Symptoms of ileus include, but are not limited to:

- moderate, diffuse abdominal discomfort

- constipation

- abdominal distension

- nausea/vomiting, especially after meals

- vomiting of bilious fluid

- lack of bowel movement and/or flatulence

- excessive belching

Decreased propulsive ability may be broadly classified as caused either by bowel obstruction or intestinal atony or paralysis. However, instances with symptoms and signs of a bowel obstruction occur, but with the absence of a mechanical obstruction, mainly in acute colonic pseudo-obstruction, Ogilvie's syndrome.

Depending on the level of obstruction, bowel obstruction can present with abdominal pain, swollen abdomen, abdominal distension, vomiting, fecal vomiting, and constipation.

Bowel obstruction may be complicated by dehydration and electrolyte abnormalities due to vomiting; respiratory compromise from pressure on the diaphragm by a distended abdomen, or aspiration of vomitus; bowel ischemia or perforation from prolonged distension or pressure from a foreign body.

In small bowel obstruction, the pain tends to be colicky (cramping and intermittent) in nature, with spasms lasting a few minutes. The pain tends to be central and mid-abdominal. Vomiting may occur before constipation.

In large bowel obstruction, the pain is felt lower in the abdomen and the spasms last longer. Constipation occurs earlier and vomiting may be less prominent. Proximal obstruction of the large bowel may present as small bowel obstruction.

Signs and symptoms may include a sudden pain in the epigastrium to the right of the midline indicating the perforation of a duodenal ulcer. In a gastric ulcer perforation creates a history of burning pain in epigastrium, with flatulence and dyspepsia.

In intestinal perforation, pain starts from the site of perforation and spreads across the abdomen.

Gastrointestinal perforation results in severe abdominal pain intensified by movement, nausea, vomiting and hematemesis. Later symptoms include fever and or chills. In any case, the abdomen becomes rigid with tenderness and rebound tenderness. After some time the abdomen becomes silent and heart sounds can be heard all over. Patient stops passing flatus and motion, abdomen is distended.

The symptoms of esophageal rupture may include sudden onset of chest pain.

Bowel obstruction, also known as intestinal obstruction, is a mechanical or functional obstruction of the intestines which prevents the normal movement of the products of digestion. Either the small bowel or large bowel may be affected. Signs and symptoms include abdominal pain, vomiting, bloating, and not passing gas. Mechanical obstruction is the cause of about 5 to 15% of cases of severe abdominal pain of sudden onset requiring admission to hospital.

Causes of bowel obstruction include adhesions, hernias, volvulus, endometriosis, inflammatory bowel disease, appendicitis, tumors, diverticulitis, ischemic bowel, tuberculosis, and intussusception. Small bowel obstructions are most often due to adhesions and hernias while large bowel obstructions are most often due to tumors and volvulus. The diagnosis may be made on plain X-rays; however, CT scan is more accurate. Ultrasound or MRI may help in the diagnosis of children or pregnant women.

The condition may be treated conservatively or with surgery. Typically intravenous fluids are given, a tube is placed through the nose into the stomach to decompress the intestines, and pain medications are given. Antibiotics are often given. In small bowel obstruction about 25% require surgery. Complications may include sepsis, bowel ischemia, and bowel perforation.

About 3.2 million cases of or bowel obstruction occurred in 2015 which resulted in 264,000 deaths. Both sexes are equally affected and the condition can occur at any age. Bowel obstruction has been documented throughout history with cases detailed in the Ebers Papyrus of 1550 BC and by Hippocrates.

Regardless of cause, volvulus causes symptoms by two mechanisms:

- Bowel obstruction manifested as abdominal distension and bilious vomiting.

- Ischemia (loss of blood flow) to the affected portion of intestine.

Depending on the location of the volvulus, symptoms may vary. For example, in patients with a cecal volvulus, the predominant symptoms may be those of a small bowel obstruction (nausea, vomiting and lack of stool or flatus), because the obstructing point is close to the ileocecal valve and small intestine. In patients with a sigmoid volvulus, although abdominal pain may be present, symptoms of constipation may be more prominent.

Volvulus causes severe pain and progressive injury to the intestinal wall, with accumulation of gas and fluid in the portion of the bowel obstructed. Ultimately, this can result in necrosis of the affected intestinal wall, acidosis, and death. This is known as a closed loop obstruction because there exists an isolated ("closed") loop of bowel. Acute volvulus often requires immediate surgical intervention to untwist the affected segment of bowel and possibly resect any unsalvageable portion.

