Alimentary System 2024 PDF

Alimentary System Dr. R. Mwenda Objectives Outline the functions and structure of the alimentary system Describe the developmental anomalies of the GIT State the circulatory disturbances associated with the GIT Outline the Inflammatory conditions and Neoplasia of the GIT  Stru...

Alimentary System Dr. R. Mwenda Objectives Outline the functions and structure of the alimentary system Describe the developmental anomalies of the GIT State the circulatory disturbances associated with the GIT Outline the Inflammatory conditions and Neoplasia of the GIT  Structure and Function of the Alimentary System The alimentary system is a long and complex tube that varies anatomically and functionally among animal species. Herbivores for example, need a fermentation chamber (either a rumen or an expanded cecum) This is for the digestion of cellulose; a feature not present in carnivores. Normal mucosal and serosal surfaces of the alimentary system should be smooth and shiny (although there may be normal papilla, folds, and ridges). The exception to this rule is the rumen, whose papillae may normally have a roughened, dull surface appearance.  Structure and Function of the Alimentary System The function of the alimentary system is to oTake ingested feedstuffs oGrind them and mix them with a variety of secretions oAbsorb the constituent nutrients into the bloodstream and lacteals. Undigested ingesta and excess secretions are passed from the body into the alimentary lumen thus become a component of the feces. The quality and quantity of the feces and clinical signs, such as regurgitation and vomiting, are often early indicators of alimentary dysfunction. Oral cavity  Provide mechanical advantage for prehension, tearing, and/ or mastication of food. Teeth Among animals there are differences in the growth pattern and numbers of teeth Salivary Glands Found in a variety of locations in the head and neck regions Vary in number and location from species to species. Produce saliva Saliva is a mixture of serous and mucoid secretions. It lubricates the mouth and esophagus and moistens ingesta. Tongue The tongue is a muscular organ covered by stratified epithelium It is functionally connected to the esophagus via the epiglottis. It is necessary for prehension, mastication, and swallowing of feedstuffs and water.  Other Structures of the Alimentary tract include Esophagus Rumen, Reticulum, and Omasum Stomach, Abomasum Intestines Peritoneum & Peritoneal Cavity  Developmental Anomalies 1. Facial clefts split palate and harelip 2. Abnormalities of the jaws 3. Polyodontia 4. Enamel hypoplasia 5. Segmental anomalies of the intestine could be partial (stenosis) or complete atresia. Atresia ani is the most common congenital abnormality in the distal GIT. Circulatory Disturbances (i) Congestion This is a common finding in the intestinal tract. Passive congestion gives a dark red to black colour to the intestines. This is frequently seen in infarction, associated with torsion and volvulus.  Circulatory Disturbances (ii) Oedema Most easily visible in the abomasal folds of ruminants in conditions such as heartwater and hypoproteinemia. The folds become thickened, with an accumulation of clear fluid in the submucosa, which is visible on incision. (iii) Haemorrhage Large haemorrhage in the wall of the intestine (suggillation) may be associated with trauma or after abdominal surgery. Haemorrhage on the surface of the intestines may be petechiae or ecchymoses.  Circulatory Disturbances Petechial and ecchymotic haemorrhage on the mucosal surface of the small and large intestines are common findings. They may originate due to: ✓Physical damage to the mucosa by parasites, e.g., Ancylostoma caninum in dogs. ✓Bleeding tendencies, e.g., canine ehrlichiosis (thrombocytopenia ✓Viral diseases: on the omasal folds in blue tongue in sheep due to vasculitis, African Horse Sickness due to increased vascular permeability. Gastrorrhagia/ Enterorrhagia is the presence of free, bright red, undigested blood in the stomach or intestines respectively. Melena is black, tarry, digested blood in the intestinal lumen. Circulatory Disturbances (iv) Necrosis There are two basic pathogeneses for necrosis in the intestinal tract. These are infarction and necrotic inflammation. Ascites Ascites or hydroperitoneum is defined as excess fluid in the peritoneal cavity. The quality of the fluid varies by cause from thick and syrupy in feline infectious peritonitis (FIP) to thin and watery in cases of hypoproteinemia. Ascites is nonspecific and can result from any cause of: hypoproteinemia such as heart, liver, or kidney failure protein-losing enteropathies such as Johne’s disease, lymphatic blockage, bladder rupture (uroperitoneum), and