Adventitia
Encyclopedia
Adventitia is the outermost connective tissue
covering of any organ
, vessel
, or other structure. It is also called the tunica adventitia or the tunica externa
.
For example, the connective tissue that surrounds an artery
is called the tunica externa
because it is considered extraneous to the artery.
To some degree, its role is complementary to that of the serosa, which also provides a layer of tissue surrounding an organ. In the abdomen, whether an organ is covered in adventitia or serosa depends upon whether it is peritoneal or retroperitoneal:
In the gastrointestinal tract
, the muscularis externa
is bounded in most cases by serosa. However, at the oral cavity, thoracic esophagus
, ascending colon, descending colon and the rectum, the muscularis externa is instead bounded by adventitia. (The muscularis externa of the duodenum
is bounded by both tissue types.) Generally, if it is a part of the digestive tract that is free to move, it is covered by serosa, and if it is relatively rigidly fixed, it is covered by adventitia.
The connective tissue of the gallbladder
is covered by adventitia where the gallbladder bounds the liver
, but by serosa for the rest of its surface.
)
Connective tissue
"Connective tissue" is a fibrous tissue. It is one of the four traditional classes of tissues . Connective Tissue is found throughout the body.In fact the whole framework of the skeleton and the different specialized connective tissues from the crown of the head to the toes determine the form of...
covering of any organ
Organ (anatomy)
In biology, an organ is a collection of tissues joined in structural unit to serve a common function. Usually there is a main tissue and sporadic tissues . The main tissue is the one that is unique for the specific organ. For example, main tissue in the heart is the myocardium, while sporadic are...
, vessel
Blood vessel
The blood vessels are the part of the circulatory system that transports blood throughout the body. There are three major types of blood vessels: the arteries, which carry the blood away from the heart; the capillaries, which enable the actual exchange of water and chemicals between the blood and...
, or other structure. It is also called the tunica adventitia or the tunica externa
Tunica externa (vessels)
The tunica externa, also known as the tunica adventitia , is the outermost layer of a blood vessel, surrounding the tunica media. It is mainly composed of collagen and is supported by external elastic lamina...
.
For example, the connective tissue that surrounds an artery
Artery
Arteries are blood vessels that carry blood away from the heart. This blood is normally oxygenated, exceptions made for the pulmonary and umbilical arteries....
is called the tunica externa
Tunica externa (vessels)
The tunica externa, also known as the tunica adventitia , is the outermost layer of a blood vessel, surrounding the tunica media. It is mainly composed of collagen and is supported by external elastic lamina...
because it is considered extraneous to the artery.
To some degree, its role is complementary to that of the serosa, which also provides a layer of tissue surrounding an organ. In the abdomen, whether an organ is covered in adventitia or serosa depends upon whether it is peritoneal or retroperitoneal:
- peritoneal organsPeritoneumThe peritoneum is the serous membrane that forms the lining of the abdominal cavity or the coelom — it covers most of the intra-abdominal organs — in amniotes and some invertebrates...
are covered in serosa (a layer of mesotheliumMesotheliumThe mesothelium is a membrane that forms the lining of several body cavities: the pleura , peritoneum and pericardium . Mesothelial tissue also surrounds the male internal reproductive organs and covers the internal reproductive organs of women...
, the visceral peritoneum) - retroperitoneal organsRetroperitoneumThe retroperitoneal space is the anatomical space in the abdominal cavity behind the peritoneum. It has no specific delineating anatomical structures...
are covered in adventitia (loose connective tissueLoose connective tissueLoose connective tissue is extremely loose. It is a category of connective tissue which includes areolar tissue, reticular tissue, and adipose tissue....
)
In the gastrointestinal tract
Gastrointestinal tract
The human gastrointestinal tract refers to the stomach and intestine, and sometimes to all the structures from the mouth to the anus. ....
, the muscularis externa
Muscularis externa
The muscular coat is a region of muscle in many organs in the vertebrate body, adjacent to the submucosa membrane...
is bounded in most cases by serosa. However, at the oral cavity, thoracic esophagus
Esophagus
The esophagus is an organ in vertebrates which consists of a muscular tube through which food passes from the pharynx to the stomach. During swallowing, food passes from the mouth through the pharynx into the esophagus and travels via peristalsis to the stomach...
, ascending colon, descending colon and the rectum, the muscularis externa is instead bounded by adventitia. (The muscularis externa of the duodenum
Duodenum
The duodenum is the first section of the small intestine in most higher vertebrates, including mammals, reptiles, and birds. In fish, the divisions of the small intestine are not as clear and the terms anterior intestine or proximal intestine may be used instead of duodenum...
is bounded by both tissue types.) Generally, if it is a part of the digestive tract that is free to move, it is covered by serosa, and if it is relatively rigidly fixed, it is covered by adventitia.
The connective tissue of the gallbladder
Gallbladder
In vertebrates the gallbladder is a small organ that aids mainly in fat digestion and concentrates bile produced by the liver. In humans the loss of the gallbladder is usually easily tolerated....
is covered by adventitia where the gallbladder bounds the liver
Liver
The liver is a vital organ present in vertebrates and some other animals. It has a wide range of functions, including detoxification, protein synthesis, and production of biochemicals necessary for digestion...
, but by serosa for the rest of its surface.
External links
- "Mammal, whole system (LM, Low)" (vermiform appendixVermiform appendix
The appendix is a blind-ended tube connected to the cecum , from which it develops embryologically. The cecum is a pouchlike structure of the colon...
)