Volvulus occurs most frequently in middle-aged and elderly men. Volvulus can also arise as a rare complication in persons with redundant colon, a normal anatomic variation resulting in extra colonic loops.

Sigmoid volvulus is the most-common form of volvulus of the gastrointestinal tract. and is responsible for 8% of all intestinal obstructions. Sigmoid volvulus is particularly common in elderly persons and constipated patients. Patients experience abdominal pain, distension, and absolute constipation.

Cecal volvulus is slightly less common than sigmoid volvulus and is associated with symptoms of abdominal pain and small bowel obstruction.

Volvulus can also occur in patients with Duchenne muscular dystrophy due to the smooth muscle dysfunction.

Underlying causes include gastric ulcers, duodenal ulcers, appendicitis, gastrointestinal cancer, diverticulitis, inflammatory bowel disease, superior mesenteric artery syndrome, trauma and ascariasis. Typhoid fever, non-steroidal anti-inflammatory drugs, ingestion of corrosives may also be responsible.

The diagnosis is suspected based on polyhydramnios in uteru, bilious vomiting, failure to pass meconium in the first day of life, and abdominal distension. The presentations of NBO may vary. It may be subtle and easily overlooked on physical examination or can involve massive abdominal distension, respiratory distress and cardiovascular collapse. Unlike older children, neonates with unrecognized intestinal obstruction deteriorate rapidly.

Signs and symptoms of a peptic ulcer can include one or more of the following:

- abdominal pain, classically epigastric strongly correlated to mealtimes. In case of duodenal ulcers the pain appears about three hours after taking a meal;

- bloating and abdominal fullness;

- waterbrash (rush of saliva after an episode of regurgitation to dilute the acid in esophagus - although this is more associated with gastroesophageal reflux disease);

- nausea and copious vomiting;

- loss of appetite and weight loss;

- hematemesis (vomiting of blood); this can occur due to bleeding directly from a gastric ulcer, or from damage to the esophagus from severe/continuing vomiting.

- melena (tarry, foul-smelling feces due to presence of oxidized iron from hemoglobin);

- rarely, an ulcer can lead to a gastric or duodenal perforation, which leads to acute peritonitis, extreme, stabbing pain, and requires immediate surgery.

A history of heartburn, gastroesophageal reflux disease (GERD) and use of certain forms of medication can raise the suspicion for peptic ulcer. Medicines associated with peptic ulcer include NSAIDs (non-steroid anti-inflammatory drugs) that inhibit cyclooxygenase, and most glucocorticoids (e.g. dexamethasone and prednisolone).

In people over the age of 45 with more than two weeks of the above symptoms, the odds for peptic ulceration are high enough to warrant rapid investigation by esophagogastroduodenoscopy.

The timing of the symptoms in relation to the meal may differentiate between gastric and duodenal ulcers: A gastric ulcer would give epigastric pain during the meal, as gastric acid production is increased as food enters the stomach. Symptoms of duodenal ulcers would initially be relieved by a meal, as the pyloric sphincter closes to concentrate the stomach contents, therefore acid is not reaching the duodenum. Duodenal ulcer pain would manifest mostly 2–3 hours after the meal, when the stomach begins to release digested food and acid into the duodenum.

Also, the symptoms of peptic ulcers may vary with the location of the ulcer and the person's age. Furthermore, typical ulcers tend to heal and recur and as a result the pain may occur for few days and weeks and then wane or disappear. Usually, children and the elderly do not develop any symptoms unless complications have arisen.

Burning or gnawing feeling in the stomach area lasting between 30 minutes and 3 hours commonly accompanies ulcers. This pain can be misinterpreted as hunger, indigestion or heartburn. Pain is usually caused by the ulcer but it may be aggravated by the stomach acid when it comes into contact with the ulcerated area. The pain caused by peptic ulcers can be felt anywhere from the navel up to the sternum, it may last from few minutes to several hours and it may be worse when the stomach is empty. Also, sometimes the pain may flare at night and it can commonly be temporarily relieved by eating foods that buffer stomach acid or by taking anti-acid medication. However, peptic ulcer disease symptoms may be different for every sufferer.

On rare occasions, a piece of small intestine (or rarely colon) can become trapped through the epiploic foramen into the omental bursa. The blood supply to this piece of intestine is immediately occluded and surgery is the only available treatment. This type of colic has been associated with cribbers, possibly due to changes in abdominal pressure, and in older horses, possibly because the foramen enlarges as the right lobe of the liver atrophies with age, although it has been seen in horses as young as 4 months old. Horses usually present with colic signs referable to small intestinal obstruction. During surgery, the foramen can not be enlarged due to the risk of rupture of the vena cava or aorta, which would result in fatal hemorrhage. Survival is 74–79%, and survival is consistently correlated with abdominocentesis findings prior to surgery.

