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===[[Colon - Anatomy & Physiology|Colon]]===

===[[Colon - Anatomy & Physiology|Colon]]===

====Ascending 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.  

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.  

The sequence of the limbs and flexures of the ascending colon is as follows; '''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 sequence of the limbs and flexures of the ascending colon is as follows; '''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 mesentery to the dorsal abdominal wall, the base of the [[Caecum - Anatomy & Physiology|caecum]], the root of the mesentry and the [[Pancreas - Anatomy & Physiology|pancreas]]. This anatomical arrangement of mesentery allows the left ascending colon to twist and is a common cause of colic ([[Large Colon Torsion - Horse|colonic torsion]]).  

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 mesentery to the dorsal abdominal wall, the base of the [[Caecum - Anatomy & Physiology|caecum]], the root of the mesentry and the [[Pancreas - Anatomy & Physiology|pancreas]]. This anatomical arrangement of mesentery allows the left ascending colon to twist and is a common cause of [[:Category:Colic in Horses|colic]] ([[Large Colon Torsion - Horse|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 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. '''Taeniae''' are present. Different parts of the colon can be distinguished by the number of taeniae present:

The right and left ventral colon and the sternal flexure have '''four''' taenia. The left dorsal colon and pelvic flexure have '''one''' taenia and the right dorsal colon and diaphragmatic flexure have '''three''' taenia.

The right and left ventral colon and the sternal flexure have '''four''' taeniae. The left dorsal colon and pelvic flexure have '''one''' taenia and the right dorsal colon and diaphragmatic flexure have '''three''' taeniae.

====Transverse Colon====

====Transverse Colon====

The transverse colon is short. It passes from across the midline from right to left. It passes cranial to the root of the mesentery  

The transverse colon is short. It passes from across the midline from right to left. It passes cranial to the root of the mesentery. It has '''two''' taeniae. It turns caudally to become the descending colon at the level of the [[Urinary System Overview - Anatomy & Physiology|left kidney]].

The transverse colon has '''two''' taenia. It turns caudally to become the descending colon at the level of the [[Urinary System Overview - Anatomy & Physiology|left kidney]].

====Descending Colon====   

====Descending Colon====   

The descending colon is between 2-4m long. It is suspended by a long mesentery; ''mesocolon descendens''. The descending colon has '''two''' taenia. Between the two taenia are distinct sacculations that house the faecal balls.

The descending colon is between 2-4 meters long. It is suspended by a long mesentery; ''mesocolon descendens''. The descending colon has '''two''' taeniae. Between the two taeniae are distinct sacculations that house the faecal balls.

===[[Rectal Examination of the Horse|Rectal Palpation]]===

===[[Rectal Examination of the Horse|Rectal Palpation]]===

[[Rectal Examination of the Horse|Rectal palpation]] is a useful technique and is often used to assess colic. Structures that can be palpated ''per rectum'' include; faecal balls in the descending colon, the [[Urinary Bladder - Anatomy & Physiology|bladder]], the [[Reproductive System Overview - Anatomy & Physiology|reproductive organs]] in the mare, the base of the [[Caecum - Anatomy & Physiology|caecum]], the root of the mesentery, the [[Urinary System Overview - Anatomy & Physiology|left kidney]], +/- the nephrosplenic ligament, the left dorsal colon and the pelvic flexure of the ascending colon. ''NB: This is a common site of impaction.''

[[Rectal Examination of the Horse|Rectal palpation]] is a useful technique and is often used to assess [[:Category:Colic in Horses|colic]]. Structures that can be palpated ''per rectum'' include; faecal balls in the descending colon, the [[Urinary Bladder - Anatomy & Physiology|bladder]], the [[Reproductive System Overview - Anatomy & Physiology|reproductive organs]] in the mare, the base of the [[Caecum - Anatomy & Physiology|caecum]], the root of the mesentery, the [[Urinary System Overview - Anatomy & Physiology|left kidney]], +/- the nephrosplenic ligament, the left dorsal colon and the pelvic flexure of the ascending colon. ''NB: This is a common site of impaction.''

===Microbial Environment===

===Microbial Environment===

Microbes convert carbohydrates to [[Volatile Fatty Acids|volatile fatty acids]] (VFAs). The horse receives 75% of it's energy requirements from VFAs. The large intestine is buffered by the secretion of large amounts of bicarbonate from the [[Pancreas - Anatomy & Physiology|pancreas]] and the [[Ileum - Anatomy & Physiology|ileum]]. Glands in the wall of the [[Large Intestine - Anatomy & Physiology|large intestine]] may also produce bicarbonate. The microbial population exists in the [[Caecum - Anatomy & Physiology|caecum]] and ventral colon.  

Microbes convert carbohydrates to [[Volatile Fatty Acids|volatile fatty acids]] (VFAs). The horse receives 75% of its energy requirements from VFAs. The large intestine is buffered by the secretion of large amounts of bicarbonate from the [[Pancreas - Anatomy & Physiology|pancreas]] and the [[Ileum - Anatomy & Physiology|ileum]]. Glands in the wall of the [[Large Intestine - Anatomy & Physiology|large intestine]] may also produce bicarbonate. The microbial population exists in the [[Caecum - Anatomy & Physiology|caecum]] and ventral colon.  

It is mixed; there are both bacteria and protozoa. Microbes are anaerobic. The microbial population is dependent on diet and frequency of feeding, as different microbes are suited to digesting different things. The number of microbes can change 100 fold in a 24 hour period. [[Volatile Fatty Acids|VFAs]] produced are absorbed across the intestinal wall. Urea from the blood is transported to the intestinal lumen to be used by microbes, which also use nitrogen from the diet. Environmental factors of the [[Caecum - Anatomy & Physiology|caecum]] and ventral colon can influence fermentation of microbial population.

The environment is mixed; there are both bacteria and protozoa. Microbes are anaerobic. The microbial population is dependent on diet and frequency of feeding, as different microbes are suited to digesting different particles. The number of microbes can change 100 fold in a 24 hour period. [[Volatile Fatty Acids|VFAs]] produced are absorbed across the intestinal wall. Urea from the blood is transported to the intestinal lumen to be used by microbes, which also use nitrogen from the diet. Environmental factors of the [[Caecum - Anatomy & Physiology|caecum]] and ventral colon can influence fermentation of microbial population.

Environmental factors include: Frequent intake of food, constant temperature, constant mixing, removal of the products of fermentation by absorption and peristalsis and the stable osmotic environment i.e. normal intake of water.

Environmental factors include: frequent intake of food, constant temperature, constant mixing, removal of the products of fermentation by absorption and peristalsis and the stable osmotic environment i.e. normal intake of water.

[[Volatile Fatty Acids|VFA's]] produced include Acetate, Propionate and Butyrate. Factors that promote VFA production include an optimum pH of 6.5, an anaerobic environment and gut motility.

[[Volatile Fatty Acids|VFA's]] produced include Acetate, Propionate and Butyrate. Factors that promote VFA production include an optimum pH of 6.5, an anaerobic environment and gut motility.