Ileus is a cause of colic in horses due to functional obstruction of the intestines. It most commonly seen in horses postoperatively, especially following colic surgery. Horses experiencing ileus are at risk for gastric rupture due to rapid reflux build-up, and require intense medical management with frequent nasogastric intubation. Ileus may increase adhesion formation, because intestinal segments have more prolonged contact and intestinal distention causes serosal injury and ischemia. It is usually treated with aggressive fluid support, prokinetics, and anti-inflammatories.

The exact incidence of ischemic colitis is difficult to estimate, as many patients with mild ischemia may not seek medical attention. Ischemic colitis is responsible for about 1 in 2000 hospital admissions, and is seen on about 1 in 100 endoscopies. Men and women are affected equally; ischemic colitis is a disease of the elderly, with more than 90% of cases occurring in people over the age of 60.

It is unclear what role dietary fibre plays in diverticulitis. It is often stated that a diet low in fibre is a risk factor; however, the evidence to support this is unclear. There is no evidence to suggest that the avoidance of nuts and seeds prevents the progression of diverticulosis to an acute case of diverticulitis. It appears in fact that a higher intake of nuts and corn could help to avoid diverticulitis in adult males.

The causes of diverticulitis are poorly understood, with approximately 40 percent due to genes and 60 percent due to environmental factors. Conditions that increase the risk of developing diverticulitis include arterial hypertension and immunosuppression. Obesity is another risk factor.

In primary chronic intestinal pseudo-obstruction (the majority of chronic cases), the condition may be caused by an injury to the smooth muscle (myopathic) or the nervous system (neuropathic) of the gastrointestinal tract.

In some cases there appears to be a genetic association. One form has been associated with DXYS154.

Secondary chronic intestinal pseudo-obstruction can occur as a consequence of a number of other conditions, including Kawasaki disease, Parkinson's disease, Chagas' disease, Hirschsprung's disease, intestinal hypoganglionosis, collagen vascular diseases, mitochondrial disease, endocrine disorders and use of certain medications. The term may be used synonymously with enteric neuropathy if a neurological cause is suspected.

Most patients with ischemic colitis recover fully, although the prognosis depends on the severity of the ischemia. Patients with pre-existing peripheral vascular disease or ischemia of the ascending (right) colon may be at increased risk for complications or death.

Non-gangrenous ischemic colitis, which comprises the vast majority of cases, is associated with a mortality rate of approximately 6%. However, the minority of patients who develop gangrene as a result of colonic ischemia have a mortality rate of 50-75% with surgical treatment; the mortality rate is almost 100% without surgical intervention.

Risperidone, an anti-psychotic medication, can result in megacolon.

Paralysis of the intestine is often termed paralytic ileus, in which the intestinal paralysis need not be complete, but it must be sufficient to prohibit the passage of food through the intestine and lead to intestinal blockage. Paralytic ileus is a common side effect of some types of surgery, commonly called postsurgical ileus. It can also result from certain drugs and from various injuries and illnesses, such as acute pancreatitis. Paralytic ileus causes constipation and bloating. On listening to the abdomen with a stethoscope, no bowel sounds are heard because the bowel is inactive.

A temporary paralysis of a portion of the intestines occurs typically after abdominal surgery. Since the intestinal content of this portion is unable to move forward, food or drink should be avoided until peristaltic sound is heard, by auscultation (use of a stethoscope) of the area where this portion lies. Intestinal atony or paralysis may be caused by inhibitory neural reflexes, inflammation or other implication of neurohumoral peptides.

Toxic megacolon is mainly seen in ulcerative colitis and pseudomembranous colitis, two chronic inflammations of the colon (and occasionally, in the other type of inflammatory bowel disease, Crohn's disease). Its mechanism is incompletely understood. It is probably due to an excessive production of nitric oxide, at least in ulcerative colitis. The prevalence is about the same for both sexes.

In patients with HIV/AIDS, cytomegalovirus (CMV) colitis is the leading cause of toxic megacolon and emergency laparotomy. CMV may also increase the risk of toxic megacolon in non-HIV/AIDS patients with IBD.

The prognosis for non-ischemic cases of SBO is good with mortality rates of 3–5%, while prognosis for SBO with ischemia is fair with mortality rates as high as 30%.

Cases of SBO related to cancer are more complicated and require additional intervention to address the malignancy, recurrence, and metastasis, and thus are associated with poorer prognosis.

All cases of abdominal surgical intervention are associated with increased risk of future small-bowel obstructions. Statistics from U.S. healthcare report 18.1% re-admittance rate within 30 days for patients who undergo SBO surgery. More than 90% of patients also form adhesions after major abdominal surgery.

