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Encyclopedia > Small intestine
Small intestine
Diagram showing the small intestine
Latin intestinum tenue
Gray's subject #248 1168
Nerve celiac ganglia, vagus [1]
MeSH Small+intestine
Dorlands/Elsevier i_11/12456563

In biology the small intestine is the part of the gastrointestinal tract (gut) between the stomach and the large intestine and comprises the duodenum, jejunum, and ileum. It is where the vast majority of digestion takes place. Nutrients diffuse through the villi, projections sticking out of the walls of the small intestine, into the blood.[2] Image File history File links Stomach_colon_rectum_diagram. ... For other uses, see Latins and Latin (disambiguation). ... For other uses, see Nerve (disambiguation). ... The Celiac Ganglia (semilunar ganglia) are two large irregularly shaped masses having the appearance of lymph glands and placed one on either side of the middle line in front of the crura of the diaphragm close to the suprarenal glands, that on the right side being placed behind the inferior... The vagus nerve is tenth of twelve paired cranial nerves and is the only nerve that starts in the brainstem (somewhere in the medulla oblongata) and extends all the way down past the head, right down to the abdomen. ... Medical Subject Headings (MeSH) is a huge controlled vocabulary (or metadata system) for the purpose of indexing journal articles and books in the life sciences. ... Elseviers logo. ... For the song by Girls Aloud see Biology (song) Biology studies the variety of life (clockwise from top-left) E. coli, tree fern, gazelle, Goliath beetle Biology (from Greek: Βιολογία - βίος, bio, life; and λόγος, logos, speech lit. ... In anatomy, the intestine 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. ... Gut redirects here. ... In anatomy, the stomach is a bean-shaped hollow muscular organ of the gastrointestinal tract involved in the second phase of digestion, following mastication. ... The large intestine is the last part of the digestive system: the final stage of the alimentary canal in vertebrate animals. ... In anatomy of the digestive system, the duodenum is a hollow jointed tube about 25-30 cm long connecting the stomach to the jejunum. ... Diagram of the Human Intestine In anatomy of the digestive system, the jejunum is the central of the three divisions of the small intestine and lies between the duodenum and the ileum. ... Not to be confused with ilium (bone). ...

Small intestine
Small intestine

In humans over 5 years old it is approximately 7 m (23 ft) long and can vary from 4-7 m (13.12-22.97 ft). Image File history File linksMetadata Illu_small_intestine. ... Image File history File linksMetadata Illu_small_intestine. ... This article is about modern humans. ...


It is divided into three structural parts:

Although the small intestine is much longer than the large intestine (typically 4-5 times longer), it is referred to as such due to its comparatively smaller diameter. On average, the diameter of the small intestine of an adult human measures approximately 2.5-3 cm, and the large intestine measures about 7.6 cm in diameter. In anatomy of the digestive system, the duodenum is a hollow jointed tube about 25-30 cm long connecting the stomach to the jejunum. ... Diagram of the Human Intestine In anatomy of the digestive system, the jejunum is the central of the three divisions of the small intestine and lies between the duodenum and the ileum. ... Not to be confused with ilium (bone). ... The large intestine is the last part of the digestive system: the final stage of the alimentary canal in vertebrate animals. ...

Contents

Peristalsis

Food from the stomach is allowed into the duodenum by a muscle called the pylorus, or pyloric sphincter, and is then pushed through the small intestine by a process of muscular-wavelike contractions called peristalsis. From Greek pylorus; pyl- = gate, -orus = guard. ... Peristalsis is the rhythmic contraction of smooth muscles to propel contents through the digestive tract. ...


Extensions into lumen

The small intestine is the site where most of the nutrients from ingested food are absorbed and is covered in wrinkles or folds called plicae circulares. These 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 (The Latin word meaning "shaggy hair"). The small intestine is lined with simple columnar epithelial tissue. The epithelial cells also have finger-like projections known as microvilli. The function of the plicae circulares, the villi and the microvilli is to increase the amount of surface area available for secretion of enzymes and absorption of nutrients. The circular folds (valves of Kerkring) are large valvular flaps projecting into the lumen of the bowel. ... Stomach. ... Villi (singular: villus) are tiny, finger-like structures that protrude from the wall of the intestine to help absorb nutrients in the lumen. ...


Absorption

Intestine for sausage making
Intestine for sausage making

The purpose of these wrinkles and projections is to increase surface area for absorption of nutrients. Each villus is covered in microvilli, which increase the surface area manyfold. Each villus contains a lacteal and capillaries. The lacteal absorbs the digested fat into the lymphatic system which will eventually drain into the circulatory system. The capillaries absorb all other digested nutrients. A wrinkle is a ridge or crease of a surface. ... Categories: Stub ... A lacteal is a lymphatic capillary that absorbs dietary fats in the villi of the small intestine. ... For other uses, see FAT. Fats consist of a wide group of compounds that are generally soluble in organic solvents and largely insoluble in water. ... The lymphatic system is a complex network of lymphoid organs, lymph nodes, lymph ducts, lymphatic tissues, lymph capillaries and lymph vessels that produce and transport lymph fluid from tissues to the circulatory system. ... For transport in plants, see Vascular tissue. ... A nutrient is a substance used in an organisms metabolism which must be taken in from the environment. ...


