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Information about Small Intestines

Small intestine
Diagram showing the small intestine
Latinintestinum tenue
subject #248 1168
Nerveceliac 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 includes the duodenum, jejunum, and ileum. It is where the vast majority of digestion takes place.

Size and sections

Enlarge picture
Small intestine
In humans over 5 years old it is approximately 7 m (21 ft) long and can vary from 4-7 m (13.12-22.97 ft).

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 2.5-3cm, and the large intestine measures about 7.6 cm in diameter. This is where bile is released into, from the gall bladder.

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.

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 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.

Absorption

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.

The surface of the cells on the microvilli are covered with a brush border of proteins which helps to catch a molecule-thin layer of water within itself. This layer, called the "unstirred water layer," 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:

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 bile salts. Bile salts attach to triglycerides which aids in making them easier for pancreatic lipase to.
  • 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.

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:

LayerDuodenumJejunumIleum
serosanormalnormalnormal
muscularis externalongitudinal and circular layers, with Auerbach's (myenteric) plexus in betweensame as duodenumsame as duodenum
submucosaBrunner's glands and Meissner's (submucosal) plexusno BGno BG
mucosa: muscularis mucosaenormalnormalnormal
mucosa: lamina propriano PPno PPPeyer's patches
mucosa: epitheliumsimple columnar. Contains goblet cells, Paneth cellsSimilar to duodenum. Villi very long.Similar to duodenum. Villi very short.

Small intestine disorders

References

  • Medical dictionary definition of small+intestine from KMLE Medical Dictionary retrieved on 2007-03-25
  • 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

Additional images


Lower half of right sympathetic cord.

Topography of thoracic and abdominal viscera.




 •  • [ e]
Anatomy of torso, digestive system: Gastrointestinal tract
Upper GI: to stomachMouth • Pharynx (nasopharynx, oropharynx, hypopharynx) • Esophagus • Crop
Upper GI: stomachrugae - gastric pits - cardia/gland - fundus/gland - pylorus/gland - pyloric antrum - greater curvature - lesser curvature
Lower GI: intestinesSmall intestine (duodenum, jejunum, ileum) • Vermiform appendix • Ileocecal valve - Large intestine: Cecum • Colon (ascending colon, hepatic flexure, transverse colon, splenic flexure, descending colon, sigmoid colon)
Lower GI: after intestinesRectum (Houston valve, rectal ampulla, pectinate line) • Anal canal (anal valves, anal sinuses, anal columns) - Anus: Sphincter ani internus muscle • Sphincter ani externus muscle
Lower GI: continuousGALT: Peyer's patches • M cells - intestinal villus • crypts of Lieberkhn • circular folds • taenia coli • haustra • epiploic appendix
Latin}}} 
Official status
Official language of: Vatican City
Used for official purposes, but not spoken in everyday speech
Regulated by: Opus Fundatum Latinitas
Roman Catholic Church
Language codes
ISO 639-1: la
ISO 639-2: lat
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A nerve is an enclosed, cable-like bundle of axons (the long, slender projection of a neuron). Neurons are sometimes called nerve cells, though this term is technically imprecise since many neurons do not form nerves, and nerves also include the glial cells that
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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
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The vagus nerve (also called pneumogastric nerve or cranial nerve X) is the tenth of twelve paired cranial nerves, and is the only nerve that starts in the brainstem (within the medulla oblongata) and extends, through the jugular foramen, down below the head, to the
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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. Created and updated by the United States National Library of Medicine (NLM), it is used by the MEDLINE/PubMed
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Elsevier, the world's largest publisher of medical and scientific literature, forms part of the Reed Elsevier group. Based in Amsterdam, the company has substantial operations in the UK, USA and elsewhere.
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Biology (from Greek: βίος, bio, "life"; and λόγος, logos, "knowledge"), also referred to as the biological sciences, is the scientific study of life.
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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.
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gastrointestinal tract (GI tract), also called the digestive tract, or the alimentary canal, is the system of organs within multicellular animals that takes in food, digests it to extract energy and nutrients, and expels the remaining waste.
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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 word stomach is derived from the Latin stomachus, which derives from the Greek word
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The large intestine, an organ which is now more commonly referred to by its Greek name, the colon, is the last part of the digestive system: the final stage of the alimentary canal in vertebrate animals.
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In anatomy of the digestive system, the duodenum is a hollow jointed tube about 25-30 cm long connecting the stomach to the jejunum. It is the first and shortest part of the small intestine and it is where most chemical digestion takes place.
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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. The change from the duodenum to the jejunum is usually defined as the ligament of Treitz.
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ileum is the final section of the small intestine. It is about 2-4 m long in humans, follows the duodenum and jejunum, and is separated from the cecum by the ileocecal valve (ICV). The pH in the ileum is usually between 7 and 8 (neutral or slightly alkaline).
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In anatomy of the digestive system, the duodenum is a hollow jointed tube about 25-30 cm long connecting the stomach to the jejunum. It is the first and shortest part of the small intestine and it is where most chemical digestion takes place.
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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. The change from the duodenum to the jejunum is usually defined as the ligament of Treitz.
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ileum is the final section of the small intestine. It is about 2-4 m long in humans, follows the duodenum and jejunum, and is separated from the cecum by the ileocecal valve (ICV). The pH in the ileum is usually between 7 and 8 (neutral or slightly alkaline).
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The large intestine, an organ which is now more commonly referred to by its Greek name, the colon, is the last part of the digestive system: the final stage of the alimentary canal in vertebrate animals.
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Not to be confused with Pillory.
The pylorus (from Greek πυλωρος = "gate guard") is the region of the stomach that connects to the duodenum.
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Peristalsis is the rhythmic contraction of smooth muscles to propel contents through the digestive tract. The word is derived from New Latin and comes from the Greek peristaltikos, peristaltic, from peristellein, "to wrap around," and stellein
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The circular folds (valves of Kerckring) are large valvular flaps projecting into the lumen of the bowel.

They are composed of reduplications of the mucous membrane, the two layers of the fold being bound together by submucous tissue; unlike the folds in the stomach,
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Rugae is a term used in anatomy that refers to a series of ridges produced by folding of the wall of an organ. Most commonly the term is applied to the internal surface of the stomach. The stomach rugae may be seen during esophagogastroduodenoscopy or in radiological studies.
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Villus (Latin: "shaggy hair"[1], plural villi) can refer to:
  • Intestinal villus. This is the most common meaning when not more precisely specified
  • Chorionic villi, found on the surface of the outermost membrane (the chorion) of the fetus

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A wrinkle is a ridge or crease of a surface. It usually refers to folds on fabric or clothes, or on the skin of an organism; the folds are generally random and do not exhibit any repeating pattern.
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The microvilli (singular: microvillus) are structures that increase the surface area of cells by approximately 600 fold (human), thus facilitating absorption and secretion.
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A lacteal is a lymphatic capillary that absorbs dietary fats in the villi of the small intestine.

The combination of fat and lymph in the lacteals is milky in appearance and called chyle.
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Fat

Fat may refer to:
  • Fat, a group of compounds that are generally soluble in organic solvents and largely insoluble in water
  • Adipose tissue, an anatomical term for loose connective tissue composed of adipocytes

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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.
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Circulatory System is a psychedelic rock musical ensemble formed by musician/painter Will Cullen Hart, and featuring Hannah Jones, Derek Almstead, Peter Erchick, John Fernandes, and Heather McIntosh.
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