Difference between revisions of "Equine Alimentary System - Anatomy & Physiology"
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− | + | <big><center>[[Alimentary - Anatomy & Physiology|'''BACK TO ALIMENTARY - ANATOMY & PHYSIOLOGY''']]</center></big> | |
+ | <big><center>[[Hindgut Fermenters - Anatomy & Physiology|'''BACK TO HINDGUT FERMENTERS- ANATOMY & PHYSIOLOGY''']]</center></big> | ||
+ | |||
+ | ==Introduction== | ||
+ | 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. | ||
+ | |||
+ | In the hindgut of the horse, | ||
+ | *75-85% of insoluble carbohydrates is digested. | ||
+ | *15-30% of soluble carbohydrates. | ||
+ | *30% of protein digestion. | ||
+ | |||
+ | ===Development=== | ||
+ | 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. | ||
+ | |||
+ | ==[[Small Intestine - Anatomy & Physiology|Small Intestine]]== | ||
+ | |||
+ | *Arrangement is similar to that of the dog's small intestine, but the position of the jejunum is influenced by the large ascending colon and caecum. | ||
+ | **The jejunum is restricted to the left dorsal part of the abdomen. | ||
+ | *Transit time of food in the small intestine is quite rapid. | ||
+ | **25% of a liquid marker has reached the caecum within 1.5 hours. | ||
+ | **Most ingesta reaches the large intestine within 3 hours after intake. | ||
+ | *70-80% of protein is digested. | ||
+ | *70%+ of starch is digested by '''enzymes'''. | ||
+ | |||
+ | ==Caecum== | ||
+ | |||
+ | *On the right side of the abdomen. | ||
+ | *Very large, roughly 1m in length with a 30L capacity. | ||
+ | *Consists of a base, body and apex (blind ending). | ||
+ | *The base lies in the right dorsal part of the abdomen in contact with the abdominal roof. | ||
+ | *Apex lies on the ventral abdominal wall, and terminates at the level of the xiphoid cartilage. | ||
+ | *Exists at the junction with the ileum and colon. | ||
+ | **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. | ||
+ | **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. | ||
+ | *Taenia are present. | ||
+ | **Taenia are formed by concentration of the ''longitudinal'' muscle layer. | ||
+ | **Between the taenia are sacculations, or haustra. | ||
+ | **Haustra appear as folds on the interior surface. | ||
+ | ***There are '''four''' taenia over the caecum: -dorsal - ventral - lateral -medial. | ||
+ | ***The ''dorsal'' taenia provides the attachment site for the ileocaecal fold, which joins the caecum to the ileum. | ||
+ | ***The ''lateral'' taenia provides the attachment site for the caecocolic fold, which joins the caecum to the ascending colon. | ||
+ | ***The ''ventral'' taenia is free. | ||
+ | ***The ''medial'' and ''lateral'' taenia are where the caecal vessels and lymph nodes are located. | ||
+ | *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. | ||
+ | *In the horse, the caecum is responsible for the digestion of complex carbohydrates such as cellulose. | ||
+ | |||
+ | ==Colon== | ||
+ | ===Ascending colon=== | ||
+ | *The ascending colon is very large and takes up most of the ventral abdomen. | ||
+ | *It is the shape of a double "U", where one "U" is on top of the other. | ||
+ | *There are four limbs that lie parallel to each other, and three flexures that change these direction of the limbs. | ||
+ | *Sequence of the limbs and flexures of the ascending colon: | ||
+ | **Right Ventral Colon ''(for those with an RVC bias remember, "the RVC comes first!")'' | ||
+ | ***Passes out of the caecocolic orifice on the right side of the abdomen and continues cranially to the xiphoid region. | ||
+ | **''Sternal Flexure'' | ||
+ | ***Passes across the midline from right to left. | ||
+ | **Left Ventral Colon | ||
+ | ***Runs caudally on the left ventral abdominal floor. | ||
+ | **''Pelvic Flexure'' | ||
+ | ***Turns dorsally just cranial to the pelvic inlet and then runs cranially to the diaphragm. | ||
+ | **Left Dorsal Colon | ||
+ | ***Runs cranially, parallel and dorsal to the left ventral colon. | ||
+ | **''Diaphragmatic Flexure'' | ||
+ | ***Turns caudally at the diaphragm. | ||
+ | **Right Dorsal Colon | ||
+ | ***Continues caudally on the right. It is the shortest limb of the ascending colon. | ||
+ | *The '''transverse colon''' continues on from the right dorsal colon as the right dorsal colon turns medially. | ||
+ | *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. | ||
+ | **This anatomical arrangement of mesentry allows the left ascending colon to twist and is a common cause of colic (colonic torsion). | ||
+ | *The ventral parts of the ascending colon are attached to the dorsal parts by a short mesocolon. | ||
+ | **The mesocolon houses the blood vessels, nerves and lymphatics. | ||
+ | *In the ventral colon many important digestive and absorptive functions take place, whilst the dorsal colon is mainly responsible for transportation of ingesta. | ||
+ | *Taenia are present. | ||
+ | **Different parts of the colon can be distinguished by the number of taenia present: | ||
+ | ***The right and left ventral colon and the sternal flexure have '''four''' taenia. | ||
+ | ***The left dorsal colon and pelvic flexure have '''one''' taenia. | ||
+ | ***The right dorsal colon and diaphragmatic flexure have '''three''' taenia. | ||
+ | |||
+ | ===Transverse Colon=== | ||
+ | *Short | ||
+ | *Passes from across the midline from right to left. It passes cranial to the root of the mesentry | ||
+ | *The transverse colon has '''two''' taenia. | ||
+ | *Turns caudally to become the descending colon at the level of the left kidney. | ||
+ | |||
+ | ===Descending Colon=== | ||
+ | *Between 2-4m long. | ||
+ | *Suspended by a long mesentry; ''mesocolon descendens''. | ||
+ | *The descending colon has '''two''' taenia. | ||
+ | **Between the two taenia are distinct sacculations that house the faecal balls. | ||
+ | |||
+ | ==Rectal Palpation== |
Revision as of 15:32, 12 July 2008
Introduction
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.
