Cambios

==Introducción==

==Introducción==

El intestino delgado se extiende desde el píloro del [[Estómago Monogástrico - Anatomía & Fisiología|estómago]] al intestino [[Ciego - Anatomía & Fisiología|ciego]]. El intestino delgado recibe el quimo del [[Estómago Monogástrico - Anatomía & Fisiología|estómago]]. Es el sitio principal de la degradación química y la absorción de quimo. Las grasas son exclusivamente desglosadas en esta parte del tubo digestivo. Los carbohidratos y las proteínas que no se degradan en el intestino delgado están disponibles para la fermentación microbiana en el [[Intestino Grueso - Anatomía & Fisiología|intestino grueso]]. El intestino delgado produce enzimas para la digestión de proteínas, carbohidratos y grasas y absorbe los productos de su digestión. Las enzimas son producidas por las glándulas de la pared intestinal y el  [[Páncreas - Anatomía & Fisiología|páncreas]]. La [[Vesícula Biliar - Anatomía & Fisiología|vesícula biliar]] produce bilis que emulsiona las grasas para la digestión. La absorción esta facilitada por las crestas en el intestino delgado y por la presencia de las vellosidades y microvellosidades.

El intestino delgado se extiende desde el píloro del [[Estómago Monogástrico - Anatomía & Fisiología|estómago]] al intestino [[Ciego - Anatomía & Fisiología|ciego]]. El intestino delgado recibe el quimo del [[Estómago Monogástrico - Anatomía & Fisiología|estómago]]. Es el sitio principal de la degradación química y la absorción de quimo. Las grasas son exclusivamente desglosadas en esta parte del tubo digestivo. Los carbohidratos y las proteínas que no se degradan en el intestino delgado están disponibles para la fermentación microbiana en el [[:Categoría:Intestino Grueso - Anatomía & Fisiología|intestino grueso]]. El intestino delgado produce enzimas para la digestión de proteínas, carbohidratos y grasas y absorbe los productos de su digestión. Las enzimas son producidas por las glándulas de la pared intestinal y el  [[Páncreas - Anatomía & Fisiología|páncreas]]. La [[Vesícula Biliar - Anatomía & Fisiología|vesícula biliar]] produce bilis que emulsiona las grasas para la digestión. La absorción esta facilitada por las crestas en el intestino delgado y por la presencia de las vellosidades y microvellosidades.

El intestino delgado se compone de tres partes. Cada parte una anatomía distinto, pero todos tienen la misma estructura y función básica:

El intestino delgado se compone de tres partes. Cada parte una anatomía distinto, pero todos tienen la misma estructura y función básica:

*[[Duodeno - Anatomía & Fisiología|Duodeno]]

*[[Duodeno - Anatomía & Fisiología|Duodeno]]

*[[Yeyuno - Anatomía & Fisiología|Yeyuno]]  

*[[Yeyuno - Anatomía & Fisiología|Yeyuno]]  

*[[Ileon - Anatomía & Fisiología|Ileon]]

*[[Íleon - Anatomía & Fisiología|Íleon]]

El intestino delgado se desarrolla a partir del tubo digestivo, que existe ventralmente en el embrión en desarrollo. El tubo digestivo es endodermo, y por lo tanto el intestino delgado y sus glándulas asociadas desarrollan principalmente del endodermo. Mesodermo esplácnico rodea el tubo digestivo y da lugar a los músculos de la túnica muscular (por el peristaltismo), los vasos sanguíneos en la submucosa y el tejido conectivo de la serosa.

El intestino delgado se desarrolla a partir del tubo digestivo, que existe ventralmente en el embrión en desarrollo. El tubo digestivo es endodermo, y por lo tanto el intestino delgado y sus glándulas asociadas desarrollan principalmente del endodermo. Mesodermo esplácnico rodea el tubo digestivo y da lugar a los músculos de la túnica muscular (por el peristaltismo), los vasos sanguíneos en la submucosa y el tejido conectivo de la serosa.

