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Sunday, June 9, 2019

Developing country

From Wikipedia, the free encyclopedia

Map of countries which are neither advanced economies, newly-industrialized countries nor Least Developed Countries.
 
World map representing Human Development Index categories (based on 2017 data, published in 2018). 
 
  1.000–0.800 (very high)
  0.700–0.799 (high)
  0.555–0.699 (medium)
  0.350–0.554 (low)
  Data unavailable

  Developing countries
  Data unavailable
A developing country (or a low and middle income country (LMIC), less developed country, less economically developed country (LEDC), or underdeveloped country) is a country with a less developed industrial base and a low Human Development Index (HDI) relative to other countries. However, this definition is not universally agreed upon. There is also no clear agreement on which countries fit this category. A nation's GDP per capita compared with other nations can also be a reference point. 

The term "developing" describes a currently observed situation and not a changing dynamic or expected direction of progress. Since the late 1990s, developing countries tended to demonstrate higher growth rates than developed countries. Developing countries include, in decreasing order of economic growth or size of the capital market: newly industrialized countries, emerging markets, frontier markets, Least Developed Countries. Therefore, the least developed countries are the poorest of the developing countries. 

Developing countries tend to have some characteristics in common. For example, with regards to health risks, they commonly have: low levels of access to safe drinking water, sanitation and hygiene; energy poverty; high levels of pollution (e.g. air pollution, indoor air pollution, water pollution); high proportion of people with tropical and infectious diseases (neglected tropical diseases); high number of road traffic accidents. Often, there is also widespread poverty, low education levels, inadequate access to family planning services, corruption at all government levels and a lack of so-called good governance. Effects of global warming (climate change) are expected to impact developing countries more than wealthier countries, as most of them have a high "climate vulnerability".

The Sustainable Development Goals, by the United Nations, were set up to help overcome many of these problems. Development aid or development cooperation is financial aid given by governments and other agencies to support the economic, environmental, social and political development of developing countries.

Definitions

  Developing economies according to the IMF
  Developing economies out of scope of the IMF
  Graduated to developed economy
(As of 2014)
 
  Graduated to developing economies (as of 2008)

 The UN acknowledges that it has "no established convention for the designation of "developed" and "developing" countries or areas". According to its so-called M49 standards, published in 1999:
The designations "developed" and "developing" are intended for statistical convenience and do not necessarily express a judgement about the stage reached by a particular country or area in the development process.
The UN implies that developing countries are those not on a tightly defined list of developed countries:
There is no established convention for the designation of "developed" and "developing" countries or areas in the United Nations system. In common practice, Japan in Asia, Canada and the United States in northern America, Australia and New Zealand in Oceania, and Europe are considered "developed" regions or areas. In international trade statistics, the Southern African Customs Union is also treated as a developed region and Israel as a developed country; countries emerging from the former Yugoslavia are treated as developing countries; and countries of eastern Europe and of the Commonwealth of Independent States [the former Soviet Union] in Europe are not included under either developed or developing regions.
However, under other criteria, some countries are at an intermediate stage of development, or, as the International Monetary Fund (IMF) put it, following the fall of the Soviet Union, "countries in transition": all those of Central and Eastern Europe (including Central European countries that still belonged to the "Eastern Europe Group" in the UN institutions); the former Soviet Union (USSR) countries in Central Asia (Kazakhstan, Uzbekistan, Kyrgyzstan, Tajikistan and Turkmenistan); and Mongolia. By 2009, the IMF's World Economic Outlook classified countries as advanced, emerging, or developing, depending on "(1) per capita income level, (2) export diversification—so oil exporters that have high per capita GDP would not make the advanced classification because around 70% of its exports are oil, and (3) degree of integration into the global financial system"

Along with the current level of development, countries can also be classified by how much their level of development has changed over a specific period of time.

In the 2016 edition of its World Development Indicators, the World Bank made a decision to no longer distinguish between "developed" and "developing" countries in the presentation of its data, considering the two-category distinction outdated. Instead, the World Bank classifies countries into four groups, based on Gross National Income per capita, re-set each year on July 1. In 2016, the four categories in US dollars were:
  • Low income countries: $995 or less.
  • Lower middle income countries: $996 to $3,895.
  • Upper middle income countries: $3,895 to $12,055.
  • High income countries: $12,056 and above

Measure and concept of development

  Least developed economies according to ECOSOC
  Least developed economies out of scope of the ECOSOC
  Graduated to developing economy
Newly industrialized countries as of 2013.
 
Kofi Annan, former Secretary General of the United Nations, defined a developed country as "one that allows all its citizens to enjoy a free and healthy life in a safe environment".

Development can be measured by economic or human factors. Developing countries are, in general, countries that have not achieved a significant degree of industrialization relative to their populations, and have, in most cases, a medium to low standard of living. There is an association between low income and high population growth. The development of a country is measured with statistical indexes such as income per capita (per person), gross domestic product per capita, life expectancy, the rate of literacy, freedom index and others. The UN has developed the Human Development Index (HDI), a compound indicator of some of the above statistics, to gauge the level of human development for countries where data is available. The UN had set Millennium Development Goals from a blueprint developed by all of the world's countries and leading development institutions, in order to evaluate growth. These goals ended in 2015, to be superseded by the Sustainable Development Goals

The concept of the developing nation is found, under one term or another, in numerous theoretical systems having diverse orientations — for example, theories of decolonization, liberation theology, Marxism, anti-imperialism, modernization, social change and political economy

Another important indicator is the sectoral changes that have occurred since the stage of development of the country. On an average, countries with a 50% contribution from the secondary sector (manufacturing) have grown substantially. Similarly countries with a tertiary sector stronghold also see a greater rate of economic development.

