What is the Difference Between Omentum and Mesentery

The main difference between omentum and mesentery is that omentum is a fatty blanket hanging down in front of all the intestines, whereas mesentery is the supporting tissue to both small and large intestines. Furthermore, omentum originates from the visceral peritoneum while mesentery originates from the parietal peritoneum. Moreover, the two main types of omentum are the greater and the lesser omentum while the two types of the mesentery are the dorsal and ventral mesentery. 

Omentum and mesentery are two tissues that originate from the peritoneum of the abdominal cavity. Generally, they deposit fat. 

Key Areas Covered 

1. What is Omentum
     – Definition, Structure, Importance
2. What is Mesentery
     – Definition, Structure, Importance
3. What are the Similarities Between Omentum and Mesentery
      – Outline of Common Features
4. What is the Difference Between Omentum and Mesentery
      – Comparison of Key Differences

Key Terms 

Greater Omentum, Lesser Omentum, Mesentery, Parietal Peritoneum, Visceral Peritoneum

What is Omentum 

Omentum is the tissue derived from the visceral peritoneum. Generally, there are two main types of omentums as the greater omentum and the lesser omentum. The greater omentum forms a large apron-like fold, hanging down from the stomach. It also has two peritoneal folds. Moreover, it extends from the greater curvature of the stomach, passing in front of the small intestine. At the transverse colon, it divides into two and ascends to the transverse colon. Then, it reaches to the posterior wall of the abdomen. Since the greater omentum floats on the small intestine, epiploic is an anatomical term used to describe omental structures. 

Figure 1: The Greater Omentum

The lesser omentum is smaller than the greater omentum. Typically, it hangs down from the liver and extends from the lesser curvature. Furthermore, omentum physically separates organs in the abdomen. Therefore, it serves as a physical barrier against the spread of infections and wounds. Moreover, it contains a variable amount of fat. Thus, it deposits fat. Additionally, it contains the milky spots of macrophages, contributing to immunity. 

What is Mesentery 

The mesentery is another tissue derived from the parietal peritoneum. In general, its main function is to attach small intestines to the posterior abdominal wall. It deposits fat and support blood vessels, lymphatic vessels, and nerves, running through it. However, the mesentery arises from the root of the mesentery or the mesenteric root. The mesenteric root connects to the structures in front of the vertebral column. Furthermore, it is a narrow structure, which is 15 cm long and 20 cm in width.

Figure 2: Development of Mesentery

Moreover, there are six flexures of the mesentery in the gastrointestinal tract. They are the mesentery of the small intestine, right mesocolon, transverse mesocolon, left mesocolon, mesosigmoid, and mesorectum. The mesentery of the small intestine connects the jejunum and ileum to the posterior wall of the abdomen. Furthermore, the right and the left mesocolon are the flattened structures against the posterior abdominal wall. On the other hand, transverse mesocolon is a mobile structure which lies between the colic flexures. However, mesosigmoid is also a mobile structure. Furthermore, mesorectum assists the attachment of the rectum through the pelvis. 

Similarities Between Omentum and Mesentery 

• Omentum and mesentery are two types of tissues derived from the double folded peritoneum of the abdomen. 
• Both are connective tissues.
• Moreover, they store fat, support blood vessels, lymph vessels, and nerves in the abdomen. 
• Also, both are attached to the posterior abdominal wall. 

Difference Between Omentum and Mesentery 

Definition 

Omentum refers to a fold of peritoneum, connecting the stomach with other abdominal organs while mesentery refers to a fold of the peritoneum, which attaches the stomach, small intestine, pancreas, spleen, and other organs to the posterior wall of the abdomen. Thus, this is the main difference between omentum and mesentery.

Derived from 

While omentum originates from the visceral peritoneum, mesentery originates from the parietal peritoneum. 

Function 

Furthermore, omentum physically separates the organs inside the abdomen, limiting the spread of infections and wounds, while mesentery attaches the small intestine and other organs into the posterior abdominal wall. Hence, this is the functional difference between omentum and mesentery.

Large Intestine 

Also, another difference between omentum and mesentery is that omentum supports the transverse colon while mesentery provides support to all parts of the colon. 

Types 

The two main types of omentum are the greater and the lesser omentum while the six types of the mesentery are mesentery of the small intestine, right mesocolon, transverse mesocolon, left mesocolon, mesosigmoid, and mesorectum.  

Conclusion 

Omentum is a tissue derived from the visceral peritoneum, hanging down from the stomach. Moreover, it extends from the great curvature of the stomach and passes in front of the small intestine. Additionally, it ascends to the transverse colon and then, attaches to the posterior wall of the abdomen. However, the main function of omentum is to separate the organs inside the abdomen physically. On the other hand, the mesentery is another tissue derived from the parietal peritoneum, attaching the small intestines to the posterior wall of the abdomen. Hence, the main function of the mesentery is to support the small intestine and other organs inside the abdomen. Therefore, the main difference between omentum and mesentery is their origin, structure, and function. 

References:

1. O’Neill, Katie. “The Peritoneum.” TeachMeAnatomy, 1 Oct. 2018, Available Here.
2. Joseph, Reshma. “The Mesentery.” TeachMeAnatomy, 30 Jan. 2018, Available Here.

Image Courtesy:

1. “Sobo 1909 564” By Dr. Johannes Sobotta – Atlas and Text-book of Human Anatomy Volume III Vascular System, Lymphatic system, Nervous system and Sense Organs (Public Domain) via Commons Wikimedia      
2. “Gray987” By Henry Vandyke Carter – Henry Gray (1918) Anatomy of the Human Body Bartleby.com: Gray’s Anatomy, Plate 987 (Public Domain) via Commons Wikimedia