Los intestinos comienzan como un tubo recto, suspendido por el mesenterio dorsal. El intestino medio y mesenterio alargan para formar un lazo. La rama descendente del lazo será el [[Duodeno - Anatomía & Fisiología|duodeno]], el [[Yeyuno - Anatomía & Fisiología|yeyuno]] y el [[Ileon - Anatomía & Fisiología|íleon]]. La rama ascendente se forma la porción terminal del [[Ileon - Anatomía & Fisiología|íleon]], [[Ciego - Anatomía & Fisiología|ciego]] y la primera mitad del [[Colon - Anatomía & Fisiología|colon]]. El asa del intestino medio gira alrededor de la arteria mesentérica craneal en el sentido de las agujas del reloj (visto dorsoventralmente). Se somete a una rotación de 270 ° para que el [[Ciego - Anatomía & Fisiología|ciego]] y [[Colon - Anatomía & Fisiología|colon]] ascendente terminan en la derecha, y el intestino delgado termina en la izquierda.

Los intestinos comienzan como un tubo recto, suspendido por el mesenterio dorsal. El intestino medio y mesenterio alargan para formar un lazo. La rama descendente del lazo será el [[Duodeno - Anatomía & Fisiología|duodeno]], el [[Yeyuno - Anatomía & Fisiología|yeyuno]] y el [[Íleon - Anatomía & Fisiología|íleon]]. La rama ascendente se forma la porción terminal del [[Ileon - Anatomía & Fisiología|íleon]], [[Ciego - Anatomía & Fisiología|ciego]] y la primera mitad del [[Colon - Anatomía & Fisiología|colon]]. El asa del intestino medio gira alrededor de la arteria mesentérica craneal en el sentido de las agujas del reloj (visto dorsoventralmente). Se somete a una rotación de 270 ° para que el [[Ciego - Anatomía & Fisiología|ciego]] y [[Colon - Anatomía & Fisiología|colon]] ascendente terminan en la derecha, y el intestino delgado termina en la izquierda.

==Estructura==

==Estructura==

El intestino delgado se une a lo largo de su longitud total a la pared abdominal dorsal por el [[Cavidad Peritoneal - Anatomía & Fisiología|mesenterio]]. El [[Cavidad Peritoneal - Anatomía & Fisiología|mesenterio]] esta relativamente largo para su mayor parte, dando el intestino delgado, una gran movilidad. La estructura básica de la pared intestinal se conserva a lo largo de toda la longitud del tubo digestivo, pero hay la mayor diversidad en la capa epitelial. Dentro de la túnica muscular son los músculos presentes para peristalis y la mezcla de los alimentos. Hay dos capas musculares, una externa longitudinal y la capa interior circular. Entre las dos capas del músculo es el '''plexo mientérico'''. Entre la capa del músculo circular interna en la túnica muscular y la submucosa es el '''plexo submucoso'''. (Ver la [[#Regulación y Control|regulación y control]]).

El intestino delgado se une a lo largo de su longitud total a la pared abdominal dorsal por el [[Cavidad Peritoneal - Anatomía & Fisiología|mesenterio]]. El [[Cavidad Peritoneal - Anatomía & Fisiología|mesenterio]] esta relativamente largo para su mayor parte, dando el intestino delgado, una gran movilidad. La estructura básica de la pared intestinal se conserva a lo largo de toda la longitud del tubo digestivo, pero hay la mayor diversidad en la capa epitelial. Dentro de la túnica muscular son los músculos presentes para peristalis y la mezcla de los alimentos. Hay dos capas musculares, una externa longitudinal y la capa interior circular. Entre las dos capas del músculo es el '''plexo mientérico'''. Entre la capa del músculo circular interna en la túnica muscular y la submucosa es el '''plexo submucoso'''. (Ver la [[#Regulación y Control|regulación y control]]).

