Difference Between Duodenum and Jejunum

Main Difference – Duodenum vs Jejunum

Duodenum and jejunum are the first two segments of the small intestine. The last part of the small intestine is the ileum. The three segments differ in their histology of the internal wall. The entire wall of the small intestine is composed of folds. Duodenum is a C-shaped structure at the beginning of the small intestine. Jejunum follows the duodenum. The main difference between duodenum and jejunum is that duodenum comprises submucosal Brunner’s glands whereas jejunum does not comprise Brunner’s glands.

Key Areas Covered

1. What is Duodenum
      – Definition, Anatomy, Function
2. What is Jejunum
      – Definition, Anatomy, Function
3. What are the Similarities Between Duodenum and Jejunum
      – Outline of Common Features
4. What is the Difference Between Duodenum and Jejunum
      – Comparison of Key Differences

Key Terms: Brunner’s Gland, Chyme, Duodenum, Ileum, Jejunum, Microvilli, Small Intestine, Villi

What is Duodenum

Duodenum is the first part of the small intestine. The four segments of the duodenum are superior, descending, horizontal, and ascending segments. The superior segment is about 5 cm long. It is connected to the undersurface of the liver. The descending segment is about 10 cm long. It is also called the C loop. The head of the pancreas lies in the concavity of the C loop. The horizontal segment is about 7.5 cm long. The ascending segment is about 2.5 cm long. The anatomy of the duodenum is shown in figure 1.

Figure 1: Duodenum

The most prominent feature of the duodenum is the submucosal Brunner’s glands. These glands secrete alkaline mucus to neutralize the chyme. Chyme is a mixture of gastric juice and food, which is acidic. Villi of the duodenum are flat. Duodenum consists of fewer plicae. Plicae are the folds found throughout the small intestine. Liver and gallbladder release bile to the duodenum. The pancreas secretes digestive enzymes such as proteases, amylase, and lipase to digest proteins, carbohydrates, and lipids in the food, respectively.

What is Jejunum

Jejunum is a segment of the small intestine, which lies between duodenum and ileum. It is the middle portion of the small intestine and absorbs most of the nutrients from the digested food. Jejunum is separated from the duodenum by the suspensory muscle. But, the separation of the jejunum from the ileum lacks an anatomical landmark. The three segments of the small intestine, duodenum, jejunum, and ileum are shown in figure 2.

Figure 2: Segments of the Small Intestine

Folds of the jejunum increases the surface area, enhancing the absorption. The internal wall of the jejunum contains villi, which also increase the surface area. The cell lining of the internal wall contains microscopic folds called microvilli as well. The absorption of carbohydrates, proteins, fats, minerals, and electrolytes occur in the jejunum.

Similarities Between Duodenum and Jejunum

Both duodenum and jejunum are two segments of the small intestine.
Both duodenum and jejunum are composed of folds.
Both duodenum and jejunum contain villi.
Both duodenum and jejunum are lined by the simple columnar epithelium.
Both chemical digestion and mechanical digestion of food occur in duodenum and jejunum.

Definition

Duodenum: Duodenum is the first part of the small intestine immediately after the stomach.

Jejunum: Jejunum is the segment of the small intestine between the duodenum and ileum.

Consequence

Duodenum: Duodenum is the first segment of the small intestine.

Jejunum: Jejunum is the second segment of the small intestine.

Brunner’s Glands

Duodenum: Duodenum consists of Brunner’s glands.

Jejunum: Jejunum lacks Brunner’s glands.

Villi

Duodenum: Villi are flatter in the duodenum.

Jejunum: Villi are longer in the jejunum.

Plicae

Duodenum: Plicae are less frequent in the duodenum.

Jejunum: Plicae are more common in the jejunum.

Goblet Cells

Duodenum: Duodenum consists of a less number of goblet cells.

Jejunum: Jejunum consists of a large number of goblet cells.

Length

Duodenum: Duodenum is the shortest segment of the small intestine.

Jejunum: Jejunum is the longest segment of the small intestine.

Function

Duodenum: Secretion of digestive enzymes and bile occurs in the duodenum.

Jejunum: Absorption of carbohydrates and proteins occurs in the jejunum.

Conclusion

Duodenum and jejunum are the first two segments of the small intestine. Duodenum is a C-shaped structure. Jejunum is the middle segment of the small intestine. Digestive enzymes are secreted into the lumen of the duodenum. Jejunum absorbs most of the nutrients from the digested food. The main difference between duodenum and jejunum is the function of each segment in the alimentary canal.

Reference:

1. “Small Intestine Anatomy.” Overview, Gross Anatomy, Microscopic Anatomy, 3 Nov. 2016, Available here.
2. “Jejunum.” InnerBody, Available here.

Image Courtesy:

1. “Duodenumanatomy” By Luke Guthmann – Own work (CC BY-SA 3.0) via Commons Wikimedia
2. “Digestive tract diagram” By Thoind83 – Own work (CC BY-SA 4.0) via Commons Wikimedia