Difference between revisions of "Monogastric Stomach - Anatomy & Physiology"

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==Overview==
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|backcolour =BCED91
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[[Image:Stomach Anatomy 1.jpg|thumb|right|250px|Stomach Anatomy 1 - Copyright Nottingham 2008]]
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|linkpage =Alimentary - Anatomy & Physiology
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|linktext =Alimentary System
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|maplink = Alimentary (Concept Map)- Anatomy & Physiology
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|pagetype =Anatomy
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}}
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<br>
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[[Image:Stomach Anatomy 1.jpg|thumb|right|150px|Stomach Anatomy 1 - Copyright Nottingham 2008]]
 +
==Introduction==
  
−
The enlarged swelling of the gastrointestinal tract between the '''[[Oesophagus - Anatomy & Physiology|oesophagus]]''' and the '''[[Duodenum - Anatomy & Physiology|duodenum]]''' is called the '''stomach'''. It is a simple structure in carnivores and a compound structure in ruminants.
+
The enlarged swelling of the gastrointestinal tract between the [[Oesophagus - Anatomy & Physiology|oesophagus]] and [[Duodenum - Anatomy & Physiology|duodenum]] is called the stomach. It is a simple structure in carnivores and a compound structure in ruminants.
  
 
The stomach functions as a reservoir of food where digestion occurs through chemical and mechanical processes. This allows food to be broken down further and absorbed.
 
The stomach functions as a reservoir of food where digestion occurs through chemical and mechanical processes. This allows food to be broken down further and absorbed.
 +
  
 
==Development==
 
==Development==
  
−
The '''gut tube''' is formed from the folding of the '''splanchnopleure''' (mesoderm and endoderm). The '''endoderm''' is the inner layer forming the epithelia and glands. The layers around it are from the '''mesoderm''' forming the skeletal muscle, ([[Oesophagus - Anatomy & Physiology|oesophagus]] and [[Anus - Anatomy & Physiology|anus]]), smooth muscle (from lateral plate mesoderm) and connective tissue.
 
  
−
The region enlarges and a swelling indicates where the stomach will form. The dorsal surface becomes convex to form the '''greater curvature''' of the stomach and the ventral surface becomes concave to form the '''lesser curvature'''. Two rotations of 90 degrees occur along the longitudinal axis and then the dorso-ventral axis. The dorsal '''mesogastrium''' becomes elongated (with the [[Spleen - Anatomy & Physiology|spleen]]) and expands into a large fold along the ventral abdominal wall. This becomes the '''greater omentum''' which covers all the abdominal organs. It is a superficial structure which is free to move. The '''ventral mesogastrium''' becomes the '''lesser omentum'''. It is in between the stomach and the [[Liver - Anatomy & Physiology|liver]]. The rest of the ventral mesentry degenerates.
+
*The gut tube is formed from the folding of splanchnopleure (mesoderm and endoderm)
 +
 
 +
*The mesoderm forms the skeletal muscle ([[Oesophagus - Anatomy & Physiology|oesophagus]] and [[Anus - Anatomy & Physiology|anus]]), smooth muscle (lateral plate mesoderm) and connective tissue layers around the inner endoderm.
  
−
[[Image:Stomach Anatomy 2.jpg|thumb|right|250px|Stomach Anatomy 2 - Copyright University of Nottingham 2008]]
+
*The endoderm is the inner layer forming the epithelia and glands.
 +
 
 +
1. Region enlarges. Swelling indicates where the stomach will form.
 +
 
 +
2. Dorsal surface becomes convex to form the greater curvature
 +
 
 +
3. Ventral surface becomes concave to form the lesser curvature
 +
 
 +
4. Two rotations of 90 degrees occur along the longitudinal axis and then then the dorso-ventral axis
 +
 
 +
5. The dorsal mesogastrium becomes elongated (with the [[Spleen - Anatomy & Physiology|spleen]]) and expands into a large fold along the ventral abdominal wall. This becomes the greater omentum which covers all the abdominal organs. It is a superficial structure which is free to move.
 +
 
 +
6. The ventral mesogastrium becomes the lesser omentum. It is in between the stomach and the [[Liver - Anatomy & Physiology|liver]]. The rest of the ventral mesentry degenerates.
 +
 
 +
[[Image:Stomach Anatomy 2.jpg|thumb|right|150px|Stomach Anatomy 2 - Copyright Nottingham 2008]]
  
