Difference Between Jejunum and Ileum

Main Difference – Jejunum vs Ileum

Jejunum and ileum are the two lower parts of the small intestine. The small intestine is a component of the alimentary canal of animals where absorption of nutrients mainly takes place. In addition to absorption, mechanical digestion, as well as chemical digestion, take place in the small intestine. Duodenum is the former part of the small intestine. It receives partially digested food or chyme from the stomach. It also receives bile from the gallbladder and digestive enzymes from the pancreas. This mixture enters the jejunum and ileum. Jejunum is the middle part of the small intestine whereas ileum is the final part. The main difference between jejunum and ileum is that jejunum absorbs fully-digested carbohydrates and proteins whereas ileum absorbs the non-absorbed particles from the jejunum.

Key Areas Covered

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

Key Terms: Alimentary Canal, Duodenum, Ileum, Jejunum, Nutrients, Small Intestine, Suspensory Muscle, Vitamin B

What is Jejunum

Jejunum is the middle portion of the small intestine, which is found between duodenum and ileum. Therefore, it is the middle portion of the small intestine. In adults, jejunum is around 8 feet long. It begins at the suspensory muscle of the duodenum. Same as the other two parts of the duodenum, jejunum is also covered with mesentery, a thin membrane that keeps the small intestine warm. The components of the small intestine are shown in figure 1.

Figure 1: Components of the Small Intestine

The main function of the jejunum is to absorb nutrients. For that reason, it contains villi and microvilli on the internal wall of the jejunum. The absorption of carbohydrates, proteins, fats, minerals, and electrolytes occur in the jejunum.

What is Ileum

Ileum refers to the final portion of the small intestine, which is found between the jejunum and caecum. It is 11.5 feet long. The ileocecal valve empties the contents of the ileum into the cecum. Since ileum contains a thin, smooth muscle layer, its wall is also thinner than the walls of the other parts of the small intestine. Small collections of lymphatic tissues called Peyer’s patches can be identified in the wall of the ileum. Ileum is shown in figure 2.

Figure 2: Ileum

Ileum contains specialized receptors for the absorption of vitamin B₁₂ as well as the receptors for bile acids. These two types of receptors are arranged in the Peyer’patches. Most of the conjugated bile acids are absorbed by the ileum.

Similarities Between Jejunum and Ileum

Both jejunum and ileum are two lower parts of the small intestine.
Both jejunum and ileum are covered with the mesentery.
Both jejunum and ileum possess a large number of coils.
Both jejunum and ileum contain villi to absorb nutrients.

Definition

Jejunum: Jejunum is the middle part of the small intestine, which is located between duodenum and ileum.

Ileum: Ileum is the final part of the small intestine, which is located between jejunum and cecum.

Correspondence

Jejunum: Jejunum is found after the duodenum.

Ileum: Ileum is found after the jejunum.

Beginning

Jejunum: The suspensory muscle of the jejunum indicates the beginning of the jejunum.

Ileum: The exact beginning of the ileum cannot be identified.

Width

Jejunum: Jejunum is slightly wider (<3 cm).

Ileum: Ileum is < 2 cm in width.

Length

Jejunum: Jejunum is shorter than the ileum.

Ileum: Ileum is the lengthiest part of the small intestine.

Folds

Jejunum: The folds of the jejunum are thicker (2-3 mm).

Ileum: The folds of the ileum are less thick (1-2 mm).

Number of Folds

Jejunum: Jejunum contains a large number of folds.

Ileum: Ileum contains a less number of folds than the jejunum does.

Function

Jejunum: Jejunum absorbs fully-digested carbohydrates and proteins.

Ileum: Ileum absorbs the non-absorbed particles from the jejunum.

Mucosa-associated Lymph Tissue

Jejunum: Jejunum consists of less mucosa-associated lymph tissue.

Ileum: Ileum consists of more mucosa-associated lymph tissue.

Conclusion

Jejunum and ileum are the lower portions of the small intestine, which are mainly involved in the absorption of nutrients. Jejunum occurs after the duodenum. Ileum follows the jejunum. Jejunum absorbs most of the nutrients from the digested food. Ileum also absorbs the non-absorbed nutrients from the jejunum such as vitamin B complexes. The main difference between jejunum and ileum is the function of each part in the alimentary canal of animals.

Reference:

1. Amber J. Tresca. “What Does the Small Intestine Do?” Verywell, Available here.
2. “Ileum.” Encyclopædia Britannica, Encyclopædia Britannica, inc., 1 Apr. 2015, Available here.