document_title: Platte River

question_text: where do the north and south platte rivers meet

text: Platte River

text: Geography[edit]

text: Headwaters[edit]

text: The Platte River is formed in western Nebraska east of the city of North Platte, Nebraska by the confluence of the North Platte and the South Platte Rivers, which both arise from snowmelt in the eastern Rockies east of the Continental Divide.

text: In central north Colorado is the North Park valley, ringed by mountains of 12,000 feet (3,700 m) height; this is where the North Platte River originates. The head of the North Platte River is essentially all of Jackson County; its boundaries are the continental divide on the west and south and the mountain drainage peaks on the east—the north boundary is the state of Wyoming. The nearest Colorado town is Walden, the county seat. The rugged Rocky Mountains Continental Divide surrounding Jackson County have at least twelve peaks over 11,000 feet (3,400 m) in height. From Jackson County, the North Platte flows north about 200 miles (320 km) out of the Routt National Forest and North Park near what is now Walden to Casper, Wyoming. Shortly after passing Casper, the North Platte turns to the east-southeast and flows about 350 miles (560 km) to the city of North Platte, Nebraska. In Colorado and Wyoming, the North Platte is narrower and much swifter flowing than it is in Nebraska, where it becomes a slow flowing, shallow braided stream.

text: The North Platte River has been dammed about eight times for water storage and irrigation purposes in Wyoming and Nebraska as it flows to its confluence with the South Platte River. The upper reaches of the river in the Rockies in Colorado and Wyoming are popular for recreation rafting and lure and fly fishing for rainbow, brown, cutthroat trout and other sport fish. In western Nebraska, the banks and riverbed of the North Platte provide a green oasis amid an otherwise semi-arid region of North America. Today, by the time the North Platte reaches Paxton, Nebraska it is much smaller due to the extensive water taken from it for irrigation. Historically, the North Platte River was up to a mile wide (1.6 km) in many places, as evidenced by the old streambed and historic written records.[citation needed]

text: The South Platte River drainage includes about 28,000 square miles (73,000 km2) in the north east corner of Colorado, parts of southeastern Wyoming in the vicinity of the city of Cheyenne and a small part of the southwest corner of Nebraska.[6] The South Platte drains a large part of the Front Range mountains east of the continental divide. The part of the river labeled the South Platte is formed in Park County, Colorado, located southwest of Denver, in the South Park grassland basin and mountains east of the continental divide. It is formed by the confluence of the South Fork South Platte River and Middle Fork South Platte River, approximately 15 miles (24 km) southeast of Fairplay, Colorado. After the South and Middle fork join, the South Platte flows east-southeast till it exits Elevenmile Reservoir; it turns almost ninety degrees to skirt the west side of Pikes Peak and flows roughly east-northeast about 100 miles (160 km) through Denver and on to Greeley, Colorado. From Greeley, the South Platte turns east and flows about 200 miles (320 km) to its confluence with the North Platte River near the city of North Platte, Nebraska.

text: The South Platte River has been dammed about 20 times for water storage, drinking water and irrigation purposes in Colorado as it flows to its confluence with the North Platte River. The total number of dams in the South Platte drainage may exceed 1,000 as nearly all major streams have at least one dam on them.[7] The South Platte River serves as the principal source of water for arid eastern Colorado. The South Platte River valley provided a major emigration path to Denver. The wagon trails followed the south side of the Platte/North Platte River. Wagon trains were ferried or waded in low water years across the swampy-bottomed South Platte River in several places to stay on the south side of the North Platte River where the trails were located. Miners who later went on to Denver followed the South Platte River trail into Colorado.

text: Main stem[edit]

text: After the North Platte and the South Platte rivers join to form the Platte River, over most of its length it is a muddy, broad, shallow, meandering stream with a swampy bottom and many islands—a braided stream. Its muddy water, many shallow channels and islands and ever-changing mud bars made it too difficult for even canoe travel; it was never used as a major water transportation route. The Platte flows in a large arc, east-southeast to near Fort Kearny and then east-northeast, across Nebraska south of Grand Island and on to Columbus.[8] The Platte River is joined from the north by the about 70-mile-long (110 km) Loup River about 5 miles (8 km) southeast of Columbus. During pioneer days, a Loup River ferry crossed the river. From Columbus, the Platte flows almost due east about 50 miles (80 km) past North Bend and then on to Fremont.

