disease they cause) is, in part, a necessary consequence of their need to reproduce and spread. Many of the most common primary pathogens of humans only infect humans, however, many serious diseases are caused by organisms acquired from the environment or that infect non-human hosts. Opportunistic pathogens can cause an infectious disease in
3328-417: A specific identification of an infectious agent only when such identification can aid in the treatment or prevention of the disease, or to advance knowledge of the course of an illness prior to the development of effective therapeutic or preventative measures. For example, in the early 1980s, prior to the appearance of AZT for the treatment of AIDS , the course of the disease was closely followed by monitoring
3456-535: A supporting tissue in stems of young plants. It provides mechanical support, elasticity, and tensile strength to the plant body. It helps in manufacturing sugar and storing it as starch. It is present in the margin of leaves and resists tearing effect of the wind. Sclerenchyma (Greek, Sclerous means hard and enchyma means infusion) consists of thick-walled, dead cells and protoplasm is negligible. These cells have hard and extremely thick secondary walls due to uniform distribution and high secretion of lignin and have
3584-536: A thin and elastic primary cell wall made of cellulose . They are compactly arranged without inter-cellular spaces between them. Each cell contains a dense cytoplasm and a prominent cell nucleus . The dense protoplasm of meristematic cells contains very few vacuoles . Normally the meristematic cells are oval, polygonal , or rectangular in shape. Meristematic tissue cells have a large nucleus with small or no vacuoles because they have no need to store anything, as opposed to their function of multiplying and increasing
3712-432: A visible mound on the surface of the plate called a colony , which may be separated from other colonies or melded together into a "lawn". The size, color, shape and form of a colony is characteristic of the bacterial species, its specific genetic makeup (its strain ), and the environment that supports its growth. Other ingredients are often added to the plate to aid in identification. Plates may contain substances that permit
3840-594: A wide range of stretch lengths. It is found in such organs as sea anemone tentacles and the body wall of sea cucumbers . Skeletal muscle contracts rapidly but has a limited range of extension. It is found in the movement of appendages and jaws. Obliquely striated muscle is intermediate between the other two. The filaments are staggered and this is the type of muscle found in earthworms that can extend slowly or make rapid contractions. In higher animals striated muscles occur in bundles attached to bone to provide movement and are often arranged in antagonistic sets. Smooth muscle
3968-508: Is a sequela or complication of that root cause. For example, an infection due to a burn or penetrating trauma (the root cause) is a secondary infection. Primary pathogens often cause primary infection and often cause secondary infection. Usually, opportunistic infections are viewed as secondary infections (because immunodeficiency or injury was the predisposing factor). Other types of infection consist of mixed, iatrogenic , nosocomial , and community-acquired infection. A mixed infection
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4096-480: Is a central element in human anatomy , and he considered organs as collections of often disparate tissues, rather than as entities in themselves". Although he worked without a microscope , Bichat distinguished 21 types of elementary tissues from which the organs of the human body are composed, a number later reduced by other authors. Mutualism (biology) Mutualism describes the ecological interaction between two or more species where each species has
4224-466: Is a living tissue of primary body like Parenchyma . Cells are thin-walled but possess thickening of cellulose , water and pectin substances ( pectocellulose ) at the corners where a number of cells join. This tissue gives tensile strength to the plant and the cells are compactly arranged and have very little inter-cellular spaces. It occurs chiefly in hypodermis of stems and leaves. It is absent in monocots and in roots. Collenchymatous tissue acts as
4352-505: Is active but does not produce noticeable symptoms may be called inapparent, silent, subclinical , or occult . An infection that is inactive or dormant is called a latent infection . An example of a latent bacterial infection is latent tuberculosis . Some viral infections can also be latent, examples of latent viral infections are any of those from the Herpesviridae family. The word infection can denote any presence of
4480-405: Is also known as conducting and vascular tissue. The common types of complex permanent tissue are: Xylem and phloem together form vascular bundles. Xylem (Greek, xylos = wood) serves as a chief conducting tissue of vascular plants. It is responsible for the conduction of water and inorganic solutes. Xylem consists of four kinds of cells: Xylem tissue is organised in a tube-like fashion along
4608-696: Is an equally important plant tissue as it also is part of the 'plumbing system' of a plant. Primarily, phloem carries dissolved food substances throughout the plant. This conduction system is composed of sieve-tube member and companion cells, that are without secondary walls. The parent cells of the vascular cambium produce both xylem and phloem. This usually also includes fibers, parenchyma and ray cells. Sieve tubes are formed from sieve-tube members laid end to end. The end walls, unlike vessel members in xylem, do not have openings. The end walls, however, are full of small pores where cytoplasm extends from cell to cell. These porous connections are called sieve plates. In spite of
4736-423: Is an infection that is caused by two or more pathogens. An example of this is appendicitis , which is caused by Bacteroides fragilis and Escherichia coli . The second is an iatrogenic infection. This type of infection is one that is transmitted from a health care worker to a patient. A nosocomial infection is also one that occurs in a health care setting. Nosocomial infections are those that are acquired during
