[Biology Class Notes] on Duodenum Pdf

Digestion is one of the basic activities of the human body. An important role in the process is played by the duodenum. The duodenum definition can be stated as the first part of the small intestine which is a 10-12 inch hollow tube. It is closely situated to the head of the pancreas and is fixed to the pylorus of the stomach The term “ duodenum” in Latin means “twelve fingers wide”. Here, we will learn the duodenum meaning, parts of duodenum, duodenum anatomy, histology, blood supply, and innervation. We will also look into the functions of this C- shaped tube in this article.

Anatomy of The Duodenum

The Duodenum, which marks the beginning of the small intestine is a 25-30 cm long hollow, C-shaped tube. It is located in the upper abdomen part at the level of L1-L3, lying adjacent to the stomach. The parts of duodenum are discussed below. 

• Superior Part – It is the first part and lies inside the peritoneum lies. This part has a proximal enlarged part known as the duodenal bulb. The hepatoduodenal ligament connects it to the liver. The superior duodenal flexure marks the end of the first part of the duodenum. 

• Descending Part – Also known as the second part of duodenum. The Ampulla of Vater contains secretions from the common bile duct and the hepatopancreatic duct empties in this part. The inferior duodenal flexure marks the transition from the descending part to the horizontal part of the duodenum.

• Horizontal Part – The third part of the duodenum runs ventrally from the abdominal aorta and the inferior vena cava.  

• Ascending Part – This part runs cranially along the vertebral column and joins the jejunum at the duodenojejunal flexure. The ligament of Treitz suspends the descending part against the abdominal wall. 

Histology of Duodenum

The histology of the duodenum is quite similar to that of the other hollow gastrointestinal tracts. Just like others, duodenum also has  mucosa ,submucosa and the muscularis coverings. The mucosal layer is composed of lamina epithelialis, lamina propria, and lamina muscularis. The submucosal layer contains loose connective tissue, blood vessels, and the Meissner’s plexus. The muscularis layer comprises inner circular and outer longitudinal muscles with the Aurbach’s plexus lying in between them. 

The Brunner’s gland is a characteristic feature of the submucosa of the duodenum. The Brunner’s gland secretes mucus which contains various bicarbonates. This secretion neutralizes the acidic effect of the gastric juices. The duodenum is rich in enterocytes, goblet cells, and endocrine cells. The microvilli contain the Crypts of Lieberkuhn and Paneth cells. 

Blood Supply and Innervation of Duodenum 

The anterior and posterior superior pancreaticoduodenal arteries and the inferior pancreaticoduodenal artery are responsible for the duodenal blood supply. The corresponding veins take care of the venous system of the duodenum.

The nerves of the Coeliac plexus are responsible for the sympathetic innervation of the duodenum. The Vagus nerve carries out the parasympathetic innervation.

Functions of Duodenum 

The duodenum is crucial to the digestion in the small intestine in a lot of ways. The duodenum neutralizes the acidic gastric juice by producing alkaline secrets. It is also responsible for the proper mixing of bile and the various pancreatic enzymes. Apart from these the main function of the duodenum includes absorption of nutrients and mechanical processing of chyme. Absorption of water, electrolytes, and other nutrients such as Vitamin A and B1, fatty acids, and calcium take place in the duodenum. The chyme is broken down by the bodily fluids in the duodenum for easy absorption of nutrients after it passes through the Ampulla of Vater which stores the secretory juices from the common bile duct and the hepatopancreatic duct.

Did You Know?