What is the Difference Between Ileum and Ilium

The main difference between ileum and ilium is that ileum, a hollow, muscular structure, is a part of the small intestine, but ilium is a bone and is a part of the pelvic girdle. Furthermore, the ileum is the last and longest division of the small intestine; the part between the jejunum and large intestine, while ilium is the upper and widest of the three bones, which make up each side of the hipbone and pelvis. Moreover, ileum absorbs nutrients in the digested food through villi, while ilium provides protection and structural support to the organs in the lower abdomen.  

In brief, ileum and ilium are two anatomical structures that occur in the lower part of the torso of most of the vertebrates. However, although their location of the body is similar, they perform totally different functions. 

Key Areas Covered 

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

Key Terms 

Hip Bone, Ileum, Ilium, Pelvis, Small Intestine

What is Ileum 

The ileum is the third or the final portion of the small intestine. Also, it is the longest. Generally, it is 2-4 m long in humans.  

Anatomy 

The wall of the ileum contains four layers; mucous membrane, submucosa, external muscular layer, and serosa. Further to this, the mucous membrane has three layers; epithelium with microvilli, lamina propria with loose connective tissue, and a thin layer of smooth muscles. Usually, the smooth muscle layer of the ileum is thin with respect to the other parts of the small intestine. Therefore, the wall of the ileum is also comparatively thinner. On the other hand, the lamina propria contains small collections of lymphatic tissues called Peyer’s patches in its wall. Meanwhile, the submucosa contains dense irregular connective tissue with large blood vessels and components of the enteric nervous system. Besides, there are two smooth muscle layers; the external smooth muscle layer is arranged in circular bundles in the inner layer and in longitudinal bundles, in the outer layer. Moreover, the serosa represents the visceral peritoneum and it is continuous with the mesentery. 

Figure 1: Wall of the Ileum

Function 

Ileum occurs between the jejunum, which is the second portion of the small intestine, and caecum, which is the initial portion of the large intestine. Although there is no line of demarcation between the jejunum and ileum, the difference in tissues helps to distinguish between them. Of these, the mesentery of the ileum contains fatter. Also, the diameter of the lumen of the ileum is large while its lumen contains small circular folds.

Figure 2: Small Intestine Anatomy

Therefore, the main function of ileum is to absorb nutrients not absorbed by the jejunum through its villi in the lumen. In addition to that, it absorbs bile salts and vitamin B₁₂. Ultimately, the ileocecal valve empties the contents of the ileum into the cecum.  

What is Ilium 

Ilium is the uppermost and the largest part of the hip bone. Importantly, it is one of the three bones, which take part in the formation of the hip bone, while the other two are ischium and pubis. Also, a pair of hip bones take part in the formation of the pelvis, which provides structural support to the lower part of the torso. 

Structure  

Structurally, the top surface of the ilium is a curved line while its external surface margins the acetabulum. Also, there are two divisible parts of the ilium; the body and the wing. The body of the ilium forms less than two-fifths of the acetabulum. Additionally, it forms part of the acetabular fossa. Other than that, the inner surface of the body forms the lesser pelvis. Meanwhile, the wing is the largely expanded portion of the ilium, binding to the greater pelvis laterally. 

Figure 3: Pelvis

Function 

In general, the main function of the ilium is to provide structural support and protection to the internal organs in the lower part of the torso, including the reproductive organs, bladder, and the rectum. Also, as it is a part of the hip bone, ilium aid in bearing body weight when sitting and standing. Apart from that, it helps to transfer body weight to the lower limbs through acetabulum.  

Similarities Between Ileum and Ilium  

• Ileum and ilium are two types of anatomical structures, which occur in the lower part of the torso.  
• They belong to completely different organ systems and therefore, they perform different functions in the body. 

Difference Between Ileum and Ilium 

Definition 

Ileum refers to the third portion of the small intestine between the jejunum and the caecum, but ilium refers to the large broad bone forming the upper part of each half of the pelvis.  

Occurrence 

Ileum occurs in higher vertebrates including mammals, reptiles, and birds, but ilium occurs in most vertebrates except snakes.  

Structure 

The ileum is a muscular tube around 2-4 m long in humans, while ilium is the largest part of the hip bone. 

Structural Significance 

The ileum is the last and longest division of the small intestine; the part between the jejunum and large intestine. Meanwhile, the ilium is the upper and widest of the three bones, which make up each side of the hipbone and pelvis. 

Function 

Ileum absorbs vitamin B12, bile salts, and nutrients in the digested food through villi, while ilium provides protection and structural support to the organs in the lower abdomen.  

Conclusion 

The ileum is the third and the last part of the small intestine of higher vertebrates. Also, it is the longest portion of the small intestine. Furthermore, it contains villi in its lumen responsible for increasing the surface area for absorbing nutrients, vitamin B12, and bile salts. In contrast, the ilium is the uppermost and largest part of the hip bone. And, it occurs in most vertebrates except snakes. Besides, its main function is to protect and provide structural support to the organs in the lower part of the torso. Additionally, its body takes part in the formation of the acetabulum. Hence, the main difference between ileum and ilium is their anatomy and function. 

References:

1. Bengochea, Kim. “Ileum.” Kenhub, Kenhub, 4 Feb. 2020, Available Here.
2. Fidoe, Sophie. “The Hip Bone.” TeachMeAnatomy, Available Here.

Image Courtesy:

1. “Gut wall” By Auawise at English Wikipedia (CC BY 3.0) via Commons Wikimedia   
2. “Illu small intestine” (Public Domain) via Commons Wikimedia   
3. “Pelvis diagram” By Je at uwo at English Wikipedia (Public Domain) via Commons Wikimedia