4864-420: Is an initial site of infection from which organisms travel via the bloodstream to another area of the body. Among the many varieties of microorganisms , relatively few cause disease in otherwise healthy individuals. Infectious disease results from the interplay between those few pathogens and the defenses of the hosts they infect. The appearance and severity of disease resulting from any pathogen depend upon
4992-508: Is called an extracellular matrix . This matrix can be liquid or rigid. For example, blood contains plasma as its matrix and bone's matrix is rigid. Connective tissue gives shape to organs and holds them in place. Blood, bone, tendon, ligament, adipose, and areolar tissues are examples of connective tissues. One method of classifying connective tissues is to divide them into three types: fibrous connective tissue, skeletal connective tissue, and fluid connective tissue. Muscle cells (myocytes) form
5120-411: Is found in the walls of the uterus , bladder , intestines , stomach , oesophagus , respiratory airways , and blood vessels . Cardiac muscle is found only in the heart , allowing it to contract and pump blood through the body. Cells comprising the central nervous system and peripheral nervous system are classified as nervous (or neural) tissue. In the central nervous system, neural tissues form
5248-696: Is generalized beyond bacteria by Yamada et al. 2015's demonstration that undernourished Drosophila are heavily dependent on their fungal symbiont Issatchenkia orientalis for amino acids. Mutualisms are not static, and can be lost by evolution. Sachs and Simms (2006) suggest that this can occur via four main pathways: There are many examples of mutualism breakdown. For example, plant lineages inhabiting nutrient-rich environments have evolutionarily abandoned mycorrhizal mutualisms many times independently. Evolutionarily, headlice may have been mutualistic as they allow for early immunity to various body-louse borne disease; however, as these diseases became eradicated,
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5376-502: Is injured. All multicellular organisms are colonized to some degree by extrinsic organisms, and the vast majority of these exist in either a mutualistic or commensal relationship with the host. An example of the former is the anaerobic bacteria species, which colonizes the mammalian colon , and an example of the latter are the various species of staphylococcus that exist on human skin . Neither of these colonizations are considered infections. The difference between an infection and
5504-443: Is known as histology or, in connection with disease, as histopathology . Xavier Bichat is considered as the "Father of Histology". Plant histology is studied in both plant anatomy and physiology . The classical tools for studying tissues are the paraffin block in which tissue is embedded and then sectioned, the histological stain , and the optical microscope . Developments in electron microscopy , immunofluorescence , and
5632-453: Is most effectively applied to free-living species that encounter a number of individuals of the mutualist part in the course of their existences. Wright notes that models of biological mutualism tend to be similar qualitatively, in that the featured isoclines generally have a positive decreasing slope, and by and large similar isocline diagrams. Mutualistic interactions are best visualized as positively sloped isoclines, which can be explained by
5760-466: Is not an enzyme and has no metabolic function. Serological methods are highly sensitive, specific and often extremely rapid tests used to identify microorganisms. These tests are based upon the ability of an antibody to bind specifically to an antigen. The antigen, usually a protein or carbohydrate made by an infectious agent, is bound by the antibody. This binding then sets off a chain of events that can be visibly obvious in various ways, dependent upon
5888-424: Is referred to as infectious diseases . Infections are caused by infectious agents ( pathogens ) including: The signs and symptoms of an infection depend on the type of disease. Some signs of infection affect the whole body generally, such as fatigue , loss of appetite, weight loss, fevers , night sweats, chills, aches and pains. Others are specific to individual body parts, such as skin rashes , coughing , or
6016-404: Is referred to as colonization. Most humans are not easily infected. Those with compromised or weakened immune systems have an increased susceptibility to chronic or persistent infections. Individuals who have a suppressed immune system are particularly susceptible to opportunistic infections . Entrance to the host at host–pathogen interface , generally occurs through the mucosa in orifices like
6144-458: Is sometimes used to refer to mutualistic interactions that are not obligate. Symbiosis involves two species living in close physical contact over a long period of their existence and may be mutualistic, parasitic , or commensal , so symbiotic relationships are not always mutualistic, and mutualistic interactions are not always symbiotic. Despite a different definition between mutualism and symbiosis, they have been largely used interchangeably in
6272-477: Is somewhat variable. Most classification schemes combine a description of the cell-shape in the upper layer of the epithelium with a word denoting the number of layers: either simple (one layer of cells) or stratified (multiple layers of cells). However, other cellular features such as cilia may also be described in the classification system. Some common kinds of epithelium are listed below: Connective tissues are made up of cells separated by non-living material, which
6400-439: Is that microbial colonization is very common even in environments that humans think of as being nearly sterile . Because it is normal to have bacterial colonization, it is difficult to know which chronic wounds can be classified as infected and how much risk of progression exists. Despite the huge number of wounds seen in clinical practice, there are limited quality data for evaluated symptoms and signs. A review of chronic wounds in