hypertension. Inflammation Cheilitis is inflammation of the lips and occurs often in cases of photosensitivity. Stomatitis is inflammation of the oral cavity. The lesion may be ulcerative (e.g. blue tongue), proliferative (e.g. gingival hyperplasia) or exudative (e.g. bacterial stomatitis) Glossitis is inflammation of the tongue and may be ulcerative e.g. in Malignant catarrhal fever. Gastritis is inflammation of the stomach. Enteritis is inflammation of the intestine. Gastroenteritis is inflammation of the entire GIT. Enteritis can be subdivided into duodenitis, jejunitis, ileitis, typhlitis, colitis and proctitis. Quiz 1. List any 3 circulatory disturbances associated with the GIT 2. List any 3 developmental abnormalities of the GIT 3. Define the following 1. Cheilitis 2. Gastroenteritis 3. Glossitis 4. Stomatitis Types of Inflammation (i) Catarrhal inflammation An indications of acute inflammation The exudate consists primarily of yellowish mucus. The intestinal wall is hyperaemic and oedematous (e.g. Colibacillosis in piglets). (iii) Purulent inflammation The lesion is usually focal in nature Associated with traumatic perforations due to foreign objects e.g traumatic reticuloperitonitis May also be associated with certain worm infestations (iv) Necrotic Inflammation This is a severe reaction where the mucosa undergoes necrosis, e.g., Parvo virus enteritis In acute cases the mucosa is dull and appears cracked to flattened, with associated acute inflammation in the wall. (v) Proliferative/granulomatous inflammation In chronic infections, a granulomatous reaction can be seen. The intestinal wall will be severely thickened, and will be thrown into folds , e.g. Johne’s disease in cattle and sheep. If it is multifocal, there will be several areas of thickening of the intestinal wall as seen in coccidiosis in sheep.  (vi) Fibrinous inflammation This lesion is rare and can only be distinguished from catarrhal enteritis on histopathology. (vii) Erosions and ulcerations Erosions are frequent occurrences in the upper portion of the GIT; e.g. Erosive stomatitis in dogs with chronic renal failure. Since some degree of inflammation usually accompanies ulceration and erosion it is common practice to refer to the lesion as an inflammation, e.g. ulcerative gastritis. Disorders of the oral cavity Inflammation-Stomatitis and gingivitis Very rare Seen in certain pathological diseases such as viral infection-FMD Erosion and ulcers Seen in condition like BVD Uremic ulcers seen in chronic renal failure Malignant catarrhal fever Neoplasia of the oral cavity In the dog 70% of tumors of the alimentary system are in the oral cavity and oropharynx. Examples include squamous cell carcinomas, oral papillomatosis and melanomas Esophagus Developmental Anomalies Achalasia. Esophageal motility disorders are termed achalasia. In this condition the sequential contractility of the esophagus is defective, and the lower cricopharyngeal sphincter fails to function properly. Achalasia results in difficulty in swallowing and may be responsible for regurgitation and weight loss. Esophagus Other Anomalies Megaesophagus. dilation of the esophagus because of insufficient, absent, or uncoordinated peristalsis in the mid and cervical esophagus. Causes include innervation or denervation disorders and partial physical obstructions and stenosis, secondary to inflammatory diseases of esophageal musculature Esophageal parasites Spirocerca lupi of dogs Is probably the most pathogenic of the esophageal parasites. These nematodes reach the esophageal submucosa after migrating from the stomach. Miscellaneous esophageal disorders Choke A clinical term referring to esophageal obstruction subsequent to stenoses or blockage. Choke most often occurs in anatomic locations in which the esophagus cannot fully expand. Choke occurs most frequently as a result of ingestion of large foreign bodies Miscellaneous esophageal disorders Esophageal erosions and ulcers One of the more common causes of esophageal erosions and ulcers is reflux of stomach acid. This reflux of gastric acids causes chemical burning of the esophagus and is commonly called acid reflux esophagitis or clinically, heartburn in human beings  Esophageal tumors The clinical signs are similar to those of other causes of esophageal blockage. Tumors of the esophagus are occasionally palpable but are most often intraluminal rather than mural. Epithelial tumors include papillomas and leiomyomas  Disorders of the forestomachs (Rumen, Reticulum, and Omasum) Bloat (Ruminal Tympany, legume bloat, dietary bloat, or frothy bloat) This is an overdistention of the rumen and reticulum by gases produced during fermentation. It generally occurs up to 3 days after animals begin a new diet. Certain legumes, such as alfalfa, and grain concentrates, promote the formation of stable foam. The nonvolatile acids of legume and ruminal fermentation lower the rumen pH to between 5 and 6, which is optimal for formation of bloat. Foam mixed with rumen contents physically blocks the cardia, preventing eructation and causing the rumen to distend with the gases of fermentation  Bloat (Ruminal Tympany, legume bloat, dietary bloat, or frothy bloat) A bloat line is the most reliable postmortem indicator of bloat This is sharp line of demarcation most evident in the mucosa between the pale, bloodless esophagus distal to the thoracic inlet and the congested proximal esophagus cranial to it.  