Terms used to classify levels of development

There are several terms used to classify countries into rough levels of development. Classification of any given country differs across sources, and sometimes these classifications or the specific terminology used is considered disparaging. Use of the term "market" instead of "country" usually indicates specific focus on the characteristics of the countries' capital markets as opposed to the overall economy.
Developing countries can also be categorized by geography:
Other classifications include:
  • Heavily indebted poor countries, a definition by a program of the IMF and World Bank
  • Transition economy, moving from a centrally planned to market-driven economy
  • Multi-dimensional clustering system: with the understanding that different countries have different development priorities and levels of access to resources and institutional capacities and to offer a more nuanced understanding of developing countries and their characteristics, scholars have categorised them into five distinct groups based on factors such as levels of poverty and inequality, productivity and innovation, political constraints and dependence on external flows.

Criticisms and other terms

There is criticism for using the term "developing country". The term could imply inferiority of this kind of country compared with a developed country. It could assume a desire to develop along the traditional Western model of economic development which a few countries, such as Cuba and Bhutan, choose not to follow. Alternative measurements such as gross national happiness have been suggested as important indicators. 

The classification of countries as "developing" implies that other countries are developed. This bipartite division is contentious.

To moderate the euphemistic aspect of the word "developing", international organizations have started to use the term less economically developed country for the poorest nations—which can, in no sense, be regarded as developing. This highlights that the standard of living across the entire developing world varies greatly. Other terms sometimes used are less developed countries, underdeveloped nations, and non-industrialized nations. Conversely, developed countries, most economically developed countries, industrialized nations are the opposite end of the spectrum. 

At the development level, anthropologist and researcher Jason Hickel has challenged the widely propagated narrative that the rich countries of the OECD help the poor countries develop their ecocomies and eradicate poverty. Hickel's findings reveal that the rich countries "aren’t developing poor countries; poor countries are developing rich ones."

Third World

Over the past few decades since the fall of the Soviet Union and the end of the Cold War, the term Third World has been used interchangeably with developing countries, but the concept has become outdated in recent years as it no longer represents the current political or economic state of the world. The three-world model arose during the Cold War to define countries aligned with NATO (the First World), the Communist Bloc (the Second World, although this term was less used), or neither (the Third World). Strictly speaking, "Third World" was a political, rather than an economic, grouping.

Global South

The term "Global South" began to be used more widely since about 2004. It can also include poorer "southern" regions of wealthy "northern" countries. The Global South refers to these countries' "interconnected histories of colonialism, neo-imperialism, and differential economic and social change through which large inequalities in living standards, life expectancy, and access to resources are maintained".

One of the early criticism that questioned the use of the terms 'developing' and 'underdeveloped' countries, but one that did not confine itself to the economic sphere, was made by prominent historian and academic Walter Rodney:
In some quarters, it has often been thought wise to substitute the term ‘developing’ for ‘underdeveloped’. One of the reasons for so doing is to avoid any unpleasantness which may be attached to the second term, which might be interpreted as meaning underdeveloped mentally, physically, morally or in any other respect. Actually, if ‘underdevelopment’ were related to anything other than comparing economies, then the most underdeveloped country in the world would be the U.S.A, which practices external oppression on a massive scale, while internally there is a blend of exploitation, brutality, and psychiatric disorder. However, on the economic level, it is best to remain with the word ‘underdeveloped’ rather than ‘developing’, because the latter creates the impression that all the countries of Africa, Asia and Latin America are escaping from a state of economic backwardness relative to the industrial nations of the world, and that they are emancipating themselves from the relationship of exploitation. That is certainly not true, and many underdeveloped countries in Africa and elsewhere are becoming more underdeveloped in comparison with the world’s great powers, because their exploitation by the metropoles is being intensified in new ways.

Common challenges

Most developing countries have these criteria in common:
  • High levels of poverty – measured based on GNI per capita averaged over three years. For example, if the GNI per capita is less than US $1,025 (as of 2018) the country is regarded as a least developed country.
  • Human resource weakness (based on indicators of nutrition, health, education and adult literacy; for example low literacy levels).
  • Economic vulnerability (based on instability of agricultural production, instability of exports of goods and services, economic importance of non-traditional activities, merchandise export concentration, handicap of economic smallness, and the percentage of population displaced by natural disasters).

Urban slums

According to UN-Habitat, around 33% of the urban population in the developing world in 2012, or about 863 million people, lived in slums. In 2012, the proportion of urban population living in slums was highest in Sub-Saharan Africa (62%), followed by South Asia (35%), Southeast Asia (31%) and East Asia (28%).

The UN-Habitat reports that 43% of urban population in developing countries and 78% of those in the least developed countries are slum dwellers.

Slums form and grow in different parts of the world for many different reasons. Causes include rapid rural-to-urban migration, economic stagnation and depression, high unemployment, poverty, informal economy, forced or manipulated ghettoization, poor planning, politics, natural disasters and social conflicts. For example, as populations expand in poorer countries, rural people are moving to cities in an extensive urban migration that is resulting in the creation of slums.

