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Diarrhea

Diarrhea

Diarrhea (AmE) or diarrhoea (CwE) is a condition in which the sufferer has frequent and watery, chunky, or loose bowel movements (from the ancient Greek word διαρροή = leakage; lit. "to run through"). In the Third World, diarrhea is the most common cause of death among infants, killing more than 1.5 million per year.

Causes

This condition can be a symptom of injury, disease or foodborne illness and is usually accompanied by abdominal pain, and often nausea and vomiting. There are other conditions which involve some but not all of the symptoms of diarrhea, and so the formal medical definition of diarrhea involves defecation of more than 200 grams per day (though formal weighing of stools to determine a diagnosis is never actually carried out). It occurs when insufficient fluid is absorbed by the colon. As part of the digestion process, or due to fluid intake, food is mixed with large amounts of water. Thus, digested food is essentially liquid prior to reaching the colon. The colon absorbs water, leaving the remaining material as a semisolid stool. If the colon is damaged or inflamed, however, absorption is inhibited, and watery stools result. Diarrhea is most commonly caused by myriad viral infections but is also often the result of bacterial toxins. In sanitary living conditions and with ample food and water available, an otherwise healthy patient typically recovers from the common viral infections in a few days and at most a week. However, for ill or malnourished individuals diarrhea can lead to severe dehydration and can become life-threatening without treatment. It can also be a symptom of more serious diseases, such as dysentery, cholera, or botulism and can also be indicative of a chronic syndrome such as Crohn's disease. Though appendicitis patients don't generally have diarrhea, it is a common symptom of a ruptured appendix. It is also an effect of severe radiation sickness. It can also be caused by excessive alcohol consumption, especially in someone who doesn't eat enough food. Symptomatic treatment for diarrhea involves the patient consuming adequate amounts of water to replace that lost, preferably mixed with electrolytes to provide essential salts and some amount of nutrients. For many people, further treatment and formal medical advice is unnecessary. The following types of diarrhea generally indicate medical supervision is desirable:
- Diarrhea in infants.
- Moderate or severe diarrhea in young children.
- Diarrhea associated with blood.
- Diarrhea that continues for more than 2 weeks.
- Diarrhea that is associated with more general illness such as non-cramping abdominal pain, fever, weight loss, etc.
- Diarrhea in travelers (more likely to have exotic infections such as parasites)
- Diarrhea in food handlers (potential to infect others)
- Diarrhea in institutions (Hospitals, child care, mental health institutes, geriatric and convalescent homes etc). Since most people will ignore very minor diarrhea, a patient who actually presents to a doctor is likely to have diarrhea that is more severe than usual.

Mechanism

To evacuate the contents of the lower digestive tract, the fluidity of the contents of the small and large intestines is increased. Active transport of Na⁺ back into the gut intiates a reverse sodium transport. This causes both Cl^- and HCO₃ to follow passively, as well as water. Now in the intestines, the water dilutes toxins as well as triggers contractions of the intestine due to increase in intestinal distension. These contractions push the contents of the lower GI tract towards and out of the anal canal. Medications such as loperamide are designed to prevent such contractions in response to the distension, and should not be used to prevent diarrhea. Such inhibition actually prolongs the infection or irritation, and can cause a worsening over time because the evacuation of the bowel contents has been delayed.

Acute diarrhea

This may be defined as diarrhea that lasts less than 2 weeks, and is also called gastroenteritis. This can nearly always be presumed to be infective, although only in a minority of cases is this formally proven. It is often reasonable to reassure a patient, ensure adequate fluid intake, and wait and see. In more severe cases, or where it is important to find the cause of the illness, stool cultures are instituted. The most common organisms found are Campylobacter (an organism of animal origin), salmonella (also often of animal origin), Cryptosporidiosis (animal origin), Giardia Lamblia (lives in drinking water). Shigella (dysentery) is less common, and usually human in origin. Cholera is rare in Western countries. It is more common in travelers and is usually related to contaminated water (its ultimate source is probably sea water). Escherichia coli is probably a very common cause of diarrhea, especially in travelers, but it can be difficult to detect using current technology. The types of E. coli vary from area to area and country to country. Viruses, particularly rotavirus, are common in children. (Viral diarrhea is probably over-diagnosed by non-doctors). The Norwalk virus is rare. Toxins and food poisoning can cause diarrhea. These include staphylococcal toxin (often milk products due to an infected wound in workers), and Bacillus cereus (eg rice in Chinese takeaways). Often "food poisoning" is really salmonella infection. Parasites and worms sometime cause diarrhea but often present with weight loss, irritability, rashes or anal itching. The most common is pinworm (mostly of nuisance value rather than a severe medical illness). Other worms, such as hookworm, ascaria, and tapeworm are more medically significant and may cause weight loss, anemia, general unwellness and allergy problems. Amoebic dysentery due to Entamoeba histolytica is an important cause of bloody diarrhea in travelers and also sometimes in western countries which requires appropriate and complete medical treatment.

Chronic diarrhea

Infective diarrhea

It is not uncommon for diarrhea to persist. Diarrhea due to some organisms may persist for years without significant long term illness. More commonly a diarrhea will slowly ameliorate but the patient becomes a carrier (harbors the infection without illness). This is often an indication for treatment, especially in food workers or institution workers. Parasites (worms and amoeba) should always be treated. Salmonella is the most common persistent bacterial organism in humans.

Malabsorption

These tend to be more severe medical illnesses. Malabsorption is the inability to absorb food, mostly in the small bowel but also due to the pancreas. Causes include celiac disease (intolerance to gluten, a wheat product), lactose intolerance (Intolerance to milk sugar, common in non-Europeans), fructose malabsorption, Pernicious anemia (impaired bowel function due to the inability to absorb vitamin B12), loss of pancreatic secretions (may be due to cystic fibrosis or pancreatitis), short bowel syndrome (surgically removed bowel), radiation fibrosis (usually following cancer treatment), other drugs such as chemotherapy, and of course, diarrhea-predominant irritable bowel syndrome.

Inflammatory bowel disease

There are of unknown origin but are likely to be abnormal immune responses to infection. There is some overlap but the two types are ulcerative colitis and Crohn's disease:
- Ulcerative colitis is marked by chronic bloody diarrhea and inflammation mostly affects the distal colon near the rectum.
- Crohn's disease typically affects fairly well demarcated segments of bowel in the colon and often affects the end of the small bowel.

Other important causes

- Ischaemic bowel disease. This usually affects older people and can be due to blocked arteries.
- Bowel cancer: Some (but NOT all) bowel cancers may have associated diarrhea. (Cancer of the large colon is most common)
- Hormone-secreting tumors: some hormones (e.g. serotonin) can cause diarrhea if excreted to excess (usually from a tumor).
- Bile salt diarrhea: excess bile salt entering the colon rather then being absorbed at the end of the small intestine can cause diarrhea, typically shortly after eating. Bile salt diarrhea is a possible side-effect of gallbladder removal. It is usually treated with cholestyramine, a bile acid sequestrant.