In the hindgut of the horse,
- 75-85% of insoluble carbohydrates is digested.
- 15-30% of soluble carbohydrates.
- 30% of protein digestion.
Development
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.
Small Intestine
- Arrangement is similar to that of the dog's small intestine, but the position of the jejunum is influenced by the large ascending colon and caecum.
- The jejunum is restricted to the left dorsal part of the abdomen.
- Transit time of food in the small intestine is quite rapid.
- 25% of a liquid marker has reached the caecum within 1.5 hours.
- Most ingesta reaches the large intestine within 3 hours after intake.
- 70-80% of protein is digested.
- 70%+ of starch is digested by enzymes.
Caecum
- On the right side of the abdomen.
- Very large, roughly 1m in length with a 30L capacity.
- Consists of a base, body and apex (blind ending).
- The base lies in the right dorsal part of the abdomen in contact with the abdominal roof.
- Apex lies on the ventral abdominal wall, and terminates at the level of the xiphoid cartilage.
- Exists at the junction with the ileum and colon.
- 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.
- 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.
- Taenia are present.
- Taenia are formed by concentration of the longitudinal muscle layer.
- Between the taenia are sacculations, or haustra.
- Haustra appear as folds on the interior surface.
- There are four taenia over the caecum: -dorsal - ventral - lateral -medial.
- The dorsal taenia provides the attachment site for the ileocaecal fold, which joins the caecum to the ileum.
- The lateral taenia provides the attachment site for the caecocolic fold, which joins the caecum to the ascending colon.
- The ventral taenia is free.
- The medial and lateral taenia are where the caecal vessels and lymph nodes are located.
- 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.
- In the horse, the caecum is responsible for the digestion of complex carbohydrates such as cellulose.
Colon
Ascending colon
- The ascending colon is very large and takes up most of the ventral abdomen.
- It is the shape of a double "U", where one "U" is on top of the other.
- There are four limbs that lie parallel to each other, and three flexures that change these direction of the limbs.
- Sequence of the limbs and flexures of the ascending colon:
- Right Ventral Colon (for those with an RVC bias remember, "the RVC comes first!")
- Passes out of the caecocolic orifice on the right side of the abdomen and continues cranially to the xiphoid region.
- Sternal Flexure
- Passes across the midline from right to left.
- Left Ventral Colon
- Runs caudally on the left ventral abdominal floor.
- Pelvic Flexure
- Turns dorsally just cranial to the pelvic inlet and then runs cranially to the diaphragm.
- Left Dorsal Colon
- Runs cranially, parallel and dorsal to the left ventral colon.
- Diaphragmatic Flexure
- Turns caudally at the diaphragm.
- Right Dorsal Colon
- Continues caudally on the right. It is the shortest limb of the ascending colon.
- Right Ventral Colon (for those with an RVC bias remember, "the RVC comes first!")
- The transverse colon continues on from the right dorsal colon as the right dorsal colon turns medially.
- 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.
- This anatomical arrangement of mesentry allows the left ascending colon to twist and is a common cause of colic (colonic torsion).
- The ventral parts of the ascending colon are attached to the dorsal parts by a short mesocolon.
- The mesocolon houses the blood vessels, nerves and lymphatics.
- In the ventral colon many important digestive and absorptive functions take place, whilst the dorsal colon is mainly responsible for transportation of ingesta.
- Taenia are present.
- Different parts of the colon can be distinguished by the number of taenia present:
- The right and left ventral colon and the sternal flexure have four taenia.
- The left dorsal colon and pelvic flexure have one taenia.
- The right dorsal colon and diaphragmatic flexure have three taenia.
- Different parts of the colon can be distinguished by the number of taenia present:
Transverse Colon
- Short
- Passes from across the midline from right to left. It passes cranial to the root of the mesentry
- The transverse colon has two taenia.
- Turns caudally to become the descending colon at the level of the left kidney.
Descending Colon
- Between 2-4m long.
- Suspended by a long mesentry; mesocolon descendens.
- The descending colon has two taenia.
- Between the two taenia are distinct sacculations that house the faecal balls.