 
==Structure and Function==
 
==Structure and Function==
  
−
The stomach is split into regions: '''cardia''', '''fundic''', '''body''' and '''pyloric'''. The entire stomach is motile. It has a pH of 0.9 to 1.5.
+
*Stomach split into regions: cardia, fundic, body and pyloric parts
 +
 
 +
*Entire stomach is motile
  
−
The larger part of the stomach lies to the left of the midline, under cover from the ribcage and in contact with the [[Liver - Anatomy & Physiology|liver]] and diaphragm. The [[Oesophagus - Anatomy & Physiology|oesophagus]] opens into it at the cardiac sphincter. The smaller part of the stomach has thicker walls and passes to the right of the midline into the [[Duodenum - Anatomy & Physiology|duodenum]] at the pyloric sphincter. The angular point between the two parts of the stomach is called the '''angular notch''' (incisura).
+
*pH 0.9 to 1.5
−
[[Image:Stomach Anatomy 3.jpg|thumb|right|250px|Stomach Anatomy 3 - Copyright University of  Nottingham 2008]]
 
  
−
The '''fundus''' is a blind dome rising above the cardia. The '''body''' extends from the cardia ventrally and the '''pyloric''' part is on the right divided into a more muscular and a less muscular half. The '''serosa''' (external peritoneum) covers the entire organ.
+
*The larger part of the stomach lies to the left of the midline, under cover from the ribcage and in contact with the [[Liver - Anatomy & Physiology|liver]] and diaphragm. The [[Oesophagus - Anatomy & Physiology|oesophagus]] opens into it at the cardiac sphincter.
  
−
Contractions start near the '''cardia''' and spread distally, accelerating and becoming more vigorous as they reach the '''pyloric''' region. The '''pyloric sphincter''' is open for 1/3 of the time during contractions. The empty stomach lies completely within the rib cage and does not contact the abdominal floor. Little secretion is produced and only small peristaltic contractions occur. Once food is offered or anticipated, the secretions begin.
+
*The smaller part of the stomach has thicker walls and passes to the right of the midline into the [[Duodenum - Anatomy & Physiology|duodenum]] at the pyloric sphincter.
  
−
The stomach is supported by 4 folds of peritoneum:
+
*The angular point between the two parts of the stomach is called the angular notch (incisura)
−
:'''Gastrophrenic ligament''' - from the greater curvature of the stomach to the crura of the diaphragm
+
[[Image:Stomach Anatomy 3.jpg|thumb|right|150px|Stomach Anatomy 3 - Copyright Nottingham 2008]]
−
:'''Lesser omentum'''- connecting the lesser curvature of the stomach and the initial segment of [[Duodenum - Anatomy & Physiology|duodenum]] to the [[Liver - Anatomy & Physiology|liver]] in the region of the hepatic porta
 
−
:'''Gastrosplenic ligament'''- connecting the greater curvature of the stomach to the [[Spleen - Anatomy & Physiology|spleen]] by a double fold of peritoneum
 
−
:'''Greater omentum'''- connecting the greater curvature of the stomach to the [[Duodenum - Anatomy & Physiology|duodenum]] and dorsal body wall
 
  
−
==Vasculature==
 
  
−
Vasculature of the stomach includes the '''coeliac artery''' (which is a branch of the dorsal aorta). The coeliac artery splits into the hepatic artery supplying the [[Liver - Anatomy & Physiology|liver]], [[Pancreas - Anatomy & Physiology|pancreas]] and stomach (right gastric and right gastro-epiploic arteries). The coeliac artery also splits into the splenic artery which supplies the [[Spleen - Anatomy & Physiology|spleen]] and the stomach (left gastro-epiploic artery), it also splits into the left gastric artery supplying the stomach.
+
*The fundus is a blind dome rising above the cardia
 +
 
 +
*The body extends from the cardia ventrally
 +
 
 +
*The pyloric part is on the right divided into a more muscular and a less muscular half
 +
 
 +
*The serosa (external peritoneum) covers the entire organ
 +
 
 +
*Contractions start near the cardia and spread distally, accelerating and becoming more vigorous as they reach the pylorus region.
 +
 
 +
*The pyloric sphincter is open for 1/3 of the time during contractions
  
−
The '''gastro-epiploic arteries''' supply the greater curvature of the stomach and the '''gastric arteries''' supply the lesser curvature of the stomach. The numerous veins join the '''portal vein'''.
+
*The empty stomach lies completely within the rib cage and does not contact the abdominal floor. Little secretion is produced and only small peristaltic contractions occur.
  