text: Near Fremont, the Platte bends south and then east around the location of Omaha in a large "L" turn. Near Fremont the Platte turns sharply and flows south-southeast about 10 miles (16 km) to about Waterloo, Nebraska—located about 20 miles (32 km) west of Omaha. Near Waterloo the Platte turns even more and heads almost due south for about 10 miles (16 km). About 30 miles (48 km) east-southeast of Waterloo and about 30 miles (48 km) from the Platte's confluence with the Missouri River, the Platte is joined from the north by the Elkhorn River. The Elkhorn, a 290-mile-long (470 km)[9] river, originates in the eastern Sandhills of Nebraska and is one of the largest tributaries of the Platte River. The Elkhorn joins the Platte on its south-bound path just southwest of Omaha, approximately 1 mile (2 km) south and 3 miles (5 km) west of Gretna. The pioneers leaving from near Omaha (established 1854) or Council Bluffs, Iowa (established 1846) used the Mormon Trail north of the Platte River and had to ferry across the Elkhorn. After the Union Pacific railroad was constructed west from Omaha in 1866, it had to build a major bridge across the Elkhorn.[10] After the confluence of the Elkhorn and the Platte River, the Platte continues southward, about 7 miles (11 km) before it turns sharply and heads almost due East for about 20 miles (32 km) before its confluence with the Missouri River. Sarpy County is shaped like a crescent, being bounded on the east by the Missouri River, on the south and west by the Platte, and on the north by Douglas County which contains Omaha. The Platte-Missouri River confluence is about 10 miles (16 km) south of Omaha.

text: Including the North Platte River, the Platte River stretches over 850 miles (1,400 km), with a drainage basin of about 90,000 square miles (230,000 km2). The mean annual flow is estimated at 3,240 cu ft/s (92 m3/s). The Platte drains one of the most arid areas of the Great Plains with a flow that is considerably lower than rivers of comparable length in North America. For much of its length, it is a classic wide, muddy and shallow braided stream which in the lower reaches flows in a floodplain bordered by bluffs.[11] During pioneer days, the common humorous description was that the Platte was "a mile wide at the mouth, but only six inches deep." 49ers said it was "too thick to drink, too thin to plow". In western Nebraska, the banks and riverbed of the Platte provide a green oasis amid an otherwise semi-arid region of North America. The central Platte River valley is an important stopover for migratory water birds, such as the whooping crane and sandhill crane, in their yearly traversal of the Central Flyway.[citation needed]

text: Since the mid-20th century, this river has shrunk significantly. This reduction in size is attributed in part to its waters being used for irrigation, and to a much greater extent to the waters diverted and used by the growing population of Colorado, which has outstripped the ability of its groundwater to sustain them.

text: History[edit]

text: Varying cultures of indigenous peoples lived intermittently along the Platte for thousands of years before European exploration. Historical tribes claimed various territories in the region. The Indian tribes typically visited different areas in different seasons, as they followed the bison herds for hunting periods. The introduction of horses, which had escaped from early Spanish explorers in the 1540s, dramatically changed life in the Great Plains. Indian tribes could more easily follow the buffalo herds as they migrated from north to south and back. Before 1870, herds of several hundred thousand bison (buffalo) periodically migrated across the Platte in following seasonal grazing. The animals often waded or swam across the Platte. The first-known European to see the Platte was the French explorer Étienne de Veniard, sieur de Bourgmont in 1714, who named it the Nebraskier, after its Oto name, meaning "flat water". The French later applied the French word plate (meaning flat, and pronounced plat, or platte) to the river.[12]

text: Occupied by various Indian tribes for part of each year, the Platte River territory had been claimed by both Spanish and French explorers trying to rule the Great Plains. Spain had "claimed" all of the Great Plains after Coronado's 1541–42 expedition. Jose Naranjo, an African-Hopi who served as a Spanish scout and explorer in the Southwest, was a war captain of the Spanish Indian auxiliaries. By 1714 (the same year the French explorers "discovered" the Platte), he and a small exploration group from the south had reportedly already reached the Platte three times.[13] He later guided the 1720 Villasur expedition to the area in a Spanish effort to stop French expansion onto the Great Plains. Naranjo and Villasur's party made the most northern of Spanish exploration trips into the central plains. A Pawnee and Otoe Indian attack defeated the Spanish forces; the survivors returned to Santa Fe, New Mexico, and the Spanish left the Great Plains to the American Indians.

