The duodenal mucosa is the lining of the section of small intestine that leads from the stomach. This part of the gut is known as the duodenum, and the mucosa which lines it is made up of simple columnar epithelium. Simple columnar epithelium consists of one layer of tall, roughly rectangular cells. In the duodenal mucosa, some of these cells are concerned with absorbing food from the gut, while others produce alkaline mucus or hormones that affect digestion. The duodenal mucosa can be affected by peptic ulcer disease, where a raw patch appears in the lining, sometimes causing gnawing abdominal pain.
In humans, the duodenum runs from the stomach to the jejunum, with the ileum making up the last section of the small intestine. The mucosal lining throughout the small intestine shares certain similarities. It is arranged into folds, or pleats, known as plicae, which help increase the total surface area.
Like the rest of the small intestine, the surface area of the duodenal mucosa is also increased by the presence of numerous small projections, shaped like tiny fingers and known as villi. These, in turn, are covered in even tinier finger-shaped protrusions called microvilli. It is important for the surface area of the small intestine to be as great as possible to maximize the possible amount of absorption. Immediately below the mucosal lining cells, a layer called the lamina propria contains a network of blood vessels which take absorbed nutrients into the circulation. Most of the body's iron absorption takes place across the duodenal mucosa.
Small tubular pits known as crypts lie in between the villi, and these are sometimes referred to as the crypts of Lieberkühn. At the bottom of the crypts are specialized cells, some of which secrete enzymes. Other cells secrete hormones such as serotonin, which affects gut movement. Stem cells are also found inside crypts, and they continually divide and mature into the different types of intestinal lining cells to replace them as they are sloughed off. The immune system cells known as lymphocytes may also be present in crypts.
Duodenal mucosa differs from mucosa in the jejunum and ileum in that it contains relatively fewer plicae and the villi are flatter in appearance. In common with the lining of the rest of the small intestine, the duodenal mucosa contains cells known as goblet cells. These are dotted amongst the absorptive cells and they secrete mucus. This helps protect the intestinal lining and lubricates the gut so food passes along more easily.