Gastrointestinal Tract

Intestine

2009-07-30T13:51:00.000-07:00

Intestine
From Wikipedia, the free encyclopedia

In anatomy, the intestine (or bowel) is the segment of the alimentary canal extending from the stomach to the anus and, in humans and 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 and colon.

Structure and function

The structure and function can be described both as gross anatomy and at a microscopic level.

Gross anatomy

The intestinal tract can be broadly divided into two different parts, the small and large intestine. Grayish-purple in color and about 35 mm (1.5 inches) in diameter, the small intestine is the first and longer, measuring 6 to 7 meters(20-23 ft) long average in an adult man. Shorter and relatively stockier, the large intestine is a dark reddish color, measuring roughly 1.5 meters (5 ft) long on average.[2] People will have different sized intestines according to their size and age.

Microanatomy
The lumen is the cavity where digested food passes through and from where nutrients are absorbed. Both intestines share a general structure with the whole gut, and are composed of several layers. Going from inside the lumen radially outwards, one passes the mucosa (glandular epithelium and muscularis mucosa), submucosa, muscularis externa (made up of inner circular and outer longitudinal), and lastly serosa.

Along the whole length of the gut in the glandular epithelium are goblet cells. These secrete mucus which lubricates the passage of food along and protects it from digestive enzymes. Villi are vaginations of the mucosa and increase the overall surface area of the intestine while also containing a lacteal, which is connected to the lymph system and aids in the removal of lipids and tissue fluid from the blood supply. Microvilli are present on the epithelium of a villus and further increase the surface area over which absorption can take place.

The next layer is the muscularis mucosa which is a layer of smooth muscle that aids in the action of continued peristalsis and catastalsis along the gut. The submucosa contains nerves, blood vessels and elastic fibre with collagen that stretches with increased capacity but maintains the shape of the intestine.

Surrounding this is the muscularis externa which comprises longitudinal and smooth muscle that again helps with continued peristalsis and the movement of digested material out of and along the gut.

Lastly there is the serosa which is made up of loose connective tissue and coated in mucus so as to prevent friction damage from the intestine rubbing against other tissue. Holding all this in place are the mesenteries which suspend the intestine in the abdominal cavity and stop it being disturbed when a person is physically active.

The large intestine hosts several kinds of bacteria that deal with molecules the human body is not able to break down itself. This is an example of symbiosis. These bacteria also account for the production of gases 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 reabsorption of sodium, as well as any nutrients that may have escaped primary digestion in the ileum.

Diseases
Gastroenteritis is inflammation of the intestines and is the most common disease of the intestines.
Ileus is a blockage of the intestines.
Ileitis is an inflammation of the ileum.
Colitis is an inflammation of the large intestine.
Appendicitis is inflammation of the vermiform appendix located at the caecum. This is a potentially fatal disease if left untreated; most cases of appendicitis require surgical intervention.
Coeliac disease is a common form of malabsorption, affecting up to 1% of people of northern European descent. Allergy to gluten proteins, found in wheat, barley and rye, causes villous atrophy in the small intestine. Life-long dietary avoidance of these foodstuffs in a gluten-free diet is the only treatment.

Crohn's disease and ulcerative colitis are examples of inflammatory bowel disease. 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. (See List of autoimmune diseases).
Enteroviruses are named by their transmission-route through the intestine (enteric = related to intestine), but their symptoms aren't mainly associated with the intestine.

Disorders

Irritable bowel syndrome (IBS) is the most common functional disorder of the intestine. Functional constipation and chronic functional abdominal pain are other disorders of the intestine that have physiological causes, but do not have identifiable structural, chemical, or infectious pathologies. They are aberrations of normal bowel function but not diseases.
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. Diverticular disease occurs when pouches form on the intestinal wall. Once the pouches become inflamed it is known as Diverticulitis, (or Diverticular disease.)
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.)