Treatment of diarrhea

#Keep hydrated. This is the most appropriate treatment in most cases of minor diarrhea. #Try eating more but smaller portions. Eat regularly. Don't eat or drink too quickly. #Intravenous fluids or a "drip": Sometimes, especially in children, dehydration can be life-theatening and intravenous fluid may be required. #Oral rehydration therapy: Taking a sugar/salt solution, which can be absorbed by the body. #Opioids and their analogs should not be used for infectious diarrhea as they are said to prolong the illness and may increase the risk of a carrier state. Opioids are the most effective antidiarrheals available. Their principal method of action is to inhibit peristalsis. Loperamide, also known as Imodium, is the most commonly used antidiarrheal. Loperamide is chemically related to the drug meperidine or Demerol, but does not cross the blood-brain barrier and does not appear to induce tolerance or dependence. Other opioids used to control diarrhea (in increasing order of strength) are: Lomotil (diphenoxylate with atropine); Lonox (difenoxin with atropine); codeine; opium tincture (laudanum); and morphine. The most potent opioids are generally reserved for chronic diarrhea (e.g., from complications of AIDS). #Antibiotics: antibiotics may be required if a bacterial cause is suspected and the patient is medically ill. They are sometimes also indicated for workers with carrier states in order to clear up an infection so that the person can resume work. Parasite-related diarrhea (e.g. giardiasis) require appropriate antibiotics. Antibiotics are not routinely used, as the cause is rarely bacterial and antibiotics may further upset intestinal flora and worsen rather than improve the diarrhea. Clostridium difficile-associated diarrhea and pseudomembranous colitis is often caused by antibiotic use. #Dietary manipulation: especially avoid wheat products with celiac disease. #Hygiene and isolation: Hygiene is important in limiting spread of the disease. #It is claimed that some fruit, such as bananas, mangoes, papaya and pineapple may have positive effects on this condition. Bananas have the merits of being easily obtainable, and they are unlikely to have any other significant unwanted side effects. Bananas are thought to be "binding," as is mucilage, which you can obtain in capsule form. Mucilage can also be used as cereal for babies, as it is easily digested. The high acid content of pineapple may make this food a bad choice for people suffering from chronic diarrhea.

External links

- [http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?cmd=Retrieve&db=PubMed&list_uids=11100619&dopt=Abstract Reducing deaths from diarrhoea through oral rehydration therapy.] 1: Bull. World Health Organ. 2000;78(10):1246-55.
- [http://rehydrate.org/diarrhoea/index.html Rehydration Project] Category:Gastroenterology Category:Symptoms ja:下痢 simple:Diarrhea

American English

American English (AmE) is the dialect of the English language used mostly in the United States of America. Crystal (1997) estimates that approximately two thirds of native speakers of English live in the United States. American English is also sometimes called United States English or U.S. English.

History

English was inherited from British colonization. The first wave of English-speaking immigrants was settled in North America in the 17th century. In that century, there were also speakers in North America of the Dutch, French, German, myriad Native American, Spanish, Swedish, Scots, Welsh, Irish, Scottish Gaelic and Finnish languages.

Phonology

In many ways, compared to British English, American English is conservative in its phonology. The conservatism of American English is largely the result of the fact that it represents a mixture of various dialects from the British Isles. Dialect in North America is most distinctive on the East Coast of the continent; this is largely because these areas were in contact with England, and imitated prestigious varieties of British English at a time when those varieties were undergoing changes. The interior of the country was settled by people who were no longer closely connected to England, as they had no access to the ocean during a time when journeys to Britain were always by sea. As such the inland speech is much more homogeneous than the East Coast speech, and did not imitate the changes in speech from England. East Coast-influenced non-rhotic pronunciations may be found among blacks throughout the country.]]Most North American speech is rhotic, as English was in most places in the 17th century. Rhoticity was further supported by Hiberno-English, Scottish English, and West Country English. In most varieties of North American English, the sound corresponding to the letter "R" is a retroflex semivowel rather than a trill or a tap. The loss of syllable-final r in North America is confined mostly to the accents of eastern New England, New York City and surrounding areas, South Philadelphia, and the coastal portions of the South. Dropping of syllable-final r sometimes happens in natively rhotic dialects if r is located in unaccented syllables or words and the next syllable or word begins in a consonant. In England, lost 'r' was often changed into (schwa), giving rise to a new class of falling diphthongs. Furthermore, the 'er' sound of (stressed) fur or (unstressed) butter, which is represented in IPA as stressed or unstressed is realized in American English as a monophthongal r-colored vowel. This does not happen in the non-rhotic varieties of North American speech. Some other British English changes in which most North American dialects do not participate:
- The shift of to (the so-called "broad A") before alone or preceded by . This is the difference between the British Received Pronunciation and American pronunciation of bath and dance. In the United States, only linguistically conservative eastern-New-England speakers took up this innovation.
- The shift of intervocalic to glottal stop , as in for bottle. This change is not universal for British English (and in fact is not considered to be part of Received Pronunciation), but it does not occur in most North American dialects. Newfoundland English and the dialect of New Britain, Connecticut are notable exceptions. On the other hand, North American English has undergone some sound changes not found in Britain, at least not in standard varieties. Many of these are instances of phonemic differentiation and include
- The merger of and , making father and bother rhyme. This change is nearly universal in North American English, occurring almost everywhere except for parts of eastern New England, like the Boston accent.
- The replacement of the lot vowel with the strut vowel in what, was, of, from, everybody, nobody, somebody, anybody, because, and in some dialects want.
- The merger of and . This is the so-called cot-caught merger, where cot and caught are homophones. This change has occurred in eastern New England, in Pittsburgh and surrounding areas, and from the Great Plains westward.
- Vowel merger before intervocalic . Which (if any) vowels are affected varies between dialects.
- The merger of and after palatals in some words, so that cure, pure, mature and sure rhyme with fir in some speech registers for some speakers.
- Dropping of after alveolar consonants so that new, duke, Tuesday, suit, resume, lute are pronounced , , , , , .
- Æ-tensing in environments that vary widely from accent to accent. In some accents, particularly those from Philadelphia to New York City, and can even contrast sometimes, as in Yes, I can vs. tin can .
- Laxing of , and to , and before , causing pronunciations like , and for pair, peer and pure.
- The flapping of intervocalic and to alveolar tap before reduced vowels. The words ladder and latter are mostly or entirely homophonous, possibly distinguished only by the length of preceding vowel. For some speakers, the merger is incomplete and 't' before a reduced vowel is sometimes not tapped following or when it represents underlying 't'; thus greater and grader, and unbitten and unbidden are distinguished. Even among those words where and are flapped, words that would otherwise be homophonous are, for some speakers, distinguished if the flapping is immediately preceded by the diphthongs or ; these speakers tend to pronounce writer with and rider with . This is called Canadian raising; it is general in Canadian English, and occurs in some northerly versions of American English as well (often just applying to the diphthong , but not to ).
- Both intervocalic and may be realized as or , making winter and winner homophones. This does not occur when the second syllable is stressed, as in entail.
- The pin-pen merger, by which is raised to before nasal consonants, making pairs like pen/pin homophonous. This merger originated in Southern American English but is now widespread in the Midwest and West as well. Some mergers found in most varieties of both American and British English include:
- The horse-hoarse merger of the vowels and before 'r', making pairs like horse/hoarse, corps/core, for/four, morning/mourning etc. homophones.
- The wine-whine merger making pairs like wine/whine, wet/whet, Wales/whales, wear/where etc. homophones. Many older varieties of southern and western American English still keep these distinct, but the merger appears to be spreading.

Differences in British English and American English

Main article: American and British English differences American English has both spelling and grammatical differences from British English (or Commonwealth English), some of which were made as part of an attempt to rationalize the English spelling used by British English at the time. Unlike many 20th century language reforms (for example, Turkey's alphabet shift, Norway's spelling reform) the American spelling changes were not driven by government, but by textbook writers and dictionary makers. The first American dictionary was written by Noah Webster in 1828. At the time America was a relatively new country and Webster's particular contribution was to show that the region spoke a different dialect from Britain, and so he wrote a dictionary with many spellings differing from the standard. Many of these changes were initiated unilaterally by Webster. Webster also argued for many "simplifications" to the idiomatic spelling of the period. Somewhat ironically, many, although not all, of his simplifications fell into common usage alongside the original versions, resulting in a situation even more confused than before. Many words are shortened and differ from other versions of English. Spellings such as center are used instead of centre in other versions of English. Conversely, American English sometimes favors words that are morphologically more complex, whereas British English uses clipped forms, such as AmE transportation and BrE transport or where the British form is a back-formation, such as AmE burglarize and BrE burgle (from burglar).

English words that arose in the U.S.

A number of words that arose in the United States have become common, to varying degrees, in English as it is spoken internationally. Although its origin is disputed, the most famous word is probably OK, which is sometimes used in other languages as well. Other American introductions include "belittle," "gerrymander" (from Elbridge Gerry), "blizzard", "teenager", and many more.