In some cities, especially in countries in Southern Asia and sub-Saharan, slums are not just marginalized neighborhoods holding a small population; slums are widespread, and are home to a large part of urban population. These are sometimes called "slum cities".

Violence against women

Several forms of violence against women are more prevalent in developing countries than in other parts of the world. For example, dowry violence and bride burning is associated with Ancient India but not the modern one, Bangladesh and Nepal. Acid throwing is also associated with these countries, as well as in Southeast Asia, including Cambodia. Honor killing is associated with the Middle East and South Asia. Marriage by abduction is found in Ethiopia, Central Asia and the Caucasus. Abuse related to payment of bride price (such as violence, trafficking and forced marriage) is linked to parts of Sub-Saharan Africa and Oceania.

Female genital mutilation is another form of violence against women which is still occurring in many developing countries. It is found mostly in Africa, and to a lesser extent in the Middle East and some other parts of Asia. Developing countries with the highest rate of women who have been cut are Somalia (with 98 per cent of women affected), Guinea (96 per cent), Djibouti (93 per cent), Egypt (91 per cent), Eritrea (89 per cent), Mali (89 per cent), Sierra Leone (88 per cent), Sudan (88 per cent), Gambia (76 per cent), Burkina Faso (76 per cent), and Ethiopia (74 per cent). Due to globalization and immigration, FGM is spreading beyond the borders of Africa and Middle East, to countries such as Australia, Belgium, Canada, France, New Zealand, the U.S., and UK.

The Istanbul Convention prohibits female genital mutilation (Article 38). As of 2016, FGM has been legally banned in many African countries.

Public health

People in developing countries usually have a lower life expectancy than people in developed countries. The burden of infectious diseases, maternal mortality, child mortality and infant mortality are typically substantially higher.

Undernutrition is more common in developing countries. Certain groups have higher rates of undernutrition, including women—in particular while pregnant or breastfeedingchildren under five years of age, and the elderly. Malnutrition in children and stunted growth of children is the cause for more than 200 million children under five years of age in developing countries not reaching their developmental potential. About 165 million children were estimated to have stunted growth from malnutrition in 2013. In some developing countries, overnutrition in the form of obesity is beginning to present within the same communities as undernutrition.

The following list shows the further significant environmentally-related causes or conditions, as well as certain diseases with a strong environmental component:

Water, sanitation, hygiene (WASH)

Access to water, sanitation and hygiene (WASH) services is at very low levels in many developing countries. In 2015 the World Health Organization (WHO) estimated that "1 in 3 people, or 2.4 billion, are still without sanitation facilities" while 663 million people still lack access to safe and clean drinking water. The estimate in 2017 by JMP states that 4.5 billion people currently do not have safely managed sanitation. The majority of these people live in developing countries. 

About 892 million people, or 12 per cent of the global population, practiced open defecation instead of using toilets in 2016. Seventy-six per cent (678 million) of the 892 million people practicing open defecation in the world live in just seven countries. India is the country with the highest number of people practicing open defecation. Further countries with a high number of people openly defecating are Nigeria (47 million), followed by Indonesia (31 million), Ethiopia (27 million), Pakistan (23 million), Niger (14 million) and Sudan (11 million).

Sustainable Development Goal 6 is one of 17 Sustainable Development Goals established by the UN in 2015. It calls for clean water and sanitation for all people. This is particularly relevant for people in developing countries.

Energy

In 2009, about 1.4 billion of people in the world lived without electricity. 2.7 billion relied on wood, charcoal, and dung (dry animal dung fuel) for home energy requirements. This lack of access to modern energy technology limits income generation, blunts efforts to escape poverty, affects people's health due to indoor air pollution, and contributes to global deforestation and climate change. Small-scale renewable energy technologies and distributed energy options, such as onsite solar power and improved cookstoves, offer rural households modern energy services.

Renewable energy can be particularly suitable for developing countries. In rural and remote areas, transmission and distribution of energy generated from fossil fuels can be difficult and expensive. Producing renewable energy locally can offer a viable alternative.

Renewable energy can directly contribute to poverty alleviation by providing the energy needed for creating businesses and employment. Renewable energy technologies can also make indirect contributions to alleviating poverty by providing energy for cooking, space heating, and lighting.

Kenya is the world leader in the number of solar power systems installed per capita.

Pollution

Indoor air pollution

Indoor air pollution in developing nations is a major health hazard. A major source of indoor air pollution in developing countries is the burning of biomass. Three billion people in developing countries across the globe rely on biomass in the form of wood, charcoal, dung, and crop residue, as their domestic cooking fuel. Because much of the cooking is carried out indoors in environments that lack proper ventilation, millions of people, primarily poor women and children face serious health risks. 

Globally, 4.3 million deaths were attributed to exposure to IAP in developing countries in 2012, almost all in low and middle income countries. The South East Asian and Western Pacific regions bear most of the burden with 1.69 and 1.62 million deaths, respectively. Almost 600,000 deaths occur in Africa. An earlier estimate from 2000 but the death toll between 1.5 million and 2 million deaths.

Finding an affordable solution to address the many effects of indoor air pollution is complex. Strategies include improving combustion, reducing smoke exposure, improving safety and reducing labor, reducing fuel costs, and addressing sustainability.