−
==Innervation==
+
*Once food is offered or anticipated, secretions begin
  
−
'''Sympathetic''' fibres run with the arteries. '''Parasympathetic''' fibres from the '''vagus''' nerve ([[Cranial Nerves - Anatomy & Physiology|CN X]]) are within the two vagal trunks. In the '''proximal''' region of the stomach, vagal stimulation '''suppresses''' muscular contraction (VIP) and in the '''distal''' region, vagal stimulation '''increases''' muscular activity (ACh).
+
*Supported by 4 folds of peritoneum
 +
**Gastrophrenic ligament- from the greater curvature of the stomach to the crura of the diaphragm
 +
**Lesser omentum- connecting the lesser curvature of the stomach and the initial segment of [[Duodenum - Anatomy & Physiology|duodenum]] to the [[Liver - Anatomy & Physiology|liver]] in the region of the hepatic porta
 +
**Gastrosplenic ligament- connecting the greater curvature of the stomach to the [[Spleen - Anatomy & Physiology|spleen]] by a double fold of peritoneum
 +
**Greater omentum- connceting the greater curvature of the stomach to the [[Duodenum - Anatomy & Physiology|duodenum]] and dorsal body wall
  
 
==Histology==
 
==Histology==
−
[[Image:Glandular Stomach Histology Dog.jpg|thumb|right|250px|Glandular Stomach Histology Dog - Copyright RVC 2008]]
 
−
The monogastric stomach has a columnar epithelium. The folded mucosa of the stomach forms '''longitudinal rugae'''. The folds form invaginations called '''gastric pits''' which are continuous with gastric glands.
 
  
−
===Layers of the stomach===
+
[[Image:Glandular Stomach Histology Dog.jpg|thumb|right|150px|Glandular Stomach Histology Dog- Copyright RVC 2008]]
 +
*Columnar epithelium
 +
 
 +
*Folded mucosa forming longitudinal rugae
 +
 
 +
*Invaginations called gastric pits which are continuous with gastric glands
 +
 
 +
*The 4 layers of the stomach wall are:
 +
**Serosa/adventitia
 +
**Tunica muscularis
 +
**Submucosa
 +
**Mucosa
 +
 
 +
*Chief (zygomatic) cells secreting pepsinogen
 +
**Secreted in response to vagus and gastrin
 +
**Basophilic
 +
**More abundant in base of glands
 +
**Pepsinogen unfolds and cleaves itself (autocatalyses) in response to hydrochloric acid
 +
**Only active in acidic envrionments
 +
 
 +
[[Image:Fundic region of glandular stomach.jpg|thumb|right|150px|Fundic Region of Glandular Stomach (Parietal and Chief cells)- Copyright RVC 2008]]
 +
*Goblet cells secreting mucous
 +
**Protects against autodigestion
 +
 
 +
*Parietal (oxyntic) cells secreting hydrochloric acid in gastric pits
 +
**Aids digestion
 +
**Activates gastric enzymes, e.g. pepsinogen to pepsin
 +
**Kills microorganisms and enzymes that enter with food
 +
**Secreted in response to vagus or pepsin 
 +
**Large, pyramid shaped
 +
**More abundant in upper region of glands
 +
 
 +
*Gastrin from pyloric G cells
 +
 
 +
*Somatostatin from pyloric D cells
 +
 
 +
*Histamine from Enterochromaffin-like cells (ECL cells)
 +
 
 +
[[Image:Lamina muscularis 3 regions.jpg|thumb|right|150px|Lamina Muscualris 3 Regions - Copyright RVC 2008]]
 +
*3 layers of lamina muscularis: the outer longitudinal, middle circular and inner oblique.
  
−
The 4 layers of the stomach wall are:
+
*Glands are short, coiled, branched tubular. Need to be replaced due to wear and tear. Only in mucosal layer.
  
