Corpus: Jejunum

The jejunum is the middle section of the small intestine, located between the duodenum and the ileum. It measures about 2 to 2.5 meters in length. The inner surface of the jejunum is marked by tall circular folds known as Kerckring folds (plicae circulares) and glandular indentations known as crypts of Lieberkühn.

The boundary between the jejunum and the ileum (the last part of the small intestine) is not clearly defined.

Like all hollow organs, the jejunum has an inner lining called the mucous membrane. Surrounding this is a double layer of smooth muscle, and the outermost layer is the serosa, which is part of the peritoneum. The jejunum is suspended from the back wall of the abdomen by a fold of tissue called the mesentery—more specifically, the mesojejunum.

The name "jejunum," meaning "empty," comes from the observation that this section is often found empty during autopsy.

The tissue structure of the jejunum is similar to that of the rest of the digestive tract. Like other parts of the small intestine, it has circular folds, finger-like projections (villi), crypts, and tiny extensions (microvilli), all of which increase the surface area for absorption.

The surface layer is a single row of tall, column-shaped cells called enterocytes, which have their nuclei located near the base and a dense brush border on top. Scattered among them are mucus-producing goblet cells, which appear bright blue when stained with Azan dye.

Unlike the duodenum, the jejunum does not contain Brunner’s glands in the submucosa. It also lacks the large lymphoid nodules called Peyer’s patches that are found in the ileum. However, solitary lymphoid follicles may occasionally be present.

Arterial blood reaches the jejunum through branches of the superior mesenteric artery known as the jejunal arteries. Venous blood is carried away by the jejunal veins, which drain into the superior mesenteric vein.