See also

Look up

intestine in Wiktionary, the free dictionary.
Inflammatory bowel disease (or "IBD")
Diarrhea
Constipation

References
Encyclopædia Britannica article on intestine retrieved on 2007-03-27
^ Maton, Anthea; Jean Hopkins, Charles William McLaughlin, Susan Johnson, Maryanna Quon Warner, David LaHart, Jill D. Wright (1993). Human Biology and Health. Englewood Cliffs, New Jersey, USA: Prentice Hall. ISBN 0-13-981176-1.
^ "Length of a Human Intestine". http://hypertextbook.com/facts/2001/AnneMarieThomasino.shtml. Retrieved on 17 January 2009.

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Gastrointestinal Tract

2008-04-01T14:04:00.000-07:00

Gastrointestinal tract
From Wikipedia, the free encyclopedia

Upper and Lower gastrointestinal tract
The digestive tract is the system of organs within multicellular animals that takes in food, digests it to extract energy and nutrients, and expels the remaining waste. The major functions of the GI tract are ingestion, digestion, absorption, and defecation.
The GI tract differs substantially from animal to animal. Some animals have multi-chambered stomachs, while some animals' stomachs contain a single chamber. In a normal human adult male, the GI tract is approximately 6.5 meters (20 feet) long and consists of the upper and lower GI tracts. The tract may also be divided into foregut, midgut, and hindgut, reflecting the embryological origin of each segment of the tract.

Upper gastrointestinal tract
The upper GI tract consists of the mouth, pharynx, esophagus, and stomach.
The mouth contains the buccal mucosa, which contains the openings of the salivary glands; the tongue; and the teeth.
Behind the mouth lies the pharynx, which leads to a hollow muscular tube, the esophagus.
Peristalsis takes place, which is the contraction of muscles to propel the food down the esophagus which extends through the chest and pierces the diaphragm to reach the stomach.

Lower gastrointestinal tract
The lower GI tract comprises the intestines and anus.

Bowel or intestine

Small intestine which has three parts
Duodenum
Jejunum
Ileum
Large intestine which has three parts
Cecum (vermiform appendix is attached to the cecum)
Colon (ascending colon, transverse colon, descending colon and sigmoid flexure)
Rectum.

Anus

Accessory organs
Accessory organs to the alimentary canal include the liver, gallbladder, and pancreas. The liver secretes bile into the small intestine via the biliary system, employing the gallbladder as a reservoir. Apart from storing and concentrating bile, the gallbladder has no other specific function. The pancreas secretes an isosmotic fluid containing bicarbonate and several enzymes, including trypsin, chymotrypsin, lipase, and pancreatic amylase, as well as nucleolytic enzymes (deoxyribonuclease and ribonuclease), into the small intestine. Both of these secretory organs aid in digestion.

Embryology
The gut is an endoderm-derived structure. At approximately the 16th 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 towards 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 can be divided into three segments: foregut, midgut, and hindgut. Although these terms are often used in reference to segments of the primitive gut, they are nevertheless used regularly to describe components of the definitive gut as well.
Each segment of the primitive gut gives rise to specific gut and gut-related structures in the adult. Components derived from the gut proper, including the stomach and colon, develop as swellings or dilatations 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 outpouchings of the primitive gut. The blood vessels supplying these structures remain constant throughout development.[1]
Part
Range in adult
Gives rise to
Arterial supply
foregut
the pharynx, to the upper duodenum
pharynx, esophagus, stomach, upper duodenum, respiratory tract (including the lungs), liver, gallbladder, and pancreas
branches of the celiac artery
midgut
lower duodenum, to the first half of the transverse colon
lower duodenum, jejunum, ileum, cecum, appendix, ascending colon, and first half of the transverse colon
branches of the superior mesenteric artery
hindgut
second half of the transverse colon, to the upper part of the anal canal
remaining half of the transverse colon, descending colon, rectum, and upper part of the anal canal
branches of the inferior mesenteric artery

Physiology

Specialization of organs
Four organs are subject to specialization in the kingdom Animalia.