The surface of the cells on the microvilli are covered with a water layer, which has a number of functions in absorption of nutrients.


Absorption of the majority of nutrients takes place in the jejunum, with the following notable exceptions: Diagram of the Human Intestine In anatomy of the digestive system, the jejunum is the central of the three divisions of the small intestine and lies between the duodenum and the ileum. ...

General Name, symbol, number iron, Fe, 26 Chemical series transition metals Group, period, block 8, 4, d Appearance lustrous metallic with a grayish tinge Standard atomic weight 55. ... Cobalamin or vitamin B12 is a chemical compound that is also known as cyanocobalamine. ... Bile is also another name for Belenus, a god in Brythonic mythology. ... Figure 1: Basic lipid structure. ... For sodium in the diet, see Salt. ... Glucose (Glc), a monosaccharide (or simple sugar), is an important carbohydrate in biology. ... This article is about the class of chemicals. ... Fructose (also levulose or laevulose) is a simple reducing sugar (monosaccharide) found in many foods and is one of the three most important blood sugars along with glucose and galactose. ... facilitated diffusion in cell membrane, showing ion channels and carrier proteins Facilitated diffusion (or facilitated transport) is a process of diffusion, a form of passive transport, where molecules diffuse across membranes, with the assistance of transport proteins. ...

Digestion

The digestion of proteins into peptides and amino acids principally occurs in the stomach but some also occurs in the small intestine. The small intestine is where the most chemical digestion takes place:

  • peptides are degraded into amino acids. Chemical break down begins in the stomach and is further broken down in the small intestine. Proteolytic enzymes, trypsin and chymotrypsin, which are secreted by the pancreas 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 is secreted here. Pancreatic lipase breaks down triglycerides into free fatty acids and monoglycerides. Pancreatic lipase performs its job with the help of the salts from the bile secreted by the liver and the gall bladder. Bile salts attach to triglycerides which aids in making them easier for pancreatic lipase to access. 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 are the "middle man" that holds 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.
  • carbohydrates are degraded into simple sugars (e.g., glucose). In the small intestine pancreatic amylase breaks down carbohydrates into oligosaccharides. 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.

This article is about the class of chemicals. ... Trypsin (EC 3. ... Chymotrypsin (bovine γ chymotrypsin: PDB 1AB9, EC 3. ... The pancreas is a gland organ in the digestive and endocrine systems of vertebrates. ... Some common lipids. ... Not to be confused with fats. ... Glycerine, Glycerin redirects here. ... Bile (or gall) is a bitter, yellow or green alkaline fluid secreted by hepatocytes from the liver of most vertebrates. ... The liver is the largest internal organ in the human body, and is an organ present in vertebrates and some other animals. ... The gallbladder (or cholecyst) is a pear-shaped organ that stores bile (or gall) until the body needs it for digestion. ... Lactose is a disaccharide found in milk. ... Glucose (Glc), a monosaccharide (or simple sugar), is an important carbohydrate in biology. ...

Histology

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:

Layer Duodenum Jejunum Ileum
serosa normal 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. Villi very long. Similar to duodenum. Villi very short.

A serosa is a serous membrane, Serous membranes line the pericardial, pleural, and peritoneal cavities, enclosing their contents. ... The muscular coat (or muscular layer, or muscular fibers, or muscularis externa) is a region of smooth muscle in many organs in the vertebrate body, adjacent to the mucous membrane. ... Part of the enteric nervous system, Auerbachs plexus exists between the longitudinal and circular layers of muscle in the gastrointestinal tract and provides motor innervation to both layers and secretomotor innervation to the mucosa. ... In the gastrointestinal tract. ... Brunners glands are submucosal glands located throughout the duodenum. ... The nerves of the small intestines are derived from the plexuses of sympathetic nerves around the superior mesenteric artery. ... The mucous membranes (or mucosa) are linings of ectodermic origin, covered in epithelium, that line various body cavities and internal organs. ... Section of mucous membrane of human rectum. ... The lamina propria is a thin vascular layer of connective tissue beneath the epithelium of an organ. ... Peyers patches are secondary lymphoid organs, named after the 17th-century Swiss anatomist Johann Conrad Peyer. ... The simple columnar epithelium is made up of one layer of cells that are relatively thick and protective of the underlying tissues due to its elongated shape. ... Goblet cells are glandular epithelial cells that are specifically designed to secrete mucus. ... paneth cells Paneth cells provide host defense against microbes in the small intestine. ...

