The duodenal bulb lies directly across the neck of the pancreas. The gastroduodenal artery passes beneath the bulb where a posterior penetrating duodenal ulcer can erode into it and cause a major upper GI bleed.
The fourth portion of the duodenum is retracted up under the body of the pancreas by a suspensory ligament (of Treitz) which originates from the lateral sides of the first two lumbar vertebrae. The peritoneal reflection around the first segment of jejunum beneath the transverse colon mesentery is often mistakenly called the ligament of Treitz.
The small bowel is run from beginning to end in the course of exploration. The bowel is held by the mesentery as it is flipped from side to side, and two fingers are used to gently palpate the bowel itself for polyps or lesions. Primary tumors of the small bowel are rare. Meckelís diverticulum, a remnant of the embryonic omphalomesenteric duct, is a rare occurrence following a rule of 2ís: 2% of the population, 2 feet from iliocecal valve, and 2 types of tissue (gastric mucosa and pancreatic rests). A Meckelís may present with inflammation, bleeding (from the normal mucosa adjacent to the neck of the diverticulum caused by acid production within the diverticulum) or internal hernia due to persistent band connected to the umbilicus.