The first organ is the tongue which is only present in the phylum Chordata.
The second organ is the esophagus. The crop is an enlargement of the esophagus in birds, insects and other invertebrates that is used to store food temporarily.
The third organ is the stomach. In addition to a glandular stomach (proventriculus), birds have a muscular "stomach" called the ventriculus or "gizzard." The gizzard is used to mechanically grind up food.
The fourth organ is the large intestine. An outpouching of the large intestine called the cecum is present in non-ruminant herbivores such as rabbits. It aids in digestion of plant material such as cellulose

The "Brain-Gut Connection
Several studies have linked the human brain and the gastrointestinal system. Emotional state is strongly linked to gastrointestinal symptoms; many people experience altered bowel habits as a result of stress, anxiety, and depression. Many researchers consider the gastrointestinal system to be a "second brain". For example, Irritable Bowel Syndrome is strongly linked to emotional state, and the symptoms of a number of gastrointestinal disorders, including IBS and inflammatory bowel disease, are exacerbated, but not caused by, stress and axiety.

Pathology
There are a number of diseases and conditions affecting the gastrointestinal system, including:

Irritable Bowel Syndrome
Inflammatory Bowel Disease (Crohn's Diseae and ulcerative colitis)
Giardiasis
Colorectal cancer
Gastroenteritis, also known as "stomach flu";an inflammation of the stomach and intestines
Diverticulitis
Pancreatitis

Immune function
The gastrointestinal tract is also a prominent part of the immune system.[2] The 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 of these microorganisms. Other factors in the GI tract help with immune function as well, including enzymes in the saliva and bile. Enzymes such as Cyp3A4, along with the antiporter activities, are also instrumental in the intestine's role of detoxification of antigens and xenobiotics, such as drugs, involved in first pass metabolism. Health-enhancing intestinal bacteria serve to prevent the overgrowth of potentially harmful bacteria in the gut. Microorganisms are also kept at bay by an extensive immune system comprising the gut-associated lymphoid tissue (GALT).

Histology

General structure of the gut wall.
The gastrointestinal tract has a uniform general histology with some differences which reflect the specialization in functional anatomy.[3] The GI tract can be divided into 4 concentric layers:

Mucosa
Submucosa
Muscularis externa (the external muscle layer)
Adventitia or serosa

Mucosa
The mucosa is the innermost layer of the gastrointestinal tract, surrounding the lumen, or space within the tube. This layer comes in direct contact with the food (or bolus), and is responsible for absorption and secretion, important processes in digestion.

The mucosa can be divided into:

The mucosae are highly specialized in each organ of the gastrointestinal tract, facing a low pH in the stomach, absorbing a multitude of different substances in the small intestine, and also absorbing specific quantities of water in the large intestine. Reflecting the varying needs of these organs, the structure of the mucosa can consist of invaginations of secretory glands (e.g., gastric pits), or it can be folded in order to increase surface area (examples include villi and plicae circulares).

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. It contains Meissner's plexus, an enteric nervous plexus, situated on the inner surface of the muscularis externa.

Muscularis externa
The muscularis externa consists of dis dick layer and a longitudinal outer muscular layer. The circular muscle layer prevents the food from going backwards and the longitudinal layer shortens the tract. The coordinated contractions of these layers is called peristalsis and propels the bolus, or balled-up food, through the GI tract. Between the two muscle layers are the myenteric or Auerbach's plexus.

Adventitia
The adventitia consists of several layers of epithelia. When the adventitia is facing the mesentery or peritoneal fold, the adventitia is covered by a mesothelium supported by a thin connective tissue layer, together forming a serosa, or serous membrane.

Uses of animal gut by humans
The stomachs of calves have commonly been used as a source of rennet for making cheese.
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 strings are now made out of cow gut.

Gut cord has also been used to produce strings for the snares which provide the snare drum's characteristic buzzing timbre. While the snare drum currently 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.
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, were made from animal intestine.