6528-416: Is the dispersal of the seeds of plants by animals. This is similar to pollination in that the plant produces food resources (for example, fleshy fruit, overabundance of seeds) for animals that disperse the seeds (service). Plants may advertise these resources using colour and a variety of other fruit characteristics, e.g., scent. Fruit of the aardvark cucumber (Cucumis humifructus) is buried so deeply that
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#17327732280966656-402: Is the relationship between sea anemones and anemone fish in the family Pomacentridae : the anemones provide the fish with protection from predators (which cannot tolerate the stings of the anemone's tentacles) and the fish defend the anemones against butterflyfish (family Chaetodontidae ), which eat anemones. However, in common with many mutualisms, there is more than one aspect to it: in
6784-587: Is used in the taxonomic classification of microbes as well. Two methods, the Gram stain and the acid-fast stain, are the standard approaches used to classify bacteria and to diagnosis of disease. The Gram stain identifies the bacterial groups Bacillota and Actinomycetota , both of which contain many significant human pathogens. The acid-fast staining procedure identifies the Actinomycetota genera Mycobacterium and Nocardia . Biochemical tests used in
6912-418: Is used rather than primers for a specific infectious agent. This amplification step is followed by next-generation sequencing or third-generation sequencing , alignment comparisons , and taxonomic classification using large databases of thousands of pathogen and commensal reference genomes . Simultaneously, antimicrobial resistance genes within pathogen and plasmid genomes are sequenced and aligned to
7040-604: The Hirtella sp. tree in the same forests, but in this relationship, the tree has turned the tables on the ants. When the tree is ready to produce flowers, the ant abodes on certain branches begin to wither and shrink, forcing the occupants to flee, leaving the tree's flowers to develop free from ant attack. The term "species group" can be used to describe the manner in which individual organisms group together. In this non-taxonomic context one can refer to "same-species groups" and "mixed-species groups." While same-species groups are
7168-547: The Acacia plant. In the neotropics , the ant Myrmelachista schumanni makes its nest in special cavities in Duroia hirsute . Plants in the vicinity that belong to other species are killed with formic acid . This selective gardening can be so aggressive that small areas of the rainforest are dominated by Duroia hirsute . These peculiar patches are known by local people as " devil's gardens ". In some of these relationships,
7296-604: The Journal of the American Medical Association 's "Rational Clinical Examination Series" quantified the importance of increased pain as an indicator of infection. The review showed that the most useful finding is an increase in the level of pain [likelihood ratio (LR) range, 11–20] makes infection much more likely, but the absence of pain (negative likelihood ratio range, 0.64–0.88) does not rule out infection (summary LR 0.64–0.88). Disease can arise if
7424-431: The brain and spinal cord . In the peripheral nervous system, neural tissues form the cranial nerves and spinal nerves , inclusive of the motor neurons . Mineralized tissues are biological tissues that incorporate minerals into soft matrices. Such tissues may be found in both plants and animals. Xavier Bichat introduced the word tissue into the study of anatomy by 1801. He was "the first to propose that tissue
7552-463: The ectoderm and endoderm (or their precursor in sponges ), with a small contribution from the mesoderm , forming the endothelium , a specialized type of epithelium that composes the vasculature . By contrast, a true epithelial tissue is present only in a single layer of cells held together via occluding junctions called tight junctions , to create a selectively permeable barrier. This tissue covers all organismal surfaces that come in contact with
7680-467: The oral cavity , nose, eyes, genitalia, anus, or the microbe can enter through open wounds. While a few organisms can grow at the initial site of entry, many migrate and cause systemic infection in different organs. Some pathogens grow within the host cells (intracellular) whereas others grow freely in bodily fluids. Wound colonization refers to non-replicating microorganisms within the wound, while in infected wounds, replicating organisms exist and tissue
7808-447: The polymerase chain reaction (PCR) method will become nearly ubiquitous gold standards of diagnostics of the near future, for several reasons. First, the catalog of infectious agents has grown to the point that virtually all of the significant infectious agents of the human population have been identified. Second, an infectious agent must grow within the human body to cause disease; essentially it must amplify its own nucleic acids to cause
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#17327732280967936-402: The "strep test", they can be inexpensive. Complex serological techniques have been developed into what are known as immunoassays . Immunoassays can use the basic antibody – antigen binding as the basis to produce an electro-magnetic or particle radiation signal, which can be detected by some form of instrumentation. Signal of unknowns can be compared to that of standards allowing quantitation of
8064-434: The ability of that pathogen to damage the host as well as the ability of the host to resist the pathogen. However, a host's immune system can also cause damage to the host itself in an attempt to control the infection. Clinicians, therefore, classify infectious microorganisms or microbes according to the status of host defenses – either as primary pathogens or as opportunistic pathogens . Primary pathogens cause disease as
