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Abomasum - Anatomy & Physiology (view source)

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==Introduction==
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The abomasum is the fourth chamber in the ruminant. It functions similarily to the [[Forestomach - Anatomy & Physiology|carnivore stomach]] as it is glandular and functions to digest food chemically, rather than mechanically or by fermentation like the other 3 chambers of the ruminant stomach.
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The abomasum differs in its position within the abdomen, depending on fullness of the other chambers of the stomach, intrinsic abomasonal activity, contractions of the [[The Rumen - Anatomy & Physiology|rumen]] and [[The Reticulum - Anatomy & Physiology|reticulum]] (to which it is attached) and by age and pregnancy.
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[[Stomach and Abomasum Physical Disruptions - Pathology#Displaced Abomasum in the Cow|Displacement of the abomasum]] to the left or to the right is a common disorder affecting dairy cows due to high concentrate feed.
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==Structure==
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[[Image:Abomasum Anatomy Sheep.jpg|thumb|right|150px|Abomasum Anatomy (Sheep) - Copyright RVC 2008]]
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*Lies upon the abdominal floor
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*Cranial part split into pylorus and body
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*Caudal part
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*Covered by lesser omentum
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*15-20 folds inside
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*Torus at pyloric exit
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*Outflow fairly constant
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*Motility at pylorus (peristalsis)
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*Some control at pyloric sphincter
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*Large in newborn
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*Proximal ends of the abomasal folds forms a plug preventing reflux into the [[The Omasum - Anatomy & Physiology|omasum]]
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*Thin walls
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*Serousa covering
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==Function==
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*Chemical breakdown of food
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*Secretes hydrochloric acid and pepsinogen
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*Some intrinsic motility
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*Impaired motility can cause distension
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*Movements are slow
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**Contraction first of proximal part
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**More forceful contraction at pyloric part
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==Vasculature==
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*Cranial mesenteric artery
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*Celiac artery
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*Left gastric and left gasrtoepiploic arteries
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==Innervation==
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*Dorsal vagus nerve ([[Nervous System - CNS - Anatomy & Physiology#Innervation - Cranial Nerves|CN X]])
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*Ventral vagus nerve ([[Nervous System - CNS - Anatomy & Physiology#Innervation - Cranial Nerves|CN X]]) (most important)
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==Lymphatics==
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*Single lymph nodules are present at the junction between epithelium and lamina propria
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*Numerous small lymph nodes are scattered in the abomasal curvatures
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*The lymph drains to larger atrial nodes between the cardia and [[The Omasum - Anatomy & Physiology|omasum]], then to the hepatic lymph nodes
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==Histology==
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[[Image:Abomasum Histology Sheep.jpg|thumb|right|150px|Abomasum Histology (Sheep) - Copyright RVC 2008]]
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*Simple columnar epithelium
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*3 layers of tunica muscularis- inner oblique, middle circular and outer longitudinal
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*Lamina muscularis thicker (3 separate layers)
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*Gastric glands in lamina propria of mucosal layer in pyloric region (lighter part)
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*Heavily coated by mucous for protection
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*Submucosa contains loose connective tissue, many blood vessels and unilocular adipocytes
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*Deep gastric pits
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*Coiled glands in lamina propria opening into gastric pits
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*Pink inner mucosa
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*Rugae are present in the pyloric region
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*Torus (large swelling) is present at the pyloric passage to narrow the lumen
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*Dark mucosa of fundus and body contain peptic glands
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==Species Differences==
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===Small Ruminants===
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*Abomasum can contact [[Liver - Anatomy & Physiology|liver]]
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*Abomasum is proportionately larger than in cattle
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==Links==
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[[The Rumen - Anatomy & Physiology|The Rumen - Anatomy & Physiology]]
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[[The Reticulum - Anatomy & Physiology|The Reticulum - Anatomy & Physiology]]
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[[The Omasum - Anatomy & Physiology|The Omasum - Anatomy & Physiology]]
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[[The Stomachs of the Ruminant - Anatomy & Physiology - Flashcards#The Abomasum|The Abomasum Flashcards]]
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'''Video'''
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[http://stream2.rvc.ac.uk/Anatomy/bovine/Pot0052.mp4 Pot 52 Lateral view of the Abdomen of a young Ruminant]
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[http://stream2.rvc.ac.uk/Anatomy/bovine/pot0175.mp4 Pot 175 Sections of the Ruminant Stomach]
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[http://stream2.rvc.ac.uk/Anatomy/ovine/Pot0047.mp4 Pot 47 Ovine Omasum and Abomasum]
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[http://stream2.rvc.ac.uk/Frean/sheep/LeftSideTopography.mp4 Left sided topography of the Ovine Abdomen and Thorax]
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[http://stream2.rvc.ac.uk/Frean/sheep/RightSideTopography.mp4 Right sided topography of the Ovine Abdomen]
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[http://stream2.rvc.ac.uk/Frean/sheep/RuminantStomachStructure.mp4 Structure of the ruminant forestomachs]
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