English words obsolete outside the U.S.

A number of words that originated in the English of the British Isles are still in everyday use in North America, but are no longer used in most varieties of British English. The most conspicuous of these words are fall, the season; to quit, as in "to cease an activity" (as opposed to "to leave a location" as still used in most other Anglophone countries); and gotten as a past participle of get. Americans are more likely than Britons to name a stream whose breadth or volume is judged insufficient for it to be a river or a creek. The word diaper goes back at least to Shakespeare, and usage was maintained in the U.S. and Canada, but was replaced in the British Isles with nappy. Some of these words are still used in various dialects of the British Isles, but not in formal standard British English. Many of these older words have cognates in Lowland Scots. The subjunctive mood is livelier in North American English than it is in British English; it appears in some areas as a spoken usage, and is considered obligatory in more formal contexts in American English. British English has a strong tendency to replace subjunctives with auxiliary verb constructions.

Regional differences

Main article: American English regional differences Spoken American English is not homogeneous throughout the country, and various regional and ethnic variants exist. These differences affect both pronunciation and the lexicon, and can make one accent a little difficult for speakers of another accent to understand. General American is the name given to any American accent that is relatively free of noticeable regional influences. It enjoys high prestige among Americans, but is not a standard accent in the way that Received Pronunciation is in England.

References

External links

- [http://www.pbs.org/speak/ Do You Speak American]: PBS special
- [http://cfprod01.imt.uwm.edu/Dept/FLL/linguistics/dialect/ Dialect Survey] of the United States, by Bert Vaux et al., Harvard University. The answers to various questions about pronunciation, word use etc. can be seen in relationship to the regions where they are predominant.
- [http://www.ling.upenn.edu/phono_atlas/home.html Phonological Atlas of North America] at the University of Pennsylvania
- [http://students.csci.unt.edu/~kun Guide to Regional English Pronunciation] includes working versions of the Telsur Project maps from the Phonologial Atlas site
- [http://www.peak.org/~jeremy/dictionary/ The American•British British•American Dictionary]
- [http://classweb.gmu.edu/accent/ Speech Accent Archive]
- [http://www.world-english.org/ World English Organization]
- [http://www.esuus.org English Speaking Union of the United States]
- [http://canadianenglish1.narod.ru American Canadian British English Lexical Differences In One Table]
- [http://australianenglish1.narod.ru Australian American British English Lexical Differences In One Table And More]
- [http://www.englisch-hilfen.de/en/words_list/british_american.htm British, American, Australian English - Lists and Online Exercises]
- [http://www.globalenglishsalon.com/ Listen to spoken American English (midwest

Commonwealth English

"Commonwealth English" is intended as a collective term for the perceived standard English language used in the Commonwealth of Nations¹, applying in theory to Australian English, British English, Caribbean English, Canadian English, Hiberno-English (Irish English)², Hong Kong English³, Indian English (includes Pakistani English), formal Malaysia English, New Zealand English, formal Singapore English (but not colloquial Singlish) and South African English. But Canadian English in particular does not fit well with the others. The term is little used, and when used is most often synonymous with British English in its narrower sense or with International English in a specialized sense which excludes American English.

Rationale for the term "Commonwealth English"

The term perhaps comes from a desire to recognise that "Standard English" of Britain, distinguished from American English, is just as much owned by those who use it in Australia or New Zealand or India or South Africa as by those who use it in the land of its origin and from a feeling that this use in multiple countries should appear in its name, that this kind of English is no longer only British.

Conflict from differences in language

Aside from spelling, there are other differences in the languages. Words used in the United States are sometimes used in England which can be insultive and derogatory.

Canadian English's unique position

Words and idioms

Canada, the Commonwealth country with the largest native-born native-English-speaking population outside of Britain, is unique in that its standard vocabulary, idiom, and accent tend to coincide with that of neighbouring speakers in the United States far more than with those of Britain or the rest of the Commonwealth. Most of the distinctive terms Britons identify as American English are used by Canadians as well, such as diaper, gasoline, elevator, and apartment. See also North American English.

Canadian spelling

There is no universally accepted standard of Canadian spelling, and standards differ from one area of English-speaking Canada to another. Historical ties with Britain tend to pull Canadian spelling in that direction; physical proximity with the United States has tended to pull it towards the American standard. As a result, Canadian spelling has tended to waver between the two, taking some of each. Most authorities, such as the Canadian Government's style manual, The Canadian Style, the Canadian Press style guide, the Gage Canadian Dictionary and the Canadian Oxford Dictionary, propose certain standards:
- the use of the "-our" ending in words such as neighbour and colour;
- the use of the "-ce" ending for nouns and the "-se" ending for the equivalent verbs, such as licence (noun), to license (verb) and practice (noun), to practise (verb);
- the use of double letters in words such as travelled, leveller, etc. Certain American spellings remain common. The spelling program is more usual than programme, airplane is universally favoured over aeroplane, tire is used rather than tyre, etc.

Australian borrowings

Australian English also borrows from both British and American spellings. However, British spelling dominates.

Internal spelling differences

Within British English and its Commonwealth variants there is disagreement as to proper spelling of words such as organise / organize. Both "-ise" and "-ize" are generally accepted as correct. The "-ise" forms are very rarely used in Canada, but they are the choice of the majority in Britain (even though most British dictionaries prefer the "-ize" forms). See British English for more details. According to Pam Peters (1994: -ise/-ize), based on British National Corpus data, in Britain: :... the -ise spellings outnumber those with -ize in the ratio of about 3:2. In Australian English, the difference is still greater (often 3:1, by frequencies in the ACE corpus), and the tendency has been reinforced by official endorsement of -ise by the Australian government Style Manual since 1966. The English Academy of South Africa website uses "-ize" forms on some pages and "-ise" forms on other pages, recognising both. The Australian Journal of Linguistics, the official journal of the Australian Linguistics Society, insists on the "-ize" forms against the Australian dictionaries and the majority in Australia.

Independent standards within "Commonwealth English"

The more extensive forms of Commonwealth English and even some of those less used have their own separate, recognised dictionaries. The Dictionary of Canadian English: The Senior Dictionary was first published by the Canadian textbook publisher Gage Learning in 1967 and updated versions have appeared regularly, the most recent being the Gage Canadian Dictionary in 1997. For South Africa there was Charles Pettman's Africanderisms, a glossary of South African colloquial words and phrases published in 1913. Philip Branford's A Dictionary of South African English was published in 1978 and the most recent edition in 1991. Australian English has had the Macquarie Dictionary since 1981. In 1996 Oxford University Press published the Concise Ulster Dictionary. In 1998 they went farther afield by releasing A Dictionary of South African English on Historical Principles, The Canadian Oxford Dictionary, and The Dictionary of New Zealand English. In 2000 they published The Australian Oxford Dictionary. All these use previous Oxford English dictionaries as a base, but modify or replace text according to research on other varieties of English. Caribbean English has Frederic G. Cassidy and Robert B. Le Page's Dictionary of Jamaican English and John A. Holm and Alison W. Shlling's Dictionary of Bahamian English.

Limited use

"Commonwealth English" is not a clear and distinctive dialect, although it becomes far closer to being one if Canadian English is not considered. Microsoft Encarta appears in four English versions, an American English version, a British English version, a Canadian English version, and an Australian English version, perhaps indicating that Microsoft did not feel that one Commonwealth English version would serve to balance the American English version, though there are likely to be few differences between the British English version and the Australian English version. A fifth version could be introduced as well: British English with Concise Oxford Dictionary spelling (IANA value en-GB-oed). Also, increasingly, spell checkers are supporting more finely grained systems of spelling, not attempting to make British English, renamed as Commonwealth English, do for all.