−
#'''Serosa/adventitia'''
+
*Cardia is a narrow muscle strip
−
#'''Tunica muscularis'''
 
−
#'''Submucosa'''
 
−
#'''Mucosa'''
 
  
−
There are 3 layers of '''muscularis''': the outer longitudinal, middle circular and inner oblique. The '''pyloric sphincter''' is a thickened tunica muscularis from the middle circular smooth muscle layer. In the '''fundic region''', the tunica muscularis is thinner, the glands are straight and the gastric pits are shallow. There is also an abundance of parietal and chief cells in the gland. In the '''pyloric region''', the tunica muscularis is thicker, the glands are coiled and the gastric pits are deep. The '''cardia''' is a narrow muscle strip. Lymphatic vessels are present in the submucosa.
+
*Pyloric sphincter is thickened tunica muscularis from the middle circular smooth muscle layer
  
−
===Cell types===
+
*In fundic region, tunica muscularis is thinner, glands are straight and gastric pits are shallow. Abundance of parietal and cheif cells in gland.
  
−
The stomach contains basophilic '''chief (zygomatic) cells''' that secrete '''pepsinogen''' in response to vagus nerve stimulation and gastrin release. Pepsinogen unfolds and cleaves itself (autocatalyses) in response to hydrochloric acid, therefore only in acidic environments.
+
*In pyloric region, tunica muscularis is thicker, glands are coiled and gastric pits are deep.
  
−
[[Image:Fundic region of glandular stomach.jpg|thumb|right|250px|Fundic Region of Glandular Stomach (Parietal and Chief cells)- Copyright RVC 2008]]
+
*Lymphatic vessels are present in the submucosa
−
The stomach also contains '''goblet cells''' that secrete mucous. This secretion protects against autodigestion.
 
  
−
There are also '''parietal (oxyntic) cells''' found in gastric pits that secrete hydrochloric acid. This secretion aids digestion by activating gastric enzymes, e.g. pepsinogen to pepsin. Hydrochloric acid kills microorganisms and enzymes that enter with food. Hydrochloric acid is secreted in response to vagus nerve stimulation or pepsin secretion. Parietal cells are large and pyramid shaped, with a higher abundance in the upper region of the glands.
+
==Vasculature==
  
−
'''Gastrin''' is released from pyloric G cells; '''Somatostatin''' is released from pyloric D cells and '''histamine''' is released from Enterochromaffin-like cells (ECL cells).
+
*Coeliac artery (which is a branch of the dorsal aorta)
 +
**Coeliac artery splits into the hepatic artery supplying the [[Liver - Anatomy & Physiology|liver]], [[Pancreas - Anatomy & Physiology|pancreas]] and stomach (right gastric and right gastro-epiploic arteries)
 +
**Coeliac artery also splits into the splenic artery which supplies the [[Spleen - Anatomy & Physiology|spleen]] and the stomach (left gastro-epiploic artery)
 +
**Coeliac artery also splits into the left gastric artery supplying the stomach
  
−
[[Image:Lamina muscularis 3 regions.jpg|thumb|right|250px|Lamina Muscularis 3 Regions - Copyright RVC 2008]]
+
*The gastro-epiploic arteries supply the greater curvature of the stomach
−
Stomach glands are short, coiled, branched and tubular. They need to be replaced due to wear and tear and are only found in the mucosal layer.
+
 
 +
*The gastric arteries supply the lesser curvature of the stomach
 +
 
 +
*The numerous veins join the portal vein
 +
 
 +
==Innervation==
 +
 
 +
*Sympathetic fibres run with the arteries
 +
 
 +
*Parasympathetic from the vagus nerve ([[Cranial Nerves - Anatomy & Physiology|CN X]]) are within the two vagal trunks
 +
**In the proximal region of the stomach, vagal stimulation suppresses muscular contraction (VIP)
 +
**In the distal region, vagal stimulation increases muscular activity (ACh)
  
 
==Digestive Enzymes==
 
==Digestive Enzymes==
  
−
The digestive enzymes include;
+
*Proteases
 +
**Inactive zymogen
 +
**Activated by hydrochloric acid
 +
**Active pepsin produced
 +
**Completed near brush border to generate small peptides and individual amino acids
 +
**Starts in the stomach, continues into the [[Small Intestine - Anatomy & Physiology|small intestine]]
  
−
===Proteases===
+
*Carbohydrases
−
They are secreted as an inactive zymogen, activated by hydrochloric acid. Active pepsin is produced and completed near the brush border to generate small peptides and individual amino acids. It starts in the stomach and continues into the [[Small Intestine Overview - Anatomy & Physiology|small intestine]].
+
**E.g. amylase
 +
**Salivary and pancreatic to produce disaccharides
 +
**Disaccharides converted to monosaccharides near brush border
 +
**Cellulases from symbiotic micro-organisms ([[Stomach and Abomasum - Anatomy & Physiology|ruminant stomachs]])
  