text: As a result of the Seven Years' War (1756–1763) (called the French and Indian War in America), the French ceded all of their lands in North America east of the Mississippi River to the British. The Spanish took over lands west of the Mississippi River. Since there were few fur-bearing animals on the Platte of interest to the fur traders, the French and British explorers and fur trappers ignored the Platte territory for some time. During the course of the Napoleonic Wars (1803–1815), France briefly reacquired the land west of the Mississippi River from Spain.

text: In 1804, Napoleon sold the area west of the Mississippi River to the US in the Louisiana Purchase; the US roughly doubled its area at a cost of about $15,000,000. In 1820 the U.S. Army ordered Major Stephen H. Long to explore and map the area around the Platte. Long reported the area as a great American "desert," ignoring that the "desert" provided habitat for more than a million buffalo and numerous American Indians had long lived in the area. As a result of his and other reports, the US initially had little interest in settling the land on the plains. The next "good" land was believed to be in Oregon or California, especially the coastal areas, and those were the destinations of most emigrant traffic. The Mormons settled Utah, largely due to religious persecution in eastern areas. Various gold and silver strikes attracted further emigration to nearly all western states.

text: The Native American trail west along the Platte, North Platte River and Sweetwater River was first written about after its discovery in 1811 by Wilson Price Hunt of the Astor Expedition. He was returning to the Missouri River posts from the newly established Fort Astoria on the Columbia River near the Pacific Ocean. Because few American trappers and settlers were then in the contested Oregon Territory, his trail discovery was little used and nearly forgotten.

text: In 1823 Jedediah Smith and several trappers "rediscovered" the route. The trail along the Platte, North Platte and Sweetwater rivers became a major route of fur traders to their summer Rocky Mountain Rendezvous. In 1824 fur trappers and traders directing mule trains carrying trade goods and supplies for the mountain men were some of the first European-American parties to use the trail. On their return trip, the fur traders carried out for furs destined for eastern markets. The fur trade route was used to about 1840.

text: By about 1832, the fur traders had improved the trail along the Platte, North Platte, and Sweetwater rivers to a rough wagon trail from the Missouri River to the Green River in Wyoming, where most of the Rocky Mountain Rendezvous were held. In 1834 Benjamin Bonneville, a U.S. Army officer on leave, led an expedition to the west financed by John Jacob Astor. They took wagons along the Platte, North Platte and Sweetwater River trail to the Green River in present-day Wyoming. The notable author Washington Irving wrote an account of Bonneville's explorations in the west that made him well known in the US.

text: Following the fur traders, the major emigration trails established along the north and south banks of the Platte and North Platte River were the Oregon (1843–1869), California (1843–1869), Mormon (1847–1869) and the Bozeman (1863–68) trails. This network of trails, sometimes called the Emigrant Trails or the Great Platte River Road, all went west along both sides of the Platte River. The route along the Platte River included all these emigration trails and was developed as an important trail route used by migrant wagon trains for westward United States expansion after 1841. The settlement of the Oregon boundary dispute with Britain in 1846, the conclusion of the Mexican–American War in 1848, and the California Gold Rush in 1849 and other gold and silver strikes rapidly attracted increased emigrant traffic west.

text: The Platte River in the future state of Nebraska and the North Platte River in Wyoming typically had many channels and islands. The waterways were often too shallow, crooked, muddy and unpredictable for a canoe to travel far. The Platte River valley provided an easily passable wagon corridor; it sloped gradually up in height as it went almost due west from the Missouri. The Platte route had access to water, grass, buffalo and buffalo 'chips,' which the Indians and emigrants used as fuel for fires.[14] Long Native American use had created trails on both sides of the muddy, about 1 mile (1.6 km) wide and shallow Platte River. The Platte's water was silty and bad tasting, but it was usable if no other water was available. Emigrants learned to let it sit in a bucket for an hour or so to settle most of the silt. The trail(s) through the Platte River Valley extended about 450 miles (720 km) in the present state of Nebraska. Nearly all the trails from the Missouri converged on the Platte River at or before Fort Kearny in mid-state Nebraska. Historians have estimated about 400,000 emigrants followed the trails along the Platte.

text: The Pony Express, operational from 1860–61, and the First Transcontinental Telegraph, completed in 1861, both followed the earlier emigrant trails along the Platte. The completion of the telegraph put the Pony Express out of business as it could provide much faster east–west communication. In 1866 the Union Pacific portion of the first transcontinental railroad was constructed along the Platte River as it started west from Omaha. In the 20th century, the Lincoln Highway and later Interstate 80 were constructed through the Platte valley. The highways parallel the Platte and the North Platte through much of Nebraska.