Notes

# There are a number of other Commonwealth nations which are not listed here but also have English as either the primary or an official, language. Examples include Malta, Singapore and Mozambique, which is a Commonwealth member but uses Portuguese as its main language of communication. # Although Hiberno-English (Irish English) is listed as Commonwealth English, the Republic of Ireland is not a member of the Commonwealth of Nations, but Northern Ireland is (as part of the United Kingdom). # Although Hong Kong English is listed as Commonwealth English, since 1997 Hong Kong is not a member of the Commonwealth of Nations, but a Special Administrative Region of China.

References and external links

- Peters, Pam (2004). . Cambridge: Cambridge University Press. ISBN 052162181X.
- [http://www.englishacademy.co.za English Academy of South Africa] (Website).
- [http://www.tandf.co.uk/journals/authors/cajlauth.asp Taylor & Francies: Instructions for Authors for the Australian Journal of Linguistics] ("The -ize suffix is used, for example, civilize, civilization rather than civilise, civilisation"). Category:Commonwealth of Nations Category:English dialects

Ancient Greek

Ancient Greek refers to the stage in the history of the Greek language corresponding to Classical Antiquity, which normally applies to two periods of Greek history: Archaic and Classical Greece. The Ancient era of Greek history normally includes also the Hellenistic (post-Classic) age; however, that period formally composes its own stage in the Greek Language known as Hellenistic Greek. For information on the Greek language prior to the creation of the Greek alphabet, see articles Mycenaean Greek and Proto-Greek.

Dialects of Ancient Greek

The Greek language had started shaping in local forms even before the settling of the Greek-speaking tribes into Greece, yet the actual dialectic variation took place afterwards. Throughout history the Greek language is presented in a number of dialects that did not apply on fixed geographical borders, and even if it did, those borders would be constantly altered because of the frequent migrations of the Hellenic peoples. According to its linguistic variations, the Ancient Greek language of the Archaic and Classic periods is composed by the following symbolic dialectic branches: The dialects of the pre-classical and classical period appear documented in writing beginning in the 8th century BC, and they certainly developed well before this date. The most standard formulation currently for the pre-classical and classical dialects is four or five major groups: # Northwest Greek (including Doric, and possibly Ancient Macedonian) # Aeolic (including Boeotian, Lesbian, Thessalian, and Aegean/Asiatic Aeolic subdivisions) # Attic-Ionic # Arcado-Cyprian # and possibly Pamphylian As each of the above dialectic branches is broken down to its individual dialects, each dialect can in turn be divided into countless local idioms. The information provided in the dialect-specific articles is a general linguistic description that is confined to the main characteristics of the Common form (Koine) of each dialect, without getting into detail about their numerous idiomatic variations. In that respect, the article on Doric describes the "Common" form of Doric as it is seen, e.g., in Pindar's poetry, which differs from local forms such as Laconian, Cretan, Sicilian or even Theban Doric. The Arcado-Cyprian group appears to be closest to Mycenaean Greek, and is likely its direct descendant. Northwest/Doric is the most distinct from the others. Controversy on the early history of Greek dialects generally focuses on the nature of Aeolic and Attic-Ionic—with various configurations of independent development or relations to Mycenaean or Northwest/Doric proposed. The relations between the dialects are likely obscured by significant amounts of influence on each other. After the conquests of Alexander the Great in the 4th century BC, a new international dialect known as Koine or Common Greek developed, largely based on Attic Greek, but with influence from other dialects. This dialect slowly replaced most of the older dialects, although Doric dialect has survived to the present in the form of the Tsakonian and Southern Italian dialect of Modern Greek. Doric has also passed down its Aorist terminations into most verbs of Demotic Greek. By about the 7th century AD., the Koine had slowly metamorphosized into Medieval Greek.

Sound changes

These sound changes since Proto-Greek affect most or all Ancient Greek dialects:
- Syllabic /r/, /l/ become /ro/ and /lo/ in Mycenean Greek and Aeolic Greek; otherwise /ra/ and /la/, but /ar/ and /al/ before resonants and analogously.
- Loss of /h/ from original /s/ (except initially) and of /j/.
- Loss of /w/ in many dialects (later than loss of /h/ and /j/).
- Loss of labiovelars, which were converted (mostly) into labials, sometimes into dentals or velars.
- Contraction of adjacent vowels resulting from loss of /h/ and /j/ (and, to a lesser extent, from loss of /w/); more in Attic Greek than elsewhere.
- Rise of a distinctive circumflex accent, resulting from contraction and certain other changes.
- Limitation of the accent to the last three syllables, with various further restrictions.
- Loss of /n/ before /s/ (incompletely in Cretan Greek), with compensatory lengthening of the preceding vowel. Note that /w/ and /j/, when following a vowel and not preceding a vowel, combined early on with the vowel to form a diphthong and were thus not lost. The loss of /h/ and /w/ after a consonant were often accompanied by compensatory lengthening of a preceding vowel. The loss of /j/ after a consonant was accompanied by a large number of complex changes, including diphthongization of a preceding vowel or palatalization or other change to a directly preceding consonant. Some examples:
- /pj/, /bj/, /phj/ -> /pt/
- /lj/ -> /ll/
- /tj/, /thj/, /kj/, /khj/ -> /s/ when following a consonant; otherwise /tt/ (Attic), /ss/ (Ionic)
- /gj/, /dj/ -> /zd/
- /mj/, /nj/, /rj/ -> /j/ is transposed before consonant and forms a diphthong with the preceding vowel
- /wj/, /sj/ -> /j/, forming a diphthong with the preceding vowel The results of vowel contraction were complex and differed from dialect to dialect. Such contractions occur in the inflection of a number of different noun and verb classes and are among the most difficult aspects of Ancient Greek grammar. They were particularly important in the large class of contracted verbs, denominative verbs formed from nouns and adjectives ending in a vowel. (In fact, the reflex of contracted verbs in Modern Greek—i.e., the set of verbs derived from Ancient Greek contracted verbs—represents one of the two main classes of verbs in that language.)

Sounds

The pronunciation of Post-Classic Greek changed considerably from Ancient Greek, although the orthography still reflects features of the older language (see W. Sidney Allen, Vox Graeca – a guide to the pronunciation of Classical Greek). For a detailed description on the phonology changes from Ancient to Hellenistic periods of the Greek language, see the article on Koine Greek. The examples below are intended to represent Attic Greek in the 5th century BC. Although ancient pronunciation can never be reconstructed with certainty, Greek in particular is very well documented from this period, and there is little disagreement among linguists as to the general nature of the sounds that the letters represented.

Vowels

Short vowels

The short e (ε in Greek orthography) is shown in the table as mid close vowel , but it may have been nearer to .

	Front	Back
Close unrounded
Close rounded
Close-mid
Open

Long Vowels

The [] (ου in Greek orthography) probably changed to [] by the fourth century.

	Front	Back
Close unrounded
Close rounded
Close-mid
Open-mid
Open

Consonants

Note: [z] was an allophone of [s], used before voiced consonants, and in particular in the combination [zd] written as zeta (ζ). The [] (voiceless r) written as rho with a rough breathing () was probably an allophone of [r].

Consonant classes

There are three main classes of consonants:
- Stops. This include three subclasses: velars (k, g, kh), labials (p, b, ph), and dentals (t, d, th).
- Sonorants are m, n, l, r.
- Fricatives are s and h.

Consonant contractions

In verb conjugation, one consonant often comes up against the other. Various sandhi rules apply. Rules:
- Most basic rule: When two sounds appear next to each other, the first assimilates in voicing and aspiration to the second.
- This applies fully to stops. Fricatives assimilate only in voicing, sonorants do not assimilate.
- Before an s (future, aorist stem), velars become k, labials p, and dentals disappear.
- Before a th (aorist passive stem), velars become kh, labials ph, dentals s.
- Before an m (perfect middle first-singular, first-plural, participle), velars become g, nasal+velar becomes g, labials m, dentals and n become s, other sonants remain.

Compensatory lengthening

There are different schemes for compensatory lengthening, depending on where it happens. The differences are in whether a becomes ā or ē, and whether e and o become the closed values ei /eː/ and ou /oː/ or the open values ē /ɛː/ and ō /ɔː/.

