Changes

==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. It 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 of the omasal canal. The opening to the [[Abomasum - Anatomy & Physiology|abomasum]] is at the caudal end of the omasal canal. It is a large oval opening, partly covered by overhanging abomasal folds.

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. There are 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.  

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==

==Innervation==

==Innervation==

The omasum is innervated by the '''dorsal vagus nerve''' ([[Cranial Nerves - Anatomy & Physiology|CN X]]) (most important) and the '''ventral vagus nerve''' ([[Cranial Nerves - Anatomy & Physiology|CN X]]).

The omasum is innervated by the '''dorsal vagus nerve''' ([[Cranial Nerves - Anatomy & Physiology|CN X]]) (most important) and the '''ventral vagus nerve'''.

==Lymphatics==

==Lymphatics==

[[Image:Omasum Histology Sheep.jpg|thumb|right|250px|Omasum Histology (Sheep) - Copyright RVC 2008]]

[[Image:Omasum Histology Sheep.jpg|thumb|right|250px|Omasum Histology (Sheep) - Copyright RVC 2008]]

The omasum has a '''keratinised stratified squamous epithelium'''. The omasum is firm in texture and can vary in size. It consists of '''lamellae''' thrown into leaves that divide the lumen into narrow and uniform recesses. It contains no glands.

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 '''cicrular 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, and so they are very motile.

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.

==Species Differences==

==Species Differences==

===Small Ruminant===

===Small Ruminant===

The small ruminants have a smaller omasum. The omasum is bean shaped.

The small ruminants have a smaller omasum, which is bean shaped.

===Bovine===

===Bovine===

'''Test yourself with the [[The Stomachs of the Ruminant - Anatomy & Physiology - Flashcards#The Omasum|The Omasum Flashcards]]'''

'''Test yourself with the [[The Stomachs of the Ruminant - Anatomy & Physiology - Flashcards#The Omasum|The Omasum Flashcards]]'''

'''Click here for information on [[Rumen - Anatomy & Physiology|rumen - Anatomy & Physiology]]'''

'''Click here for information on [[Rumen - Anatomy & Physiology|rumen]]'''

'''Click here for information on [[Reticulum - Anatomy & Physiology|reticulum - Anatomy & Physiology]]'''

'''Click here for information on [[Reticulum - Anatomy & Physiology|reticulum]]'''

'''Click here for information on [[Abomasum - Anatomy & Physiology|abomasum- Anatomy & Physiology]]'''

'''Click here for information on [[Abomasum - Anatomy & Physiology|abomasum]]'''

'''Video links:'''

'''Video links:'''

[[Category:Stomach - Anatomy & Physiology]]

[[Category:Stomach - Anatomy & Physiology]]

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