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| − | <big><center>[[Alimentary - Anatomy & Physiology|'''BACK TO ALIMENTARY - ANATOMY & PHYSIOLOGY''']]</center></big>
| + | #redirect[[Alimentary System - Horse Anatomy]] |
| − | <big><center>[[Hindgut Fermenters - Anatomy & Physiology|'''BACK TO HINDGUT FERMENTERS- ANATOMY & PHYSIOLOGY''']]</center></big>
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| − | ==Introduction==
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| − | The typical horse's diet consists of 7-12% protein and 4% fat, the remainder being made up of carbohydrate. A high proportion of the carbohydrate is in the form of '''starch'''. A mature horse eats 2-2.5% of it's body weight in dry matter every day, 1.5-1.75% of this should be fibre (hay/haylage). This is to prevent a rapid drop in pH in the large intestine and also to stimulate peristalsis in the gut and prevent build up of gas.
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| − | ===Development===
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| − | The ascending colon expands '''cranially''' (compared to ox, where it expands caudally) around the root of the mesentry on the left side of the mesentry.
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| − | ==[[Small Intestine - Anatomy & Physiology|Small Intestine]]==
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| − | ==Caecum==
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| − | *On the right side of the abdomen.
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| − | *Very large, roughly 1m in length with a 30L capacity.
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| − | *Consists of a base, body and apex (blind ending).
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| − | *The base lies in the right dorsal part of the abdomen in contact with the abdominal roof.
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| − | *Apex lies on the ventral abdominal wall, and terminates at the level of the xiphoid cartilage.
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| − | *Exists at the junction with the ileum and colon.
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| − | **The '''caecocolic orifice''' is where the caecum opens into the ascending colon. This exists as a transverse slit formed by a constriction of the ascending colon.
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| − | **The ileum opens into the caecum at the '''ileal papilla'''. This is a small projection into the caecum housing the ileal sphincter and venous plexus that, together, control the ileal orifice.
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| − | *Taenia are present.
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| − | **Taenia are formed by concentration of the ''longitudinal'' muscle layer.
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| − | **Between the taenia are sacculations, or haustra.
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| − | **Haustra appear as folds on the interior surface.
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| − | ***There are '''four''' taenia over the caecum: -dorsal - ventral - lateral -medial.
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| − | ***The ''dorsal'' taenia provides the attachment site for the ileocaecal fold, which joins the caecum to the ileum.
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| − | ***The ''lateral'' taenia provides the attachment site for the caecocolic fold, which joins the caecum to the ascending colon.
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| − | ***The ''ventral'' taenia is free.
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| − | ***The ''medial'' and ''lateral'' taenia are where the caecal vessels and lymph nodes are located.
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| − | In the horse, the caecum is responsible for the digestion of complex carbohydrates such as cellulose. Ingesta is regularly transported from the ileum to the caecum, this movement can be heard upon auscultation of the right dorsal quadrant of the caudal abdomen. Ausculatation of this area is carried out in assesment of colic.
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| − | ==Colon==
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| − | ===Ascending colon===
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| − | *The ascending colon is very large and takes up most of the ventral abdomen.
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| − | *It is the shape of a double "U", where one "U" is on top of the other.
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| − | *There are four limbs that lie parallel to each other, and three flexures that change these direction of the limbs.
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| − | *Sequence of the limbs and flexures of the ascending colon:
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| − | **Right Ventral Colon ''(for those with an RVC bias remember, "the RVC comes first!")''
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| − | ***Passes out of the caecocolic orifice on the right side of the abdomen and continues cranially to the xiphoid region.
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| − | **''Sternal Flexure''
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| − | ***Passes across the midline from right to left.
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| − | **Left Ventral Colon
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| − | ***Runs caudally on the left ventral abdominal floor.
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| − | **''Pelvic Flexure''
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| − | ***Turns dorsally just cranial to the pelvic inlet and then runs cranially to the diaphragm.
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| − | **Left Dorsal Colon
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| − | ***Runs cranially, parallel and dorsal to the left ventral colon.
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| − | **''Diaphragmatic Flexure''
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| − | ***Turns caudally at the diaphragm.
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| − | **Right Dorsal Colon
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| − | ***Continues caudally on the right. It is the shortest limb of the ascending colon.
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| − | *The '''transverse colon''' continues on from the right dorsal colon as the right dorsal colon turns medially.
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| − | *The right dorsal colon is attached by a mesentry to the dorsal abdominal wall, the base of the caecum, the root of the mesentry and the pancreas.
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| − | **This anatomical arrangement of mesentry allows the left ascending colon to twist and is a common cause of colic (colonic torsion).
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| − | *The ventral parts of the ascending colon are attached to the dorsal parts by a short mesocolon.
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| − | **The mesocolon houses the blood vessels, nerves and lymphatics.
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| − | *In the ventral colon many important digestive and absorptive functions take place, whilst the dorsal colon is mainly responsible for transportation of ingesta.
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| − | *Taenia are present.
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| − | **Different parts of the colon can be distinguished by the number of taenia present:
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| − | ***The right and left ventral colon and the sternal flexure have '''four''' taenia.
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| − | ***The left dorsal colon and pelvic flexure have '''one''' taenia.
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| − | ***The right dorsal colon and diaphragmatic flexure have '''three''' taenia.
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| − | ===Transverse Colon===
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| − | *Short
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| − | *Passes from across the midline from right to left. It passes cranial to the root of the mesentry
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| − | *The transverse colon has '''two''' taenia.
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| − | *Turns caudally to become the descending colon at the level of the left kidney.
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| − | ===Descending Colon===
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| − | *Between 2-4m long.
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| − | *Suspended by a long mesentry; ''mesocolon descendens''.
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| − | *The descending colon has '''two''' taenia.
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| − | **Between the two taenia are distinct sacculations that house the faecal balls.
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| − | ==Rectal Palpation==
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