Difference between revisions of "Omasum - Anatomy & Physiology"
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==Introduction== | ==Introduction== | ||
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==Structure== | ==Structure== | ||
[[Image:Omasum Anatomy Sheep.jpg|thumb|right|250px|Omasum Anatomy (Sheep) - Copyright RVC 2008]] | [[Image:Omasum Anatomy Sheep.jpg|thumb|right|250px|Omasum Anatomy (Sheep) - Copyright RVC 2008]] | ||
| − | The omasum is right of the midline. The [[Rumen - Anatomy & Physiology|Rumen]] and [[Reticulum - Anatomy & Physiology|reticulum]] are located to the left and the liver and body wall to the right. The omasum is covered by lesser omentum and is bilaterally flattened. It is located at ribs 8-11. The lower pole has an extensive connection to the fundic region of the [[Abomasum - Anatomy & Physiology|abomasum]]. | + | The omasum is right of the midline. The [[Rumen - Anatomy & Physiology|Rumen]] and [[Reticulum - Anatomy & Physiology|reticulum]] are located to the left and the liver and body wall to the right. The omasum is covered by lesser omentum and is bilaterally flattened. It is located at ribs 8-11. The lower pole has an extensive connection to the fundic region of the [[Abomasum - Anatomy & Physiology|abomasum]]. An '''omasal canal''' is present known as the '''omasal groove'''. The floor is smooth except for low ridges and projections around the upper opening. The opening to the [[Reticulum - Anatomy & Physiology|reticulum]] is at the cranial end and the opening to the [[Abomasum - Anatomy & Physiology|abomasum]] is at the caudal end of the omasal canal. The exit to the abomasum is a large oval opening, partly covered by overhanging abomasal folds. |
==Function== | ==Function== | ||
| − | A function of the omasum is absorption. Food enters omasum at second biphasic reticular contraction. The omasum itself has biphasic contractions. The first contraction expels fluid by squeezing the ingesta from the omasal canal between the lamellae. The second contraction expels solids by mass contraction of the omasum. Contractions are slower than the rumenoreticular contractions (see [[Rumination|rumination]]). Food is squeezed between lamellae. | + | A function of the omasum is absorption. Food enters omasum at second biphasic reticular contraction. The omasum itself has biphasic contractions. The first contraction expels fluid by squeezing the ingesta from the omasal canal between the lamellae. The second contraction expels solids by mass contraction of the omasum. Contractions are slower than the rumenoreticular contractions (see [[Rumination - Anatomy & Physiology|rumination]]). Food is squeezed between lamellae. |
==Vasculature== | ==Vasculature== | ||
| − | The blood supply to the omasum includes the '''cranial mesenteric artery''', the '''left gastric''' and | + | The blood supply to the omasum includes the '''cranial mesenteric artery''', the '''caudal mesenteric artery''' and the '''left gastric''' and '''left gastroepiploic arteries'''. |
==Innervation== | ==Innervation== | ||
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{{Template:Learning | {{Template:Learning | ||
|flashcards = [[Omasum Flashcards]] | |flashcards = [[Omasum Flashcards]] | ||
| − | |videos = [[ | + | |videos = [http://stream2.rvc.ac.uk/Anatomy/bovine/Pot0052.mp4 Lateral view of the Abdomen of a young Ruminant]<br>[http://stream2.rvc.ac.uk/Anatomy/bovine/pot0175.mp4 Sections of the Ruminant Stomach]<br>[http://stream2.rvc.ac.uk/Anatomy/ovine/Pot0047.mp4 Ovine Omasum and Abomasum]<br>[http://stream2.rvc.ac.uk/Frean/sheep/LeftSideTopography.mp4 Left sided topography of the Ovine Abdomen and Thorax]<br>[http://stream2.rvc.ac.uk/Frean/sheep/RightSideTopography.mp4 Right sided topography of the Ovine Abdomen]<br>[http://stream2.rvc.ac.uk/Frean/sheep/RuminantStomachStructure.mp4 Structure of the ruminant forestomachs] |
|powerpoints = [[Ruminant Gastrointestinal Tract Histology resource|Histology of the ruminant gastrointestinal tract]] | |powerpoints = [[Ruminant Gastrointestinal Tract Histology resource|Histology of the ruminant gastrointestinal tract]] | ||
}} | }} | ||
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[[Category:Stomach - Anatomy & Physiology]] | [[Category:Stomach - Anatomy & Physiology]] | ||
[[Category:A&P Done]] | [[Category:A&P Done]] | ||
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Revision as of 17:58, 30 June 2011
Introduction
The omasum is the third chamber in the ruminant stomach. It lies within the intrathoracic part of the abdomen so cannot be palpated manually. Instead it is examined by ausculation. The omasum has biphasic contractions which squeeze fluid out of the food before allowing the ingesta to continue into the abomasum. Absorption of volatile fatty acids continues in the omasum.
Structure
The omasum is right of the midline. The Rumen and reticulum are located to the left and the liver and body wall to the right. The omasum is covered by lesser omentum and is bilaterally flattened. It is located at ribs 8-11. The lower pole has an extensive connection to the fundic region of the abomasum. An omasal canal is present known as the omasal groove. The floor is smooth except for low ridges and projections around the upper opening. The opening to the reticulum is at the cranial end and the opening to the abomasum is at the caudal end of the omasal canal. The exit to the abomasum is a large oval opening, partly covered by overhanging abomasal folds.
Function
A function of the omasum is absorption. Food enters omasum at second biphasic reticular contraction. The omasum itself has biphasic contractions. The first contraction expels fluid by squeezing the ingesta from the omasal canal between the lamellae. The second contraction expels solids by mass contraction of the omasum. Contractions are slower than the rumenoreticular contractions (see rumination). Food is squeezed between lamellae.
Vasculature
The blood supply to the omasum includes the cranial mesenteric artery, the caudal mesenteric artery and the left gastric and left gastroepiploic arteries.
Innervation
The omasum is innervated by the dorsal vagus nerve (CN X) (most important) and the ventral vagus nerve.
Lymphatics
There are numerous small lymph nodes that are scattered in the omasal curvatures. The lymph drains to larger atrial nodes between the cardia and the omasum, then to the cistera chyli.
Histology
The omasum has a keratinised stratified squamous epithelium. It is firm in texture and can vary in size. Lamellae thrown into leaves divide the lumen into narrow and uniform recesses. It contains no glands.
The papillae of the omasum are mostly small and lenticular, although some can be large and conical. The circular tunica muscularis extends into papillae of long laminae and the lamina muscualris extends into papillae encircling the tunica muscularis. The omasum has 3 smooth muscle layers in the papillae therefore they are very motile.
Species Differences
Small Ruminant
The small ruminants have a smaller omasum, which is bean shaped.
Bovine
The lower pole of the omasum contacts the abdominal floor below the costal arch.
Links
Click here for information on rumen
Click here for information on reticulum
Click here for information on abomasum
| Omasum - Anatomy & Physiology Learning Resources | |
|---|---|
 Test your knowledge using flashcard type questions |
Omasum Flashcards |
 Selection of relevant videos |
Lateral view of the Abdomen of a young Ruminant Sections of the Ruminant Stomach Ovine Omasum and Abomasum Left sided topography of the Ovine Abdomen and Thorax Right sided topography of the Ovine Abdomen Structure of the ruminant forestomachs |
 Selection of relevant PowerPoint tutorials |
Histology of the ruminant gastrointestinal tract |