−
===Carbohydrases===
+
*Lipases
−
Carbohydrases, e.g. amylase, are within salivary and pancreatic secretions and act to produce disaccharides. Disaccharides are converted to monosaccharides near the brush border. Cellulases are digested by symbiotic micro-organisms in the ([[Ruminant Stomach - Anatomy & Physiology|ruminant stomachs]]).
+
**Assisted by bile salts which neutralise stomach acids and emulsifies fats
 +
**Generates free fatty acids, monoglycerides and diglycerides
  
−
===Lipases===
+
==Innervation==
−
Lipases are assisted by bile salts which neutralise stomach acids and emulsifies fats. The process generates free fatty acids, monoglycerides and diglycerides.
 
  
−
==Control of secretions==
+
*Control of gastric secretions under hormonal (gastrin), paracrine (histamine) and neural (ACh) mediators in the cephalic and gastric phases
  
−
The release of gastric secretions is under '''hormonal''' (gastrin), '''paracrine''' (histamine) and '''neural''' (ACh) mediator control in the cephalic and gastric phases. Gastric secretions are inhibited during the intestinal phase by CCK and secretin.
+
*Gastric secretions inhibited during the intestinal phase by CCK and secretin
  
−
For more information, see [[Control of Feeding - Anatomy & Physiology#Control of GIT Secretions|control of secretions]].
+
*See [[Control of Feeding - Anatomy & Physiology#Control of GIT Secretions|control of secretions]]
  
 
==Species Differences==
 
==Species Differences==
  
−
The size of the non-glandular region in the simple stomach varies between species. It is largest in the horse, pig and then smallest in the dog.
+
*The size of the non-glandular region in the simple stomach varies between species. It is largest in the horse, pig and then smallest in the dog.
−
[[Image:Margo Plicatus.jpg|thumb|right|250px|Equine Stomch with Margo Plicatus - Copyright RVC 2008]]
+
[[Image:Margo Plicatus.jpg|thumb|right|150px|Equine Stomch with Margo Plicatus - Copyright RVC 2008]]
 +
===Equine===
 +
*A region called the margo plicatus is present which separates the glandular and non-glandular parts of the equine stomach. The non-glandular area is lined with squamous epithelium (not columnar).
  
−
===[[Alimentary System - Horse Anatomy#Stomach|Equine]]===
+
*The stomach is relatively small (10% GIT) with a strong cardiac sphincter which prevents the animal from [[Control of Feeding - Anatomy & Physiology#The Vomit Reflex|vomiting]]. The equine stomach is rarely empty and retention time is short as expulsion into the [[Duodenum - Anatomy & Physiology|duodenum]] stops when feeding stops.
−
A region called the '''margo plicatus''' is present which separates the glandular and non-glandular parts of the equine stomach. The non-glandular area is lined with squamous epithelium (not columnar).
+
 
−
The stomach is relatively small (10% GIT) with a strong '''cardiac sphincter''' which prevents the animal from [[Vomiting|vomiting]]. The equine stomach is rarely empty, retention time is short and expulsion into the [[Duodenum - Anatomy & Physiology|duodenum]] stops when feeding stops. A 500kg horse can produce 30l of gastric juice in 24 hours.
+
*A 500kg horse can produce 30ml of gastric juice in 24 hours
  
 
===Canine===
 
===Canine===
−
The stomach is of variable size ranging from 0.5 to 6l according to breed. A full stomach can touch the [[Urinary Bladder - Anatomy & Physiology|bladder]]. The subglandular layer of fibroblasts and collagen fibres are for protection, e.g. from consuming bones. It is between the glands and the lamina muscularis. A 25kg dog can produce 0.5 to 1l gastric juice in 24 hours.
+
*Stomach is of variable size ranging from 0.5 to 6L according to breed.  
 +
 
 +
*A full stomach can touch the [[Urinary Bladder - Anatomy & Physiology|bladder]].
 +
 
 +
*Subglandular layer of fibroblasts and collagen fibres for protection, e.g. from consuming bones. It is between the glands and the lamina muscularis.
 +
 
