Difference between revisions of "User:Mayazoey"
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| − | <big><center>[[Alimentary - | + | <big><center>[[Alimentary System - Pathology|'''BACK TO ALIMENTARY''']]</center></big> |
| + | |||
| + | |||
| + | ==Introduction to the Intestines== | ||
| + | |||
| + | === Basic Anatomy and Physiology === | ||
| + | |||
| + | The intestines are a portion of the alimentary tract extending from the pylorus to the anus. In mammals, the intestines are divided into two main segments: the small intestine and the large intestine. The small intestine, consisting of the duodenum, jejunum and ileum, acts as the main site of absorption for digestive products in the gastrointestinal tract. The large intestine, consisting of the caecum and colon, functions to extract water, electrolytes and nutrients as well as to concentrate and propulse faecal material to the rectum for defaecation. | ||
| + | Functional differences between the small and large intestine are reflected in their anatomic and histologic organisation (Figure 1). The small intestinal mucosa in many species is highly folded and made up of numerous villi that greatly increase the absorptive surface area. Enterocytes, the main absorptive cells, are the most numerous and characteristic cells of the small intestinal epithelium. Others include goblet cells, paneth cells, neuroendocrine cells, stem cells, and intraepithelial lymphocytes. Another important feature of the small intestine is the presence of Peyer's patches within the lamina propria. They contribute to immune function and generation of immune responses within the mucosa. | ||
| + | |||
| + | In contrast to the small intestine, the large intestinal mucosa has no villi and consists of 2 main cell types: absorptive cells and mucus secreting goblet cells. A distinguishing histologic and anatomic characteristic is the thick muscularis mucosa layer that aids in propulsion of faeces to the rectum. Another important feature is the presence of commensal bacteria which plays different roles depending upon the type of animal (Dyce et. al, 2002; Young & Heath, 2000). | ||
| + | |||
| + | === Defense Mechanisms === | ||
| + | |||
| + | '''Secretions''' | ||
| + | |||
| + | *Mucus - inhibits contact and protects the mucosal surface | ||
| + | *Digestive enzymes - nonspecifically target bacteria and viruses | ||
| + | *Bile - kills some bacteria and viruses | ||
| + | |||
| + | '''Epithelium''' | ||
| + | |||
| + | *"Tight junctions" between epithelial cells prevent entry of macromolecules and pathogens into the intestinal tract. | ||
| + | *Epithelial cells have a very high turnover rate thus preventing pathogens with a longer life cycle from successfully colonising. | ||
| + | |||
| + | '''Commensal flora''' | ||
| + | |||
| + | *Commensal flora competitively inhibit attachment of pathogens to enterocytes in addition to competing for nutrition and substrates. Many also produce inhibitory growth substances that are toxic to other bacteria (McGavin and Zachary, 2007). | ||
| + | |||
| + | '''Movement''' | ||
| + | |||
| + | *Continuous peristalsis discourages persistence of toxins and aids in their elimination from the gut. | ||
| + | |||
| + | '''Cell-mediated and humoural defences''' | ||
| + | |||
| + | *The lamina propria contains macrophages, B and T lymphocytes, plasma cells, and mast cells. | ||
| + | *Lymphoid aggregates known as Peyer's patches within the small intestine aid in immunity. | ||
| + | *Secretory IgA and IgM provide humoural immunity and help prevent attachment of pathogens to the intestinal epithelium. | ||
| + | *Lysozyme from Paneth cells inhibits bacterial growth (McGavin & Zachary, 2007). | ||
| + | |||
| + | === Comparative === | ||
| + | The natural diets of different animal species largely govern the structure and function of the gastrointestinal tract. | ||
| + | Broadly, animals can be classified as carnivores, herbivores or omnivores according to diet. Digestion and absorption of nutrients in carnivorous animals such as the dog and cat takes place largely in the small intestine. Because only a small amount of fermentation occurs in the large intestine of carnivores, they have a minimally developed caecum in comparison to nonruminating herbivores such as the horse which relies heavily on the end products of microbial digestion from the large intestine. The pig, an omnivorous animal has both a relatively long small intestine and an expanded portion of the colon that aids in fermentation of the fibrous material in the diet. Ruminants are an exception as fermentation largely occurs in the stomach (Reece, 2005). | ||