Foreign bodies in the forestomach Traumatic reticuloperitonitis and its complications Perforation of the forestomachs by foreign bodies is virtually always caused by a long, thin, and sharp foreign body These are usually a wire or nail, penetrating the reticular wall Ingestion of nails and wire, common where straw and hay bails are packaged in wire can result in perforation of the wall of the reticulum. This will result in reticulitis, peritonitis or pericarditis (Hardware disease)  Disorders of the Stomach and Abomasum Gastric Dilation and Volvulus Gastric dilation occurs in a variety of animals. More common in dogs, less in cats In dogs, particularly in the large, deep-chested breeds, the acute gastric dilation and volvulus syndrome occurs. This lesion is life threatening and should not be confused with simple gastric dilation, which is common in young puppies after overeating. Predisposing factors to acute gastric dilation include ✓a source of distending gas, fluid, or feed ✓a diet of small feed particles, having a raised food bowl ✓obstruction of the cardia that prevents eructation and emesis ✓obstruction of the pylorus that prevents passage of gastric contents into the small intestine  Gastric Dilation and Volvulus The source of gas is not well understood. Theories include gas production by: ✓C. perfringens ✓Spores of which are present in the feed ✓Carbon dioxide from physiologic mechanisms of digestion ✓or simple aerophagia.  Gastric Dilation and Volvulus Abomasal displacement and volvulus is a common clinical problem in high- producing, intensively managed dairy cattle particularly around the time of parturition It also occurs in animals that are predominantly pasture fed. The displacement is usually ventral and to the left of the rumen In swine, gastric volvulus is a cause of sudden death in adult sows. It is associated with excitement in anticipation of feeding among pigs that are fed at regular, often long, intervals It may be a sequel to unduly rapid ingestion of feed, water, and air. Obstruction of veins by volvulus may cause reduced perfusion of intra-abdominal organs, reduced cardiac output, and circulatory shock Simple Gastric Dilation, Stomach, Rabbit. The stomach is markedly dilated and filled with gas. Dilation occurs most commonly following aerophagia or overeating and is relieved by eructation or vomiting.  Gastric Dilation and Volvulus, Abdomen, Dog. The stomach is filled with gas and its serosa is congested (dark red). The duodenum and engorged spleen have been displaced to the right The result of repeated episodes of gastric dilation is stretching and relaxation of the gastrohepatic ligament. The stomach generally is rotated clockwise on the ventro-dorsal axis when the abdomen is viewed from the ventral surface. Rotation is 180 to 360 degrees Gastric Dilation and Rupture Gastric dilation occurs in horses as a result of the ingestion of fermentable feeds or grain a situation analogous to grain overload with lactic acidosis in cattle. Acute gastric dilation and rupture in horses occurs most frequently as a terminal event in intestinal obstruction and displacement.  Abomasal displacement Normally the abomasum lies over the xiphoid process at the abdominal ventral midline. Abomasal displacement is usually to the left side, although right-sided displacements also occur. Left-sided displacement of the abomasum is a generally nonfatal entity seen in high-producing dairy cattle during the 6 weeks after parturition. Strenuous activity can predispose nonpregnant cows to displacement. Pregnancy Gastric ulcers An imbalance between acid secretion and mucosal protection result in ulcers. This imbalance occurs as a result of the following: Local disturbances or trauma to the mucosal epithelial barrier. ✓can be due to back flush of bile salts from the duodenum or ingestion of lipid solvents such as alcohol. High gastric acidity. Local disturbances in blood flow resulting in ischemia. Steroids and NSAIDs.  