Augment

The indicative of past tenses adds (conceptually, at least) a prefix /e-/. This was probably originally a separate word, meaning something like "then", added because tenses in PIE had primarily aspectual meaning. The augment is added to the indicative of the aorist, imperfect and pluperfect, but not to any of the other forms of the aorist (no other forms of the imperfect and pluperfect exist). There are two kinds of augment in Greek, syllabic and quantitative. The syllabic augment is added to stems beginning with consonants, and simply prefixes e (stems beginning with r, however, add er). The quantitative augment is added to stems beginning with vowels, and involves lengthening the vowel:
- a, ā, e, ē -> ē
- i, ī -> ī
- o, ō -> ō
- u, ū -> ū
- ai -> ēi
- ei -> ēi or ei
- oi -> ōi
- au -> ēu or au
- eu -> ēu or eu
- ou -> ou Some verbs augment irregularly; the most common variation is e -> ei. The irregularity can be explained diachronically by the loss of s between vowels. The augment is sometimes omitted in poetry (Epic Greek). The augment sometimes substitutes for reduplication; see below.

Reduplication

All forms of the perfect, pluperfect and future perfect reduplicate the initial syllable of the verb stem. There are three types of reduplication:
- Syllabic reduplication: Most verbs beginning with a single consonant, or a cluster of a stop with a sonorant, add a syllable consisting of the initial consonant followed by e. An aspirated consonant, however, reduplicates in its unaspirated equivalent: this is often referred to as Grassman's Law.
- Augment: Verbs beginning with a vowel, as well as those beginning with a cluster other than those indicated previously (and occasionally for a few other verbs) reduplicate in the same fashion as the augment. Note that this remains in all forms of the perfect, not just the indicative.
- Attic reduplication: Some verbs beginning with an a, e or o, followed by a sonorant (or occasionally d or g), reduplicate by adding a syllable consisting of the initial vowel and following consonant, and lengthening the following vowel. Hence er -> erēr, an -> anēn, ol -> olōl, ed -> edēd. This is not actually specific to Attic Greek, despite its name. This originally involved reduplicating a cluster consisting of a laryngeal and sonorant; hence h₃l -> h₃leh₃l -> olōl with normal Greek development of laryngeals. (Forms with a stop were analogous.) Irregular duplication can be understood diachronically. For example, lambanō (root lab) has the perfect stem eilēpha (not
- lelēpha) because it was originally slambanō, with perfect seslēpha, becoming eilēpha through (semi-)regular change.

Grammatical forms

Ancient Greek, like all of the older Indo-European languages, is highly inflected. Ancient Greek is highly archaic in its preservation of Proto-Indo-European forms. Nouns (including proper nouns) have five cases (nominative, genitive, dative, accusative and vocative), three genders (masculine, feminine and neuter), and three numbers (singular, dual and plural). Verbs have four moods (indicative, imperative, subjunctive and optative), three voices (active, middle and passive), as well as three persons (first, second and third) and various other forms. Verbs are conjugated in four main tenses (present, aorist, perfect, and future), with a full complement of moods for each main tense, although there is no future subjunctive or imperative. (The distinction of the "tenses" in moods other than the indicative is actually mostly of aspect.) In addition, indicative forms of the imperfect and pluperfect exist. Infinitives and participles for all corresponding finite combinations of tense and voice, excluding the imperfect and pluperfect.

Nouns

Ancient Greek nouns have three numbers (singular, dual, and plural), three genders (masculine, feminine, and neuter) and five cases (nominative, genitive, dative, accusative and vocative). The two major noun declensions are the vowel declension and the consonant declension. The vowel declension is split into the alpha-declension and the omicron-declension. There is also the minor consonant declension.

Alpha Declension

The alpha declension is predominantly, but not exclusively, feminine. Nouns belonging to the alpha declension have stems ending in alpha, short or long. In certain circumstances the alpha may change its length or become eta. In the table below of feminine nouns there are three examples: long-alpha stem (-stems), short-alpha stems (-stems), and a stems which can end in eta (-stems).

Symptom

The term symptom (from the Greek syn = con/plus and pipto = fall, together meaning co-exist) has two similar meanings in the context of physical and mental health:
- A symptom may loosely be said to be a physical condition which shows that one has a particular illness or disorder (see e.g. Longman, 1995). An example of a symptom in this sense of the word would be a rash. However, correctly speaking, this is known as a sign, as would any indication detectable by a person other than the sufferer in the absence of verbal information from the patient.
- Strictly, a symptom is a sensation or change in health function experienced by a patient. In this, medically correct, sense of the word, it is a subjective report, as opposed to a sign, which is objective evidence of the presence of a disease or disorder. Examples of symptoms are fatigue/tiredness, pain, or nausea. The symptom that leads to a diagnosis is called a cardinal symptom. In contrast, elevated blood pressure, or abnormal appearance of the retina, would be a medical sign indicating the nature of the disease. The term "Presenting symptom" is used to describe the initial concern which brings a patient to a doctor.

Reference

- Longman dictionary of contemporary English (1995). Third edition.

External links

- [http://my.webmd.com/medical_information/check_symptoms/default.htm Online Medical Symptom Checker] Category:Medical terms
- simple:Symptom

Disease

A disease is any abnormal condition of the body or mind that causes discomfort, dysfunction, or distress to the person affected or those in contact with the person. Sometimes the term is used broadly to include injuries, disabilities, syndromes, symptoms, deviant behaviors, and atypical variations of structure and function, while in other contexts these may be considered distinguishable categories. Pathology is the study of diseases. The subject of systematic classification of diseases is referred to as nosology. The broader body of knowledge about diseases and their treatments is medicine.

Syndromes, illness and disease

Medical usage sometimes distinguishes a disease, which has a known specific cause or causes (called its etiology), from a syndrome, which is a collection of signs or symptoms that occur together. However, many conditions have been identified, yet continue to be referred to as "syndromes". Furthermore, numerous conditions of unknown etiology are referred to as "diseases" in many contexts. Illness, although often used to mean disease, can also refer to a person's perception of their health, regardless of whether they in fact have a disease. A person without any disease may feel unhealthy and believe he has an illness. Another person may feel healthy and believe he does not have an illness even though he may have a disease such as dangerously high blood pressure which may lead to a fatal heart attack or stroke.

Transmission of disease

Some diseases, such as influenza, are contagious or infectious, and can be transmitted by any of a variety of mechanisms, including droplets from coughs and sneezes, by bites of insects or other vectors, from contaminated water or food, etc. Other diseases, such as cancer and heart disease are not considered to be due to infection, although micro-organisms may play a role.

Social significance of disease

The identification of a condition as a disease, rather than as simply a variation of human structure or function, can have significant social or economic implications. The controversial recognitions as diseases of post-traumatic stress disorder, also known as "shell shock"; repetitive motion injury or repetitive stress injury (RSI); and Gulf War syndrome has had a number of positive and negative effects on the financial and other responsibilities of governments, corporations and institutions towards individuals, as well as on the individuals themselves. The social implication of viewing aging as a disease could be profound, though this classification is not yet widespread. A condition may be considered to be a disease in some cultures or eras but not in others. Oppositional-defiant disorder, attention-deficit hyperactivity disorder, and, increasingly, obesity are conditions considered to be diseases in the United States and Canada today, but were not so-considered decades ago and are not so-considered in some other countries. Conversely, the number of people in the West who consider homosexuality to be a disease became widespread in the 20th century but has been decreasing in the last two decades. To consider a condition to be a disease can sometimes involve a negative social value judgement. Lepers were a group of afflicted individuals who were historically shunned and the term "leper" still evokes social stigma. Fear of disease can still be a widespread social phenomena, though not all diseases evoke extreme social stigma.

Other uses of the term

In biology, disease refers to any abnormal condition of an organism that impairs function. The term disease is often used metaphorically for disordered, dysfunctional, or distressing conditions of other things, as in disease of society.

