Serous membrane

Serous membrane
Stomach. (Serosa is labeled at far right, and is colored yellow.)
Details
Precursor	Mesoderm
Identifiers
Latin	tunica serosa
MeSH	D012704
FMA	9581
Anatomical terminology

Serous membrane lines the pericardial cavity and reflects back to cover the heart—much the same way that an underinflated balloon would form two layers surrounding a fist.

Theserous membrane(orserosa) is a smoothtissue membraneofmesotheliumlining the contents and inner walls ofbody cavities,which secreteserous fluidto allowlubricatedsliding movementsbetween opposing surfaces. The serous membrane that coversinternal organsis calledvisceral,while the one that covers the cavity wall is calledparietal.For instance theparietal peritoneumis attached to theabdominal walland thepelvic walls.Thevisceral peritoneumis wrapped around the visceral organs. For the heart, the layers of the serous membrane are called parietal and visceralpericardium.For the lungs they are called parietal and visceral pleura. The visceral serosa of theuterusis called theperimetrium.Thepotential spacebetween two opposing serosal surfaces is mostly empty except for the small amount of serous fluid.

The Latin anatomical name istunicaserosa.Serous membranes line and enclose severalbody cavities,also known as serous cavities, where they secrete a lubricating fluid which reduces friction from movements. Serosa is entirely different from theadventitia,aconnective tissuelayer which binds together structures rather than reducing friction between them. The serous membrane covering theheartand lining themediastinumis referred to as thepericardium,the serous membrane lining thethoracic cavityand surrounding thelungsis referred to as thepleura,and that lining theabdominopelvic cavityand theviscerais referred to as theperitoneum.

Structure

Serous membranes have two layers. The parietal layers of the membranes line the walls of the body cavity (pariet- refers to a cavity wall). The visceral layer of the membrane covers the organs (the viscera). Between the parietal and visceral layers is a very thin, fluid-filled serous space, or cavity.

Visceral and parietal layers

Each serous membrane is composed of a secretoryepitheliallayer and aconnective tissuelayer underneath.

• Theepithelial layer,known asmesothelium,consists of a single layer ofavascularflatnucleatedcells (simple squamous epithelium) which produce the lubricating serous fluid. This fluid has a consistency similar to thinmucus.These cells are bound tightly to the underlying connective tissue.
• Theconnective tissue layerprovides theblood vesselsandnervesfor the overlying secretory cells, and also serves as the binding layer which allows the whole serous membrane to adhere to organs and other structures.

For the heart, the layers of the serous membrane are called the parietalpericardium,and the visceral pericardium (sometimes called theepicardium). Other parts of the body may also have specific names for these structures. For example, the serosa of theuterusis called theperimetrium.

Schematic diagram of an organ invaginating into a serous cavity

Thepericardial cavity(surrounding theheart),pleural cavity(surrounding thelungs) andperitoneal cavity(surrounding most organs of theabdomen) are the three serous cavities within the human body. While serous membranes have a lubricative role to play in all three cavities, in the pleural cavity it has a greater role to play in the function of breathing.

The serous cavities are formed from the intraembryonic coelom and are basically an empty space within the body surrounded by serous membrane. Early in embryonic life visceral organs develop adjacent to a cavity and invaginate into the bag-like coelom. Therefore, each organ becomes surrounded by serous membrane - theydo notlie within the serous cavity. The layer in contact with the organ is known as the visceral layer, while the parietal layer is in contact with the body wall.

Examples

In the human body, there are three serous cavities with associated serous membranes:

• A serous membrane lines thepericardial cavityof the heart, and reflects back to cover the heart, much like an under-inflated balloon would form two layers surrounding a fist. Called thepericardium,this serous membrane is a two-layered sac that surrounds the entire heart except where blood vessels emerge on the heart's superior side;
• Thepleurais the serous membrane that surrounds the lungs in the pleural cavity;
• Theperitoneumis the serous membrane that surrounds several organs in the abdominopelvic cavity.
• Thetunica vaginalisis the serous membrane, which surrounds the male gonad, the testis.

The two layers of serous membranes are namedparietalandvisceral.Between the two layers is a thin fluid filled space.The fluid is produced by the serous membranes and stays between the two layers to reduce friction between the walls of the cavities and the internal organs when they move with respect to one another, such as when the lungs inflate or the heart beats. Such movement could otherwise lead to inflammation of the organs.

Development

All serous membranes found in the human body formed ultimately from themesodermof thetrilaminar embryo.The trilaminar embryo consists of three relatively flat layers ofectoderm,endoderm(also known as "entoderm" ) andmesoderm.

As the embryo develops, the mesoderm starts to segment into three main regions: theparaxial mesoderm,theintermediate mesodermand thelateral plate mesoderm.

The lateral plate mesoderm later splits in half to form two layers bounding a cavity known as theintraembryonic coelom.Individually, each layer is known assplanchnopleureandsomatopleure.

• Thesplanchnopleureis associated with the underlying endoderm with which it is in contact, and later becomes the serous membrane in contact with visceral organs within the body.
• Thesomatopleureis associated with the overlying ectoderm and later becomes the serous membrane in contact with the body wall.

Theintraembryonic coelomcan now be seen as a cavity within the body which is covered with serous membrane derived from the splanchnopleure. This cavity is divided and demarcated by the folding and development of the embryo, ultimately forming the serous cavities which house many different organs within thethoraxandabdomen.

Diseases

Mesotheliomasareneoplasiasthat are relatively specific for serous membranes. The modifiedMüllerian-derived serous membranes that surrounds theovariesin females can give rise toserous tumors,a solid to papillary tumor type that may also arise within theuterus.

Anatomical images

• 
  Layers of stomach wall
• 
  Section of duodenum of cat

See also

This article usesanatomical terminology.

• Adventitia
• Pericardial cavity

References

This Wikipedia entry incorporates text from the freely licensed Connexions[1]edition of Anatomy & Physiology[2]text-book by OpenStax College

External links

• UIUC Histology Subject844
• Parsons, Frederick Gymer (1911)."Coelom and Serous Membranes".Encyclopædia Britannica.Vol. 6 (11th ed.). pp. 642–644.