text: Many of Nebraska’s larger cities originated on or near the Platte River, as it was the first path of transportation. These include Omaha (est. 1854), Fort Kearny (est. 1848), Grand Island (est. 1857) and North Platte (est. 1869). In 1859 settlers built the first irrigation ditch to divert water from the Platte for farming.

text: Birds[edit]

text: The Platte is in the middle of the Central Flyway,[15] a primary north–south corridor for migratory birds from their summer nesting grounds in the north (Alaska and Canada), south for the winter, and the return in the spring. The Central Flyway bird species include trumpeter swans, tundra swans, over one million Canada geese, greater white-fronted geese, sandhill cranes, canvasback ducks and others.[16] Other species such as bald eagles, herons and several species of ducks migrate through the Platte River area but over shorter distances. The whooping crane, piping plover, and the interior least tern are birds using the flyway which have been classified as endangered and are protected under the Platte River Endangered Species Partnership.

text: Common plants in the Platte River area are big and little bluestem, switch grass, and cottonwood trees. White-tail deer, many types of catfish, Canada geese, and bald eagles attract fans. The Platte River area has long supported many animals but recently, due to urbanization and farming causing loss of habitat, the numbers have declined. Canada geese have adapted to the farm fields and scavenge a large part of their fare from unharvested grain. Many have taken up residence at suburban office parks and stopped seasonal migrations.

text: Management and policy[edit]

text: The Platte River flowing through an arid part of the mid-west has been widely overused. The claims on the Platte River water have exceeded the supply of water in drier years. The criteria for water over-appropriation, according to the final reading of LB 962, is that if the river basin, sub basin, or reach is subject to an interstate cooperative agreement among three or more states and if, prior to such date, the department has declared a moratorium on the issuance of new surface water appropriations in such river basin, sub basin or reach and has requested each natural resource district with jurisdiction in the affected area in such river basin, sub basin or reach either to close or to continue in effect a previously adopted closure of all or part of such river basin, sub basin, or reach to the issuance of additional water well permits in accordance with subdivision. Most of the Platte River basin is currently considered as overappropriated.

text: Beginning in 2004, a number of Nebraska stakeholders embarked upon the Platte River Cooperative Hydrology Study (COHYST). Conducted with assistance from the United States Geological Survey and the Natural Resources Conservation Service, this study attempts to arrive at a better understanding of the geology and hydrology of the Platte River basin from the Colorado and Wyoming borders to Columbus, including the Loup basin. This improved understanding could be used to develop policies for management of the river system, both for human use and for the sake of the basin's endangered species. As of October 2009, the study is still ongoing.[17][18]


document_title: Small intestine

question_text: the terminal part of the stomach that opens into the duodenum is the

root

text: Small intestine

text: Structure[edit]

text: Size[edit]

text: The length of the small intestine can vary greatly, from as short as 2.75 m (9.0 ft) to as long as 10.49 m (34.4 ft).[3] The average length in a living person is 3m-5m.[4][5] The length depends both on how tall the person is and how the length is measured.[3] Taller people generally have a longer small intestine and measurements are generally longer after death and when the bowel is empty.[3]

tag: p

text: It is approximately 1.5 cm in diameter in newborns after 35 weeks of gestational age,[6] and 2.5–3 cm (1 inch) in diameter in adults. On abdominal X-rays, the small intestine is considered to be abnormally dilated when the diameter exceeds 3 cm.[7][8] On CT scans, a diameter of over 2.5 cm is considered abnormally dilated.[7][9] The surface area of the human small intestinal mucosa, due to enlargement caused by folds, villi and microvilli, averages 30 square meters.[10]

text: Parts[edit]

text: The small intestine is divided into three structural parts.

text:
The duodenum is a short structure ranging from 20 cm (7.9 inches) to 25 cm (9.8 inches) in length, and shaped like a "C".[11] It surrounds the head of the pancreas. It receives gastric chyme from the stomach, together with digestive juices from the pancreas (digestive enzymes) and the liver (bile). 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 gastric chyme.
The jejunum is the midsection of the small intestine, connecting the duodenum to the ileum. It is about 2.5 m long, and contains the plicae circulares, and villi that increase its surface area. Products of digestion (sugars, amino acids, and fatty acids) are absorbed into the bloodstream here. The suspensory muscle of duodenum marks the division between the duodenum and the jejunum.
The 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. The ileum joins to the cecum of the large intestine at the ileocecal junction.