| + | |||
| + | '''References''' <br /br> | ||
| + | |||
| + | Dyce KM, Sack WO, Wensing, CJG: Textbook of Veterinary Anatomy, 3rd ed, p. 129. Saunders, London, England, 2002. | ||
| + | |||
| + | McGavin DM & Zachary, JF: Pathologic Basis of Veterinary Disease, 4th ed, pp. 301-393. Elsevier, St. Louis, Missouri, 2007. | ||
| + | |||
| + | Reece, WO: Functional Anatomy and Physiology of Domestic Animals, 3rd ed., pp. 312-368. Lippincott Williams & Wilkins, London, England, 2005. | ||
| + | |||
| + | Young B, Heath, JW: Wheater's Functional Histology: A Text and Colour Atlas, 4th ed, pp. 249-274. Churchill Livingstone, London, England, 2000. | ||
| + | |||
| + | ==Contents== | ||
| + | |||
| + | ===[[Intestines Developmental - Pathology|Developmental Anomalies]]=== | ||
| + | |||
| + | ===[[Physical Disturbances]]=== | ||
| + | |||
| + | ===[[Intestines Vascular Disturbances - Pathology|Vascular Disturbances]]=== | ||
| + | |||
| + | ===[[Intestines Proliferative - Pathology|Proliferative Pathology]]=== | ||
| + | |||
| + | ===[[Intestines Inflammation - Pathology|Inflammatory Pathology]]=== | ||
| + | |||
| + | ===[[Diarrhoea]]=== | ||
| + | |||
| + | ===[[Parasites]]=== | ||
| + | |||
| + | ===[[Diseases due to pathogens]]=== | ||
| + | |||
| + | ===[[Diseases in animal species]]=== | ||
| + | |||
| + | ===[[Clinical Pathology - Pathology|Clinical Pathology]]=== | ||
| + | |||
| + | |||
'''Intestine''' | '''Intestine''' | ||
== Basic Anatomy and Physiology == | == Basic Anatomy and Physiology == | ||
| − | === Introduction === | + | === Introduction === |
| − | The intestines are a portion of the alimentary tract extending from the pylorus to the anus. In mammals, the intestines are divided into two main segments: the small intestine and the large intestine. The small intestine, consisting of the duodenum, jejunum and ileum, acts as the main site of absorption for digestive products in the gastrointestinal tract. The large intestine, consisting of the caecum and colon, functions to extract water, electrolytes and nutrients as well as to concentrate and propulse faecal material to the rectum for defaecation | + | The intestines are a portion of the alimentary tract extending from the pylorus to the anus. In mammals, the intestines are divided into two main segments: the small intestine and the large intestine. The small intestine, consisting of the duodenum, jejunum and ileum, acts as the main site of absorption for digestive products in the gastrointestinal tract. The large intestine, consisting of the caecum and colon, functions to extract water, electrolytes and nutrients as well as to concentrate and propulse faecal material to the rectum for defaecation. |
| − | + | Functional differences between the small and large intestine are reflected in their anatomic and histologic organisation (Figure 1). The small intestinal mucosa in many species is highly folded and made up of numerous villi that greatly increase the absorptive surface area. Enterocytes, the main absorptive cells, are the most numerous and characteristic cells of the small intestinal epithelium. Others include goblet cells, paneth cells, neuroendocrine cells, stem cells, and intraepithelial lymphocytes. Another important feature of the small intestine is the presence of Peyer's patches within the lamina propria. They contribute to immune function and generation of immune responses within the mucosa. | |
| − | Functional differences between the small and large intestine are reflected in their anatomic and histologic organisation (Figure 1). The small intestinal mucosa in many species is highly folded and made up of numerous villi that greatly increase the absorptive surface area. Enterocytes, | ||
