Pseudostratified epithelium
Encyclopedia
A pseudostratified epithelium is a type of epithelium
that, though comprising only a single layer of cells
, has its cell nuclei
positioned in a manner suggestive of stratified epithelia. As it rarely occurs as squamous
or cuboidal epithelia
, it is usually considered synonymous with the term pseudostratified columnar epithelium.
The term pseudostratified is derived from the appearance of this epithelium in section which conveys the erroneous (pseudo means false) impression that there is more than one layer of cells, when in fact this is a true simple epithelium since all the cells rest on the basal lamina
. The nuclei of these cells, however, are disposed at different levels, thus creating the illusion of cellular stratification. Not all ciliated cells extend to the luminal surface; such cells are capable of cell division providing replacements for cells lost or damaged.
Pseudostratified epithelia function in secretion or absorption. If a specimen looks stratified but has cilia, then it is a pseudostratified ciliated epithelium, since stratified epithelia do not have cilia.
Three types of epithelium occur:
Squamous is flattened cells.
Cuboidal is cube shaped cells.
Columnar consists of elongated cells. they are many layers also
Epithelium
Epithelium is one of the four basic types of animal tissue, along with connective tissue, muscle tissue and nervous tissue. Epithelial tissues line the cavities and surfaces of structures throughout the body, and also form many glands. Functions of epithelial cells include secretion, selective...
that, though comprising only a single layer of cells
Cell (biology)
The cell is the basic structural and functional unit of all known living organisms. It is the smallest unit of life that is classified as a living thing, and is often called the building block of life. The Alberts text discusses how the "cellular building blocks" move to shape developing embryos....
, has its cell nuclei
Cell nucleus
In cell biology, the nucleus is a membrane-enclosed organelle found in eukaryotic cells. It contains most of the cell's genetic material, organized as multiple long linear DNA molecules in complex with a large variety of proteins, such as histones, to form chromosomes. The genes within these...
positioned in a manner suggestive of stratified epithelia. As it rarely occurs as squamous
Squamous epithelium
In anatomy, squamous epithelium is an epithelium characterised by its most superficial layer consisting of flat, scale-like cells called squamous epithelial cells...
or cuboidal epithelia
Cuboidal epithelia
Cuboidal epithelia are epithelial cells having a cube-like shape; that is, their width is approximately equal to their height. They may exist in single layers or multiple layers depending on their location in the body....
, it is usually considered synonymous with the term pseudostratified columnar epithelium.
The term pseudostratified is derived from the appearance of this epithelium in section which conveys the erroneous (pseudo means false) impression that there is more than one layer of cells, when in fact this is a true simple epithelium since all the cells rest on the basal lamina
Basal lamina
The basal lamina is a layer of extracellular matrix secreted by the epithelial cells, on which the epithelium sits. It is often confused with the basement membrane, and sometimes used inconsistently in the literature, see below....
. The nuclei of these cells, however, are disposed at different levels, thus creating the illusion of cellular stratification. Not all ciliated cells extend to the luminal surface; such cells are capable of cell division providing replacements for cells lost or damaged.
Pseudostratified epithelia function in secretion or absorption. If a specimen looks stratified but has cilia, then it is a pseudostratified ciliated epithelium, since stratified epithelia do not have cilia.
Three types of epithelium occur:
Squamous is flattened cells.
Cuboidal is cube shaped cells.
Columnar consists of elongated cells. they are many layers also
Examples
- Ciliated pseudostratified columnar epithelia are found in the lines of the tracheaVertebrate tracheaIn tetrapod anatomy the trachea, or windpipe, is a tube that connects the pharynx or larynx to the lungs, allowing the passage of air. It is lined with pseudostratified ciliated columnar epithelium cells with goblet cells that produce mucus...
as well as the upper respiratory tractUpper respiratory tractThe upper respiratory tract or upper airway primarily refers to the parts of the respiratory system lying outside of the thorax or above the sternal angle. Another definition commomly used in medicine is the airway above the glottis or vocal cords...
. - Non-ciliated pseudostratified columnar epithelia are located in the membranous part of male vas deferensVas deferensThe vas deferens , also called ductus deferens, , is part of the male anatomy of many vertebrates; they transport sperm from the epididymis in anticipation of ejaculation....
. - Pseudostratified columnar epithelia with stereociliaStereociliaIn the inner ear, stereocilia are the mechanosensing organelles of hair cells, which respond to fluid motion in numerous types of animals for various functions, including hearing and balance. They are about 10–50 micrometers in length and share some similar features of microvilli...
are located in the epididymisEpididymisThe epididymis is part of the male reproductive system and is present in all male amniotes. It is a narrow, tightly-coiled tube connecting the efferent ducts from the rear of each testicle to its vas deferens. A similar, but probably non-homologous, structure is found in cartilaginous...
. Stereocilia of the epididymis are not cilia. They might be better defined as giant microvilli.