tag: ul

text: The jejunum and ileum are suspended in the abdominal cavity by mesentery. The mesentery is part of the peritoneum. Arteries, veins, lymph vessels and nerves travel within the mesentery.[12]

text: Blood supply[edit]

text: The small intestine receives a blood supply from the coeliac trunk and the superior mesenteric artery. These are both branches of the aorta. The duodenum receives blood from the coeliac trunk via the superior pancreaticoduodenal artery and from the superior mesenteric artery via the inferior pancreaticoduodenal artery. These two arteries both have anterior and posterior branches that meet in the midline and anastomose. The jejunum and ileum receive blood from the superior mesenteric artery.[13] Branches of the superior mesenteric artery form a series of arches within the mesentery known as arterial arcades, which may be several layers deep. Straight blood vessels known as vasa recta travel from the arcades closest to the ileum and jejunum to the organs themselves.[13]

text: Histology[edit]

text: The three sections of the small intestine look similar to each other at a microscopic level, but there are some important differences. The parts of the intestine are as follows:

text:
Layer
Duodenum
Jejunum
Ileum

Serosa
1st part serosa, 2nd–4th adventitia
Normal
Normal

Muscularis externa
Longitudinal and circular layers, with Auerbach's (myenteric) plexus in between
Same as duodenum
Same as duodenum

Submucosa
Brunner's glands and Meissner's (submucosal) plexus
No BG
No BG

Mucosa: muscularis mucosae
Normal
Normal
Normal

Mucosa: lamina propria
No PP
No PP
Peyer's patches

Mucosa: intestinal epithelium
Simple columnar. Contains goblet cells, Paneth cells
Similar to duodenum
?

tag: table

text: Development[edit]

text: The small intestine develops from the midgut of the primitive gut tube.[14] By the fifth week of embryological life, the ileum begins to grow longer at a very fast rate, forming a U-shaped fold called the primary intestinal loop. The loop grows so fast in length that it outgrows the abdomen and protrudes through the umbilicus. By week 10, the loop retracts back into the abdomen. Between weeks six and ten the small intestine rotates anticlockwise, as viewed from the front of the embryo. It rotates a further 180 degrees after it has moved back into the abdomen. This process creates the twisted shape of the large intestine.[14]

text: Function[edit]

text: Food from the stomach is allowed into the duodenum through the pylorus by a muscle called the pyloric sphincter.

text: Digestion[edit]

text: The small intestine is where most chemical digestion takes place. Many of the digestive enzymes that act in the small intestine are secreted by the pancreas and liver and enter the small intestine via the pancreatic duct. Pancreatic enzymes and bile from the gallbladder enter the small intestine in response to the hormone cholecystokinin, which is produced in the small intestine in response to the presence of nutrients. Secretin, another hormone produced in the small intestine, causes additional effects on the pancreas, where it promotes the release of bicarbonate into the duodenum in order to neutralize the potentially harmful acid coming from the stomach.

text: The three major classes of nutrients that undergo digestion are proteins, lipids (fats) and carbohydrates:

text:
Proteins are degraded into small peptides and amino acids before absorption.[15] Chemical breakdown begins in the stomach and continues in the small intestine. Proteolytic enzymes, including trypsin and chymotrypsin, are secreted by the pancreas and cleave proteins into smaller peptides. Carboxypeptidase, which is a pancreatic brush border enzyme, splits one amino acid at a time. Aminopeptidase and dipeptidase free the end amino acid products.
Lipids (fats) are degraded into fatty acids and glycerol. Pancreatic lipase breaks down triglycerides into free fatty acids and monoglycerides. Pancreatic lipase works with the help of the salts from the bile secreted by the liver and stored in the gall bladder. Bile salts attach to triglycerides to help emulsify them, which aids access by pancreatic lipase. This occurs because the lipase is water-soluble but the fatty triglycerides are hydrophobic and tend to orient towards each other and away from the watery intestinal surroundings. The bile salts emulsify the triglycerides in the watery surroundings until the lipase can break them into the smaller components that are able to enter the villi for absorption.
Some carbohydrates are degraded into simple sugars, or monosaccharides (e.g., glucose). Pancreatic amylase breaks down some carbohydrates (notably starch) into oligosaccharides. Other carbohydrates pass undigested into the large intestine and further handling by intestinal bacteria. Brush border enzymes take over from there. The most important brush border enzymes are dextrinase and glucoamylase, which further break down oligosaccharides. Other brush border enzymes are maltase, sucrase and lactase. Lactase is absent in some adult humans and, for them, lactose, like most poly-saccharides, is not digested in the small intestine. Some carbohydrates, such as cellulose, are not digested at all, despite being made of multiple glucose units. This is because the cellulose is made out of beta-glucose, making the inter-monosaccharidal bindings different from the ones present in starch, which consists of alpha-glucose. Humans lack the enzyme for splitting the beta-glucose-bonds, something reserved for herbivores and bacteria from the large intestine.

