Structure and Function of the Gastrointestinal Tract in Dogs
Dr. Bari Spielman
Congenital defects. They may lead to defects in swallowing or movement of food through the esophagus, inability to properly digest food, or inability to defecate.
What Are Common Diseases of the Gastrointestinal Tract?
There are many primary disorders that affect the GI tract. Vomiting and/or diarrhea are commonly seen with gastrointestinal disease. Regurgitation (the effortless evacuation of fluid, mucus and undigested food from the esophagus) is commonly seen with esophageal disease. Some common diseases of the GI tract include:
Infectious agents including bacteria, viruses, fungal and protozoal organisms, as well as intestinal parasites are quite common in both cats and dogs. Different infections often involve isolated portions of the GI tract.
Inflammation. Various inflammations can develop any where along the GI tract. When inflammation arises in the mouth, it is called stomatitis. Inflammation of the esophagus is esophagitis. Gastritis is inflammation of the stomach. Enteritis is inflammation of the intestine. Colitis is inflammation of the colon. Inflammation of the rectum is proctitis. These types of inflammation can be either acute or chronic.
Inflammatory bowel disease (IBD) is a microscopic infiltration of the small intestinal wall with inflammatory cells. It is believed to be associated with an abnormal immune response to environmental stimuli that, when continued, creates a self-perpetuating inflammation resulting in the disease.
Intussusceptions (telescoping of part of the bowel into an adjacent segment of bowel) are seen in both cats and dogs. They are often associated with parasites, foreign bodies, tumors or chronic diarrhea, and usually affect the small intestines of young animals.
Foreign bodies (rocks, bits of clothing) of the GI tract are common in cats and dogs due to their indiscriminate eating habits. They result in local inflammation, obstruction and sometimes perforation of the GI tract.
Ulcerative gastroenteritis (interruptions in the lining of the gastrointestinal tract) may develop and be secondary to inflammation, drug administration, neoplasia or foreign bodies.
Hemorrhagic gastroenteritis (HGE) is a dramatic, potentially fatal disorder causing sudden onset bloody diarrhea in adult dogs. Although the exact cause is unknown, it may be due to some sort of bacterial toxin. HGE has a predilection for small breed dogs.
Acute gastric dilatation or bloat is a condition seen mainly in large, deep-chested breeds of dogs. For a variety of reasons, the stomach suddenly dilates like a balloon and fails to empty. It may twist upon itself (called a volvulus), and entirely obstruct the opening/exit passages of the stomach. Acute gastric dilatation is a life-threatening emergency that may rapidly result in shock and collapse of the dog.
Paralysis of portions of the GI tract may occur. Paralysis of the esophagus results in a grossly enlarged esophagus, known as megaesophagus, and regurgitation of food and water. Paralysis of the stomach results in delayed gastric emptying. Paralysis of the intestines is known as ileus. Paralysis of the colon results in enlargement of the colon (megacolon) and constipation.
Certain abnormalities in the digestion and absorption of nutrients can occur, particularly in the small intestines. These are known as maldigestion and malabsorption disorders. Diseases can also arise that result in the excessive loss of nutrients into the intestines, which then pass out of the body through the feces.
Trauma can occur along different segments of the GI tract. Trauma to the esophagus most often arises with bite wounds to the neck. The intestines may be injured through either blunt abdominal trauma (e.g. automobile accidents, falling from heights, kicking injuries) or penetrating trauma (e.g. bite wounds, bullet and arrow wounds, falling on sharp objects). Trauma to the pelvis and tail may affect the rectum and anal canal.
Tumors may develop anywhere along the entire length of the intestinal tract. Different tumors arise in different areas because the types of cells present in each area are unique. Tumors of the gastrointestinal tract may be either benign or malignant. They can grow into the cavity of the tract, and can involve the wall of the tract or the surrounding soft tissues.