==Function==

==Función==

===To mix content and transport chyme===

===Para mezclar el contenido y transportar quimo===

[[Image:tunica muscularis.jpg|thumb|right|250px|Orientation of muscle in the tunica muscularis- © RVC 2008]]

[[Image:tunica muscularis.jpg|thumb|right|250px|Orientación del músculo en la túnica muscular- © RVC 2008]]

Contraction of the two muscle layers facilitates mixing and transportation. There are two types of muscle contraction:  

La contracción de las dos capas musculares facilita la mezcla y el transporte. Hay dos tipos de contracción muscular:

'''Segmental'''

La contracción rítmica del ''músculo circular'', crea contracciones como un anillo. Se divide el contenido en muchos sectores y segmentos se mueve adelante y hacia atrás haciendo la mezcla con los jugos digestivos. Este tipo de contracción predomina durante la digestión.

Rhythmic contraction of ''circular muscle'', creates ring like contractions. It divides content into many segments and moves segments backwards and forth causing mixing with digestive juices. This type of contraction predominates during digestion.

'''Peristáltico'''

'''Peristaltic'''

Contracción antagonisticas de los músculos longitudinales ''y'' circulares. Transporte quimo por el intestino delgado, pero las contracciones pueden ser débil para que haya tiempo para la absorción. Cuando un ''onda'' peristáltica de contracción alcanza el final del [[Íleon - Anatomía & Fisiología|íleon]], otro comienza en el [[Duodeno - Anatomía & Fisiología|duodeno]]. Esto se conoce como un complejo ''mioeléctrica migrando''.

===Para segregar enzimas para la digestión del quimo y absorción de productos de la digestión===

 

===To secrete enzymes for the digestion of chyme and absorb the products of digestion===

[[Image:Dissacharidase.jpg|thumb|right|250px|Dissacharidase - © RVC 2008]]

[[Image:Dissacharidase.jpg|thumb|right|250px|Dissacharidase - © RVC 2008]]

====Digestión y Absorción de Carbohidratos====   

 

====Carbohydrate Digestion and Absorption====   

The main soluble carbohdrates found in food are starch, found mainly in plants, and glycogen, found mainly in animal meat. There are two types of starch, ''amylose'' which has α1-4 glycosidic links and, ''amylopectin'' which has α1-4 glycosidic links and α1-6 glycosidic links making it branched (branches every glucose 25 residues). ''Glycogen'' is synthesised in the [[Hígado - Anatomía & Fisiología|hígado]] and [[Muscles - Anatomía & Fisiología|muscle]] and is similar to amylopectin as it has both α1-4 glycosidic links and α1-6 glycosidic links. However, it is more highly branched with shorter branches (branches every 12-18 glucose residues).

The main soluble carbohdrates found in food are starch, found mainly in plants, and glycogen, found mainly in animal meat. There are two types of starch, ''amylose'' which has α1-4 glycosidic links and, ''amylopectin'' which has α1-4 glycosidic links and α1-6 glycosidic links making it branched (branches every glucose 25 residues). ''Glycogen'' is synthesised in the [[Hígado - Anatomía & Fisiología|hígado]] and [[Músculos - Anatomía & Fisiología|músculo]] and is similar to amylopectin as it has both α1-4 glycosidic links and α1-6 glycosidic links. However, it is more highly branched with shorter branches (branches every 12-18 glucose residues).

The '''first stage''' of carbohydrate digestion begins with α-amylase, which is an endoglycosidase. ''(This means it breaks bonds in the middle of the polymer to produce di-, tri- and oligo-saccharides).'' α-Amylase is present in [[Salivary Glands - Anatomía & Fisiología|saliva]]. Salivary α-amylase is inactivated when it enters the [[Estómago Monogástrico - Anatomía & Fisiología|stomach]] due to it's acidic pH.

The '''first stage''' of carbohydrate digestion begins with α-amylase, which is an endoglycosidase. ''(This means it breaks bonds in the middle of the polymer to produce di-, tri- and oligo-saccharides).'' α-Amylase is present in [[:Categoría:Glándulas Salivares - Anatomía & Fisiología|saliva]]. Salivary α-amylase is inactivated when it enters the [[Estómago Monogástrico - Anatomía & Fisiología|stomach]] due to it's acidic pH.