8192-420: The active contractile tissue of the body. Muscle tissue functions to produce force and cause motion, either locomotion or movement within internal organs. Muscle is formed of contractile filaments and is separated into three main types; smooth muscle , skeletal muscle and cardiac muscle . Smooth muscle has no striations when examined microscopically. It contracts slowly but maintains contractibility over
8320-447: The anemonefish-anemone mutualism, waste ammonia from the fish feeds the symbiotic algae that are found in the anemone's tentacles. Therefore, what appears to be a service-service mutualism in fact has a service-resource component. A second example is that of the relationship between some ants in the genus Pseudomyrmex and trees in the genus Acacia , such as the whistling thorn and bullhorn acacia . The ants nest inside
8448-458: The basis of a biochemical diagnosis of an infectious disease. For example, humans can make neither RNA replicases nor reverse transcriptase , and the presence of these enzymes are characteristic., of specific types of viral infections. The ability of the viral protein hemagglutinin to bind red blood cells together into a detectable matrix may also be characterized as a biochemical test for viral infection, although strictly speaking hemagglutinin
8576-466: The brain, remain undiagnosed, despite extensive testing using the standard of care ( microbiological culture ) and state-of-the-art clinical laboratory methods. Metagenomic sequencing-based diagnostic tests are currently being developed for clinical use and show promise as a sensitive, specific, and rapid way to diagnose infection using a single all-encompassing test. This test is similar to current PCR tests; however, an untargeted whole genome amplification
8704-462: The case of viral identification, a region of dead cells results from viral growth, and is called a "plaque". Eukaryotic parasites may also be grown in culture as a means of identifying a particular agent. In the absence of suitable plate culture techniques, some microbes require culture within live animals. Bacteria such as Mycobacterium leprae and Treponema pallidum can be grown in animals, although serological and microscopic techniques make
8832-475: The causative agent, Trypanosoma cruzi in a patient, which therefore makes it difficult to definitively make a diagnosis. In this case, xenodiagnosis involves the use of the vector of the Chagas agent T. cruzi , an uninfected triatomine bug, which takes a blood meal from a person suspected of having been infected. The bug is later inspected for growth of T. cruzi within its gut. Another principal tool in
8960-435: The cause of the disease are based upon the likelihood that a patient came in contact with a particular agent, the presence of a microbe in a community, and other epidemiological considerations. Given sufficient effort, all known infectious agents can be specifically identified. Diagnosis of infectious disease is nearly always initiated by medical history and physical examination. More detailed identification techniques involve
9088-456: The colourless substance that covers the sieve plate. Callose stays in solution as long as the cell contents are under pressure. Phloem transports food and materials in plants upwards and downwards as required. Animal tissues are grouped into four basic types: connective , muscle , nervous , and epithelial . Collections of tissues joined in units to serve a common function compose organs. While most animals can generally be considered to contain
9216-431: The composition of patient blood samples, even though the outcome would not offer the patient any further treatment options. In part, these studies on the appearance of HIV in specific communities permitted the advancement of hypotheses as to the route of transmission of the virus. By understanding how the disease was transmitted, resources could be targeted to the communities at greatest risk in campaigns aimed at reducing
9344-550: The consequences of this network structure for the stability of pollinator communities suggest that the specific way in which plant-pollinator networks are organized minimizes competition between pollinators, reduce the spread of indirect effects and thus enhance ecosystem stability and may even lead to strong indirect facilitation between pollinators when conditions are harsh. This means that pollinator species together can survive under harsh conditions. But it also means that pollinator species collapse simultaneously when conditions pass
9472-489: The cost of the ant's protection can be quite expensive. Cordia sp. trees in the Amazonian rainforest have a kind of partnership with Allomerus sp. ants, which make their nests in modified leaves. To increase the amount of living space available, the ants will destroy the tree's flower buds. The flowers die and leaves develop instead, providing the ants with more dwellings. Another type of Allomerus sp. ant lives with
9600-483: The culture of infectious agents isolated from a patient. Culture allows identification of infectious organisms by examining their microscopic features, by detecting the presence of substances produced by pathogens, and by directly identifying an organism by its genotype. Many infectious organisms are identified without culture and microscopy. This is especially true for viruses, which cannot grow in culture. For some suspected pathogens, doctors may conduct tests that examine
9728-400: The destruction of the virus. Instrumentation can be used to read extremely small signals created by secondary reactions linked to the antibody – antigen binding. Instrumentation can control sampling, reagent use, reaction times, signal detection, calculation of results, and data management to yield a cost-effective automated process for diagnosis of infectious disease. Technologies based upon
9856-427: The diagnosis of infectious disease is microscopy . Virtually all of the culture techniques discussed above rely, at some point, on microscopic examination for definitive identification of the infectious agent. Microscopy may be carried out with simple instruments, such as the compound light microscope , or with instruments as complex as an electron microscope . Samples obtained from patients may be viewed directly under