External links

- [http://www.nlm.nih.gov/medlineplus/healthtopics.html Health Topics], MedlinePlus descriptions of most diseases, with access to current research articles.
- [http://www.cdc.gov/health/default.htm Center for Disease Control Health Topics A-Z], fact sheets about many common diseases
- [http://rarediseases.about.com/ Rare/Orphan Diseases]
- [http://www.national-health.org/rarediseases/ National Organization for Rare Disorders] Extensive, useful information on rare diseases.
- [http://www.merck.com/pubs/mmanual/sections.htm The Merck Manual], detailed description of most diseases, freely searchable online. Category:Diseases Category:Medical terms als:Krankheit zh-min-nan:Pīⁿ ms:Penyakit ja:病気 simple:Disease th:โรค

Nausea

Nausea (Greek Ναυτεία) is the sensation of unease and discomfort in the stomach with an urge to vomit.

Causes

Nausea is a symptom of many conditions. It is also an adverse effect of many drugs. In medicine, nausea is a particular problem during some chemotherapy regimens and following general anaesthesia. Nausea is also a common symptom of pregnancy. Other causes include: altitude sickness, angina, brain tumor, cirrhosis, clinical depression, coeliac disease, colorectal cancer, crohn's disease, decompression sickness, esophagitis, gastroesophageal reflux disease, gastroenteritis, hangover, head injury, hepatitis C, hepatocellular carcinoma, hydrocephalus, hyperthyroidism, hypoglycemia, hyponatremia, hypoxia (medical), intestinal parasite, irritable bowel syndrome, kidney stone, lassa fever, lead poisoning, mastocytosis, ménière’s disease, morning sickness, motion sickness, myocardial infarction, panic attack, peptic ulcer, peritonitis, pneumonia, porphyria, postoperative nausea and vomiting, pseudomembranous colitis, psoriasis, Rocky mountain spotted fever, strep throat, trichinosis, ulcerative colitis, viral infections

Treatment

While short-term nausea and vomiting are generally harmless, they may sometimes indicate a more serious disease. When associated with prolonged vomiting, it may cause dangerous levels of dehydration and/or electrolyte imbalances. Symptomatic treatment for nausea and vomiting may include short-term avoidance of solid food. This is usually easy as nausea is nearly always associated with loss of appetite. Dehydration may require rehydration with oral or intravenous electrolyte solutions. Oral rehydration is safer and simpler in most cases. There are many antiemetics (drugs to treat nausea), although researchers continue to look for more effective treatments. Celiac Disease may also be a symptom if you consume wheat.

Digestion

Digestion is the process whereby a biological entity processes a substance, in order to chemically convert the substance into nutrients. Digestion occurs at the multicellular, cellular, and sub-cellular levels. Digestion usually involves mechanical manipulation and chemical action. In most vertebrates, digestion is a multi-stage process in the digestive system, following ingestion of the raw materials, most often other organisms. The process of ingestion usually involves some type of mechanical manipulation.

Human digestion

See: Gastrointestinal tract In humans, digestion begins in the mouth where food is chewed with the teeth. The process stimulates exocrine glands in the mouth to release digestive enzymes such as salivary amylase, which aid in the breakdown of food, particularly carbohydrates. Chewing also causes the release of saliva, which helps condense food into a bolus that can be easily passed through the esophagus to the stomach. In the stomach, food is churned and thoroughly mixed with acid and other digestive enzymes with digestive fluid to further decompose it chemically. As the acidic level changes in the stomach and later parts of the digestive tract, more enzymes are activated or deactivated to extract and process various nutrients. After being processed in the stomach, food is passed to the small intestine, it is pushed through the small intestine via a process called peristalsis, this is a squeezing action, it then passes through the pyloric sphincter where it is further mixed with secretions such as bile, which helps aid in fat digestion, and the enzymes maltase, lactase and sucrase, to process sugars. (Bile also contains pigments that are by-products of red blood cell destruction in the liver; these bile pigments are eliminated from the body with the feces). Most nutrient absorption takes place in the small intestine, after which food is passed to the large intestine. Blood which has absorbed nutrients passes through the liver for filtering, removal of toxins and help processing of nutrients. In the large intestine, water is reabsorbed, and leftover waste is excreted by defecation.

Digestive organs

Organisms develop specialized organs to aid in the digestion of their food, for example different types of tongues or teeth. Insects may have a crop (or the enlargement of esophagus) while birds and cockroachs may develop a gizzard (or a stomach that acts as teeth and mechanically digests food). A herbivore may have a caecum that contains bacteria which can produce cellulase that helps break down the cellulose in plants. Ruminants, for example cows and sheep, have a specialised fore-stomach called a rumen where microbes help to break down cellulose before the food passes onto the "true" stomach or abomasum.

Digestive hormones

There are at least four hormones that aid and regulate the digestive system:
- Gastrin - is in the stomach and stimulates the gastric glands to secrete pepsinogen and hydrochloric acid. Secretion of gastrin is stimulated by food arriving in stomach. The secretion is inhibited by low pH .
- Secretin - is in the duodenum and signals the secretion of sodium bicarbonate in the pancreas and it stimulates the bile secretion in the liver. This hormone responds to the acidity of the chyme.
- Cholecystokinin (CCK) - is in the duodenum and stimulates the release of digestive enzymes in the pancreas and stimulates the emptying of bile in the gall bladder. This hormone is secreted in resonse to fat in chyme.
- Gastric inhibitory peptide (GIP) - is in the duodenum and decreases the stomach churning in turn slowing the emptying in the stomach.

Digestion in plants and fungi

Not only animals digest food. Some carnivorous plants capture other organisms, usually invertebrate animals, and chemically digest them. Fungi also are very effective at digesting organic material in a saprobiontic manner, releasing digestive enzymes externally and then absorbing the digested products.

External links

- [http://www2.ufp.pt/~pedros/qfisio/digestion.htm Human Physiology - Digestion] Category:Digestive system Category:Metabolism ja:消化

Virus (biology)