Carbohydrate digestion continues in the lumen of the [[Intestino Delgado - Resumen - Anatomy & Physiology|intestino delgado]] as pancreatic α-amylase enters the [[Duodeno - Anatomía & Fisiología|duodeno]] in the pancreatic duct. This is the site of the majority of carbohydrate digestion. The '''second stage''' is the digestion of di-, tri-, and oligo-saccharides to monosaccharides. This is done by di-, tri-, and oligo-saccharidases which have a glycocalyx to trap their substrate. They are bound to enterocytes. The main dissacharides that are broken down are; Maltose into two glucose molecules, sucrose into a glucose and fructose molecule and lactose into a glucose and galactose molecule. These monomers can then be absorbed.

Carbohydrate digestion continues in the lumen of the [[Intestino Delgado - Resumen - Anatomía & Fisiología|intestino delgado]] as pancreatic α-amylase enters the [[Duodeno - Anatomía & Fisiología|duodeno]] in the pancreatic duct. This is the site of the majority of carbohydrate digestion. The '''second stage''' is the digestion of di-, tri-, and oligo-saccharides to monosaccharides. This is done by di-, tri-, and oligo-saccharidases which have a glycocalyx to trap their substrate. They are bound to enterocytes. The main dissacharides that are broken down are; Maltose into two glucose molecules, sucrose into a glucose and fructose molecule and lactose into a glucose and galactose molecule. These monomers can then be absorbed.

Absorption of glucose and galactose is coupled to sodium absorption and occurs through a symport called SGLT-1. Sodium potassium pumps in the enterocyte plasma membrane pump sodium out of the cell so that there is a higher concentration in the intestinal lumen than in the enterocyte. There is a net negative charge on the cell. Sodium diffuses down it's concentration and electrochemical gradient back into the enterocyte through the symport. This releases some energy. The energy release is used to transport glucose and galactose up their concentration gradients into the enterocyte. Glucose and galactose can then diffuse into the blood (portal vein) by carrier mediated diffusion via a GLUT-5 transporter.

Absorption of glucose and galactose is coupled to sodium absorption and occurs through a symport called SGLT-1. Sodium potassium pumps in the enterocyte plasma membrane pump sodium out of the cell so that there is a higher concentration in the intestinal lumen than in the enterocyte. There is a net negative charge on the cell. Sodium diffuses down it's concentration and electrochemical gradient back into the enterocyte through the symport. This releases some energy. The energy release is used to transport glucose and galactose up their concentration gradients into the enterocyte. Glucose and galactose can then diffuse into the blood (portal vein) by carrier mediated diffusion via a GLUT-5 transporter.

====Triacylglycerol Digestion and Absorption====

====Digestión y Absorción de Triacilgliceroles====

Triacylglycerols (TAGs) are digested by lipases. TAG digestion begins in the [[Cavidad Oral - Resumen - Anatomía & Fisiología|cavidad oral]], where lingual lipase is secreted in the [[Salivary Glands - Anatomía & Fisiología|saliva]]. It removes a fatty acid from the 3 position on the glycerol molecule producing 1,2-diacylglycerol(1,2 DAG) and a free fatty acid. TAG digestion continues in the small intestine, with pancreatic lipase and bile from the [[Hígado - Anatomía & Fisiología|hígado]]. Pancreatic lipase is water soluble and the TAG and 1,2-DAG are lipid soluble. Bile creates an interface for the enzyme to digest the lipid molecules. Bile also emulsifies fats; it reduces the size of lipid droplets increasing the surface area available for digestion. Pancreatic lipase removes any further fatty acids from the 3 position and then from the 1 position to produce 2-monoacylglycerol (2-MAG) and a fatty acid. Pancreatic lipase is unable to remove the fatty acid from the 2 position, so an enzyme called '''isomerase''' transfers the fatty acid from the 2 postion to the 1 postion to produce 1-monoacylglycerol (1-MAG). Pancreatic lipase can then remove the fatty acid from the 1 position to produce a fatty acid and glycerol.

