A Meckels diverticulum, a true congenital diverticulum, is a slight bulge in the small intestine present at birth and a vestigial remnant of the omphalomesenteric duct (also called the vitelline duct or yolk stalk). It is the most common malformation of the gastrointestinal tract and is present in approximately 2% of the population, with males more frequently experiencing symptoms. Meckels diverticulum was first explained by Fabricius Hildanus in the sixteenth century and later named after Johann Friedrich Meckel, who described the embryological origin of this type of diverticulum in 1809. Signs and symptoms
The majority of people with a Meckels diverticulum are asymptomatic. An asymptomatic Meckels diverticulum is called a silent Meckels diverticulum. If symptoms do occur, they typically appear before the age of two years. The most common presenting symptom is painless rectal bleeding such as melaena-like black offensive stools, followed by intestinal obstruction, volvulus and intussusception. Occasionally, Meckels diverticulitis may present with all the features of acute appendicitis. Also, severe pain in the epigastric region is experienced by the person along with bloating in the epigastric and umbilical regions. At times, the symptoms are so painful that they may cause sleepless nights with acute pain felt in the foregut region, specifically in the epigastric and umbilical regions. In some cases, bleeding occurs without warning and may stop spontaneously. The symptoms can be extremely painful, often mistaken as just stomach pain resulting from not eating or constipation.
Biological models
Biological models explaining the origins of kleptomania have been based mostly on pharmacotherapy treatment studies that used selective serotonin reuptake inhibitors (SSRIs), mood stabilizers, and opioid receptor antagonists.Some studies using SSRIs have observed that opioid antagonists appear to reduce the urge to steal and mute the "rush" typically experienced immediately after stealing by some subjects with kleptomania. This would suggest that poor regulation of serotonin, dopamine, and/or natural opioids within the brain are to blame for kleptomania, linking it with impulse control and affective disorders.An alternative explanation too based on opioid antagonist studies states that kleptomania is similar to the "self-medication" model, in which stealing stimulates the persons natural opioid system. "The opioid release soothes the patients, treats their sadness, or reduces their anxiety. Thus, stealing is a mechanism to relieve oneself from a chronic state of hyperarousal, perhaps produced by prior stressful or traumatic events, and thereby modulate affective states. ": 354

Diagnosis
Disagreement surrounds the method by which kleptomania is considered and diagnosed. On one hand, some researchers believe that kleptomania is merely theft and dispute the suggestion that there are psychological mechanisms involved, while others observe kleptomania as part of a substance-related addiction. Yet others categorize kleptomania as a variation of an impulse control disorder, such as obsessive-compulsive disorder or eating disorders.