9984-433: The ends. They do not have end openings such as the vessels. The end overlap with each other, with pairs of pits present. The pit pairs allow water to pass from cell to cell. Though most conduction in xylem tissue is vertical, lateral conduction along the diameter of a stem is facilitated via rays. Rays are horizontal rows of long-living parenchyma cells that arise out of the vascular cambium. Phloem consists of: Phloem
10112-445: The environment as a result of traumatic introduction (as in surgical wound infections or compound fractures ). An opportunistic disease requires impairment of host defenses, which may occur as a result of genetic defects (such as chronic granulomatous disease ), exposure to antimicrobial drugs or immunosuppressive chemicals (as might occur following poisoning or cancer chemotherapy ), exposure to ionizing radiation , or as
10240-426: The expression of symptoms is often atypical, making a clinical diagnosis based on presentation more difficult. Thirdly, diagnostic methods that rely on the detection of antibodies are more likely to fail. A rapid, sensitive, specific, and untargeted test for all known human pathogens that detects the presence of the organism's DNA rather than antibodies is therefore highly desirable. There is usually an indication for
10368-414: The external environment such as the skin , the airways, and the digestive tract. It serves functions of protection, secretion , and absorption, and is separated from other tissues below by a basal lamina . The connective tissue and the muscular are derived from the mesoderm. The nervous tissue is derived from the ectoderm. The epithelial tissues are formed by cells that cover the organ surfaces, such as
10496-412: The fact that the saturation of benefits accorded to mutualism or restrictions posed by outside factors contribute to a decreasing slope. The type II functional response is visualized as the graph of b a M 1 + a T H M {\displaystyle {\cfrac {baM}{1+aT_{H}M}}} vs. M . Mutualistic networks made up out of
10624-399: The fact that their cytoplasm is actively involved in the conduction of food materials, sieve-tube members do not have nuclei at maturity. It is the companion cells that are nestled between sieve-tube members that function in some manner bringing about the conduction of food. Sieve-tube members that are alive contain a polymer called callose, a carbohydrate polymer, forming the callus pad/callus,
10752-400: The four tissue types, the manifestation of these tissues can differ depending on the type of organism. For example, the origin of the cells comprising a particular tissue type may differ developmentally for different classifications of animals. Tissue appeared for the first time in the diploblasts , but modern forms only appeared in triploblasts . The epithelium in all animals is derived from
10880-566: The function of distal organs and systems. Breakdown of the protective mucosal barrier of the gut can contribute to the development of colon cancer . Every generation of every organism needs nutrients – and similar nutrients – more than they need particular defensive characteristics, as the fitness benefit of these vary heavily especially by environment. This may be the reason that hosts are more likely to evolve to become dependent on vertically transmitted bacterial mutualists which provide nutrients than those providing defensive benefits. This pattern
11008-400: The girth and length of the plant, with no intercellular spaces. Permanent tissues may be defined as a group of living or dead cells formed by meristematic tissue and have lost their ability to divide and have permanently placed at fixed positions in the plant body. Meristematic tissues that take up a specific role lose the ability to divide. This process of taking up a permanent shape, size and
11136-403: The growth of some bacteria and not others, or that change color in response to certain bacteria and not others. Bacteriological plates such as these are commonly used in the clinical identification of infectious bacterium. Microbial culture may also be used in the identification of viruses : the medium, in this case, being cells grown in culture that the virus can infect, and then alter or kill. In
11264-408: The gut population. The mucous layer of the intestine contains commensal bacteria that produce bacteriocins , modify the pH of the intestinal contents, and compete for nutrition to inhibit colonization by pathogens. The gut microbiota, containing trillions of microorganisms , possesses the metabolic capacity to produce and regulate multiple compounds that reach the circulation and act to influence
11392-483: The host's protective immune mechanisms are compromised and the organism inflicts damage on the host. Microorganisms can cause tissue damage by releasing a variety of toxins or destructive enzymes. For example, Clostridium tetani releases a toxin that paralyzes muscles, and staphylococcus releases toxins that produce shock and sepsis . Not all infectious agents cause disease in all hosts. For example, less than 5% of individuals infected with polio develop disease. On
11520-597: The host, preventing infection and speeding wound healing . The variables involved in the outcome of a host becoming inoculated by a pathogen and the ultimate outcome include: As an example, several staphylococcal species remain harmless on the skin, but, when present in a normally sterile space, such as in the capsule of a joint or the peritoneum , multiply without resistance and cause harm. An interesting fact that gas chromatography–mass spectrometry , 16S ribosomal RNA analysis, omics , and other advanced technologies have made more apparent to humans in recent decades
11648-531: The identification of infectious agents include the detection of metabolic or enzymatic products characteristic of a particular infectious agent. Since bacteria ferment carbohydrates in patterns characteristic of their genus and species , the detection of fermentation products is commonly used in bacterial identification. Acids , alcohols and gases are usually detected in these tests when bacteria are grown in selective liquid or solid media. The isolation of enzymes from infected tissue can also provide