Water pollution

Water pollution is a major problem in many developing countries. It requires ongoing evaluation and revision of water resource policy at all levels (international down to individual aquifers and wells). It has been suggested that water pollution is the leading worldwide cause of death and diseases, and that it accounts for the deaths of more than 14,000 people daily.

India and China are two countries with high levels of water pollution: An estimated 580 people in India die of water pollution related illness (including waterborne diseases) every day. About 90 per cent of the water in the cities of China is polluted. As of 2007, half a billion Chinese had no access to safe drinking water.

Further details of water pollution in several countries, including many developing countries:

Global warming

The effects of global warming such as extreme weather events, droughts, floods, biodiversity loss, disease and sea level rise are dangerous for humans and the environment. Developing countries are the least able to adapt to climate change (and are therefore called "highly climate vulnerable") due to their relatively low levels of wealth, technology, education, infrastructure and access to resources. This applies to many countries in Sub-Saharan Africa or Small Island Developing States. Some of those island states are likely to face total inundation. Fragile states or failed states like Afghanistan, Haiti, Myanmar, Sierra Leone, and Somalia are among the worst affected. 

Climate vulnerability has been quantified in the Climate Vulnerability Monitor reports of 2010 and 2012. Climate vulnerability in developing countries occurs in four impact areas: health, extreme weather, habitat loss, and economic stress. A report by the Climate Vulnerability Monitor in 2012 estimated that climate change causes 400,000 deaths on average each year, mainly due to hunger and communicable diseases in developing countries. These effects are most severe for the world’s poorest countries. 

A changing climate also results in economic burdens. The economies in Least Developed Countries have lost an average of 7% of their gross domestic product for the year 2010, mainly due to reduced labor productivity. Rising sea levels cost 1% of GDP to the least developed countries in 2010 – 4% in the Pacific – with 65 billion dollars annually lost from the world economy. Another example is the impact on fisheries: approximately 40 countries are acutely vulnerable to the impact of greenhouse gas emissions on fisheries. Developing countries with large fisheries sectors are particularly affected.

In many cases, developing countries produce only small quantities of greenhouse gas emissions per capita but are very vulnerable to the negative effects of global warming. Such countries include Comoros, The Gambia, Guinea-Bissau, São Tomé and Príncipe, Solomon Islands and Vanuatu - they have been called "forced riders" as opposed to the "free riders". Internationally there is recognition of this issue, which is known under the term "climate justice". It has been a key topic at the United Nations Climate Change Conferences (COP). 

During the Cancún COP16 in 2010, donor countries promised an annual $100 billion by 2020 through the Green Climate Fund for developing countries to adapt to climate change. However, concrete pledges by developed countries have not been forthcoming. Emmanuel Macron (President of France) said at the 2017 United Nations Climate Change Conference in Bonn (COP 23): "Climate change adds further injustice to an already unfair world".

Climate stress is likely to add to existing migration patterns in developing countries and beyond but is not expected to generate entirely new flows of people. A report by World Bank in 2018 estimated that around 143 million people in three regions (Sub-Saharan Africa, South Asia, and Latin America) could be forced to move within their own countries to escape the slow-onset impacts of climate change. They will migrate from less viable areas with lower water availability and crop productivity and from areas affected by rising sea level and storm surges.

Economic development and climate are inextricably linked, particularly around poverty, gender equality, and energy. Tackling climate change will only be possible if the Sustainable Development Goals (SDGs) are met (goal number 13 is on climate action).

Population growth

Over the last few decades, global population growth has largely been driven by developing countries, which often have higher birth rates (higher fertility rate) than developed countries. According to the United Nations, family planning can help to slow population growth and decrease poverty in these countries.

Others

The economies of many developing nations are tried to primary products and a majority of their exports go to advanced nations. When advanced nations encounter economic downturns, they can quickly transmitted to their developing country trading partners as seen in global economic downturn of 2008-2009.

Opportunities

  • Human Capital
  • Trade Policy: Countries with more restrictive policies have not grown as fast as countries with open and less distorted trade policies.
  • Investment: Investment has a positive effect on growth.
  • Education

Gastrointestinal tract

From Wikipedia, the free encyclopedia

Human gastrointestinal tract
Stomach colon rectum diagram-en.svg
Diagram of stomach, intestines and rectum
Details
SystemDigestive system
Identifiers
LatinTractus digestorius (mouth to anus),
canalis alimentarius (esophagus to large intestine),
canalis gastrointestinales (stomach to large intestine)
MeSHD041981

The gastrointestinal tract (digestive tract, digestional tract, GI tract, GIT, gut, or alimentary canal) is an organ system within humans and other animals which takes in food, digests it to extract and absorb energy and nutrients, and expels the remaining waste as feces. The mouth, esophagus, stomach and intestines are part of the gastrointestinal tract. Gastrointestinal is an adjective meaning of or pertaining to the stomach and intestines. A tract is a collection of related anatomic structures or a series of connected body organs.