See also

Wikimedia Commons has media related to:
Digestive system
Dysbiosis
Gastrointestinal hormone
Dorland's Illustrated Medical Dictionary
Major systems of the human body

Notes
^ Bruce M. Carlson (2004). Human Embryology and Developmental Biology, 3rd edition, Saint Louis: Mosby. ISBN 0-323-03649-X.
^ Richard Coico, Geoffrey Sunshine, Eli Benjamini (2003). Immunology: a short course. New York: Wiley-Liss. ISBN 0-471-22689-0.
^ Abraham L. Kierszenbaum (2002). Histology and cell biology: an introduction to pathology. St. Louis: Mosby. ISBN 0-323-01639-1.

References
National Institute of Diabetes and Digestive and Kidney Diseases, National Institutes of Health.

External links
Anatomy atlas of the Digestive System
Overview at Colorado State University

v • d • e Anatomy of torso, digestive system: Gastrointestinal tract
Upper GI: to stomach
Mouth • Pharynx (nasopharynx, oropharynx, hypopharynx) • Esophagus • Crop
Upper GI: stomach
rugae - gastric pits - cardia/gland - fundus/gland - pylorus/gland - pyloric antrum - pyloric canal - greater curvature - lesser curvature - angular incisure
Lower GI: intestines
Small intestine: Duodenum (Suspensory muscle, Major duodenal papilla, Minor duodenal papilla) • Duodenojejunal flexure • Jejunum • Ileum • continuous (intestinal villus, crypts of Lieberkühn, circular folds)
Junction: Vermiform appendix • Ileocecal valve Large intestine: Cecum • Colon (ascending colon, hepatic flexure, transverse colon, splenic flexure, descending colon, sigmoid colon) • continuous (taenia coli, haustra, epiploic appendix)
Lower GI: termination
Rectum: Houston valve • rectal ampulla • pectinate line
Anal canal: anal valves • anal sinuses • anal columns • Hilton's white line Anus: Sphincter ani internus muscle • Sphincter ani externus muscle
Lower GI: lymph
GALT: Peyer's patches (M cells)
[show]
v • d • e Anatomy of torso, digestive system: Digestive glands
Liver
by region: Left lobe (Caudate lobe, Quadrate lobe) - Right lobe - Transverse fissure of liver
by function (Fibrous capsule of Glisson, Hepatocyte, Space of Disse, Space of Mall, Kupffer cell, Liver sinusoid, Ito cell, Hepatic lobule)bile ducts: (Bile canaliculus, Canals of Hering, Interlobular bile ducts, Intrahepatic bile ducts, Left and Right hepatic ducts, Common hepatic duct)
Gallbladder
by region (Body, Fundus, Neck)ducts: Cystic duct
Pancreas
by region (Tail, Body, Head, Uncinate process)
by function (Islets of Langerhans, Exocrine pancreas)ducts: Pancreatic duct • Accessory pancreatic duct
Common
Common bile duct - Hepatopancreatic ampulla - Sphincter of Oddi
[show]
v • d • e Prenatal development/Mammalian development of digestive system
Gut
Stomodeum
Foregut (Buccopharyngeal membrane, Rathke's pouch, Tracheoesophageal septum, Pancreatic bud, Hepatic diverticulum)
Midgut
Hindgut (Urorectal septum )Proctodeum
Mesentery
Dorsal mesentery - Ventral mesentery
Other
Septum transversum
[show]
v • d • e Digestive system - Gastroenterology (primarily K20-K93, 530-579)
Esophagus
Esophagitis - GERD - Achalasia - Boerhaave syndrome - Nutcracker esophagus - Zenker's diverticulum - Mallory-Weiss syndrome - Barrett's esophagus
Stomach/duodenum
Peptic (gastric/duodenal) ulcer - Gastritis - Gastroenteritis - Duodenitis - Dyspepsia - Pyloric stenosis - Achlorhydria - Gastroparesis - Gastroptosis - Portal hypertensive gastropathy
Hernia
Inguinal (Indirect, Direct) - Femoral - Umbilical - Incisional - Diaphragmatic - Hiatus
Noninfectiveenteritis & colitis