11776-627: The improvement needed to return to conditions at which the pollinator community collapsed. Humans are involved in mutualisms with other species: their gut flora is essential for efficient digestion . Infestations of head lice might have been beneficial for humans by fostering an immune response that helps to reduce the threat of body louse borne lethal diseases. Some relationships between humans and domesticated animals and plants are to different degrees mutualistic. For example, agricultural varieties of maize provide food for humans and are unable to reproduce without human intervention because
11904-410: The infection cycle in other hosts, they (or their progeny) must leave an existing reservoir and cause infection elsewhere. Infection transmission can take place via many potential routes: The relationship between virulence versus transmissibility is complex; with studies have shown that there were no clear relationship between the two. There is still a small number of evidence that partially suggests
12032-496: The infectious agent also develop the disease. These postulates were first used in the discovery that Mycobacteria species cause tuberculosis . Tissue (biology) Biological organisms follow this hierarchy : Cells < Tissue < Organ < Organ System < Organism The English word "tissue" derives from the French word " tissu ", the past participle of the verb tisser, "to weave". The study of tissues
12160-425: The infectious agent does not occur, this limits the ability of PCR to detect the presence of any bacteria. Given the wide range of bacterial, viral, fungal, protozoal, and helminthic pathogens that cause debilitating and life-threatening illnesses, the ability to quickly identify the cause of infection is important yet often challenging. For example, more than half of cases of encephalitis , a severe illness affecting
12288-401: The infectious agent, reservoir, entering a susceptible host, exit and transmission to new hosts. Each of the links must be present in a chronological order for an infection to develop. Understanding these steps helps health care workers target the infection and prevent it from occurring in the first place. Infection begins when an organism successfully enters the body, grows and multiplies. This
12416-415: The interaction between plants and pollinators were found to have a similar structure in very different ecosystems on different continents, consisting of entirely different species. The structure of these mutualistic networks may have large consequences for the way in which pollinator communities respond to increasingly harsh conditions and on the community carrying capacity. Mathematical models that examine
12544-400: The leafy sheath does not fall open, and the seedhead (the "corn on the cob") does not shatter to scatter the seeds naturally. In traditional agriculture , some plants have mutualist as companion plants , providing each other with shelter, soil fertility and/or natural pest control . For example, beans may grow up cornstalks as a trellis, while fixing nitrogen in the soil for the corn,
12672-425: The light microscope, and can often rapidly lead to identification. Microscopy is often also used in conjunction with biochemical staining techniques, and can be made exquisitely specific when used in combination with antibody based techniques. For example, the use of antibodies made artificially fluorescent (fluorescently labeled antibodies) can be directed to bind to and identify a specific antigens present on
12800-471: The main axes of stems and roots. It consists of a combination of parenchyma cells, fibers, vessels, tracheids, and ray cells. Longer tubes made up of individual cellssels tracheids, while vessel members are open at each end. Internally, there may be bars of wall material extending across the open space. These cells are joined end to end to form long tubes. Vessel members and tracheids are dead at maturity. Tracheids have thick secondary cell walls and are tapered at
12928-550: The norm, examples of mixed-species groups abound. For example, zebra ( Equus burchelli ) and wildebeest ( Connochaetes taurinus ) can remain in association during periods of long distance migration across the Serengeti as a strategy for thwarting predators. Cercopithecus mitis and Cercopithecus ascanius , species of monkey in the Kakamega Forest of Kenya , can stay in close proximity and travel along exactly
13056-530: The number of new infections. The specific serological diagnostic identification, and later genotypic or molecular identification, of HIV also enabled the development of hypotheses as to the temporal and geographical origins of the virus, as well as a myriad of other hypothesis. The development of molecular diagnostic tools have enabled physicians and researchers to monitor the efficacy of treatment with anti-retroviral drugs . Molecular diagnostics are now commonly used to identify HIV in healthy people long before
13184-455: The onset of illness and have been used to demonstrate the existence of people who are genetically resistant to HIV infection. Thus, while there still is no cure for AIDS, there is great therapeutic and predictive benefit to identifying the virus and monitoring the virus levels within the blood of infected individuals, both for the patient and for the community at large. Symptomatic infections are apparent and clinical , whereas an infection that
13312-513: The other hand, some infectious agents are highly virulent. The prion causing mad cow disease and Creutzfeldt–Jakob disease invariably kills all animals and people that are infected. Persistent infections occur because the body is unable to clear the organism after the initial infection. Persistent infections are characterized by the continual presence of the infectious organism, often as latent infection with occasional recurrent relapses of active infection. There are some viruses that can maintain