| − | In contrast to the small intestine, the large intestinal mucosa has no villi and consists of 2 main cell types: absorptive cells and mucus secreting goblet cells. A distinguishing histologic and anatomic characteristic is the thick muscularis mucosa layer that aids in propulsion of faeces to the rectum. Another important feature is the presence of commensal bacteria which plays different roles depending upon the type of animal | + | In contrast to the small intestine, the large intestinal mucosa has no villi and consists of 2 main cell types: absorptive cells and mucus secreting goblet cells. A distinguishing histologic and anatomic characteristic is the thick muscularis mucosa layer that aids in propulsion of faeces to the rectum. Another important feature is the presence of commensal bacteria which plays different roles depending upon the type of animal (Dyce et. al, 2002; Young & Heath, 2000). |
=== Defense Mechanisms === | === Defense Mechanisms === | ||
| Line 30: | Line 105: | ||
*Lysozyme from Paneth cells inhibits bacterial growth (McGavin & Zachary, 2007). | *Lysozyme from Paneth cells inhibits bacterial growth (McGavin & Zachary, 2007). | ||
=== Comparative === | === Comparative === | ||
| − | carnivores, | + | The natural diets of different animal species largely govern the structure and function of the gastrointestinal tract. |
| − | + | Broadly, animals can be classified as carnivores, herbivores or omnivores according to diet. Digestion and absorption of nutrients in carnivorous animals such as the dog and cat takes place largely in the small intestine. Because only a samll amount of fermentation occurs in the large intestine of carnivores, they have a minimally developed caecum in comparison to nonruminating herbivores such as the horse which reies heavily on the end products of microbial digestion that occur in the large intestine. The pig, an omnivorous animal has both a relatively long small intestine and an expanded portion of the colon that aids in fermentation of the fibrous material in the diet. Ruminants are an exception as fermentation largely occurs in the stomach. The following figures illustrate the differences between the gastrointestinal tracts of the main domestic animal species (Reece, 2005). [Figures!!] | |
'''References''' <br /br> | '''References''' <br /br> | ||
| Line 38: | Line 113: | ||
McGavin DM & Zachary, JF: Pathologic Basis of Veterinary Disease, 4th ed, pp. 301-393. Elsevier, St. Louis, Missouri, 2007. | McGavin DM & Zachary, JF: Pathologic Basis of Veterinary Disease, 4th ed, pp. 301-393. Elsevier, St. Louis, Missouri, 2007. | ||
| + | |||
| + | Reece, WO: Functional Anatomy and Physiology of Domestic Animals, 3rd ed., pp. 312-368. Lippincott Williams & Wilkins, London, England, 2005. | ||
Young B, Heath, JW: Wheater's Functional Histology: A Text and Colour Atlas, 4th ed, pp. 249-274. Churchill Livinstone, London, England, 2000. | Young B, Heath, JW: Wheater's Functional Histology: A Text and Colour Atlas, 4th ed, pp. 249-274. Churchill Livinstone, London, England, 2000. | ||
| Line 73: | Line 150: | ||
==== Obstruction ==== | ==== Obstruction ==== | ||
Intestinal obstruction can be the sequel to either mechanical or functional causes. Mechanical obstruction occurs due to physical blockage of the intestinal lumen whereas functional obstruction results from a decrease or inhibition of intestinal motility due to loss of smooth muscle contraction. (Brown et. al, 2007). | Intestinal obstruction can be the sequel to either mechanical or functional causes. Mechanical obstruction occurs due to physical blockage of the intestinal lumen whereas functional obstruction results from a decrease or inhibition of intestinal motility due to loss of smooth muscle contraction. (Brown et. al, 2007). | ||
| − | ===== | + | ===== Mechanical ===== |
| − | + | Mechanical obstruction of the intestine, either acute or chronic, can occur in all species of animals. Acute obstruction usually involves the upper or middle small intestine whereas chronic obstruction typically occurs in the distal small intestine or large intestine. Causes of obstruction can be divided into three main categories: intraluminal, intramural, or extrinsic. Intraluminal causes include food impaction and foreign bodies, intramural causes include neoplasia and extrinsic causes include adhesions, neoplasia and prostate enlargement. The following figure illustrates the pathogenesis occurring in intestinal obstruction [Figure]. | |
| − | |||
====== Foreign Bodies ====== | ====== Foreign Bodies ====== | ||
| + | *Foreign bodies of all types can be found in the intestines. While some may pass through posing no problems, others can cause acute obstruction, pressure necrosis and eventually perforation. Foreign bodies can also be chronic, remaining for long periods of time without causing disturbance. | ||