Midgut volvulus occurs in people (usually babies) that are predisposed because of congenital intestinal malrotation. Segmental volvulus occurs in people of any age, usually with a predisposition because of abnormal intestinal contents (e.g. meconium ileus) or adhesions. Volvulus of the cecum, transverse colon, or sigmoid colon occurs, usually in adults, with only minor predisposing factors such as redundant (excess, inadequately supported) intestinal tissue and constipation.

Colic can be divided broadly into several categories:

1. excessive gas accumulation in the intestine (gas colic)

2. simple obstruction

3. strangulating obstruction

4. non-strangulating infarction

5. inflammation of the gastrointestinal tract (enteritis, colitis) or the peritoneum (peritonitis)

6. ulceration of the gastrointestinal mucosa

These categories can be further differentiated based on location of the lesion and underlying cause (See Types of colic).

The upper GI tract is defined as the organs involved in digestion above the ligament of Treitz and comprises the esophagus, stomach, and duodenum. Upper gastrointestinal bleeding is typically characterized by melena (black stool). Bright red blood may be seen with active, rapid bleeding.

Bleeding of the lower GI tract will typically appear as hematochezia and can vary in degree of seriousness. Slow bleeding from the ascending portion of the colon can result in partial digestion of the blood and the appearance of melena in the stool.

In about 50-70% of patients with dyspepsia, no definite organic cause can be determined. In this case, dyspepsia is referred to as non-ulcer dyspepsia and its diagnosis is established by the presence of epigastralgia for at least 6 months, in the absence of any other cause explaining the symptoms.

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.

Signs and symptoms of DIOS include a sudden onset of crampy abdominal pain, vomiting, and a palpable mass (often in the right lower quadrant) in the abdomen. The characteristic abdominal pain is typically located in the center or right lower quadrant of the abdomen. X-rays of the abdomen may reveal stool in the colon and air-fluid levels in the small intestines.

The small intestine consists of the duodenum, jejunum and ileum. Inflammation of the small intestine is called enteritis, which if localised to just part is called duodenitis, jejunitis and ileitis, respectively. Peptic ulcers are also common in the duodenum.

Chronic diseases of malabsorption may affect the small intestine, including the autoimmune coeliac disease, infective Tropical sprue, and congenital or surgical short bowel syndrome. Other rarer diseases affecting the small intestine include Curling's ulcer, blind loop syndrome, Milroy disease and Whipple's disease. Tumours of the small intestine include gastrointestinal stromal tumours, lipomas, hamartomas and carcinoid syndromes.

Diseases of the small intestine may present with symptoms such as diarrhoea, malnutrition, fatigue and weight loss. Investigations pursued may include blood tests to monitor nutrition, such as iron levels, folate and calcium, endoscopy and biopsy of the duodenum, and barium swallow. Treatments may include renutrition, and antibiotics for infections.

Bleeding of the diverticulum is most common in young children, especially in males who are less than 2 years of age. Symptoms may include bright red blood in stools (hematochezia), weakness, abdominal tenderness or pain, and even anaemia in some cases.

Hemorrhage may be caused by:

- Ectopic gastric or pancreatic mucosa:

1. Where diverticulum contains embryonic remnants of mucosa of other tissue types.

2. Secretion of gastric acid or alkaline pancreatic juice from the ectopic mucosa leads to ulceration in the adjacent ileal mucosa i.e. peptic or pancreatic ulcer.

3. Pain, bleeding or perforation of the bowel at the diverticulum may result.

4. Mechanical stimulation may also cause erosion and ulceration.

- Gastrointestinal bleeding may be self-limiting but chronic bleeding may lead to iron deficiency anaemia.

The appearance of stools may indicate the nature of the haemorrhage:

- "Tarry stools": Alteration of blood produced by slow bowel transit due to minor bleeding in upper gastrointestinal tract

- "Bright red blood stools": Brisk haemorrhage

- "Stools with blood streak": Anal fissure

- ""Currant jelly" stools": Ischaemia of the intestine leads to copious mucus production and may indicate that one part of the bowel invaginates into another intussusception.