All bilaterians have a gastrointestinal tract, also called a gut or an alimentary canal. This is a tube that transfers food to the organs of digestion. In large bilaterians, the gastrointestinal tract also has an exit, the anus, by which the animal disposes of feces (solid wastes). Some small bilaterians have no anus and dispose of solid wastes by other means (for example, through the mouth). The human gastrointestinal tract consists of the esophagus, stomach, and intestines, and is divided into the upper and lower gastrointestinal tracts. The GI tract includes all structures between the mouth and the anus, forming a continuous passageway that includes the main organs of digestion, namely, the stomach, small intestine, and large intestine. However, the complete human digestive system is made up of the gastrointestinal tract plus the accessory organs of digestion (the tongue, salivary glands, pancreas, liver and gallbladder). The tract may also be divided into foregut, midgut, and hindgut, reflecting the embryological origin of each segment. The whole human GI tract is about nine metres (30 feet) long at autopsy. It is considerably shorter in the living body because the intestines, which are tubes of smooth muscle tissue, maintain constant muscle tone in a halfway-tense state but can relax in spots to allow for local distention and peristalsis.

The gastrointestinal tract contains trillions of microbes, with some 4,000 different strains of bacteria having diverse roles in maintenance of immune health and metabolism. Cells of the GI tract release hormones to help regulate the digestive process. These digestive hormones, including gastrin, secretin, cholecystokinin, and ghrelin, are mediated through either intracrine or autocrine mechanisms, indicating that the cells releasing these hormones are conserved structures throughout evolution.

Human gastrointestinal tract

Structure

Salivary glandsParotid glandSubmandibular glandSublingual glandpharynxTongueEsophagusPancreasStomachPancreatic ductIleumAnusRectumVermiform appendixCecumDescending colonAscending colonTransverse colonColon (anatomy)Bile ductDuodenumGallbladderLiveroral cavity
Upper and lower human gastrointestinal tract
 
Illustration of human gastrointestinal tract
 
The structure and function can be described both as gross anatomy and as microscopic anatomy or histology. The tract itself is divided into upper and lower tracts, and the intestines small and large parts.

Upper gastrointestinal tract

The upper gastrointestinal tract consists of the mouth, pharynx, esophagus, stomach, and duodenum. The exact demarcation between the upper and lower tracts is the suspensory muscle of the duodenum. This differentiates the embryonic borders between the foregut and midgut, and is also the division commonly used by clinicians to describe gastrointestinal bleeding as being of either "upper" or "lower" origin. Upon dissection, the duodenum may appear to be a unified organ, but it is divided into four segments based upon function, location, and internal anatomy. The four segments of the duodenum are as follows (starting at the stomach, and moving toward the jejunum): bulb, descending, horizontal, and ascending. The suspensory muscle attaches the superior border of the ascending duodenum to the diaphragm

The suspensory muscle is an important anatomical landmark which shows the formal division between the duodenum and the jejunum, the first and second parts of the small intestine, respectively. This is a thin muscle which is derived from the embryonic mesoderm.

Lower gastrointestinal tract

The lower gastrointestinal tract includes most of the small intestine and all of the large intestine. In human anatomy, the intestine (bowel, or gut. Greek: éntera) is the segment of the gastrointestinal tract extending from the pyloric sphincter of the stomach to the anus and, as in other mammals, consists of two segments, the small intestine and the large intestine. In humans, the small intestine is further subdivided into the duodenum, jejunum and ileum while the large intestine is subdivided into the, cecum, ascending, transverse, descending and sigmoid colon, rectum, and anal canal.
Small intestine
The small intestine begins at the duodenum and is a tubular structure, usually between 6 and 7 m long. Its mucosal area in an adult human is about 30 m2. Its main function is to absorb the products of digestion (including carbohydrates, proteins, lipids, and vitamins) into the bloodstream. There are three major divisions:
  1. Duodenum: A short structure (about 20–25 cm long) which receives chyme from the stomach, together with pancreatic juice containing digestive enzymes and bile from the gall bladder. The digestive enzymes break down proteins, and bile emulsifies fats into micelles. The duodenum contains Brunner's glands which produce a mucus-rich alkaline secretion containing bicarbonate. These secretions, in combination with bicarbonate from the pancreas, neutralize the stomach acids contained in the chyme.
  2. Jejunum: This is the midsection of the small intestine, connecting the duodenum to the ileum. It is about 2.5 m long, and contains the circular folds also known as plicae circulares, and villi that increase its surface area. Products of digestion (sugars, amino acids, and fatty acids) are absorbed into the bloodstream here.
  3. Ileum: The final section of the small intestine. It is about 3 m long, and contains villi similar to the jejunum. It absorbs mainly vitamin B12 and bile acids, as well as any other remaining nutrients.
Large intestine
The large intestine also called the colon, consists of the cecum, rectum, and anal canal. It also includes the appendix, which is attached to the cecum. The colon is further divided into:
  1. Cecum (first portion of the colon) and appendix
  2. Ascending colon (ascending in the back wall of the abdomen)
  3. Right colic flexure (flexed portion of the ascending and transverse colon apparent to the liver)
  4. Transverse colon (passing below the diaphragm)
  5. Left colic flexure (flexed portion of the transverse and descending colon apparent to the spleen)
  6. Descending colon (descending down the left side of the abdomen)
  7. Sigmoid colon (a loop of the colon closest to the rectum)
  8. Rectum
  9. Anus
The main function of the large intestine is to absorb water. The area of the large intestinal mucosa of an adult human is about 2 m2.

