What is Jejunum?

All of the foods and liquids which we ingest possess a variety of micro and macronutrients which need to be extracted from those foods and liquids during the time they spend passing through our digestive system. After being in contact with the gastric acid of the stomach these foods and liquids get emulsified by the pancreas secretions, in the first part of the small intestine, in order for the fat to be separated and the process of necessary nutrients absorption started. After passing through the first part they enter the second part of the small intestine which is called “Jejunum”. This second part of the small intestine is approximately 2.5 meters long (out of the 6 to 7 meters of the small intestine’s total length) and it is the place where the most nutrients which are ingested through the food are absorbed. These nutrients, absorbed in the jejunum, include: amino acids, water soluble vitamins and fat while the rest of food passes further to the third and last part of the small intestine known as “ileum”.


Jejunum is the second of the three segments which, together, make up the small intestine. The beginning of the jejunum is clearly marked by the duodenojejunal flexure, encircled by the Ligament of Treitz. The end of the jejunum is not clearly identified by any anatomic structure but it is recognized through the changes which occur in the jejunum histology and anatomy during its gradual passing into the ileum after taking a long and winding path through the abdomen.

Structure of the Jejunum

structure and location of jejunum

Picture 1: Diagram of Jejunum

The jejunum is made up of a combination of different tissues. The combination of these layers is responsible for the adequate absorption and movement, through the digestive system, of all the food that needs to be digested. From the outside to the inside of the jejunum’s structure we differentiate:

  • Serosa, a layer of tissue which has the protective function. Serosa provides protection to the jejunum from any shock and trauma that could possibly be caused by rubbing with other organs located in the abdomen. This protection is provided through secretion of serous fluids which coat the jejunum in lubricating liquid.
  • Muscularis has an important role in mixing the food contained inside the jejunum and moving it through to the next part of the digestive system. This action is made possible because of the presence of the smooth muscle tissue layer within the Muscularis which is responsible for the synchronized contractions needed to perform movement through the jejunum.
  • Submucosa has a function of providing support to other tissue layers composing the jejunum. This support is provided through the blood vessels and nerves present in the submucosa.
  • Mucosa is the inner layer of the jejunum and it is the only tissue layer in direct contact with the macro and micro nutrients. This layer is composed out of many folds of epithelial tissue (a type of tissue specialized for absorption). The mucosa layer produces mucus through its goblet cells in order to coat all the surfaces and provide lubrication to all the food that is moving along the organ.
  • Jejunum receives its blood irrigation by the superior mesenteric artery and receives its innervation by the Vagus nerve (cranial nerve X) .


The jejunum’s main function is to absorb micro and macro nutrients contained within the ingested foods and to move the foods and liquids further through the digestive tube in order to complete the digestion process.

The anatomy of the jejunum is best explained with its main function in focus. Jejunum is characterized by being covered in many folds and wrinkles, which can be observed even in a microscopic view. This feature is present to ensure the adequate absorption of the chyme (partially digested food) and it enables the jejunum to absorb approximately 90% of the nutrients present in the digested food. The appropriate and synchronized muscular contraction of the smooth muscle tissue found within the jejunum is important for keeping the chyme present the amount of time needed for desired absorption to take place.

Clinical significance

Due to the fact that the most important function of the jejunum is the appropriate absorption of micro and macro nutrients, any condition affecting the normal course of this function may directly interfere with the nutrition quality of the affected subject. Any obstruction of this organ will most commonly affect its delicate absorption mechanisms, significantly, and this will likely lead to a loss of fluids. Some symptoms that can usually be present is the case of jejunum obstruction are vomiting, nausea, dehydration, absence of flatus and abdominal pain. As it is the case with any other organ, jejunum is also not exempted from a possibility of being affected by a tumor formation although this is not considered to be a frequent pathology since it only makes up approximately 1% of all gastrointestinal neoplasms and 0,3% of all tumors in the body. The neoplastic pathologies in the jejunum are classically diagnosed as a consequence of the malabsorption symptoms presentation or the signs of obstruction appearing.