Inflammatory bowel disease (IBD, Crohn's disease, Ulcerative colitis) - noninfective gastroenteritis
Other intestinal
vascular (Abdominal angina, Mesenteric ischemia, Ischemic colitis, Angiodysplasia) - Ileus/Bowel obstruction (Intussusception, Volvulus) - Diverticulitis/Diverticulosis - Irritable bowel syndrome (IBS)other functional intestinal disorders (Constipation, Diarrhea, Megacolon/Toxic megacolon, Proctalgia fugax) - Anal fissure/Anal fistula - Anal abscess - Rectal prolapse - Proctitis (Radiation proctitis)
Liver/hepatitis
Alcoholic liver disease - Liver failure (Acute liver failure) - Cirrhosis - PBC - NASH - Fatty liver - Peliosis hepatis - Portal hypertension - Hepatorenal syndrome
Accessorydigestive
Gallbladder (Gallstones, Choledocholithiasis, Cholecystitis, Cholesterolosis, Rokitansky-Aschoff sinuses)
Biliary tree (Cholangitis, Cholestasis/Mirizzi's syndrome, PSC, Biliary fistula, Ascending cholangitis)Pancreas (Acute pancreatitis, Chronic pancreatitis, Pancreatic pseudocyst, Hereditary pancreatitis)
Other/general
Appendicitis - Peritonitis (Spontaneous bacterial peritonitis)
Malabsorption (celiac, Tropical sprue, Blind loop syndrome, Whipple's)
postprocedural: Gastric dumping syndrome - Postcholecystectomy syndromebleeding: Hematemesis - Melena - Gastrointestinal bleeding (Upper, Lower)
See also congenital
[show]
v • d • e Digestive system, physiology: gastrointestinal physiology
Enteric nervous system
Meissner's plexus - Auerbach's plexus
Exocrine
Chief cells (Pepsinogen) - Parietal cells (Gastric acid, Intrinsic factor) - Goblet cells (Mucus)
Endocrine/paracrine
G cells (gastrin), D cells (somatostatin) - ECL cells (Histamine) - enterogastrone: I cells (CCK), K cells (GIP), S cells (secretin)
Border
Brunner's glands - Paneth cells - Enterocytes
Fluids
Saliva - Bile - Intestinal juice - Gastric juice - Pancreatic juice
Processes
Swallowing - Vomiting - Peristalsis (Interstitial cell of Cajal) - Migrating motor complex - Borborygmus - Gastrocolic reflex - Segmentation contractions - Defecation
[show]
v • d • e Digestive system surgical and other procedures (ICD-9-CM V3 42-54)
Digestive tract
esophagus: Esophagectomy
stomach: Gastrostomy (Percutaneous endoscopic gastrostomy) - Gastrectomy (Billroth I, Billroth II, Roux-en-Y)- Gastric bypass surgery - Gastroenterostomy - Nissen fundoplication - Gastropexy
small bowel: Duodenal switch - Jejunoileal bypass - Ileostomy
large bowel: Colectomy - Colostomy - Appendicectomy - Hartmann's procedure
rectum: Lower anterior resection - Abdominoperineal resection endoscopy: Esophagogastroduodenoscopy - Colonoscopy - Proctoscopy - Sigmoidoscopy
Accessory
liver: Hepatectomy - Liver transplantation - Artificial extracorporeal liver support (Liver dialysis, Bioartificial liver devices)
gallbladder/bile duct: Endoscopic retrograde cholangiopancreatography - Percutaneous transhepatic cholangiography - Cholecystectomy pancreas: Pancreatectomy - Pancreaticoduodenectomy - Pancreas transplantation - Puestow procedure - Frey's procedure
Other
Herniorrhaphy - Laparotomy - Paracentesis
[show]
v • d • e Human organ systems
Cardiovascular system • Digestive system • Endocrine system • Immune system • Integumentary system • Lymphatic system • Muscular system • Nervous system • Reproductive system • Respiratory system • Skeletal system • Urinary system
Retrieved from "http://en.wikipedia.org/wiki/Gastrointestinal_tract"
Categories: Gastroenterology Digestive system Abdomen