Development

The gut is an endoderm-derived structure. At approximately the sixteenth day of human development, the embryo begins to fold ventrally (with the embryo's ventral surface becoming concave) in two directions: the sides of the embryo fold in on each other and the head and tail fold toward one another. The result is that a piece of the yolk sac, an endoderm-lined structure in contact with the ventral aspect of the embryo, begins to be pinched off to become the primitive gut. The yolk sac remains connected to the gut tube via the vitelline duct. Usually this structure regresses during development; in cases where it does not, it is known as Meckel's diverticulum

During fetal life, the primitive gut is gradually patterned into three segments: foregut, midgut, and hindgut. Although these terms are often used in reference to segments of the primitive gut, they are also used regularly to describe regions of the definitive gut as well. 

Each segment of the gut is further specified and gives rise to specific gut and gut-related structures in later development. Components derived from the gut proper, including the stomach and colon, develop as swellings or dilatations in the cells of the primitive gut. In contrast, gut-related derivatives — that is, those structures that derive from the primitive gut but are not part of the gut proper, in general develop as out-pouchings of the primitive gut. The blood vessels supplying these structures 
remain constant throughout development.

Part Part in adult Gives rise to Arterial supply
Foregut Esophagus to first 2 sections of the duodenum Esophagus, Stomach, Duodenum (1st and 2nd parts), Liver, Gallbladder, Pancreas, Superior portion of pancreas
(Note that though the Spleen is supplied by the celiac trunk, it is derived from dorsal mesentery and therefore not a foregut derivative)
celiac trunk
Midgut lower duodenum, to the first two-thirds of the transverse colon lower duodenum, jejunum, ileum, cecum, appendix, ascending colon, and first two-third of the transverse colon branches of the superior mesenteric artery
Hindgut last third of the transverse colon, to the upper part of the anal canal last third of the transverse colon, descending colon, rectum, and upper part of the anal canal branches of the inferior mesenteric artery

Histology

General structure of the gut wall
  • 1: Mucosa: Epithelium
  • 2: Mucosa: Lamina propria
  • 3: Mucosa: Muscularis mucosae
  • 4: Lumen
  • 5: Lymphatic tissue
  • 6: Duct of gland outside tract
  • 7: Gland in mucosa
  • 8: Submucosa
  • 9: Glands in submucosa
  • 10: Meissner's submucosal plexus
  • 11: Vein
  • 12: Muscularis: Circular muscle
  • 13: Muscularis: Longitudinal muscle
  • 14: Serosa: Areolar connective tissue
  • 15: Serosa: Epithelium
  • 16: Auerbach's myenteric plexus
  • 17: Nerve
  • 18: Artery
  • 19: Mesentery
The gastrointestinal tract has a form of general histology with some differences that reflect the specialization in functional anatomy. The GI tract can be divided into four concentric layers in the following order:
Mucosa
The mucosa is the innermost layer of the gastrointestinal tract. The mucosa surrounds the lumen, or open space within the tube. This layer comes in direct contact with digested food (chyme). The mucosa is made up of:
  • Epithelium – innermost layer. Responsible for most digestive, absorptive and secretory processes.
  • Lamina propria – a layer of connective tissue. Unusually cellular compared to most connective tissue
  • Muscularis mucosae – a thin layer of smooth muscle that aids the passing of material and enhances the interaction between the epithelial layer and the contents of the lumen by agitation and peristalsis.
The mucosae are highly specialized in each organ of the gastrointestinal tract to deal with the different conditions. The most variation is seen in the epithelium.
Submucosa
The submucosa consists of a dense irregular layer of connective tissue with large blood vessels, lymphatics, and nerves branching into the mucosa and muscularis externa. It contains the submucosal plexus, an enteric nervous plexus, situated on the inner surface of the muscularis externa.
Muscular layer
The muscular layer consists of an inner circular layer and a longitudinal outer layer. The circular layer prevents food from traveling backward and the longitudinal layer shortens the tract. The layers are not truly longitudinal or circular, rather the layers of muscle are helical with different pitches. The inner circular is helical with a steep pitch and the outer longitudinal is helical with a much shallower pitch. Whilst the muscularis externa is similar throughout the entire gastrointestinal tract, an exception is the stomach which has an additional inner oblique muscular layer to aid with grinding and mixing of food. The muscularis externa of the stomach is composed of the inner oblique layer, middle circular layer and outer longitudinal layer.

Between the circular and longitudinal muscle layers is the myenteric plexus. This controls peristalsis. Activity is initiated by the pacemaker cells, (myenteric interstitial cells of Cajal). The gut has intrinsic peristaltic activity (basal electrical rhythm) due to its self-contained enteric nervous system. The rate can be modulated by the rest of the autonomic nervous system.

The coordinated contractions of these layers is called peristalsis and propels the food through the tract. Food in the GI tract is called a bolus (ball of food) from the mouth down to the stomach. After the stomach, the food is partially digested and semi-liquid, and is referred to as chyme. In the large intestine the remaining semi-solid substance is referred to as faeces.
Adventitia and serosa
The outermost layer of the gastrointestinal tract consists of several layers of connective tissue

Intraperitoneal parts of the GI tract are covered with serosa. These include most of the stomach, first part of the duodenum, all of the small intestine, caecum and appendix, transverse colon, sigmoid colon and rectum. In these sections of the gut there is clear boundary between the gut and the surrounding tissue. These parts of the tract have a mesentery

Retroperitoneal parts are covered with adventitia. They blend into the surrounding tissue and are fixed in position. For example, the retroperitoneal section of the duodenum usually passes through the transpyloric plane. These include the esophagus, pylorus of the stomach, distal duodenum, ascending colon, descending colon and anal canal. In addition, the oral cavity has adventitia.

