Main Difference – Serosa vs Adventitia
Serosa and adventitia are two membranes that cover the external surfaces of internal organs in the body. Serosa is made up of two mesothelial layers. In between the two layers, a connective tissue layer can be observed. Adventitia is made up of loose connective tissue. The main difference between serosa and adventitia is that serosa covers the organs in the body cavities whereas adventitia attaches the organ to the surrounding tissues. The outermost layer of the serosa secretes the serous fluid, which lubricates the organs in the serous cavity. Adventitia provides support to the internal structures. Based on the location, both serosa and adventitia have specific names.
Key Areas Covered
1. What is Serosa
– Definition, Structure, Role
2. What is Adventitia
– Definition, Structure, Role
3. What are the Similarities Between Serosa and Adventitia
– Outline of Common Features
4. What is the Difference Between Serosa and Adventitia
– Comparison of Key Differences
Key Terms: Adventitia, Connective Tissue, Mesothelial Layers, Organs (viscera), Serosa, Serous Cavity, Serous Fluid
What is Serosa
Serosa refers to the outermost layer of the visceral layers of the abdomen and thorax. It covers the body cavities that do not directly open to the outside. The serosa also covers the organs in that cavity. The cavity is then referred to as the serous cavity. The serosa is made up of a connective tissue layer covered by two mesothelial layers. The connective tissue layer holds the two mesothelial layers together. It also contains the blood vessels and nerves. The inner mesothelial layer is referred to as the visceral membrane whereas the outermost layer is called the parietal layer. The outermost parietal layer secretes the serous fluid. This fluid lubricates the structures in the serous cavity, reducing the abrasion and friction in the thoracic and abdomen cavity. The serosa that surrounds the stomach is shown in figure 1.
Figure 1: Serosa of the Stomach
Based on the anatomical structures covered, each serosa has a specific name. For example, the serosa that covers the thoracic cavity and the lungs is called the pleura. The pericardium is the serous membrane which covers the heart and the mediastinum. The peritoneum is the serous membrane which covers the abdominopelvic cavity and the viscera.
What is Adventitia
Adventitia refers to the outermost of the connective tissue layer that covers a blood vessel, organ or other structure. The adventitia is made up of loose connective tissue. It binds the blood vessels and organs to the surrounding structures such as body wall to provide support. The adventitia is also called the tunica externa or tunica adventitia. Tunica externa is a type of adventitia that covers the blood vessels. The adventitia of a blood vessel is shown in figure 2.
Figure 2: Tunica Adventitia
The muscular layer of the gastrointestinal tract is often bound with the serosa. But, in the oral cavity, thoracic esophagus, ascending and descending colon, and rectum, the muscular layer is bound with the adventitia. Hence, the freely-moving structures of the gastrointestinal tract are bound to the serosa. On the other hand, the fixed and rigid structures are bound with the adventitia.
Similarities Between Serosa and Adventitia
- Both serosa and adventitia are membranes that cover the external surfaces of the internal organs.
- Connective tissues are a component of both serosa and adventitia.
- Based on the anatomical structures covered by each membrane, both serosa and adventitia have different names.
Difference Between Serosa and Adventitia
Definition
Serosa: Serosa is the outermost layer of the visceral layers of the abdomen and thorax.
Adventitia: Adventitia is the outermost connective tissue layer that covers a blood vessel, organ or other structure.
Significance
Serosa: Serosa covers the external surfaces of the organs that are faced with the body cavities.
Adventitia: Adventitia attaches the organs to the surrounding tissues.
Types of Organs
Serosa: The serosa covers the intraperitoneal organs.
Adventitia: The adventitia covers the retroperitoneal organs.
Made up of
Serosa: Serosa is made up of two mesothelial layers held together by a connective tissue layer.
Adventitia: Adventitia is made up of a connective tissue layer.
Secretions
Serosa: The mesothelial layers of the serosa secrete the serous fluid.
Adventitia: The cells of the adventitia do not secrete any fluid.
Specific Names
Serosa: Pleura, pericardium, and peritoneum are the specific names of the serosa.
Adventitia: Tunica adventitia and tunica externa are the specific names of the adventitia.
Function
Serosa: The main function of the serosa is to lubricate the internal structures of the body.
Adventitia: The main function of adventitia is to hold the internal structures together.
Visceral Peritoneum
Serosa: The outermost layer of the serosa is covered by the visceral peritoneum.
Adventitia: The adventitia is not covered by the visceral peritoneum.
Conclusion
Serosa and adventitia are two membranous structures that cover the external surface of the internal organs. Serosa covers the organs that freely move inside a cavity. On the other hand, adventitia covers the organs that should be bound with the surrounding structures for support. Serosa secretes the serous fluid, which lubricates the cavity. The main difference between serosa and adventitia is the structure and function of the two membranes.
Reference:
1. “Serosa – National Library of Medicine – PubMed Health.” National Center for Biotechnology Information, U.S. National Library of Medicine, Available here.
2. “Adventitia.” Wikipedia, Wikimedia Foundation, 23 Nov. 2017, Available here.
Image Courtesy:
1. “Illu stomach2” By NIH / National Cancer Institute – (Public Domain) via Commons Wikimedia
2. “Microscopic anatomy of an artery en” By en:User:Stijn Ghesquiere, user:Drsrisenthil – Complete Recreation and colorization based on the diagram originally produced by at File:Anatomy artery.png (CC BY-SA 4.0) via Commons Wikimedia
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