text: Absorption[edit]

text: Digested food is now able to pass into the blood vessels in the wall of the intestine through either diffusion or active transport. The small intestine is the site where most of the nutrients from ingested food are absorbed. The inner wall, or mucosa, of the small intestine is lined with simple columnar epithelial tissue. Structurally, the mucosa is covered in wrinkles or folds called plicae circulares, which are considered permanent features in the wall of the organ. They are distinct from rugae which are considered non-permanent or temporary allowing for distention and contraction. From the plicae circulares project microscopic finger-like pieces of tissue called villi (Latin for "shaggy hair"). The individual epithelial cells also have finger-like projections known as microvilli. The functions of the plicae circulares, the villi, and the microvilli are to increase the amount of surface area available for the absorption of nutrients, and to limit the loss of said nutrients to intestinal fauna.

text: Each villus has a network of capillaries and fine lymphatic vessels called lacteals close to its surface. The epithelial cells of the villi transport nutrients from the lumen of the intestine into these capillaries (amino acids and carbohydrates) and lacteals (lipids). The absorbed substances are transported via the blood vessels to different organs of the body where they are used to build complex substances such as the proteins required by our body. The material that remains undigested and unabsorbed passes into the large intestine.

text: Absorption of the majority of nutrients takes place in the jejunum, with the following notable exceptions:

text:
Iron is absorbed in the duodenum.
Vitamin B12 and bile salts are absorbed in the terminal ileum.
Water and lipids are absorbed by passive diffusion throughout the small intestine.
Sodium bicarbonate is absorbed by active transport and glucose and amino acid co-transport.
Fructose is absorbed by facilitated diffusion.

text: Immunological[edit]

text: The small intestine supports the body's immune system.[16] The presence of gut flora appears to contribute positively to the host's immune system. Peyer's patches, located within the ileum of the small intestine, are an important part of the digestive tract's local immune system. They are part of the lymphatic system, and provide a site for antigens from potentially harmful bacteria or other microorganisms in the digestive tract to be sampled, and subsequently presented to the immune system.[17]

text: Gene and protein expression[edit]

text: About 20,000 protein coding genes are expressed in human cells and 70% of these genes are expressed in the normal duodenum.[18][19] Some 300 of these genes are more specifically expressed in the duodenum with very few genes expressed only in the small intestine. The corresponding specific proteins are expressed in glandular cells of the mucosa, such as fatty acid binding protein FABP6. Most of the more specifically expressed genes in the small intestine are also expressed in the duodenum, for example FABP2 and the DEFA6 protein expressed in secretory granules of Paneth cells.[20]

text: Clinical significance[edit]

text: The small intestine is a complex organ, and as such, there are a very large number of possible conditions that may affect the function of the small bowel. A few of them are listed below, some of which are common, with up to 10% of people being affected at some time in their lives, while others are vanishingly rare.

text:
Small intestine obstruction or obstructive disorders

Paralytic ileus
Volvulus
Hernia
Intussusception
Adhesions
Obstruction from external pressure
Obstruction by masses in the lumen (foreign bodies, bezoar, gallstones)

Infectious diseases

Giardiasis
Ascariasis
Tropical sprue
Tape worm (Diphyllobothrium latum, Taenia solium, Hymenolepsis nana)
Hookworm (e.g. Necator americanus, Ancylostoma duodenale)
Nematodes (e.g. Ascaris lumbricoides)
Other Protozoa (e.g. Cryptosporidium parvum, Cyclospora, Microsporidia, Entamoeba histolytica)
Bacterial infections