 +
*A 25kg dog can produce 0.5 to 1L gastric juice in 24 hours
  
 
===Porcine===
 
===Porcine===
−
The '''cardia''' is thickened, taking up nearly half the area of the stomach. The '''internal diverticulum''' is present, which can be seen externally.
+
*The cardia is thickened, taking up nearly half the area of the stomach
  
 +
*Internal diverticulum present which can be seen externally
  
 
==Links==
 
==Links==
  
−
Click here for [[:Category:Stomach and Abomasum - Pathology|Stomach Pathology]].
+
[[Monogastric Stomach - Anatomy & Physiology - Flashcards|Stomach Flashcards]]
 +
 
 +
[[Stomach and Abomasum Inflammation - Pathology|Stomach Pathology]]
 +
 
 +
[[Control of Feeding - Anatomy & Physiology|Control of Feeding]]
 +
 
 +
'''Video'''
 +
 
 +
[http://stream2.rvc.ac.uk/Anatomy/canine/Pot0036.mp4 Pot 36 The Canine Abdomen]
 +
 
 +
[http://stream2.rvc.ac.uk/Anatomy/equine/Pony_abdomen.mp4 Lateral View of the Equine Abdomen]
 +
 
 +
[http://stream2.rvc.ac.uk/Frean/Pony/left_topography.mp4 Left Sided topography of the Equine abdomen]
 +
 
 +
[http://stream2.rvc.ac.uk/Frean/Pony/right_topography.mp4 Right sided topography of the Equine Abdomen]
 +
 
 +
[http://stream2.rvc.ac.uk/Anatomy/equine/Pot0039.mp4 Pot 39 The Equine Stomach]
  
−
Click here for [[Control of Feeding - Anatomy & Physiology|Control of Feeding]].
+
[http://stream2.rvc.ac.uk/Frean/sheep/LeftSideTopography.mp4 Left sided topography of the Ovine Abdomen and Thorax]
  
−
{{Learning
+
[http://stream2.rvc.ac.uk/Frean/sheep/RightSideTopography.mp4 Right sided topography of the Ovine Abdomen]
−
|dragster =[[Comparative Stomach Anatomy Dragster resources]]
+
 
−
|flashcards = [[Monogastric Stomach - Anatomy & Physiology - Flashcards]]
+
[http://stream2.rvc.ac.uk/Anatomy/feline/pot0357.mp4 Pot 357 The Feline Abdomen]
−
|videos =[[Canine Abdomen video|The Canine Abdomen potcast]]<br>[[Video: Abdominal viscera of the horse dissection|Abdominal viscera of the horse dissection]]<br>[[Video: Equine left-sided abdominal and thoracic topography dissection|Equine left-sided abdominal and thoracic topography dissection]]<br>[[Video: Equine left-sided abdominal and thoracic topography dissection 2|Equine left-sided abdominal and thoracic topography dissection 2]]<br>[[Video: Equine stomach potcast|Equine stomach potcast]]<br>[[Video: Equine Stomach with Horse Bot Larvae|Equine Stomach with Horse Bot Larvae potcast]]<br>[[Video: Feline Abdomen|Feline abdomen potcast]]<br>[[Video: Porcine abdomen dissection|Porcine abdomen dissection]]<br>[[Video: Piglet Anatomy|Anatomy of the piglet potcast]]
 
−
|powerpoints = [[Gastrointestinal Tract Histology resource|Histology of the monogastric stomach - see part 1]]
 
−
|OVAM = [http://www.onlineveterinaryanatomy.net/content/pig-stomach Image - Pig Stomach]<br>[http://www.onlineveterinaryanatomy.net/content/dog-stomach Image - Dog Stomach]<br>[http://www.onlineveterinaryanatomy.net/content/horse-stomach Image - Equine Stomach]<br>[http://www.onlineveterinaryanatomy.net/content/interactive-pig-anatomy-stomach Porcine Interactive Anatomy - Stomach 1]<br>[http://www.onlineveterinaryanatomy.net/content/interactive-pig-anatomy-stomach-0 Porcine Interactive Anatomy - Stomach 2]<br>[http://www.onlineveterinaryanatomy.net/content/canine-stomach-histology Canine Stomach Histology]
 
−
|Vetstream = [https://www.vetstream.com/canis/search?s=stomach Stomach diseases and surgery]
 
−
}}
 
  
−
==Webinars==
+
[http://stream2.rvc.ac.uk/Anatomy/swine/Pig_abdomen.mp4 The Porcine Abdomen]
−
<rss max="10" highlight="none">https://www.thewebinarvet.com/gastroenterology-and-nutrition/webinars/feed</rss>
 
−
[[Category:Stomach - Anatomy & Physiology]]
 
−
[[Category:A&P Done]]
 

Revision as of 09:01, 24 April 2010

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()Map ALIMENTARY SYSTEM (Map)



Stomach Anatomy 1 - Copyright Nottingham 2008

Introduction

The enlarged swelling of the gastrointestinal tract between the oesophagus and duodenum is called the stomach. It is a simple structure in carnivores and a compound structure in ruminants.