| + | *Enteroliths, stones consisting of magnesium ammonium phosphate around a central nidus (often a metallic foreign body) occur mostly in horses greater than 4 years of age. Typically, they lodge at the pelvic flexure or the transverse colon. | ||
| + | |||
====== Impaction ====== | ====== Impaction ====== | ||
| + | Impaction of the colon can occur in all species. | ||
| + | *In the dog and cat, dehydrated faecal material is the main cause of impaction. | ||
| + | *In the horse, faeces, digesta, sand, or fibrous material can all contribute to impaction Predisposing factors include poor dentition, water deprivation, a high roughage diet and general debility. | ||
| + | *Antihelminthic administration or large parasite burdens can also lead to impaction. | ||
| + | |||
====== Extrinsic ====== | ====== Extrinsic ====== | ||
| − | Neoplasia, | + | Obstruction of the intestine due to external factors such as tumours, abscesses, and fibrous adhesions is a common occurrence. |
| + | *Neoplasia in structures adjacent to the intestines can spread and cause external compression. Pancreatic tumours in particular can extend and impinge on the duodenum. | ||
| + | *Inflammatory adhesions, following gut perforation, peritonitis or surgery, consist of fibrous tissue bands that may restrict intestinal motility and cause kinks in the mesentery. | ||
| + | *Pedicles of tumours such as lipomas in horses can become wound in loops of intestine leading to obstruction and possible strangulation. | ||
| + | *Prostatic enlargement in the dog can lead to compression of the rectum. | ||
===== Functional ===== | ===== Functional ===== | ||
| − | + | *Paralytic ileus is a common condition that can occur following trauma or abdominal surgery. Intestinal stasis leads to distension with gas and fluid as well as a flaccid intestinal wall. | |
| − | + | *Dysautonomia is a condition that most notably affects horses and cats. | |
| − | + | **Equine dysautonomia (grass sickness) occurs mostly in the UK and western Europe. ''Clostridium botulinum'' is thought to be implicated although the exact cause is still unknown. Affected animals are dull, restless, show signs of colic, and in acute cases become severly tympanic, avoid swallowing and salivate excessively. Degenerative lesions are seen in the autonomic nerve ganglia, including enteric plexuses. | |
| + | **Feline dysautonomia (Key-Gaskell syndrome) occurs mostly in the UK and continental Europe. It is also of unknown aetiology although environmental toxins, infectious agents and botulinum toxins have been suggested as causative factors. Clinical signs include anorexia, depression, bradycardia, decreased lacrimation, altered pupillary dilataion, megaoesphagus and constipation. As in equine dysautonomia, degenerative lesions of autonomic nerve ganglia can be seen. | ||
| + | |||
==== Displacement ==== | ==== Displacement ==== | ||
Latest revision as of 19:12, 6 June 2010
Introduction to the Intestines
Basic Anatomy and Physiology
The intestines are a portion of the alimentary tract extending from the pylorus to the anus. In mammals, the intestines are divided into two main segments: the small intestine and the large intestine. The small intestine, consisting of the duodenum, jejunum and ileum, acts as the main site of absorption for digestive products in the gastrointestinal tract. The large intestine, consisting of the caecum and colon, functions to extract water, electrolytes and nutrients as well as to concentrate and propulse faecal material to the rectum for defaecation. Functional differences between the small and large intestine are reflected in their anatomic and histologic organisation (Figure 1). The small intestinal mucosa in many species is highly folded and made up of numerous villi that greatly increase the absorptive surface area. Enterocytes, the main absorptive cells, are the most numerous and characteristic cells of the small intestinal epithelium. Others include goblet cells, paneth cells, neuroendocrine cells, stem cells, and intraepithelial lymphocytes. Another important feature of the small intestine is the presence of Peyer's patches within the lamina propria. They contribute to immune function and generation of immune responses within the mucosa.