Common consequences of these adhesions include small-bowel obstruction, chronic abdominal pain, pelvic pain, and infertility.

The predisposition to diverticulosis for specific individuals is likely explained by a genetic component, a theory which is supported by studies examining the rates of diverticulosis among twins. The heritability of diverticulosis is estimated to be approximately 40%.

Prucalopride, pyridostigmine, metoclopramide, cisapride, and erythromycin may be used, but they have not been shown to have great efficacy. In such cases, treatment is aimed at managing the complications. Linaclotide is a new drug that received approval from Food and Drug Administration in August 2012 and looks promising in the treatment of chronic intestinal pseudo-obstruction, gastroparesis and inertia coli.

Intestinal stasis, which may lead to bacterial overgrowth and subsequently, diarrhea or malabsorption, is treated with antibiotics.

Nutritional deficiencies are treated by encouraging patients to avoid food high in fat and fibre, which are harder to digest and increase abdominal distention and discomfort, and have small, frequent meals (5–6 per day), focusing on liquids and soft food. Reducing intake of poorly absorbed sugar alcohols may be of benefit. Referral to an accredited dietitian is recommended. If dietary changes are unsuccessful in meeting nutritional requirements and stemming weight loss, enteral nutrition is used. Many patients eventually require parenteral nutrition.

Total parenteral nutrition (TPN) is a form of long-term nutritional treatment needed for patients that have severe pseudoobstruction. After a period of no improvement of intestinal function or motility the decision to start TPN will be made, and the surgical procedure to add a long-term, more permanent IV to administer TPN will occur. Types of IV catheters to be placed will be a PICC line or central line which include mediports, Broviac, or Hickman lines depending on how long the physicians believe the patient will require TPN. Patients that are deemed TPN dependent will require constant checkups to monitor the catheter is working properly, check liver enzyme levels and look for signs of blood infections, as catheter blockage, liver damage, and infections of catheters are the main complications associated with long term TPN use and can result in sepsis and/or additional surgeries if not properly monitored. TPN nutritional feeds are given over a period of several hours to all day infusions, and are a mixture of all the vitamins, minerals, and calories similar to what one would get eating orally daily as well as any other specific nutritional needs the patient has at the moment. TPN format is typically changed depending on loss/gain of weight and bloodwork results, and is specially formulated to meet each individual patient's needs.

Use of octreotide has been described.

Cannabis has long been known to limit or prevent nausea and vomiting from a variety of causes. This has led to extensive investigations that have revealed an important role for cannabinoids and their receptors in the regulation of nausea and emesis. With the discovery of the endocannabinoid system, novel ways to regulate both nausea and vomiting have been discovered that involve the production of endogenous cannabinoids acting centrally. The plant cannabis has been used in clinics for centuries, and has been known to be beneficial in a variety of gastrointestinal diseases, such as emesis, diarrhea, inflammatory bowel disease and intestinal pain. Moreover, modulation of the endogenous cannabinoid system in the gastrointestinal tract may provide a useful therapeutic target for gastrointestinal disorders. While some GI disorders may be controlled by diet and pharmaceutical medications, others are poorly moderated by conventional treatments. Symptoms of GI disorders often include cramping, abdominal pain, inflammation of the lining of the large and/or small intestine, chronic diarrhea, rectal bleeding and weight loss. Patients with these disorders frequently report using cannabis therapeutically.

In a 2012 animal study, cannabichromene was shown to normalize gastrointestinal hypermotility without reducing the transit time. The study notes that this result is of potential clinical interest, as the only drugs available for intestinal dysmotility are often associated with constipation.

The prevalence of diverticulosis progressively increases with age. Approximately 50% of people over the age of 60 and 70% of people over the age of 80 have diverticulosis. This disease is common in the U.S., Britain, Australia, Canada, and is uncommon in Asia and Africa. Large-mouth diverticula are associated with scleroderma. Diverticular disease is more common in collagen disorders such as Ehlers Danlos Syndrome.

Causes of large bowel obstruction include:

- Neoplasms / cancer

- Diverticulitis / Diverticulosis

- Hernias

- Inflammatory bowel disease

- Colonic volvulus (sigmoid, caecal, transverse colon)

- Adhesions

- Constipation

- Fecal impaction

- Fecaloma

- Colon atresia

- Intestinal pseudoobstruction

- Endometriosis

- Narcotic induced (especially with the large doses given to cancer or palliative care patients)

Emergency action may be required if severe abdominal pain develops, particularly if it is accompanied by fever, rapid heart rate, tenderness when the abdomen is pressed, bloody diarrhea, frequent diarrhea, or painful bowel movements.

