In
anatomyAnatomy is a branch of biology and medicine that is the consideration of the structure of living things. It is a general term that includes human anatomy, animal anatomy and plant anatomy...
, a
serous membrane (or
serosa) is a smooth
membraneThe 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...
consisting of a thin layer of
cellsThe cell is the basic 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 the building block of life. The Alberts text discusses how the "cellular building blocks" move to shape developing embryos...
which excrete
serous fluidIn physiology, the term serous fluid is used for various bodily fluids that are typically pale yellow and transparent, and of a benign nature, that fill the inside of body cavities....
. 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
adventitiaAdventitia is the outermost connective tissue covering of any organ, vessel, or other structure. It is also called the tunica adventitia....
, a connective tissue layer which binds together structures rather than reducing friction between them.
Each serous membrane is composed of a secretory
epithelialIn biology and medicine, an epithelium is a tissue composed of cells that line the cavities and surfaces of structures throughout the body. Many glands are also formed from epithelial tissue...
layer and a
connective tissueConnective tissue is a form of fibrous tissue.. It is one of the four types of tissue in traditional classifications ....
layer underneath.
- The epithelial layer, known as mesothelium
The 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...
, consists of a single layer of avascularThe blood vessels are the part of the circulatory system that transport 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...
flat nucleated cells (simple squamous epitheliumIn simple squamous epithelia all the cells are in contact with the basal lamina of the epithelium. Examples are found in capillaries, alveoli, glomeruli, and other tissues where rapid diffusion is required....
) which produce the lubricating serous fluid.
In
anatomyAnatomy is a branch of biology and medicine that is the consideration of the structure of living things. It is a general term that includes human anatomy, animal anatomy and plant anatomy...
, a
serous membrane (or
serosa) is a smooth
membraneThe 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...
consisting of a thin layer of
cellsThe cell is the basic 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 the building block of life. The Alberts text discusses how the "cellular building blocks" move to shape developing embryos...
which excrete
serous fluidIn physiology, the term serous fluid is used for various bodily fluids that are typically pale yellow and transparent, and of a benign nature, that fill the inside of body cavities....
. 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
adventitiaAdventitia is the outermost connective tissue covering of any organ, vessel, or other structure. It is also called the tunica adventitia....
, a connective tissue layer which binds together structures rather than reducing friction between them.
Structure
Each serous membrane is composed of a secretory
epithelialIn biology and medicine, an epithelium is a tissue composed of cells that line the cavities and surfaces of structures throughout the body. Many glands are also formed from epithelial tissue...
layer and a
connective tissueConnective tissue is a form of fibrous tissue.. It is one of the four types of tissue in traditional classifications ....
layer underneath.
- The epithelial layer, known as mesothelium
The 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...
, consists of a single layer of avascularThe blood vessels are the part of the circulatory system that transport 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...
flat nucleated cells (simple squamous epitheliumIn simple squamous epithelia all the cells are in contact with the basal lamina of the epithelium. Examples are found in capillaries, alveoli, glomeruli, and other tissues where rapid diffusion is required....
) which produce the lubricating serous fluid. This fluid has a consistency similar to thin mucusIn vertebrates, mucus is a slippery secretion produced by, and covering, mucous membranes. It is a viscous colloid containing antiseptic enzymes and immunoglobulins that serves to protect epithelial cells in the respiratory,...
. 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.
For the heart, the surrounding serous membranes include:
| Outer |
Inner
>-
| Parietal pericardiumThe pericardium is a double-walled sac that contains the heart and the roots of the great vessels.-Layers:There are two layers to the pericardial sac: the fibrous pericardium and the serous pericardium...
|
Visceral pericardium (epicardium Epicardium describes the outer layer of heart tissue . When considered as a part of the pericardium, it is the inner layer, or visceral pericardium....
) |
Other parts of the body may also have specific names for these structures. For example, the serosa of the
uterusThe uterus is a major female hormone-responsive reproductive sex organ of most mammals, including humans. It is within the uterus that the fetus develops during gestation. The term uterus is used consistently within the medical and related professions; the Germanic term, womb is more common in...
is called the
perimetriumThe perimetrium is the outer serosa layer of the uterus, equivalent to peritoneum.-External links: - "The Female Pelvis: The uterus" - "Mammal, uterus "...
.
The
pericardial cavityThe pericardium is a double-walled sac that contains the heart and the roots of the great vessels.-Layers:There are two layers to the pericardial sac: the fibrous pericardium and the serous pericardium...