In contrast to the small intestine, the large intestinal mucosa has no villi and consists of 2 main cell types: absorptive cells and mucus secreting goblet cells. A distinguishing histologic and anatomic characteristic is the thick muscularis mucosa layer that aids in propulsion of faeces to the rectum. Another important feature is the presence of commensal bacteria which plays different roles depending upon the type of animal (Dyce et. al, 2002; Young & Heath, 2000).
Defense Mechanisms
Secretions
- Mucus - inhibits contact and protects the mucosal surface
- Digestive enzymes - nonspecifically target bacteria and viruses
- Bile - kills some bacteria and viruses
Epithelium
- "Tight junctions" between epithelial cells prevent entry of macromolecules and pathogens into the intestinal tract.
- Epithelial cells have a very high turnover rate thus preventing pathogens with a longer life cycle from successfully colonising.
Commensal flora
- Commensal flora competitively inhibit attachment of pathogens to enterocytes in addition to competing for nutrition and substrates. Many also produce inhibitory growth substances that are toxic to other bacteria (McGavin and Zachary, 2007).
Movement
- Continuous peristalsis discourages persistence of toxins and aids in their elimination from the gut.
Cell-mediated and humoural defences
- The lamina propria contains macrophages, B and T lymphocytes, plasma cells, and mast cells.
- Lymphoid aggregates known as Peyer's patches within the small intestine aid in immunity.
- Secretory IgA and IgM provide humoural immunity and help prevent attachment of pathogens to the intestinal epithelium.
- Lysozyme from Paneth cells inhibits bacterial growth (McGavin & Zachary, 2007).
Comparative
The natural diets of different animal species largely govern the structure and function of the gastrointestinal tract. Broadly, animals can be classified as carnivores, herbivores or omnivores according to diet. Digestion and absorption of nutrients in carnivorous animals such as the dog and cat takes place largely in the small intestine. Because only a small amount of fermentation occurs in the large intestine of carnivores, they have a minimally developed caecum in comparison to nonruminating herbivores such as the horse which relies heavily on the end products of microbial digestion from the large intestine. The pig, an omnivorous animal has both a relatively long small intestine and an expanded portion of the colon that aids in fermentation of the fibrous material in the diet. Ruminants are an exception as fermentation largely occurs in the stomach (Reece, 2005).
References
Dyce KM, Sack WO, Wensing, CJG: Textbook of Veterinary Anatomy, 3rd ed, p. 129. Saunders, London, England, 2002.
McGavin DM & Zachary, JF: Pathologic Basis of Veterinary Disease, 4th ed, pp. 301-393. Elsevier, St. Louis, Missouri, 2007.
Reece, WO: Functional Anatomy and Physiology of Domestic Animals, 3rd ed., pp. 312-368. Lippincott Williams & Wilkins, London, England, 2005.
Young B, Heath, JW: Wheater's Functional Histology: A Text and Colour Atlas, 4th ed, pp. 249-274. Churchill Livingstone, London, England, 2000.
Contents
Developmental Anomalies
Physical Disturbances
Vascular Disturbances
Proliferative Pathology
Inflammatory Pathology
Diarrhoea
Parasites
Diseases due to pathogens
Diseases in animal species
Clinical Pathology
Intestine
Basic Anatomy and Physiology
Introduction
The intestines are a portion of the alimentary tract extending from the pylorus to the anus. In mammals, the intestines are divided into two main segments: the small intestine and the large intestine. The small intestine, consisting of the duodenum, jejunum and ileum, acts as the main site of absorption for digestive products in the gastrointestinal tract. The large intestine, consisting of the caecum and colon, functions to extract water, electrolytes and nutrients as well as to concentrate and propulse faecal material to the rectum for defaecation. Functional differences between the small and large intestine are reflected in their anatomic and histologic organisation (Figure 1). The small intestinal mucosa in many species is highly folded and made up of numerous villi that greatly increase the absorptive surface area. Enterocytes, the main absorptive cells, are the most numerous and characteristic cells of the small intestinal epithelium. Others include goblet cells, paneth cells, neuroendocrine cells, stem cells, and intraepithelial lymphocytes. Another important feature of the small intestine is the presence of Peyer's patches within the lamina propria. They contribute to immune function and generation of immune responses within the mucosa.