Small intestine disorders

Endoscopic image of adenocarcinoma of duodenum seen in the post-bulbar duodenum. ... The word Foreign means originating elsewhere or in the physiological context outside the body. ... A bezoar or enterolith is a sort of calculus or concretion, a stone found in the intestines of mostly ruminant animals, but occurring among others including humans. ... This article does not cite any references or sources. ... Ileus, formerly called iliac passion, refers to limited or absent intestinal passage. ... Crohns disease (also known as regional enteritis) is a chronic, episodic, inflammatory bowel disease (IBD) and is generally classified as an autoimmune disease. ... Coeliac disease (also termed non-tropical sprue, celiac disease and gluten intolerance) is an autoimmune disease characterised by chronic inflammation of the proximal portion of the small intestine caused by exposure to certain dietary gluten proteins. ... Picture of a carcinoid tumour that encroaches into lumen of the small bowel. ... A Meckels diverticulum is a true congenital diverticulum. ... Gastric dumping syndrome, or rapid gastric emptying, happens when the lower end of the small intestine, the jejunum, fills too quickly with undigested food from the stomach. ... In medicine, infectious disease or communicable disease is disease caused by a biological agent (e. ... Giardiasis (also known as beaver fever) is a disease caused by the flagellate protozoan Giardia lamblia (also sometimes called Giardia intestinalis and Giardia duodenalis). ... Tropical sprue is a malabsorption disease commonly found in the tropical regions, marked with abnormal flattening of the villi and inflammation of the lining of the small intestine. ... Adult tapeworm infection is the infection of the digestive tract by parasitic flatworms called cestodes or tapeworms. ... This page may meet Wikipedias criteria for speedy deletion. ... Short bowel syndrome is a malabsorption disorder caused by either the surgical removal of the small intestine or the loss of its absorptive function due to diseases. ...

References

  • Solomon et al (2002) Biology Sixth Edition, Brooks-Cole/Thomson Learning ISBN 0-03-033503-5
  • Townsend et al (2004) Sabiston Textbook of Surgery, Elsevier ISBN 0-7216-0409-9
  • Thomson A, Drozdowski L, Iordache C, Thomson B, Vermeire S, Clandinin M, Wild G (2003). "Small bowel review: Normal physiology, part 1.". Dig Dis Sci 48 (8): 1546-64. PMID 12924651. 
  • Thomson A, Drozdowski L, Iordache C, Thomson B, Vermeire S, Clandinin M, Wild G (2003). "Small bowel review: Normal physiology, part 2.". Dig Dis Sci 48 (8): 1565-81. PMID 12924652. 

Notes

  1. ^ Physiology at MCG 6/6ch2/s6ch2_30
  2. ^ 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. 

In 1828 the Medical Academy of Georgia was chartered by the state of Georgia with plans to offer a single course of lectures leading to a bachelors degree. ...

Additional images

This article is about the bodily orifice. ... The Sphincter ani internus muscle is a muscle of the human body. ... The Sphincter ani externus muscle is a muscle of the human body. ... Overview About 70% of the bodys immune system is found in the digestive tract. ... Peyers patches are secondary lymphoid organs, named after the 17th-century Swiss anatomist Johann Conrad Peyer. ... M cells (or Microfold cells) are cells found in the follicle-associated epithelium of the Peyers patch that have the unique ability to sample antigen from the lumen of the small intestine and deliver it via transcytosis to antigen presenting cells and lymphocytes located in a unique pocket-like...

  Results from FactBites:
 
XI. Splanchnology. 2g. The Small Intestine. Gray, Henry. 1918. Anatomy of the Human Body. (3458 words)
The small intestine is a convoluted tube, extending from the pylorus to the colic valve, where it ends in the large intestine.
The rest of the small intestine is surrounded by the peritoneum, excepting along its attached or mesenteric border; here a space is left for the vessels and nerves to pass to the gut.
It is the strongest layer of the intestine.
Small Intestinal Bacterial Overgrowth (SIBO) causes, symptoms, diagnosis, and treatment by MedicineNet.com (694 words)
The small bowel, also known as the small intestine, is the section of the gastrointestinal tract that connects the stomach with the colon.
The small intestine is approximately 21 feet in length and begins in the duodenum (into which food from the stomach empties), followed by the jejunum, and then the ileum (which empties the food that has not been digested into the large intestine or colon).
Small intestinal bacterial overgrowth (SIBO) refers to a condition in which abnormally large numbers of bacteria (at least 100,000 bacteria per ml of fluid) are present in the small intestine and the types of bacteria in the small intestine resemble more the bacteria of the colon than the small intestine.
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