The stomach functions as a reservoir of food where digestion occurs through chemical and mechanical processes. This allows food to be broken down further and absorbed.


Development

  • The gut tube is formed from the folding of splanchnopleure (mesoderm and endoderm)
  • The mesoderm forms the skeletal muscle (oesophagus and anus), smooth muscle (lateral plate mesoderm) and connective tissue layers around the inner endoderm.
  • The endoderm is the inner layer forming the epithelia and glands.

1. Region enlarges. Swelling indicates where the stomach will form.

2. Dorsal surface becomes convex to form the greater curvature

3. Ventral surface becomes concave to form the lesser curvature

4. Two rotations of 90 degrees occur along the longitudinal axis and then then the dorso-ventral axis

5. The dorsal mesogastrium becomes elongated (with the spleen) and expands into a large fold along the ventral abdominal wall. This becomes the greater omentum which covers all the abdominal organs. It is a superficial structure which is free to move.

6. The ventral mesogastrium becomes the lesser omentum. It is in between the stomach and the liver. The rest of the ventral mesentry degenerates.

Stomach Anatomy 2 - Copyright Nottingham 2008

Structure and Function

  • Stomach split into regions: cardia, fundic, body and pyloric parts
  • Entire stomach is motile
  • pH 0.9 to 1.5
  • The larger part of the stomach lies to the left of the midline, under cover from the ribcage and in contact with the liver and diaphragm. The oesophagus opens into it at the cardiac sphincter.
  • The smaller part of the stomach has thicker walls and passes to the right of the midline into the duodenum at the pyloric sphincter.
  • The angular point between the two parts of the stomach is called the angular notch (incisura)
Stomach Anatomy 3 - Copyright Nottingham 2008


  • The fundus is a blind dome rising above the cardia
  • The body extends from the cardia ventrally
  • The pyloric part is on the right divided into a more muscular and a less muscular half
  • The serosa (external peritoneum) covers the entire organ
  • Contractions start near the cardia and spread distally, accelerating and becoming more vigorous as they reach the pylorus region.
  • The pyloric sphincter is open for 1/3 of the time during contractions
  • The empty stomach lies completely within the rib cage and does not contact the abdominal floor. Little secretion is produced and only small peristaltic contractions occur.
  • Once food is offered or anticipated, secretions begin
  • Supported by 4 folds of peritoneum
    • Gastrophrenic ligament- from the greater curvature of the stomach to the crura of the diaphragm
    • Lesser omentum- connecting the lesser curvature of the stomach and the initial segment of duodenum to the liver in the region of the hepatic porta
    • Gastrosplenic ligament- connecting the greater curvature of the stomach to the spleen by a double fold of peritoneum
    • Greater omentum- connceting the greater curvature of the stomach to the duodenum and dorsal body wall