In contrast to the small intestine, the large intestinal mucosa has no villi and consists of 2 main cell types: absorptive cells and mucus secreting goblet cells. A distinguishing histologic and anatomic characteristic is the thick muscularis mucosa layer that aids in propulsion of faeces to the rectum. Another important feature is the presence of commensal bacteria which plays different roles depending upon the type of animal (Dyce et. al, 2002; Young & Heath, 2000).
Defense Mechanisms
Secretions
- Mucus - inhibits contact and protects the mucosal surface
- Digestive enzymes - nonspecifically target bacteria and viruses
- Bile - kills some bacteria and viruses
Epithelium
- "Tight junctions" between epithelial cells prevent entry of macromolecules and pathogens into the intestinal tract.
- Epithelial cells have a very high turnover rate thus preventing pathogens with a longer life cycle from successfully colonising.
Commensal flora
- Commensal flora competitively inhibit attachment of pathogens to enterocytes in addition to competing for nutrition and substrates. Many also produce inhibitory growth substances that are toxic to other bacteria (McGavin and Zachary, 2007).
Movement
- Continuous peristalsis discourages persistence of toxins and aids in their elimination from the gut.
Cell-mediated and humoural defences
- The lamina propria contains macrophages, B and T lymphocytes, plasma cells, and mast cells.
- Lymphoid aggregates known as Peyer's patches within the small intestine aid in immunity.
- Secretory IgA and IgM provide humoural immunity and help prevent attachment of pathogens to the intestinal epithelium.
- Lysozyme from Paneth cells inhibits bacterial growth (McGavin & Zachary, 2007).
Comparative
The natural diets of different animal species largely govern the structure and function of the gastrointestinal tract. Broadly, animals can be classified as carnivores, herbivores or omnivores according to diet. Digestion and absorption of nutrients in carnivorous animals such as the dog and cat takes place largely in the small intestine. Because only a samll amount of fermentation occurs in the large intestine of carnivores, they have a minimally developed caecum in comparison to nonruminating herbivores such as the horse which reies heavily on the end products of microbial digestion that occur in the large intestine. The pig, an omnivorous animal has both a relatively long small intestine and an expanded portion of the colon that aids in fermentation of the fibrous material in the diet. Ruminants are an exception as fermentation largely occurs in the stomach. The following figures illustrate the differences between the gastrointestinal tracts of the main domestic animal species (Reece, 2005). [Figures!!]
References
Dyce KM, Sack WO, Wensing, CJG: Textbook of Veterinary Anatomy, 3rd ed, p. 129. Saunders, London, England, 2002.
McGavin DM & Zachary, JF: Pathologic Basis of Veterinary Disease, 4th ed, pp. 301-393. Elsevier, St. Louis, Missouri, 2007.
Reece, WO: Functional Anatomy and Physiology of Domestic Animals, 3rd ed., pp. 312-368. Lippincott Williams & Wilkins, London, England, 2005.
Young B, Heath, JW: Wheater's Functional Histology: A Text and Colour Atlas, 4th ed, pp. 249-274. Churchill Livinstone, London, England, 2000.
Pathology
Developmental Anomalies
Segmental
Segmental anomalies of the intestines are common and range from incomplete occlusion (stenosis) to complete occlusion (atresia) of the lumen.
Atresia ani
- A common congenital defect of the lower gastrointestinal tract.
- Both the anus and rectum can be affected.
- Occurs in all species but is most often seen in calves and pigs.
Atresia coli
- Considered the most common segmental anomaly of the intestine in domestic animals.
- Can affect in particular the spiral colon of Holstein calves and the small colon of foals.