Triacylglycerols (TAGs) are digested by lipases. TAG digestion begins in the [[Cavidad Oral - Resumen - Anatomía & Fisiología|cavidad oral]], where lingual lipase is secreted in the [[:Categoría:Glándulas Salivares - Anatomía & Fisiología|saliva]]. It removes a fatty acid from the 3 position on the glycerol molecule producing 1,2-diacylglycerol(1,2 DAG) and a free fatty acid. TAG digestion continues in the small intestine, with pancreatic lipase and bile from the [[Hígado - Anatomía & Fisiología|hígado]]. Pancreatic lipase is water soluble and the TAG and 1,2-DAG are lipid soluble. Bile creates an interface for the enzyme to digest the lipid molecules. Bile also emulsifies fats; it reduces the size of lipid droplets increasing the surface area available for digestion. Pancreatic lipase removes any further fatty acids from the 3 position and then from the 1 position to produce 2-monoacylglycerol (2-MAG) and a fatty acid. Pancreatic lipase is unable to remove the fatty acid from the 2 position, so an enzyme called '''isomerase''' transfers the fatty acid from the 2 postion to the 1 postion to produce 1-monoacylglycerol (1-MAG). Pancreatic lipase can then remove the fatty acid from the 1 position to produce a fatty acid and glycerol.

''NB: Pancreatic lipase works quickly, whilst isomerase works slowly. Thus, 2-MAG often accumulates and is absorbed (70% of digested TAG are absorbed as 2-MAG). A small proportion is absorbed as 1-MAG (6%).''

''NB: Pancreatic lipase works quickly, whilst isomerase works slowly. Thus, 2-MAG often accumulates and is absorbed (70% of digested TAG are absorbed as 2-MAG). A small proportion is absorbed as 1-MAG (6%).''

The products of TAG digestion diffuse passively into the enterocyte as they are lipid soluble. They are then recombined to produce TAG. Fatty acids are converted to fatty acyl CoA by the addition of CoA. Fatty acyl CoAs are then added successively to 2-MAG to produce a TAG. In the golgi apparatus, TAG are then packaged with proteins, phospholipid and cholesterol into lipoproteins called '''chylomicrons'''. Chylomicrons are too large to enter the capillaries but instead enter the lymph to eventually join the blood via the thoracic duct. This enables the lipid soluble TAG to be transported in the blood.

The products of TAG digestion diffuse passively into the enterocyte as they are lipid soluble. They are then recombined to produce TAG. Fatty acids are converted to fatty acyl CoA by the addition of CoA. Fatty acyl CoAs are then added successively to 2-MAG to produce a TAG. In the golgi apparatus, TAG are then packaged with proteins, phospholipid and cholesterol into lipoproteins called '''chylomicrons'''. Chylomicrons are too large to enter the capillaries but instead enter the lymph to eventually join the blood via the thoracic duct. This enables the lipid soluble TAG to be transported in the blood.

====Protein Digestion and Absorption====

====Digestión y Absorción de Proteínas====

Protein digestion begins in the [[Estómago Monogástrico - Anatomy & Physiology|stomach]] where pepsin is secreted as a zymogen, pepsinogen. Pepsin is an endopeptidase and produces smaller polypeptides. Pepsin prefers to break peptide bonds of larger polypeptides, where there is a large hydrophobic amino acid on the N-terminal side. Protein digestion continues in the small intestine. There are three endopeptidases in the small intestine; trypsin; chymotrypsin; and elastase. They are all secreted as zymogens; inactive precursors.