:This article is concerned with virus as a biological infectious particle; for other uses see virus (disambiguation). virus (disambiguation) A virus is a microscopic parasite that infects cells in biological organisms. Viruses are obligate intracellular parasites; they can reproduce only by invading and controlling other cells as they lack the cellular machinery for self-reproduction. The term virus usually refers to those particles that infect eukaryotes (multi-celled organisms and many single-celled organisms), whilst the term bacteriophage or phage is used to describe those infecting prokaryotes (bacteria and bacteria-like organisms lacking a nucleus). Typically these particles carry a small amount of nucleic acid (either DNA or RNA, but not both) surrounded by some form of protective coat consisting of proteins, lipids, glycoproteins or a combination. Importantly, viral genomes code not only for the proteins needed to package its genetic material, but for proteins needed by the virus during its life cycle (the term "life cycle" is used loosely here—see Living or non-living?).
Origins and Beginnings
The origins of viruses are not entirely clear and there may not be a single mechanism that can account for all viruses. Some of the smaller viruses that have only a few genes may have originated from host organisms. Their genetic material could have been derived from transferrable elements like plasmids or transposons. Viruses with large genomes may represent extremely reduced microbes which established symbiotic relations with host organisms, allowing the loss of some genes needed for existence independent of a host. Other infectious particles which are even simpler in structure than viruses include viroids, virusoids, and prions.
Size, structure, and anatomy
Virus particles comprise a nucleic acid genome that may be either DNA or RNA, single- or double-stranded, and positive or negative sense. This is surrounded (encapsidated) by a protective coat of protein called a capsid. The viral capsid may be either spherical or helical and is composed of proteins encoded by the viral genome. In helical viruses, the capsid protein (frequently called the nucleocapsid protein) binds directly to the viral genome. For example, in the case of the measles virus, one nucleocapsid protein binds every six bases of RNA to form a helix approximately 1.3 micrometers in length. This complex of protein and nucleic acid is called the nucleocapsid, and, in the case of the measles virus, is enclosed in a lipid "envelope" acquired from the host cell, in which virus-encoded glycoproteins are embedded. These are responsible for binding to and entering the host cell at the start of a new infection. Spherical virus capsids completely enclose the viral genome and do not generally bind as tightly to the nucleic acid as helical capsid proteins do. These structures can range in size from less than 20 nanometers up to 400 nanometers and are composed of viral proteins arranged with icosahedral symmetry. Icosahedral architecture is the same principle employed by R. Buckminster-Fuller in his geodesic dome, and it is the most efficient way of creating an enclosed robust structure from multiple copies of a single protein. The number of proteins required to form a spherical virus capsid is denoted by the "T-number" whereby 60t proteins are necessary. In the case of the hepatitis B virus, the T-number is 4, therefore 240 proteins assemble to form the capsid. As in the helical viruses, the spherical virus capsid may be enclosed in a lipid envelope, although frequently spherical viruses are not enveloped, and the capsid proteins themselves are directly involved in attachment and entry into the host cell. The complete virus particle is referred to as a virion. A virion is little more than a gene transporter, and components of the envelope and capsid provide the mechanism for injecting the viral genome into a host cell..
Replication
Because viruses are acellular and do not have their own metabolism, they must utilize the machinery and metabolism of the host to reproduce. Before a virus has entered a host cell, it is called a virion — a package of viral genetic material. Virions can be passed from host to host either through direct contact or through a vector, or carrier. Inside the organism, the virus can enter a cell in various ways. Bacteriophages—bacterial viruses—attach to the cell wall surface in specific places. Once attached, enzymes make a small hole in the cell wall, and the virus injects its DNA into the cell. Other viruses (such as HIV) enter the host via endocytosis, the process whereby cells take in material from the external environment. After entering the cell, the virus's genetic material begins the destructive process of causing the cell to produce new viruses. There are three different ways genetic information contained in a viral genome can be reproduced. The form of genetic material contained in the viral capsid, the protein coat that surrounds the nucleic acid, determines the exact replication process. Some viruses have DNA, which once inside the host cell is replicated by the host along with its own DNA. There are two different replication processes for viruses containing RNA. In the first process, the viral RNA is directly copied using an enzyme called RNA replicase. This enzyme then uses that RNA copy as a template to make hundreds of duplicates of the original RNA. A second group of RNA-containing viruses, called the retroviruses, uses the enzyme reverse transcriptase to synthesize a complementary strand of DNA so that the virus's genetic information is contained in a molecule of DNA rather than RNA. The viral DNA can then be further replicated using the resources of the host cell.
Outline
#Attachment, sometimes called absorption: The virus attaches to receptors on the host cell wall. #Injection: The nucleic acid of the virus moves through the plasma membrane and into the cytoplasm of the host cell. The capsid of a phage, a bacterial virus, remains on the outside. In contrast, many viruses that infect animal cells enter the host cell intact. #Replication: The viral genome contains all the information necessary to produce new viruses. Once inside the host cell, the virus induces the host cell to synthesize the necessary components for its replication. #Assembly: The newly synthesized viral components are assembled into new viruses. #Release: Assembled viruses are released from the cell and can now infect other cells, and the process begins again. When the virus has taken over the cell, it immediately causes the host to begin manufacturing the proteins necessary for virus reproduction. Some viruses, like herpes, cause the host to produce three kinds of proteins: early proteins, enzymes used in nucleic acid replication; late proteins, proteins used to construct the virus coat; and lytic proteins, enzymes used to break open the cell for viral exit. The final viral product is assembled spontaneously, that is, the parts are made separately by the host and are joined together by chance. This self-assembly is often aided by molecular chaperones, or proteins made by the host that help the capsid parts come together. The new viruses then leave the cell either by exocytosis or by lysis. Envelope-bound animal viruses cause the host's endoplasmic reticulum to make certain proteins, called glycoproteins, which then collect in clumps along the cell membrane. The virus is then discharged from the cell at these exit sites, referred to as exocytosis. On the other hand, bacteriophages must break open, or lyse, the cell to exit. To do this, the phages have a gene that codes for an enzyme called lysozyme. This enzyme breaks down the cell wall, causing the cell to swell and burst. The new viruses are released into the environment, killing the host cell in the process.
Lifeform debate
A virus makes use of existing host enzymes and other molecules of a host cell to create more virus particles (virions). Some viruses encode part or all of their own genome replication machinery and are not entirely reliant on host polymerases for replication of their genetic material. Such viruses can be targeted by antiviral drugs that specifically inhibit the virally encoded replicase molecule(s). Viruses rely on host cell ribosomes for the production of viral proteins and utilize several distinct strategies to make the host cell synthesize the viral proteins. For example, at least some +RNA viruses use Internal Ribosome Entry Site IRES segments to drive the translation from their genomic +RNA molecule. Viruses are neither unicellular nor multicellular organisms; they are somewhere between being living and non-living. Viruses have genes and show inheritance, but are reliant on host cells to produce new generations of viruses. Many viruses have similarities to complex molecules. Because viruses are dependent on host cells for their replication they are generally not classified as "living". Whether or not they are "alive", they are obligate parasites, and have no form which can reproduce independently of their host. Like most parasites, they have a specific host range, sometimes specific to one species (or even limited cell types of one species) and sometimes more general. Some viruses form by self-assembly of protein and nucleic acid molecules. These macromolecules are assembled within host cells from smaller organic compounds. Virus self-assembly has implications for the study of the origin of life. Some viruses also incorporate lipids from the host cell membrane when their core protein-nucleic acid complex buds from the surface of a host cell. Concerning whether viruses are alive or not, if the requirement for autonomous self-reproduction is abandoned, it can be argued strongly that viruses are indeed alive. Some small viruses are more efficient than most cellular life forms as their ratio of functions to working parts is so high. If viruses are alive then the prospect of creating artificial life is enhanced or at least the standards required to call something artificially alive are reduced.
Study and applications