Gene and protein expression

Approximately 20,000 protein coding genes are expressed in human cells and 75% of these genes are expressed in at least one of the different parts of the digestive organ system. Over 600 of these genes are more specifically expressed in one or more parts of the GI tract and the corresponding proteins have functions related to digestion of food and uptake of nutrients. Examples of specific proteins with such functions are pepsinogen PGC and the lipase LIPF, expressed in chief cells, and gastric ATPase ATP4A and gastric intrinsic factor GIF, expressed in parietal cells of the stomach mucosa. Specific proteins expressed in the stomach and duodenum involved in defence include mucin proteins, such as mucin 6 and intelectin-1.

Function

The time taken for food or other ingested objects to transit through the gastrointestinal tract varies depending on many factors, but roughly, it takes less than an hour after a meal for 50% of stomach contents to empty into the intestines while total emptying takes around 2 hours. Subsequently, 50% emptying of the small intestine takes between 1 and 2 hours. Finally, transit through the colon takes 12 to 50 hours with wide variation between individuals.

Immune function

Immune barrier
The gastrointestinal tract forms an important part of the immune system. The surface area of the digestive tract is estimated to be about 32 square meters, or about half a badminton court. With such a large exposure (more than three times larger than the exposed surface of the skin), these immune components function to prevent pathogens from entering the blood and lymph circulatory systems. Fundamental components of this protection are provided by the intestinal mucosal barrier which is composed of physical, biochemical, and immune elements elaborated by the intestinal mucosa. Microorganisms also are kept at bay by an extensive immune system comprising the gut-associated lymphoid tissue (GALT) 

There are additional factors contributing to protection from pathogen invasion. For example, low pH (ranging from 1 to 4) of the stomach is fatal for many microorganisms that enter it. Similarly, mucus (containing IgA antibodies) neutralizes many pathogenic microorganisms. Other factors in the GI tract contribution to immune function include enzymes secreted in the saliva and bile.
Immune system homeostasis
Beneficial bacteria also can contribute to the homeostasis of the gastrointestinal immune system. For example, Clostridia, one of the most predominant bacterial groups in the GI tract, play an important role in influencing the dynamics of the gut's immune system. It has been demonstrated that the intake of a high fiber diet could be the responsible for the induction of T-regulatory cells (Tregs). This is due to the production of short-chain fatty acids during the fermentation of plant-derived nutrients such as butyrate and propionate. Basically, the butyrate induces the differentiation of Treg cells by enhancing histone H3 acetylation in the promoter and conserved non-coding sequence regions of the FOXP3 locus, thus regulating the T cells, resulting in the reduction of the inflammatory response and allergies.

Intestinal microbiota

The large intestine hosts several kinds of bacteria that can deal with molecules that the human body cannot otherwise break down. This is an example of symbiosis. These bacteria also account for the production of gases at host-pathogen interface, inside our intestine(this gas is released as flatulence when eliminated through the anus). However the large intestine is mainly concerned with the absorption of water from digested material (which is regulated by the hypothalamus) and the re absorption of sodium, as well as any nutrients that may have escaped primary digestion in the ileum.

Health-enhancing intestinal bacteria of the gut flora serve to prevent the overgrowth of potentially harmful bacteria in the gut. These two types of bacteria compete for space and "food," as there are limited resources within the intestinal tract. A ratio of 80-85% beneficial to 15–20% potentially harmful bacteria generally is considered normal within the intestines.

Detoxification and drug metabolism

Enzymes such as CYP3A4, along with the antiporter activities, are also instrumental in the intestine's role of drug metabolism in the detoxification of antigens and xenobiotics.

Clinical significance

Diseases

There are many diseases and conditions that can affect the gastrointestinal system, including infections, inflammation and cancer

Various pathogens, such as bacteria that cause foodborne illnesses, can induce gastroenteritis which results from inflammation of the stomach and small intestine. Antibiotics to treat such bacterial infections can decrease the microbiome diversity of the gastrointestinal tract, and further enable inflammatory mediators. Gastroenteritis is the most common disease of the GI tract.
Diverticular disease is a condition that is very common in older people in industrialized countries. It usually affects the large intestine but has been known to affect the small intestine as well. Diverticulosis occurs when pouches form on the intestinal wall. Once the pouches become inflamed it is known as diverticulitis

Inflammatory bowel disease is an inflammatory condition affecting the bowel walls, and includes the subtypes Crohn's disease and ulcerative colitis. While Crohn's can affect the entire gastrointestinal tract, ulcerative colitis is limited to the large intestine. Crohn's disease is widely regarded as an autoimmune disease. Although ulcerative colitis is often treated as though it were an autoimmune disease, there is no consensus that it actually is such. 

Functional gastrointestinal disorders the most common of which is irritable bowel syndrome. Functional constipation and chronic functional abdominal pain are other functional disorders of the intestine that have physiological causes, but do not have identifiable structural, chemical, or infectious pathologies.