Atresia ilei
- It is less common to see atresia in the small intestine.
- Mostly seen in calves.
Persistent Meckel's diverticulum
- Meckel's diverticulum is a remnant of the omphalomesenteric duct of the yolk sac.
- Is usually an incidental finding though it can be associated with impaction and or intussusception.
Megacolon
- Occurs in cats, dogs, and pigs.
- May be due to a lack of myenteric plexuses that occurs when neuroblasts fail to migrate from the nerual crest to the colorectal myenteric plexuses.
- Congenital colonic agangliosis, a condition occurring in white foals, can lead to megacolon. It is thought to be an autosomal recessive condition.
References
Brown CC, Baker DC, Barker IK: Alimentary System. In: Jubb, Kennedy and Palmer's Pathology of Domestic Animals, ed. Maxie MG, 5th ed., pp. 1-296. Elsevier, Philadelphia, PA, 2007.
McGavin DM & Zachary, JF: Pathologic Basis of Veterinary Disease, 4th ed, pp. 301-393. Elsevier, St. Louis, Missouri, 2007.
Physical Disturbances
Obstruction
Intestinal obstruction can be the sequel to either mechanical or functional causes. Mechanical obstruction occurs due to physical blockage of the intestinal lumen whereas functional obstruction results from a decrease or inhibition of intestinal motility due to loss of smooth muscle contraction. (Brown et. al, 2007).
Mechanical
Mechanical obstruction of the intestine, either acute or chronic, can occur in all species of animals. Acute obstruction usually involves the upper or middle small intestine whereas chronic obstruction typically occurs in the distal small intestine or large intestine. Causes of obstruction can be divided into three main categories: intraluminal, intramural, or extrinsic. Intraluminal causes include food impaction and foreign bodies, intramural causes include neoplasia and extrinsic causes include adhesions, neoplasia and prostate enlargement. The following figure illustrates the pathogenesis occurring in intestinal obstruction [Figure].
Foreign Bodies
- Foreign bodies of all types can be found in the intestines. While some may pass through posing no problems, others can cause acute obstruction, pressure necrosis and eventually perforation. Foreign bodies can also be chronic, remaining for long periods of time without causing disturbance.
- Enteroliths, stones consisting of magnesium ammonium phosphate around a central nidus (often a metallic foreign body) occur mostly in horses greater than 4 years of age. Typically, they lodge at the pelvic flexure or the transverse colon.
Impaction
Impaction of the colon can occur in all species.
- In the dog and cat, dehydrated faecal material is the main cause of impaction.
- In the horse, faeces, digesta, sand, or fibrous material can all contribute to impaction Predisposing factors include poor dentition, water deprivation, a high roughage diet and general debility.
- Antihelminthic administration or large parasite burdens can also lead to impaction.
Extrinsic
Obstruction of the intestine due to external factors such as tumours, abscesses, and fibrous adhesions is a common occurrence.
- Neoplasia in structures adjacent to the intestines can spread and cause external compression. Pancreatic tumours in particular can extend and impinge on the duodenum.
- Inflammatory adhesions, following gut perforation, peritonitis or surgery, consist of fibrous tissue bands that may restrict intestinal motility and cause kinks in the mesentery.
- Pedicles of tumours such as lipomas in horses can become wound in loops of intestine leading to obstruction and possible strangulation.
- Prostatic enlargement in the dog can lead to compression of the rectum.
Functional
- Paralytic ileus is a common condition that can occur following trauma or abdominal surgery. Intestinal stasis leads to distension with gas and fluid as well as a flaccid intestinal wall.
- Dysautonomia is a condition that most notably affects horses and cats.
- Equine dysautonomia (grass sickness) occurs mostly in the UK and western Europe. Clostridium botulinum is thought to be implicated although the exact cause is still unknown. Affected animals are dull, restless, show signs of colic, and in acute cases become severly tympanic, avoid swallowing and salivate excessively. Degenerative lesions are seen in the autonomic nerve ganglia, including enteric plexuses.
