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The junction between the foregut and midgut occurs directly below the major duodenal papilla. [3]: 274 The major duodenal papilla projects less than a centimetre into the lumen of the duodenum. [4] It appears rounded and is often covered by a fold on the uppermost side of the papilla; that is, the side which receives contents from the stomach. [4]
The minor duodenal papilla is contained within the second part of the duodenum. It is situated 2 cm proximal to the major duodenal papilla, and thus 5–8 cm from the opening of the pylorus. The gastroduodenal artery lies posterior. [1]
The common duct then opens medially into the descending part of the duodenum at the major duodenal papilla. The common duct usually measures 2-10mm in length. [1] The ampulla of Vater is an important landmark halfway along the second part of the duodenum marking the transition from foregut to midgut. [citation needed]
Upon dissection, the duodenum may appear to be a unified organ, but it is divided into four segments based on function, location, and internal anatomy. The four segments of the duodenum are as follows (starting at the stomach, and moving toward the jejunum): bulb , descending, horizontal, and ascending.
The sphincter regulates the secretion of pancreatic juice and bile into the duodenum. [3] It also prevents reflux of duodenal contents into the ampulla of Vater. [4] By preventing reflux of the contents of the duodenum, the sphincter of Oddi prevents the accumulation of particulate matter and sludge in the bile ducts, reducing the risk of cholangitis.
Barium X-ray examinations are useful tools for the study of appearance and function of the parts of the gastrointestinal tract. They are used to diagnose and monitor esophageal reflux, dysphagia, hiatus hernia, strictures, diverticula, pyloric stenosis, gastritis, enteritis, volvulus, varices, ulcers, tumors, and gastrointestinal dysmotility, as well as to detect foreign bodies.
The horizontal part of the duodenum slopes upwards to the left of the vertical midline, following which the vertical ascending part of the duodenum reaches the transpyloric plane. [6] It ends in the duodenojejunal junction, which lies approximately 2.5 cm to the left of the midline and just below the transpyloric plane. [1]
The microvilli create a brush border that increases the area for absorption. In the ileum there are occasionally Peyer's patches in the lamina propria. Brunner's glands are found in the duodenum but not in other parts of the small intestine. [1] In the colon, epithelium is simple columnar and without villi.