Protein digestion begins in the [[Estómago Monogástrico - Anatomía & Fisiología|estómago]] where pepsin is secreted as a zymogen, pepsinogen. Pepsin is an endopeptidase and produces smaller polypeptides. Pepsin prefers to break peptide bonds of larger polypeptides, where there is a large hydrophobic amino acid on the N-terminal side. Protein digestion continues in the small intestine. There are three endopeptidases in the small intestine; trypsin; chymotrypsin; and elastase. They are all secreted as zymogens; inactive precursors.

Trypsin is secreted as trypsinogen, chymotrypsin is secreted as chymotrypsinogen and elastase is secreted as proelastase. Trypsinogen is initially activated by enterokinase (activation involves the cleavage of 6 amino acids). Trypsinogen can then activate itself, and also chymotrypsin and elastase. The short polypeptides produced from their digestion are further digested by exopeptidases which remove amino acids from the end of the polypeptide chain.  

Trypsin is secreted as trypsinogen, chymotrypsin is secreted as chymotrypsinogen and elastase is secreted as proelastase. Trypsinogen is initially activated by enterokinase (activation involves the cleavage of 6 amino acids). Trypsinogen can then activate itself, and also chymotrypsin and elastase. The short polypeptides produced from their digestion are further digested by exopeptidases which remove amino acids from the end of the polypeptide chain.  

Amino acids within the same group compete with each other for the transport molecule. Amino acids are transported with sodium through a symport (like glucose), where amino acids travel up their concentration gradient and sodium travels down its concentration gradient. Di-,tri- and oligo- peptides are absorbed by the γ glutamyl transfer cycle. γ Glutamyl transferase spans the enterocyte membrane and combines glutathione from the inside of the cell with a di-,tri- or oligo-peptide from the intestinal lumen forming a γ-glu-aa complex which is transported into the cell. The aas are then released and glutathione is recombined to enter the process again.

Amino acids within the same group compete with each other for the transport molecule. Amino acids are transported with sodium through a symport (like glucose), where amino acids travel up their concentration gradient and sodium travels down its concentration gradient. Di-,tri- and oligo- peptides are absorbed by the γ glutamyl transfer cycle. γ Glutamyl transferase spans the enterocyte membrane and combines glutathione from the inside of the cell with a di-,tri- or oligo-peptide from the intestinal lumen forming a γ-glu-aa complex which is transported into the cell. The aas are then released and glutathione is recombined to enter the process again.

==Regulation & Control==

==Regulación y Control==

The functions of the small (and large) intestine are regulated by three mechanisms: Endocrine hormones, paracrine hormones and neural transmitters. Unlike the [[Estómago Monogástrico - Anatomía & Fisiología|stomach]], control is mainly local, with superimposed co-ordination through the extrinsic ANS. All signals affect the small intestine via sensory neurones. Neurones interact with two plexuses in the intestinal wall. Neurones in the ''myenteric plexus'' produce changes in muscle ''contractility''. Neurones in the ''submucosal plexus'' produce changes in ''secretion'' and ''blood flow'' to the small intestine. Plexuses are connected via interneurones.

The functions of the small (and large) intestine are regulated by three mechanisms: Endocrine hormones, paracrine hormones and neural transmitters. Unlike the [[Estómago Monogástrico - Anatomía & Fisiología|stomach]], control is mainly local, with superimposed co-ordination through the extrinsic ANS. All signals affect the small intestine via sensory neurones. Neurones interact with two plexuses in the intestinal wall. Neurones in the ''myenteric plexus'' produce changes in muscle ''contractility''. Neurones in the ''submucosal plexus'' produce changes in ''secretion'' and ''blood flow'' to the small intestine. Plexuses are connected via interneurones.

==Enlaces==

==Enlaces==

'''Test yourself with the [[Small Intestine - Anatomy & Physiology - Flashcards|Small Intestine  Flashcards]]'''

'''Test yourself with the [[Intestino Delgado - Anatomy & Physiology - Flashcards|Flashcards del Intestino Delgado]]'''

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'''Click here for information on [[Peyer's Patches - Anatomy & Physiology|Peyer's Patches]]'''