- Feline dysautonomia (Key-Gaskell syndrome) occurs mostly in the UK and continental Europe. It is also of unknown aetiology although environmental toxins, infectious agents and botulinum toxins have been suggested as causative factors. Clinical signs include anorexia, depression, bradycardia, decreased lacrimation, altered pupillary dilataion, megaoesphagus and constipation. As in equine dysautonomia, degenerative lesions of autonomic nerve ganglia can be seen.
Displacement
Hernias
Internal
External
Volvulus and Torsion
Ruminants
caecal dilatation and torsion
Equine
right and left dorsal displacement colonic torsion and volvulus
Intussusception
Renosplenic entrapment
Vascular Disturbances
pathogenesis
Venous congestion
Arterial thromboembolism
Inflammation
pathogenesis
- enteritis
- typhlitis
- colitis
- proctitis
? about subheadings as many fit under specific pathogens notes subcategorising by types of enteritis???
Diseases of the epithelium
Diseases of absorptive enterocytes
Diseases of undifferentiated crypt cells
Diseases of the lamina propria
Inflammatory bowel disease
description of
Lymphocytic/plasmacytic enteritis
Idiopathic mucosal colitis
Eosinophilic enteritis
Granulomatous enteritis
Colitis
Typhlocolitis
in dogs: pipe to species specific section includes histiocytic unlcerative colitis trichuris vulpis, pipe to parasites
Neoplastic and Proliferative Lesions
description
Intesinal adenoma
Intestinal adenocarcinoma
Lymphoma
Mast cell tumours
Intestinal stromal tumours
Diarrhoea
definition and pathogenesis characteristics of l.i. diarrhoea
Miscellaneous
Caecal or large intestine rupture
Diverticula
Intestinal lipofuscinosis
Diseases due to pathogens
Bacteria, Viral, Mycotic brief explanation then pipe to different page
Bacterial
brief explanation
Escherichia coli
description
Enterotoxogenic colibacillosis
Enteropatholgenic colibacillosis
Postweaning colibacillosis
Enteroinvasive colibacillosis
Septicaemic colibacillosis
Salmonellosis
description Link to salmonellosis in specific species
Peracute Salmonella septicaemia
Acute enteric salmonellosis
Chronic enteric salmonellosis
Clostridial enteritis
description
Clostridium perfringens type A
Clostridium perfringens type B
Clostridium perfringens type C
Clostridium perfringens type D
Other Clostridial diseases
Clostridium difficile
= Clostridium piliforme
Yersiniosis
Lawsonian intracellularis
Campylobacter spp.
Paratuberculosis (Johne's disease)
Viral
description Bovine viral diarrhoea Rinderpest Peste des petits ruminants Malignant catarrhal fever Herpesvirus Adenovirus Coronavirus Rotavirus Parvovirus
Mycotic
description Intestinal phycomycosis and aspergillosis Candidiasis Intestinal histoplasmosis
Diseases in Animal Species
Avian
coccidiosis
Carnivores
Cats
Panleucopenia Feline infectious peritonitis Feline leukaemia Feline immunodeficiency virus
Dogs
Parvovirus 2 Distemper Salmonella Rotavirus Coronavirus Ascarids Hookworms Giardiasis Neoplasms Salmon poisoning Haemorrhagic enteritis
Horses
Rhodococcus equi Equine monocytic ehrlichiosis Equine granulomatous enteritis Clostridial enteritis Lawsonian associated Potomac horse fever Parasites Antibiotic associated diarrhoea
Rabbits
Ruminants
Bovine viral diarrhoea Rinderpest Malignant catarrhal fever Paratuberculosis Chlamydiosis Parasitism (list specifics to l.i.) Copper deficiency Salmonellosis Yersiniosis Coccidiosis Escherichia coli Poisoning Winter dysentery
Swine
Rotavirus Transmissible gastroenteritis Escherichia coli Salmonella Lawsonian intracellularis Swine dysentery Porcine circovirus 2 Intestinal spirochaetosis Ascaris suum
Parasites
Cryptosporidiosis Giaridasis Ascariasis Hookworm diseas Trichuriasis Strongyloidosis Pinworms Cestodes Trematodes