Histology

Glandular Stomach Histology Dog- Copyright RVC 2008
  • Columnar epithelium
  • Folded mucosa forming longitudinal rugae
  • Invaginations called gastric pits which are continuous with gastric glands
  • The 4 layers of the stomach wall are:
    • Serosa/adventitia
    • Tunica muscularis
    • Submucosa
    • Mucosa
  • Chief (zygomatic) cells secreting pepsinogen
    • Secreted in response to vagus and gastrin
    • Basophilic
    • More abundant in base of glands
    • Pepsinogen unfolds and cleaves itself (autocatalyses) in response to hydrochloric acid
    • Only active in acidic envrionments
Fundic Region of Glandular Stomach (Parietal and Chief cells)- Copyright RVC 2008
  • Goblet cells secreting mucous
    • Protects against autodigestion
  • Parietal (oxyntic) cells secreting hydrochloric acid in gastric pits
    • Aids digestion
    • Activates gastric enzymes, e.g. pepsinogen to pepsin
    • Kills microorganisms and enzymes that enter with food
    • Secreted in response to vagus or pepsin
    • Large, pyramid shaped
    • More abundant in upper region of glands
  • Gastrin from pyloric G cells
  • Somatostatin from pyloric D cells
  • Histamine from Enterochromaffin-like cells (ECL cells)
Lamina Muscualris 3 Regions - Copyright RVC 2008
  • 3 layers of lamina muscularis: the outer longitudinal, middle circular and inner oblique.
  • Glands are short, coiled, branched tubular. Need to be replaced due to wear and tear. Only in mucosal layer.
  • Cardia is a narrow muscle strip
  • Pyloric sphincter is thickened tunica muscularis from the middle circular smooth muscle layer
  • In fundic region, tunica muscularis is thinner, glands are straight and gastric pits are shallow. Abundance of parietal and cheif cells in gland.
  • In pyloric region, tunica muscularis is thicker, glands are coiled and gastric pits are deep.
  • Lymphatic vessels are present in the submucosa

Vasculature

  • Coeliac artery (which is a branch of the dorsal aorta)
    • Coeliac artery splits into the hepatic artery supplying the liver, pancreas and stomach (right gastric and right gastro-epiploic arteries)
    • Coeliac artery also splits into the splenic artery which supplies the spleen and the stomach (left gastro-epiploic artery)
    • Coeliac artery also splits into the left gastric artery supplying the stomach
  • The gastro-epiploic arteries supply the greater curvature of the stomach
  • The gastric arteries supply the lesser curvature of the stomach
  • The numerous veins join the portal vein

Innervation

  • Sympathetic fibres run with the arteries
  • Parasympathetic from the vagus nerve (CN X) are within the two vagal trunks
    • In the proximal region of the stomach, vagal stimulation suppresses muscular contraction (VIP)
    • In the distal region, vagal stimulation increases muscular activity (ACh)

Digestive Enzymes

  • Proteases
    • Inactive zymogen
    • Activated by hydrochloric acid
    • Active pepsin produced
    • Completed near brush border to generate small peptides and individual amino acids
    • Starts in the stomach, continues into the small intestine
  • Carbohydrases
    • E.g. amylase
    • Salivary and pancreatic to produce disaccharides
    • Disaccharides converted to monosaccharides near brush border
    • Cellulases from symbiotic micro-organisms (ruminant stomachs)
  • Lipases
    • Assisted by bile salts which neutralise stomach acids and emulsifies fats
    • Generates free fatty acids, monoglycerides and diglycerides

Innervation

  • Control of gastric secretions under hormonal (gastrin), paracrine (histamine) and neural (ACh) mediators in the cephalic and gastric phases
  • Gastric secretions inhibited during the intestinal phase by CCK and secretin

Species Differences

  • The size of the non-glandular region in the simple stomach varies between species. It is largest in the horse, pig and then smallest in the dog.
Equine Stomch with Margo Plicatus - Copyright RVC 2008

Equine

  • A region called the margo plicatus is present which separates the glandular and non-glandular parts of the equine stomach. The non-glandular area is lined with squamous epithelium (not columnar).
  • The stomach is relatively small (10% GIT) with a strong cardiac sphincter which prevents the animal from vomiting. The equine stomach is rarely empty and retention time is short as expulsion into the duodenum stops when feeding stops.
  • A 500kg horse can produce 30ml of gastric juice in 24 hours

Canine

  • Stomach is of variable size ranging from 0.5 to 6L according to breed.
  • A full stomach can touch the bladder.
  • Subglandular layer of fibroblasts and collagen fibres for protection, e.g. from consuming bones. It is between the glands and the lamina muscularis.
  • A 25kg dog can produce 0.5 to 1L gastric juice in 24 hours

Porcine

  • The cardia is thickened, taking up nearly half the area of the stomach
  • Internal diverticulum present which can be seen externally

Links

Stomach Flashcards

Stomach Pathology

Control of Feeding

Video

Pot 36 The Canine Abdomen

Lateral View of the Equine Abdomen

Left Sided topography of the Equine abdomen

Right sided topography of the Equine Abdomen

Pot 39 The Equine Stomach

Left sided topography of the Ovine Abdomen and Thorax

Right sided topography of the Ovine Abdomen

Pot 357 The Feline Abdomen

The Porcine Abdomen

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