Enterotoxigenic Escherichia coli
Salmonella enterica
Campylobacter
Shigella
Yersinia
Clostridium difficile (antibiotic-associated colitis, Pseudomembranous colitis)
Mycobacterium (Mycobacterium avium paratuberculosis, disseminated Mycobacterium tuberculosis)
Whipple's disease
Vibrio (cholera)
Enteric (typhoid) fever (Salmonella enterica var. typhii) and paratyphoid fever
Bacillus cereus
Clostridium perfringens (gas gangrene)

Viral infections

Rotavirus
Norovirus
Astrovirus
Adenovirus
Calicivirus

Neoplasms (cancers)

Adenocarcinoma
Carcinoid
Gastrointestinal stromal tumor (GIST)
Lymphoma
Sarcoma
Leiomyoma
Metastatic tumors, especially SCLC or melanoma

Developmental, congenital or genetic conditions

Duodenal (intestinal) atresia
Hirschsprung's disease
Meckel's diverticulum
Pyloric stenosis
Pancreas divisum
Ectopic pancreas
Enteric duplication cyst
Situs inversus
Cystic fibrosis
Malrotation
Persistent urachus
Omphalocele
Gastroschisis
Disaccharidase (lactase) deficiencies
Primary bile acid malabsorption
Gardner syndrome
Familial adenomatous polyposis syndrome (FAP)

Other conditions

Crohn's disease, and the more general inflammatory bowel disease
Typhlitis (neutropenic colitis in the immunosuppressed
Coeliac disease (sprue or non-tropical sprue)
Mesenteric ischemia
Embolus or thrombus of the superior mesenteric artery or the superior mesenteric vein
Arteriovenous malformation
Gastric dumping syndrome
Irritable bowel syndrome
Duodenal (peptic) ulcers
Gastrointestinal perforation
Hyperthyroidism
Diverticulitis
Radiation enterocolitis
Mesenteric cysts
Peritoneal Infection
Sclerosing retroperitonitis
Small intestinal bacterial overgrowth

text: Other animals[edit]

text: The small intestine is found in all tetrapods and also in teleosts, although its form and length vary enormously between species. In teleosts, it is relatively short, typically around one and a half times the length of the fish's body. It commonly has a number of pyloric caeca, small pouch-like structures along its length that help to increase the overall surface area of the organ for digesting food. There is no ileocaecal valve in teleosts, with the boundary between the small intestine and the rectum being marked only by the end of the digestive epitheliu [21]

text: In tetrapods, the ileocaecal valve is always present, opening into the colon. The length of the small intestine is typically longer in tetrapods than in teleosts, but is especially so in herbivores, as well as in mammals and birds, which have a higher metabolic rate than amphibians or reptiles. The lining of the small intestine includes microscopic folds to increase its surface area in all vertebrates, but only in mammals do these develop into true villi.[21]

text: The boundaries between the duodenum, jejunum, and ileum are somewhat vague even in humans, and such distinctions are either ignored when discussing the anatomy of other animals, or are essentially arbitrary.[21]

text: There is no small intestine as such in non-teleost fish, such as sharks, sturgeons, and lungfish. Instead, the digestive part of the gut forms a spiral intestine, connecting the stomach to the rectum. In this type of gut, the intestine itself is relatively straight, but has a long fold running along the inner surface in a spiral fashion, sometimes for dozens of turns. This valve greatly increases both the surface area and the effective length of the intestine. The lining of the spiral intestine is similar to that of the small intestine in teleosts and non-mammalian tetrapods.[21]

text: In lampreys, the spiral valve is extremely small, possibly because their diet requires little digestion. Hagfish have no spiral valve at all, with digestion occurring for almost the entire length of the intestine, which is not subdivided into different regions.[21]

text: Society and culture[edit]

text: In traditional Chinese medicine, the small intestine is a yang organ.[22]

text: Additional images[edit]

text:
Small intestine in situ, greater omentum folded upwards.

Third state of the development of the intestinal canal and peritoneum, seen from in front (diagrammatic). The mode of preparation is the same as in Fig 400

Second stage of development of the intestinal canal and peritoneum, seen from in front (diagrammatic). The liver has been removed and the two layers of the ventral mesogastrium (lesser omentum) have been cut. The vessels are represented in black and the peritoneum in the reddish tint.

First stage of the development of the intestinal canal and the peritoneum, seen from the side (diagrammatic). From colon 1 the ascending and transverse colon will be formed and from colon 2 the descending and sigmoid colons and the rectum.