Colonoscopy is contraindicated, as it may rupture the dilated colon resulting in peritonitis and septic shock.

Incidence and prevalence of microscopic colitis nears those of ulcerative colitis and Crohn’s disease. Recent studies in North America found incidence rates of 7.1 per 100,000 person-years and 12.6 per 100,000 person-years for collagenous colitis for lymphocytic colitis, respectively.

A higher incidence of autoimmune diseases, for example arthritis, Sjögren's syndrome, thyroid disorders, and coeliac disease, has been reported in patients with microscopic colitis. Associations with various drugs have been found, especially proton pump inhibitors, H blockers, selective serotonin reuptake inhibitors (SSRIs), and non-steroidal anti-inflammatory drugs (NSAIDs). Bile acid diarrhea is found in 41% of patients with collagenous colitis and 29% with lymphocytic colitis. Additionally, smoking has been identified as a significant risk factor of microscopic colitis.

With early intervention, morbidity and mortality of cases of intestinal obstruction is low. The outcome is in part dependent upon congenital comorbidities and delays in diagnosis and management.

Laparotomy for other forms of volvulus, especially anal volvulus.

Toxic megacolon ("megacolon toxicum") is an acute form of colonic distension. It is characterized by a very dilated colon (megacolon), accompanied by abdominal distension (bloating), and sometimes fever, abdominal pain, or shock.

Toxic megacolon is usually a complication of inflammatory bowel disease, such as ulcerative colitis and, more rarely, Crohn's disease, and of some infections of the colon, including "Clostridium difficile" infections, which have led to pseudomembranous colitis. Other forms of megacolon exist and can be congenital (present since birth, such as Hirschsprung's disease). Also, it can be caused by "Entamoeba histolytica" and "Shigella".

It is a serious medical disorder and the mortality rate can be as high as 30%. The high mortality rate is likely a measure that this syndrome is seen in critically ill patients, rather than this syndrome being in itself lethal, although it can also present in otherwise healthy individuals (especially if the disorder was induced by pharmacologic agents). Drug induced megacolon (i.e. from Clozapine) has been associated with mortality as high as 27.5%.

Gastric diseases refer to diseases affecting the stomach. Inflammation of the stomach by infection from any cause is called gastritis, and when including other parts of the gastrointestinal tract called gastroenteritis. When gastritis persists in a chronic state, it is associated with several diseases, including atrophic gastritis, pyloric stenosis, and gastric cancer. Another common condition is gastric ulceration, peptic ulcers. Ulceration erodes the gastric mucosa, which protects the tissue of the stomach from the stomach acids. Peptic ulcers are most commonly caused by a bacterial "Helicobacter pylori" infection.

As well as peptic ulcers, vomiting blood may result from abnormal arteries or veins that have ruptured, including Dieulafoy's lesion and Gastric antral vascular ectasia. Congenital disorders of the stomach include pernicious anaemia, in which a targeted immune response against parietal cells results in an inability to absorb vitamin B12. Other common symptoms that stomach disease might cause include indigestion or dyspepsia, vomiting, and in chronic disease, digestive problems leading to forms of malnutrition. In addition to routine tests, an endoscopy might be used to examine or take a biopsy from the stomach.

Oesophageal diseases include a spectrum of disorders affecting the oesophagus. The most common condition of the oesophagus in Western countries is gastroesophageal reflux disease, which in chronic forms is thought to result in changes to the epithelium of the oesophagus, known as Barrett's oesophagus.

Acute disease might include infections such as oesophagitis, trauma caused ingestion of corrosive substances, or rupture of veins such as oesophageal varices, Boerhaave syndrome or Mallory-Weiss tears. Chronic diseases might include congenital diseases such as Zenker's diverticulum and esophageal webbing, and oesophageal motility disorders including the nutcracker oesophagus, achalasia, diffuse oesophageal spasm, and oesophageal stricture.

Oesophageal disease may result in a sore throat, throwing up blood, difficulty swallowing or vomiting. Chronic or congenital diseases might be investigated using barium swallows, endoscopy and biopsy, whereas acute diseases such as reflux may be investigated and diagnosed based on symptoms and a medical history alone.

In a cecal volvulus, the cecum may be returned to a normal position and sutured in place, a procedure known as cecopexy. If identified early, before presumed intestinal wall ischemia has resulted in tissue breakdown and necrosis, the cecal volvulus can be detorsed laparoscopically.

Neonatal bowel obstruction (NBO) or neonatal intestinal obstruction is the most common surgical emergency in the neonatal period. It may occur due to a variety of conditions and has an excellent outcome based on timely diagnosis and appropriate intervention.