13440-572: The past, and confusion on their use has persisted. Mutualism plays a key part in ecology and evolution . For example, mutualistic interactions are vital for terrestrial ecosystem function as: A prominent example of pollination mutualism is with bees and flowering plants. Bees use these plants as their food source with pollen and nectar. In turn, they transfer pollen to other nearby flowers, inadvertently allowing for cross-pollination. Cross-pollination has become essential in plant reproduction and fruit/seed production. The bees get their nutrients from
13568-537: The pathogens are present but that no clinically apparent infection (no disease) is present. Different terms are used to describe how and where infections present over time. In an acute infection, symptoms develop rapidly; its course can either be rapid or protracted. In chronic infection, symptoms usually develop gradually over weeks or months and are slow to resolve. In subacute infections, symptoms take longer to develop than in acute infections but arise more quickly than those of chronic infections. A focal infection
13696-411: The plant consists of a single layer of cells called epidermis or surface tissue. The entire surface of the plant has this outer layer of the epidermis. Hence it is also called surface tissue. Most of the epidermal cells are relatively flat. The outer and lateral walls of the cell are often thicker than the inner walls. The cells form a continuous sheet without intercellular spaces. It protects all parts of
13824-545: The plant is solely reliant upon the aardvark's keen sense of smell to detect its ripened fruit, extract, consume and then scatter its seeds; C. humifructus's geographical range is thus restricted to that of the aardvark's. Another type is ant protection of aphids , where the aphids trade sugar -rich honeydew (a by-product of their mode of feeding on plant sap ) in return for defense against predators such as ladybugs . Strict service-service interactions are very rare, for reasons that are far from clear. One example
13952-553: The plant providing carbohydrates to the fungus in return for primarily phosphate but also nitrogenous compounds. Other examples include rhizobia bacteria that fix nitrogen for leguminous plants (family Fabaceae) in return for energy-containing carbohydrates . Metabolite exchange between multiple mutualistic species of bacteria has also been observed in a process known as cross-feeding . Service-resource relationships are common. Three important types are pollination , cleaning symbiosis, and zoochory . In pollination ,
14080-466: The plant's thorns. In exchange for shelter, the ants protect acacias from attack by herbivores (which they frequently eat when those are small enough, introducing a resource component to this service-service relationship) and competition from other plants by trimming back vegetation that would shade the acacia. In addition, another service-resource component is present, as the ants regularly feed on lipid -rich food-bodies called Beltian bodies that are on
14208-464: The plant. The outer epidermis is coated with a waxy thick layer called cutin which prevents loss of water. The epidermis also consists of stomata (singular:stoma) which helps in transpiration . The complex permanent tissue consists of more than one type of cells having a common origin which work together as a unit. Complex tissues are mainly concerned with the transportation of mineral nutrients, organic solutes (food materials), and water. That's why it
14336-689: The plant. The primary growth of a plant occurs only in certain specific regions, such as in the tips of stems or roots. It is in these regions that meristematic tissue is present. Cells of this type of tissue are roughly spherical or polyhedral to rectangular in shape, with thin cell walls . New cells produced by meristem are initially those of meristem itself, but as the new cells grow and mature, their characteristics slowly change and they become differentiated as components of meristematic tissue, being classified as: There are two types of meristematic Tissue 1.Primary meristem. 2.Secondary meristem. The cells of meristematic tissue are similar in structure and have
14464-500: The plants, and allow for successful fertilization of plants, demonstrating a mutualistic relationship between two seemingly-unlike species. Mutualism has also been linked to major evolutionary events, such as the evolution of the eukaryotic cell ( symbiogenesis ) and the colonization of land by plants in association with mycorrhizal fungi. Mutualistic relationships can be thought of as a form of " biological barter" in mycorrhizal associations between plant roots and fungi , with
14592-491: The relationship has become less mutualistic and more parasitic. Measuring the exact fitness benefit to the individuals in a mutualistic relationship is not always straightforward, particularly when the individuals can receive benefits from a variety of species, for example most plant- pollinator mutualisms. It is therefore common to categorise mutualisms according to the closeness of the association, using terms such as obligate and facultative . Defining "closeness", however,
14720-463: The same routes through the forest for periods of up to 12 hours. These mixed-species groups cannot be explained by the coincidence of sharing the same habitat. Rather, they are created by the active behavioural choice of at least one of the species in question. Mathematical treatments of mutualisms, like the study of mutualisms in general, have lagged behind those for predation , or predator-prey, consumer-resource, interactions. In models of mutualisms,
14848-428: The size of parameter α, species densities would increase indefinitely. Because that is not possible due to environmental constraints and carrying capacity, a model that includes saturation would be more accurate. Wright's mathematical theory is based on the premise of a simple two-species mutualism model in which the benefits of mutualism become saturated due to limits posed by handling time. Wright defines handling time as