(surrounding the
heartThe heart is a muscular organ found in all vertebrates that is responsible for pumping blood throughout the blood vessels by repeated, rhythmic contractions...
), pleural cavity (surrounding the
lungThe lung or pulmonary system is the essential respiration organ in air-breathing animals, including most tetrapods, a few fish and a few snails. In mammals and the more complex life forms, the two lungs are located in the chest on either side of the heart...
s) and
peritoneal cavityThe 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 higher vertebrates and some invertebrates...
(surrounding most organs of the
abdomenIn vertebrates such as mammals the abdomen constitutes the part of the body between the thorax and pelvis. The region enclosed by the abdomen is termed the abdominal cavity...
) are the three serous cavities within the human body. 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
mesodermIn humans, the mesoderm is one of the three primary germ cell layers - the other two are the ectoderm and endoderm - in the very early embryo. The mesoderm is the middle layer. It differentiates to gives rise to a number of tissues and structures including bone, muscle, connective tissue, and the...
of the
trilaminar embryoA trilaminar embryo is an early stage in the development of triploblastic organisms, which include humans and many other animals....
. The trilaminar embryo consists of three relatively flat layers of
ectodermThe ectoderm is the start of a tissue that covers the body surfaces. It emerges first and forms from the outermost of the germ layers.Generally speaking, the ectoderm differentiates to form the nervous system, and the epidermis .In vertebrates, the ectoderm has three parts: external ectoderm , the ...
,
endodermEndoderm, is one of the germ layers formed during animal embryogenesis. Cells migrating inward along the archenteron form the inner layer of the gastrula, which develops into the endoderm....
(also known as "entoderm") and
mesodermIn humans, the mesoderm is one of the three primary germ cell layers - the other two are the ectoderm and endoderm - in the very early embryo. The mesoderm is the middle layer. It differentiates to gives rise to a number of tissues and structures including bone, muscle, connective tissue, and the...
.
As the embryo develops, the mesoderm starts to segment into three main regions: the
paraxial mesodermParaxial mesoderm is the area of mesoderm that forms just lateral to the neural tube on both sides.It gives rise to the somitomeres/somites and mesoderm of the branchial arches.*Somites form the vertebral column, dermis and skeletal muscle...
, the
intermediate mesodermIntermediate mesoderm is a type of mesoderm that is located between the paraxial mesoderm and the lateral plate.It develops into the part of the urogenital system * forms of urogenital system...
and the
lateral plate mesodermLateral plate mesoderm is a type of mesoderm that is found at the periphery of the embryo.-Division into layers:It will split into two layers, the somatic layer/mesoderm and the splanchnic layer/mesoderm* The somatic layer forms the future body wall....
.
The lateral plate mesoderm later splits in half to form two layers bounding a cavity known as the
intraembryonic coelomThe intraembryonic coelom is a portion of the conceptus forming in the mesoderm. During the second week of development, the lateral mesoderm splits into a dorsal somatic mesoderm and a ventral splanchnic mesoderm . The resulting cavity between the somatopleure and splanchnopleure is called the...
. Collectively, both layers are known as
splanchnopleureIn the anatomy of an embryo, the splanchnopleure is a structure created during embryogenesis when the lateral mesoderm splits into two layers. The inner layer adheres to the endoderm, and with it forms the splanchnopleure.-External links:...
. Individually, each are known as visceropleure and
somatopleureIn the anatomy of an embryo, the somatopleure is a structure created during embryogenesis when the lateral mesoderm splits into two layers. The outer layer becomes applied to the inner surface of the ectoderm, and with it forms the somatopleure....
.
- 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
thoraxThe thorax is a division of an animal's body that lies between the head and the abdomen.In mammals, the thorax is the region of the body formed by the sternum, the thoracic vertebrae and the ribs. It extends from the neck to the diaphragm, and does not include the upper limbs. The heart and the...
and
abdomenIn vertebrates such as mammals the abdomen constitutes the part of the body between the thorax and pelvis. The region enclosed by the abdomen is termed the abdominal cavity...
.
External links
- "Tissues, Layers, and Organs: transverse section of rat gut" - "
UterusThe uterus is a major female hormone-responsive reproductive sex organ of most mammals, including humans. It is within the uterus that the fetus develops during gestation. The term uterus is used consistently within the medical and related professions; the Germanic term, womb is more common in...
" - "
JejunumThe jejunum is the middle 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 middle intestine or mid-gut may be used instead of jejunum.The jejunum lies between the duodenum...
"