Administration of nonsteroidal anti-inflammatory drugs causes extensive ulceration Gastric ulcers Proliferating ulcer Large volume of clotted and unclotted blood from a gastric ulcer Impaction Impaction of the monogastric stomach and abomasum has a variety of causes. Intrathoracic lesions, such as pneumonia, pleuritis, lymphadenopathy, and lymphoma of mediastinal lymph nodes, can infiltrate and damage the vagal nerves. This can result in a problem with abomasal/gastric motility and emptying. Roughage, hairballs, and other foreign materials also cause impaction. Impaction Neoplasia Gastric neoplasia, although uncommon, manifests in different ways in domestic animals. Most common are tumors such as lymphomas, leiomyomas and squamous cell carcinomas  Miscellaneous Disorders of the stomach Uremic gastritis occurs most frequently in carnivores as a result of chronic renal disease Amyloidosis occasionally is present in the stomach concomitant with systemic amyloid infiltrates. Pyloric stenosis-inability of the pyloric sphincter to function properly.  Developmental Anomalies Atresia Disorders of the Occlusion of the intestinal lumen as the result of anomalous development of the intestinal wall is called Intestines atresia. Atresia is generally named for the part of the bowel that is occluded, such as atresia ani or atresia coli. Obstructive conditions of the gut Disturbances of passage of ingesta may be created by numerous abnormalities. The result is often ileus (lack of tone) and diminished or absence of peristalsis. Signs may include ✓abdominal distension ✓abdominal pain and vomiting. Hindrance to movement of the bowel may be termed intestinal obstruction. It may be divided as follows: ✓Mechanical obstruction ✓Vascular obstruction ✓Neurological obstruction Mechanical obstruction There is a mechanical hindrance in the intestinal wall e.g.,: i. luminal abnormalities ii. strangulation of the intestines iii. Intussusception iv. peritoneal adhesion v. tumor growing from outside  (I) Luminal Abnormalities In dogs, impaction of the large bowel may be associated with masses of bone fragment. Pressure necrosis and ileus are caused by spasmodic contraction of the bowel at the site of the foreign body. A shock syndrome may develop due to combined effects of: ✓Bacterial overgrowth in the stagnant gut ✓Absorption of the bacterial toxins through devitalised mucosa and ✓Electrolyte disturbance and hypovolaemia from vomiting. (II) Strangulation This occurs when there is substantial occlusion on the mesenteric veins associated with obstruction of the lumen of the gut. Its a severe type of obstruction due to marked hemorrhagic effects from vascular congestion. Various conditions may lead to this state: Incarceration Volvulus Torsion Pedunculated lipomas Rectal prolapse  Scrotal hernias Umbilical hernia Incarceration Diaphragmatic hernias Volvulus Volvulus of the intestine has resulted in vascular compromise and infarction Volvulus involves twisting of the intestine on its mesenteric axis  A. Rotation of the colon on its long axis has resulted in severe colic with strangulation. Torsion B. Note the sharp line of demarcation between viable colon and nonviable colon caused by obstruction of venous blood flow Pendunculated Lipomas (arrows) have wrapped around the mesentery and strangled the bowel resulting Lipomas in infarction  Rectal prolapse may occur secondary to: tenesmus Rectal prolapse excessive postpartum straining Sequelae of strangulation Gaseous distension Transudation of plasma and haemorrhage into the gut lumen and peritoneal cavity. Gangrene of gut wall from intense congestion Acute peritonitis.  The necrotic intussuscipiens is present in the lumen of the opened cecum. (III) Intussusception The intussusceptum is the trapped segment, and the intussuscipiens is the enveloping portion of the intestine. Peritoneal adhesions Fibrous adhesions in peritonitis connect bowel segments to each other, and fix bowels to other organs as well. This may cause ileus. Cords and strands of fibrous tissue then extend between serosal surfaces. In this way ileus may occur as the late sequela to an inflammatory event.  Pathophysiology of enteric diseases Diarrhea Diarrhea is defined as secretion of abnormally fluid feces accompanied by an increased volume of feces and increased frequency of defecation. Normal feces are 75% water. Diarrheal feces are greater than 85% water. The consequence of excess fluid loss in the feces through diarrhea is dehydration. Dehydration results in hypovolemia. Hypovolemia results in hemoconcentration that results in inadequate tissue perfusion.  Pathophysiology of enteric diseases Mechanisms of Diarrhoea 1. Malabsorption-due to villous atrophy 2. Maldigestion -mucosa is structurally normal, but due to an enzyme deficiency such as seen in lactose intolerance. 3. Chloride (Cl−) hypersecretion 4. Exudation 5. Hypermotility