Difference between revisions of "Omasum - Anatomy & Physiology"

Revision as of 14:02, 6 September 2010

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

Omasum Anatomy (Sheep) - Copyright RVC 2008

Right of the midline

Rumen and reticulum to the left, liver and body wall to the right

Covered by lesser omentum

Bilaterally flattened

Ribs 8-11

Lower pole has an extensive connection to fundic region of the abomasum

Omasal canal present
- Known as the omasal groove
- Floor smooth except for low ridges and projections around the upper opening

Opening to the reticulum at the cranial end of the omasal canal

Opening to the abomasum at the caudal end of the omasal canal. It is a large oval opening, partly covered by overhanging abomasal folds.

Function

Absorption

Food enters omasum at second biphasic reticular contraction

Biphasic contractions

First contraction expels fluid by squeezing the ingesta from the omasal canal between the lamellae

Second contraction expels solids by mass contraction of the omasum

Contractions are slower than the rumenoreticular contractions (see rumination)

Food squeezed between lamellae

Vasculature

Cranial mesenteric artery

Caudal mesenteric artery

Left gastric and left gastroepiploic arteries

Innervation

Dorsal vagus nerve (CN X) (most important)

Ventral vagus nerve (CN X)

Lymphatics

Numerous small lymph nodes 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

Species Differences

Small Ruminant

Smaller omasum

Omasum is bean shaped

Bovine

Lower pole of omasum contacts the the abdominal floor below the costal arch

Test yourself with the stomachs of the ruminant flashcards

The Omasum Flashcards

Links

The Rumen - Anatomy & Physiology

The Reticulum - Anatomy & Physiology

The Abomasum- Anatomy & Physiology

Video

Pot 52 Lateral view of the Abdomen of a young Ruminant

Pot 175 Sections of the Ruminant Stomach

Pot 47 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

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-{{OpenPagesTop}}
 ==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 - Anatomy & Physiology|abomasum]]. Absorption of [[Volatile Fatty Acids|volatile fatty acids]] continues in the omasum.
+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 [[The Abomasum - Anatomy & Physiology|abomasum]].
+Absorption of [[Volatile Fatty Acids - Anatomy & Physioogy|volatile fatty acids]] continues in the omasum.
 ==Structure==
-[[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 '''omasal canal''' is formed between the end of the '''laminae''' and the '''omasal groove''', part of the '''gastric groove''' between the cardia and the pyloric sphincter. The omasal canal passes between the [[Reticulum - Anatomy & Physiology|reticulum]] and the [[Abomasum - Anatomy & Physiology|abomasum]].  Its mucosa is smooth except for particularly large papillae around the reticulo-omasal opening. The omaso-abomasal opening is a large and oval, partly covered by overhanging abomasal folds.
+[[Image:Omasum Anatomy Sheep.jpg|thumb|right|150px|Omasum Anatomy (Sheep) - Copyright RVC 2008]]
+*Right of the midline
+*[[Rumen - Anatomy & Physiology|Rumen]] and [[Reticulum - Anatomy & Physiology|reticulum]] to the left, liver and body wall to the right
+*Covered by lesser omentum
+*Bilaterally flattened
+*Ribs 8-11
+*Lower pole has an extensive connection to fundic region of the [[The Abomasum - Anatomy & Physiology|abomasum]]
+*Omasal canal present
+**Known as the omasal groove
+**Floor smooth except for low ridges and projections around the upper opening
+*Opening to the [[Reticulum - Anatomy & Physiology|reticulum]] at the cranial end of the omasal canal
+*Opening to the [[The Abomasum - Anatomy & Physiology|abomasum]] at the caudal end of the omasal canal. It 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|rumination]]). Food is squeezed between lamellae.
+*Absorption
+*Food enters omasum at second biphasic reticular contraction
