The duodenum is the first section of the small intestine[3] in most higher vertebrates, including mammals, reptiles, and birds.
In human beings, the duodenum is a hollow jointed tube about 25–38 centimetres (10–15 inches) long connecting the stomach to the middle part of the small intestine.
[8] In humans, the duodenum is a C-shaped hollow jointed tube, 25–38 centimetres (10–15 inches) in length, lying adjacent to the stomach (and connecting it to the small intestine).
The duodenal bulb is a remnant of the mesoduodenum, a mesentery that suspends the organ from the posterior abdominal wall in fetal life.
The fourth part of the duodenum is at the vertebral level L3, and may pass directly on top, or slightly to the left, of the aorta.
The duodenum's close anatomical association with the pancreas creates differences in function based on the position and orientation of the organs.
Secretin and cholecystokinin are released from cells in the duodenal epithelium in response to acidic and fatty stimuli present there when the pylorus opens and emits gastric chyme into the duodenum for further digestion.
[18] As the first part of the small intestine, the duodenum is the initial site of nutrient absorption in the gastrointestinal tract.
The duodenum senses nutrient intake and composition, and signals to the liver, pancreas, adipose tissue and brain[19] through the direct and indirect[20] release of several key hormones and signaling molecules, including the incretin peptides Glucose-dependent insulinotropic polypeptide (GIP) and Glucagon-like peptide-1 (GLP-1),[20] as well as Cholecystokinin (CCK) and Secretin.
The duodenum also signals to the brain directly via vagal afferents enabling neural control over food intake and glycemia.
[22] Incretin peptides, principally GLP-1 and GIP, regulate islet hormone secretion, glucose concentrations, lipid metabolism, gut motility, appetite and body weight, and immune function.
These bacteria, through a number of mechanisms, erode the protective mucosa of the duodenum, predisposing it to damage from gastric acids.
[25] The British Society of Gastroenterology guidelines specify that a duodenal biopsy is required for the diagnosis of adult celiac disease.
[28] A western diet induces duodenal mucosal hyperplasia and dysfunction that underlie insulin resistance, type 2 diabetes and obesity.
[44] The name duodenum is Medieval Latin, short for intestīnum duodēnum digitōrum, meaning intestine of twelve finger-widths (in length), genitive pl.
Coined by Gerard of Cremona (d. 1187) in his Latin translation of "Canon Avicennae," "اثنا عشر" itself a loan-translation of Greek dodekadaktylon, literally "twelve fingers long."
The intestine part was so called by the Greek physician Herophilus (c. 335–280 BCE) for its length, about equal to the breadth of 12 fingers.