A perforated ulcer, is a condition in which untreated ulcer can burn through the wall of the stomach (or other areas of the gastrointestinal tract), allowing digestive juices and food to leak into the abdominal cavity. Treatment generally requires immediate surgery. The ulcer is known initially as a peptic ulcer before the ulcer burns through the full thickness of the stomach or duodenal wall. A diagnosis is made by taking an erect abdominal/chest X-ray (seeking air under the diaphragm). This is in fact one of the very few occasions in modern times where surgery is undertaken to treat an ulcer. Many perforated ulcers have been attributed to the bacterium "Helicobacter pylori". The incidence of perforated ulcer is steadily declining, though there are still incidents where it occurs. Causes include smoking and nonsteroidal anti-inflammatory drugs (NSAIDs). A perforated ulcer can be grouped into a stercoral perforation which involves a number of different things that causes perforation of the intestine wall. The first symptom of a perforated peptic ulcer is usually sudden, severe, sharp pain in the abdomen. The experience is typically so intense that most people precisely recall the exact moment the pain began. The pain is typically at its maximum immediately and persists. It is characteristically made worse by any movement, and greatly intensifies with coughing or sneezing.

Inflammation of the diverticulum can mimic symptoms of appendicitis, i.e., periumbilical tenderness and intermittent crampy abdominal pain. Perforation of the inflamed diverticulum can result in peritonitis. Diverticulitis can also cause adhesions, leading to intestinal obstruction.

Diverticulitis may result from:

- Association with the mesodiverticular band attaching to the diverticulum tip where torsion has occurred, causing inflammation and ischaemia.

- Peptic ulceration resulting from ectopic gastric mucosa of the diverticulum

- Following perforation by trauma or ingested foreign material e.g. stalk of vegetable, seeds or fish/chicken bone that become lodged in Meckel's diverticulum.

- Luminal obstruction due to tumors, enterolith, foreign body, causing stasis or bacterial infection.

- Association with acute appendicitis

Diseases that affect the large intestine may affect it in whole or in part. Appendicitis is one such disease, caused by inflammation of the appendix. Generalised inflammation of the large intestine is referred to as colitis, which when caused be the bacteria "Clostridium difficile" is referred to as pseudomembranous colitis. Diverticulitis is a common cause of abdominal pain resulting from outpouchings that particularly affects the colon. Functional colonic diseases refer to disorders without a known cause, and include irritable bowel syndrome and intestinal pseudoobstruction. Constipation may result from lifestyle factors, impaction of a rigid stool in the rectum, or in neonates, Hirschprung's disease.

Diseases affecting the large intestine may cause blood to be passed with stool, may cause constipation, or may result in abdominal pain or a fever. Tests that specifically examine the function of the large intestine include barium swallows, abdominal x-rays, and colonoscopy.

DIOS is sometimes classified by the degree of obstruction as incomplete or complete DIOS.

In most cases, the clinical history is of limited use in distinguishing between organic causes and functional dyspepsia. A large systematic review of the literature was recently performed to evaluate the effectiveness of diagnosing organic dyspepsia by clinical opinion versus computer models in patients referred for upper endoscopy. The computer models were based on patient demographics, risk factors, historical items, and symptoms. The study showed that neither clinical impression nor computer models were able to adequately distinguish organic from functional disease.

In a recent study, patients with peptic ulcer disease were compared with patients with functional dyspepsia in an age and sex-matched study. Although the functional dyspepsia group reported more upper abdominal fullness, nausea, and overall greater distress and anxiety, almost all the same symptoms were seen in both groups.

Therefore, it is the clinician’s challenging task to separate patients who may have an organic disorder, and thus warrant further diagnostic testing, from patients who have functional dyspepsia, who are given empiric symptomatic treatment.The workup should be targeted to identify or rule out specific causes. Traditionally, people at high-risk have been identified by “alarm” features. However, the utility of these features in identifying the presence of upper cancer of the esophagus or stomach has been debated. A meta analysis looking at the sensitivity and specificity of alarm features found a range of 0–83% and 40–98%, respectively. However, there was high heterogeneity between studies.

The physical examination may elicit abdominal tenderness, but this finding is nonspecific. A positive Carnett sign, or focal tenderness that increases with abdominal wall contraction and palpation, suggests an etiology involving the abdominal wall musculature. Cutaneous dermatomal distribution of pain may suggest a thoracic polyradiculopathy. Thump tenderness over the right upper quadrant may suggest chronic cholecystitis.

Proximal enteritis, also known as anterior enteritis or duodenitis-proximal jejunitis (DPJ), is inflammation of the duodenum and upper jejunum. It produces a functional stasis of the affected intestine (ileus) and hypersecretion of fluid into the lumen of that intestine. This leads to large volumes of gastric reflux, dehydration, low blood pressure, and potentially shock. Although the exact cause is not yet definitively known, proximal enteritis requires considerable supportive care.