Serous membrane
Layers of the enteric nervous system. The enteric nervous system ( ENS) is a subdivision of the Peripheral Nervous System, that directly controls the Gastrointestinal system. (Serosa at top, in red. )
Stomach. (Serosa is labeled at far right, and is colored yellow. )
Latin	tunica serosa
Precursor	mesoderm
MeSH	Serous+membrane
Dorlands/Elsevier	t_22/12832289

In anatomy, a serous membrane (or serosa) is a smooth membrane consisting of a thin layer of cells which excrete serous fluid. Latin ( lingua Latīna, laˈtiːna is an Italic language, historically spoken in Latium and Ancient Rome. Embryology (from Greek grc ἔμβρυον embryon, "unborn embryo" and grc -λογία -logia) is the study of the development One of the three Germ layers found in the Embryos of Animals more complex than Cnidarians making them Triploblastic. Medical Subject Headings ( MeSH) is a huge Controlled vocabulary (or metadata system for the purpose of indexing journal articles and books Elsevier, the world's largest Publisher of Medical and Scientific literature, forms part of the Reed Elsevier group Anatomy (from the Greek anatomia, from ana separate apart from and temnein, to cut up cut open is a branch of Biology that is the consideration The mesothelium is a membrane that forms the lining of several body cavities the Pleura (thoracal cavity Peritoneum (abdominal cavity including the mesentery and The cell is the structural and functional unit of all known living Organisms It is the smallest unit of an organism that is classified as living and is often called In Physiology, the term serous fluid is used for various Bodily fluids that are typically pale yellow and transparent and of a Benign nature Serous membranes line and enclose several body cavities, known as serous cavities, where they secrete a lubricating fluid which reduces friction from muscle movement. Serosa is not to be confused with adventitia, a connective tissue layer which binds together structures rather than reducing friction between them. Adventitia is the outermost Connective tissue covering of any organ, vessel, or other structure

Structure

Each serous membrane is composed of a secretory epithelial layer and a connective tissue layer underneath. In biology and medicine epithelium is a tissue composed of cells that line the cavities and surfaces of structures throughout the body Connective tissue is one of the four types of tissue in traditional classifications (the others being epithelial, Muscle, and Nervous tissue)

• The epithelial layer, known as mesothelium, consists of a single layer of avascular flat nucleated cells (simple squamous epithelium) which produce the lubricating serous fluid. The mesothelium is a membrane that forms the lining of several body cavities the Pleura (thoracal cavity Peritoneum (abdominal cavity including the mesentery and The blood vessels are part of the Circulatory system and function to transport Blood throughout the body In Cell biology, the nucleus (pl nuclei; from Latin la ''nucleus'' or la ''nuculeus'' "little nut" or kernel is a membrane-enclosed In Anatomy, squamous epithelium (from Latin squama, "scale" is an Epithelium characterised by its most superficial layer consisting This fluid has a consistency similar to thin mucous. In vertebrates mucus is a slippery secretion produced by and covering Mucous membranes It is a viscous Colloid containing Antiseptic enzymes (such as These cells are bound tightly to the underlying connective tissue.
• The connective tissue layer provides the blood vessels and nerves for the overlying secretory cells, and also serves as the binding layer which allows the whole serous membrane to adhere to organs and other structures. The blood vessels are part of the Circulatory system and function to transport Blood throughout the body A nerve is an enclosed cable-like bundle of peripheral Axons (the long slender projections of Neurons.

For the heart, the surrounding serous membranes include:

Other parts of the body may also have specific names for these structures. In higher Vertebrates the peritoneum is the Serous membrane that forms the lining of the abdominal cavity &mdash it covers most of the intra-abdominal The portion of the Pleura external to the Pulmonary pleura lines the inner surface of the Chest wall covers the diaphragm, and is reflected over the structures Each Lung is invested by an exceedingly delicate serous membrane the Pleura, which is arranged in the form of a closed invaginated sac The pericardium is a double-walled sac that contains the Heart and the roots of the Great vessels. Epicardium describes the outer layer of Heart tissue (from Greek; epi- outer cardium heart For example, the serosa of the uterus is called the perimetrium. The uterus (from the Latin word for womb) is the major Female reproductive organ of most Mammals including Humans One end the The perimetrium is the outer Serosa layer of the Uterus, covered in Peritoneum.

Highly schematic diagram of an organ invaginating into a serous cavity

The pericardial cavity (surrounding the heart), pleural cavity (surrounding the lungs) and peritoneal cavity (surrounding most organs of the abdomen) are the three serous cavities within the human body. The pericardium is a double-walled sac that contains the Heart and the roots of the Great vessels. The heart is a muscular organ in all Vertebrates responsible for pumping Blood through the Blood vessels by repeated rhythmic lung is the essential Respiration organ in air-breathing Animals including most Tetrapods a few Fish and a few Snails The most primitive In higher Vertebrates the peritoneum is the Serous membrane that forms the lining of the abdominal cavity &mdash it covers most of the intra-abdominal In Vertebrates such as Mammals the abdomen (belly constitutes the part of the body between the Thorax (chest and Pelvis. It should be noted that 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 - they do not lie 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.

Embryological origins

All serous membranes found in the human body formed ultimately from the mesoderm of the trilaminar embryo. One of the three Germ layers found in the Embryos of Animals more complex than Cnidarians making them Triploblastic. A trilaminar embryo (or trilaminary blastoderm, or trilaminar germ disk) is an early stage in the development of Triploblastic organisms which include The trilaminar embryo consists of three relatively flat layers of ectoderm, endoderm (also known as "entoderm") and mesoderm. The ectoderm is the start of a tissue that covers the body surfaces Endoderm, (sometimes called Entoderm) is one of the Germ layers formed during animal Embryogenesis. One of the three Germ layers found in the Embryos of Animals more complex than Cnidarians making them Triploblastic.

As the embryo develops, the mesoderm starts to segment into three main regions: the paraxial mesoderm, the intermediate mesoderm and the lateral plate mesoderm. Paraxial mesoderm is the area of Mesoderm that forms just lateral to the Neural tube on both sides Intermediate mesoderm is a type of Mesoderm that is located between the Paraxial mesoderm and the Lateral plate. Lateral plate mesoderm (or hypomere) is a type of Mesoderm that is found at the periphery of the Embryo.

The lateral plate mesoderm later splits in half to form two layers bounding a cavity known as the intraembryonic coelom. The intraembryonic coelom (or somatic coelom) is a a portion of the Conceptus forming in the Mesoderm. Collectively, both layers are known as splanchnopleure. In the Anatomy of an Embryo, the splanchnopleure is a structure created during Embryogenesis when the Lateral mesoderm splits into two layers Individually, each are known as visceropleure and somatopleure. In the Anatomy of an Embryo, the somatopleure is a structure created during Embryogenesis when the Lateral mesoderm splits into two layers

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

The intraembronic coelom can 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 the thorax and abdomen. The thorax is a division of an Animal 's body that lies between the head and the Abdomen. In Vertebrates such as Mammals the abdomen (belly constitutes the part of the body between the Thorax (chest and Pelvis.

Additional images

Layers of stomach wall

Section of duodenum of cat. X 60.

External links

• MeSH serous+membrane
• serosa at eMedicine Dictionary
• Histology at BU 00102loa - "Tissues, Layers, and Organs: transverse section of rat gut"
• Histology at OU 21_02 - "Uterus"
• Histology at OU 54_07 - "Jejunum"
• UIUC Histology Subject 844