14976-639: The surface of skin , the airways , surfaces of soft organs, the reproductive tract , and the inner lining of the digestive tract . The cells comprising an epithelial layer are linked via semi-permeable, tight junctions ; hence, this tissue provides a barrier between the external environment and the organ it covers. In addition to this protective function, epithelial tissue may also be specialized to function in secretion , excretion and absorption . Epithelial tissue helps to protect organs from microorganisms, injury, and fluid loss. Functions of epithelial tissue: There are many kinds of epithelium, and nomenclature
15104-457: The target antigen. To aid in the diagnosis of infectious diseases, immunoassays can detect or measure antigens from either infectious agents or proteins generated by an infected organism in response to a foreign agent. For example, immunoassay A may detect the presence of a surface protein from a virus particle. Immunoassay B on the other hand may detect or measure antibodies produced by an organism's immune system that are made to neutralize and allow
15232-559: The taxonomically classified pathogen genomes to generate an antimicrobial resistance profile – analogous to antibiotic sensitivity testing – to facilitate antimicrobial stewardship and allow for the optimization of treatment using the most effective drugs for a patient's infection. Metagenomic sequencing could prove especially useful for diagnosis when the patient is immunocompromised . An ever-wider array of infectious agents can cause serious harm to individuals with immunosuppression, so clinical screening must often be broader. Additionally,
15360-472: The terms "type I" and "type II" functional responses refer to the linear and saturating relationships, respectively, between the benefit provided to an individual of species 1 ( dependent variable ) and the density of species 2 (independent variable). One of the simplest frameworks for modeling species interactions is the Lotka–Volterra equations . In this model, the changes in population densities of
15488-503: The test. For example, " Strep throat " is often diagnosed within minutes, and is based on the appearance of antigens made by the causative agent, S. pyogenes , that is retrieved from a patient's throat with a cotton swab. Serological tests, if available, are usually the preferred route of identification, however the tests are costly to develop and the reagents used in the test often require refrigeration . Some serological methods are extremely costly, although when commonly used, such as with
15616-551: The time needed to process a food item, from the initial interaction to the start of a search for new food items and assumes that processing of food and searching for food are mutually exclusive. Mutualists that display foraging behavior are exposed to the restrictions on handling time. Mutualism can be associated with symbiosis. In 1959, C. S. Holling performed his classic disc experiment that assumed that where The equation that incorporates Type II functional response and mutualism is: where or, equivalently, where This model
15744-458: The two mutualists are quantified as: where Mutualism is in essence the logistic growth equation modified for mutualistic interaction. The mutualistic interaction term represents the increase in population growth of one species as a result of the presence of greater numbers of another species. As the mutualistic interactive term β is always positive, this simple model may lead to unrealistic unbounded growth. So it may be more realistic to include
15872-581: The use of frozen tissue-sections have enhanced the detail that can be observed in tissues. With these tools, the classical appearances of tissues can be examined in health and disease , enabling considerable refinement of medical diagnosis and prognosis . In plant anatomy , tissues are categorized broadly into three tissue systems: the epidermis , the ground tissue , and the vascular tissue . Plant tissues can also be divided differently into two types: Meristematic tissue consists of actively dividing cells and leads to increase in length and thickness of
16000-454: The use of PCR as a standard tool of diagnosis are in its cost and application, neither of which is insurmountable. The diagnosis of a few diseases will not benefit from the development of PCR methods, such as some of the clostridial diseases ( tetanus and botulism ). These diseases are fundamentally biological poisonings by relatively small numbers of infectious bacteria that produce extremely potent neurotoxins . A significant proliferation of
16128-411: The use of live animals unnecessary. Viruses are also usually identified using alternatives to growth in culture or animals. Some viruses may be grown in embryonated eggs. Another useful identification method is Xenodiagnosis, or the use of a vector to support the growth of an infectious agent. Chagas disease is the most significant example, because it is difficult to directly demonstrate the presence of
16256-654: The vacuole is of much smaller size than of normal animal cells. This tissue provides support to plants and also stores food. Chlorenchyma is a special type of parenchyma that contains chlorophyll and performs photosynthesis. In aquatic plants, aerenchyma tissues, or large air cavities, give support to float on water by making them buoyant. Parenchyma cells called idioblasts have metabolic waste. Spindle shaped fibers are also present in this cell to support them and known as prosenchyma, succulent parenchyma also noted. In xerophytes , parenchyma tissues store water. Collenchyma (Greek, 'Colla' means gum and 'enchyma' means infusion)
16384-449: Was introduced by Pierre-Joseph van Beneden in his 1876 book Animal Parasites and Messmates to mean "mutual aid among species". Mutualism is often conflated with two other types of ecological phenomena: cooperation and symbiosis . Cooperation most commonly refers to increases in fitness through within-species (intraspecific) interactions, although it has been used (especially in the past) to refer to mutualistic interactions, and it
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