Symptoms

Several symptoms are used to indicate problems with the gastrointestinal tract:

Treatment

Gastrointestinal surgery can often be performed in the outpatient setting. In the United States in 2012, operations on the digestive system accounted for 3 of the 25 most common ambulatory surgery procedures and constituted 9.1 percent of all outpatient ambulatory surgeries.

Imaging

Various methods of imaging the gastrointestinal tract include the upper and lower gastrointestinal series:

Other related diseases

  • Cholera
  • Enteric duplication cyst
  • Giardiasis
  • Pancreatitis
  • Peptic ulcer disease
  • Yellow fever
  • Helicobacter pylori is a gram-negative spiral bacterium. Over half the world's population is infected with it, mainly during childhood; it is not certain how the disease is transmitted. It colonizes the gastrointestinal system, predominantly the stomach. The bacterium has specific survival conditions that our gastric microenvironment: it is both capnophilic and microaerophilic. Helicobacter also exhibits a tropism for gastric epithelial lining and the gastric mucosal layer about it. Gastric colonization of this bacterium triggers a robust immune response leading to moderate to severe inflammation. Signs and symptoms of infection are gastritis, burning abdominal pain, weight loss, loss of appetite, bloating, burping, nausea, bloody vomit, and black tarry stools. Infection can be detected in a number of ways: GI X-rays, endoscopy, blood tests for anti-Helicobacter antibodies, a stool test, and a urease breath test (which is a by-product of the bacteria). If caught soon enough, it can be treated with three doses of different proton pump inhibitors as well as two antibiotics, taking about a week to cure. If not caught soon enough, surgery may be required.
  • Intestinal pseudo-obstruction is a syndrome caused by a malformation of the digestive system, characterized by a severe impairment in the ability of the intestines to push and assimilate. Symptoms include daily abdominal and stomach pain, nausea, severe distension, vomiting, heartburn, dysphagia, diarrhea, constipation, dehydration and malnutrition. There is no cure for intestinal pseudo-obstruction. Different types of surgery and treatment managing life-threatening complications such as ileus and volvulus, intestinal stasis which lead to bacterial overgrowth, and resection of affected or dead parts of the gut may be needed. Many patients require parenteral nutrition.
  • Ileus is a blockage of the intestines.
  • Coeliac disease is a common form of malabsorption, affecting up to 1% of people of northern European descent. An autoimmune response is triggered in intestinal cells by digestion of gluten proteins. Ingestion of proteins found in wheat, barley and rye, causes villous atrophy in the small intestine. Lifelong dietary avoidance of these foodstuffs in a gluten-free diet is the only treatment.
  • Enteroviruses are named by their transmission-route through the intestine (enteric meaning intestinal), but their symptoms aren't mainly associated with the intestine.
  • Endometriosis can affect the intestines, with similar symptoms to IBS.
  • Bowel twist (or similarly, bowel strangulation) is a comparatively rare event (usually developing sometime after major bowel surgery). It is, however, hard to diagnose correctly, and if left uncorrected can lead to bowel infarction and death. (The singer Maurice Gibb is understood to have died from this.)
  • Angiodysplasia of the colon
  • Constipation
  • Diarrhea
  • Hirschsprung's disease (aganglionosis)
  • Intussusception
  • Polyp (medicine)
  • Pseudomembranous colitis
  • Toxic megacolon usually a complication of ulcerative colitis

Uses of animal guts

Intestines from animals other than humans are used in a number of ways. From each species of livestock that is a source of milk, a corresponding rennet is obtained from the intestines of milk-fed calves. Pig and calf intestines are eaten, and pig intestines are used as sausage casings. Calf intestines supply calf-intestinal alkaline phosphatase (CIP), and are used to make goldbeater's skin. Other uses are:
  • The use of animal gut strings by musicians can be traced back to the third dynasty of Egypt. In the recent past, strings were made out of lamb gut. With the advent of the modern era, musicians have tended to use strings made of silk, or synthetic materials such as nylon or steel. Some instrumentalists, however, still use gut strings in order to evoke the older tone quality. Although such strings were commonly referred to as "catgut" strings, cats were never used as a source for gut strings.
  • Sheep gut was the original source for natural gut string used in racquets, such as for tennis. Today, synthetic strings are much more common, but the best gut strings are now made out of cow gut.
  • Gut cord has also been used to produce strings for the snares that provide a snare drum's characteristic buzzing timbre. While the modern snare drum almost always uses metal wire rather than gut cord, the North African bendir frame drum still uses gut for this purpose.
  • "Natural" sausage hulls, or casings, are made of animal gut, especially hog, beef, and lamb.
  • The wrapping of kokoretsi, gardoubakia, and torcinello is made of lamb (or goat) gut.
  • Haggis is traditionally boiled in, and served in, a sheep stomach.
  • Chitterlings, a kind of food, consist of thoroughly washed pig's gut.
  • Animal gut was used to make the cord lines in longcase clocks and for fusee movements in bracket clocks, but may be replaced by metal wire.
  • The oldest known condoms, from 1640 AD, were made from animal intestine.

Other animals

Many birds and other animals have a specialised stomach in the digestive tract called a gizzard used for grinding up food. 

Another feature not found in the human but found in a range of other animals is the crop. In birds this is found as a pouch alongside the esophagus. 

Other animals including amphibians, birds, reptiles, and egg-laying mammals have a major difference in their GI tract in that it ends in a cloaca and not an anus.

Classical radicalism

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