+*Biphasic contractions
+*First contraction expels fluid by squeezing the ingesta from the omasal canal between the lamellae
+*Second contraction expels solids by mass contraction of the omasum
+*Contractions are slower than the rumenoreticular contractions (see [[Rumination - Anatomy & Physiology|rumination]])
+*Food squeezed between lamellae
 ==Vasculature==
-The blood supply to the omasum includes the '''cranial mesenteric artery''', the '''left gastric''' and the '''left gastroepiploic arteries'''.
+*Cranial mesenteric artery
+*Caudal mesenteric artery
+*Left gastric and left gastroepiploic arteries
 ==Innervation==
-The omasum is innervated by the '''dorsal vagus nerve''' ([[Cranial Nerves - Anatomy & Physiology|CN X]]) (most important) and the '''ventral vagus nerve'''.
+*Dorsal vagus nerve ([[Cranial Nerves - Anatomy & Physiology|CN X]]) (most important)
+*Ventral vagus nerve ([[Cranial Nerves - Anatomy & Physiology|CN X]])
 ==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.
+*Numerous small lymph nodes are scattered in the omasal curvatures
-==Histology==
+*The lymph drains to larger atrial nodes between the cardia and the omasum, then to the cistera chyli
-[[Image:Omasum Histology Sheep.jpg|thumb|right|250px|Omasum Histology (Sheep) - Copyright RVC 2008]]
-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 [[Tongue - Anatomy & Physiology#Types of Papillae|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.
+==[[Omasum - Histology|Histology]]==
 ==Species Differences==
 ===Small Ruminant===
-The small ruminants have a smaller omasum, which is bean shaped.
+*Smaller omasum
+*Omasum is bean shaped
 ===Bovine===
-The lower pole of the omasum contacts the abdominal floor below the costal arch.
+*Lower pole of omasum contacts the the abdominal floor below the costal arch
+==Test yourself with the stomachs of the ruminant flashcards==
+[[The Stomachs of the Ruminant - Anatomy & Physiology - Flashcards#The Omasum|The Omasum Flashcards]]
 ==Links==
-'''Click here for information on [[Rumen - Anatomy & Physiology|rumen]]'''
+[[Rumen - Anatomy & Physiology|The Rumen - Anatomy & Physiology]]
+[[Reticulum - Anatomy & Physiology|The Reticulum - Anatomy & Physiology]]
+[[The Abomasum - Anatomy & Physiology|The Abomasum- Anatomy & Physiology]]
+'''Video'''
+[http://stream2.rvc.ac.uk/Anatomy/bovine/Pot0052.mp4 Pot 52 Lateral view of the Abdomen of a young Ruminant]
+[http://stream2.rvc.ac.uk/Anatomy/bovine/pot0175.mp4 Pot 175 Sections of the Ruminant Stomach]
-'''Click here for information on [[Reticulum - Anatomy & Physiology|reticulum]]'''
+[http://stream2.rvc.ac.uk/Anatomy/ovine/Pot0047.mp4 Pot 47 Ovine Omasum and Abomasum]
-'''Click here for information on [[Abomasum - Anatomy & Physiology|abomasum]]'''
+[http://stream2.rvc.ac.uk/Frean/sheep/LeftSideTopography.mp4 Left sided topography of the Ovine Abdomen and Thorax]
+[http://stream2.rvc.ac.uk/Frean/sheep/RightSideTopography.mp4 Right sided topography of the Ovine Abdomen]
-{{Template:Learning
+[http://stream2.rvc.ac.uk/Frean/sheep/RuminantStomachStructure.mp4 Structure of the ruminant forestomachs]
-|flashcards = [[Omasum Flashcards]]
-|videos = [[Video: Bovine omasum potcast|Bovine omasum potcast]]<br>[[Video: Ovine omasum and abomasum potcast|Ovine omasum and abomasum potcast]]<br>[[Video: Sections of the interior of the complex ruminant stomach potcast|Sections of the interior of the complex ruminant stomach potcast]]<br>[[Video: Ruminant forestomach structure dissection|Ruminant forestomach structure dissection]]
-|powerpoints = [[Ruminant Gastrointestinal Tract Histology resource|Histology of the ruminant gastrointestinal tract]]
-}}
-==Webinars==
-<rss max="10" highlight="none">https://www.thewebinarvet.com/gastroenterology-and-nutrition/webinars/feed</rss>
 [[Category:Stomach - Anatomy & Physiology]]
-[[Category:A&P Done]]
-[[Category:Alimentary Anatomy - Cattle]]