Exploring basic cellular processes
Viruses are important to the study of molecular and cellular biology because they provide simple systems that can be used to manipulate and investigate the functions of cells. The study and use of viruses have provided valuable information about many aspects of cell biology. For example, viruses have further simplified the study of genetics and have deepened our understanding of the basic mechanisms of molecular genetics (DNA replication, transcription, RNA processing), Translation (genetics), protein transport, and immunology.
Genetic engineering
Geneticists regularly use viruses as vectors to introduce genes into cells that they are studying. Attempts to treat human diseases through the use of viruses as tools of genetic engineering is one goal of gene therapy.
Materials science and nanotechnology
Scientists at MIT have recently been able to use viruses to create metallic wires, and they have the potential to be used for binding to exotic materials, self-assembly, liquid crystals, solar cells, batteries, fuel cells, and many other interesting areas. The essential idea is to use a virus with a known protein on its surface. The location of the code for this protein is in a known location in the DNA, and by randomizing that sequence it can create a phage library of millions of different viruses, each with a different protein expressed on its surface. By using natural selection, one can then find a particular strain of this virus which has a binding affinity for a given material. For example, one can isolate a virus which has a high affinity for gold. Taking this virus and growing gold nanoparticles around it results in the gold nanoparticles being incorporated into the virus coat, resulting in a gold wire of precise length and shape with biological origins. Current thinking is that viruses will one day be created which can act as agents on behalf of bio-mechanical healing devices giving humans or other animals extended life.
Human viral diseases
Examples of diseases caused by viruses include the common cold, which is caused by any one of a variety of related viruses; smallpox; AIDS, which is caused by HIV; and cold sores, which are caused by herpes simplex. Other connections are being studied such as the connection of HHV-6 in organic neurological diseases such as Multiple Sclerosis and Chronic Fatigue Syndrome. Recently it has been shown that cervical cancer is caused at least partly by papillomavirus (which causes papillomas, or warts), representing the first significant evidence in humans for a link between cancer and an infective agent. There is current controversy over whether borna virus, previously thought of primarily as the causative agent of neurological disease in horses, could be responsible for psychiatric illness in humans. The relative ability of viruses to cause disease is described in terms of virulence. The ability of viruses to cause devastating epidemics in human societies has led to concern that viruses will be weaponized for biological warfare. Further concern was raised by the successful recreation of a virus in a laboratory. Much concern revolves around the smallpox virus, which has devastated numerous societies throughout history, and today is extinct in the wild. In fact, smallpox has been used in a crude form of biological warfare by British colonists against a tribe of Native Americans. This episode of biological warfare was part of a larger phenomenon of Native American populations being devastated by contagious diseases, particularly smallpox, brought to the Americas by European colonists. It is unclear how many Native Americans were killed by smallpox after the arrival of Columbus in the Americas, but it may have been very large. The damage done by this disease may have significantly aided European attempts to displace or conquer the native population. Jared Diamond argued in his book Guns, Germs, and Steel that highly contagious diseases develop in agricultural societies and regularly aid those societies when they expand into the territories of non-agricultural peoples. Of all types of virus, the most deadly are known as filovirus. The Filovirus group consists of Marburg, first discovered in 1967 in Marburg Germany, and ebola. Filovirus are long, worm-like virus particles that, in large groups, resemble a plate of noodles. As of April 2005, the Marburg virus is attracting widespread press attention for an outbreak in Angola. Beginning in October 2004 and continuing into 2005, the outbreak, which now appears to be coming under control, is the world's worst epidemic of any kind of hemorrhagic fever.
Laboratory diagnosis of pathogenic viruses
Detection and subsequent isolation of viruses from patients is a very specialised laboratory subject. Normally it requires the use of large facilities, expensive equipment, and highly trained specialists such as technicians, molecular biologists, and virologists. Often, this effort is undertaken by state and national governments and shared internationally through organizations like WHO.
Prevention and treatment of viral diseases
Because they use the machinery of their host cells to reproduce, viruses are difficult to kill. The most effective medical approaches to viral diseases, thus far, are vaccination to provide resistance to infection, and drugs that treat the symptoms of viral infections. Patients often ask for antibiotics, which are useless against viruses, and their misuse against viral infections is one of the causes of antibiotic resistance in bacteria. That said, sometimes, in life-threatening situations, the prudent course of action is to begin a course of antibiotic treatment while waiting for test results to determine whether the patient's symptoms are caused by a virus or a bacterial infection.
Etymology
Although the viruses were discovered by the Russian biologist Dmitry Ivanovsky in 1892, the name for them was coined later. The original word comes from the Latin virus referring to poison and other noxious things. Today it is used to describe the biological viruses discussed above and also as a metaphor for other parasitically-reproducing things, such as memes or computer viruses. The word virion or viron is used to refer to a single infective viral particle. The English plural form of virus is viruses. No reputable dictionary gives any other form, including such "reconstructed" Latin plural forms as viri (which actually means men). (No plural form appears in any extant Latin manuscript). (See plural of virus). The word does not have a traditional Latin plural because its original sense, poison is a mass noun like the English word furniture.
See also

- Horizontal gene transfer
- List of viruses
- Microbiology
- Prion
- Viral plaque
- Viroids
- Virology
- Virus classification
See also

- Wikipedia:WikiProject Viruses
- WikiSpecies:Virus
- Wiktionary:en:virus
References

- [http://www.virology.net/ All the Virology on the WWW]
- Radetsky, Peter (1994). The Invisible Invaders: Viruses and the Scientists Who Pursue Them. Backbay Books, ISBNs 0316732168 (hc), 0316732176 (pb).
- Theiler, Max and Downs, W. G. (1973). The Arthropod-Borne Viruses of Vertebrates: An Account of the Rockefeller Foundation Virus Program 1951-1970. Yale University Press.
-
- Chronic Active Human Herpesvirus-6 (HHV-6) Infection: A New Disease Paradigm - Joseph H. Brewer, M.D. http://www.plazamedicine.com/index.html
Numbered references
# Gelderblom, Hans R. (1996). [http://www.ncbi.nlm.nih.gov/books/bv.fcgi?rid=mmed.chapter.2252 41. Structure and Classification of Viruses] in [http://www.ncbi.nlm.nih.gov/books/bv.fcgi?rid=mmed Medical Microbiology] 4th ed. Samuel Baron ed. The University of Texas Medical Branch at Galveston. ISBN 0963117211 Category:Virology als:Virus (Medizin) ko:바이러스 ms:Virus ja:ウイルス simple:Virus

Dehydration

Dehydration is the removal of water (hydor in ancient Greek) from an object. Medically, dehydration is a serious and potentially life-threatening condition in which the body contains an insufficient volume of water for normal functioning. The term "volume depletion" is similar to dehydration, but it refers to the loss of salts as well as water. Also see Hypovolemia.

Medical causes of dehydration

In humans, dehydration can be caused by a wide range of diseases and states that impair water homeostasis in the body. These include:
- External or stress-related causes
- Blood loss or hypotension due to physical trauma
- Diarrhea
- Hyperthermia
- Shock
- Prolonged physical activity without consuming adequate water, especially in a hot environment
- Survival situations, especially desert survival conditions
- Vomiting
- Infectious diseases
- Cholera
- Gastroenteritis
- Shigellosis
- Yellow fever
- Malnutrition
- Electrolyte imbalance
- Hypernatremia (also caused by dehydration)
- Hyponatremia, especially from restricted salt diets
- excessive consumption of alcohol
- Fasting
- Patient refusal of nutrition and hydration
- Other causes of obligate water loss
- Severe hyperglycemia, especially in Diabetes mellitus
- Glycosuria

Symptoms and prognosis

Symptoms may include headaches similar to what is experienced as a hangover, a sudden episode of visual snow, decreased blood pressure (hypotension), and dizziness or fainting when standing up due to orthostatic hypotension. Untreated dehydration generally results in delirium, unconsciousness, and death. Dehydration symptoms generally become noticeable after 2% of one's normal water volume has been lost. Initially, one experiences thirst and discomfort, possibly along with loss of appetite and dry skin. Athletes may suffer a loss of performance of up to 50%, and experience flushing, low endurance, rapid heart rates, elevated body temperatures, and rapid onset of fatigue. The symptoms become increasingly severe with greater water loss. One's heart and respiration rates will increase to compensate for decreased plasma volume and blood pressure, while body temperature may rise due to decreased sweating. Around 5% to 6% water loss, one may become groggy or sleepy, experience headaches or nausea, and may feel tingling in one's limbs (paresthesia). With 10% to 15% fluid loss, muscles may become spastic, skin may shrivel and wrinkle, vision may dim, urination will be greatly reduced and may become painful, and delirium may begin. Losses of greater than 15% are usually fatal. [http://faculty.washington.edu/kepeter/118/notes/water_balance.htm]

Treatment

Correction of a dehydrated state is accomplished by the replenishment of necessary water and electrolytes (rehydration). Even in the case of serious lack of fresh water (e.g. at sea or in a desert), drinking seawater or urine does not help, nor does the consumption of alcohol. When dehydrated, unnecessary sweating should be avoided, as it wastes water. If there is only dry food, it is better not to eat, as water is necessary for digestion. The best treatment for minor dehydration is consumption of an electrolyte-balanced fluid like a sports drink. For severe cases of dehydration where fainting, unconsciousness, or any other severely inhibiting symptom is present (the patient is incapable of standing or thinking clearly), emergency attention is required. Fluids will be given through an IV, and within a few hours, the patient will return to normal unless a complication occurred.

Avoiding dehydration

A person's body loses, during an average day in a temperate climate such as the United Kingdom, approximately 2.5 litres of water. This can be through the lungs as water vapor, through the skin as sweat, or through the kidneys as urine. Some (a less significant amount, in the absence of diarrhea) is also lost through the bowels. During vigorous exercise or in a hot environment, it is easy to lose several times this amount. Heavy ex

Diarrhea

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Malabsorption

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Treatment of diarrhea

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American English

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Nausea

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