Epithelium

Epithelium

Types of epytheliums

The epithelia are tissues made from cells closely juxtaposed, without the interposition of fiber or ground substance (which distinguishes them from connective tissue). The cells are linked to each other through intercellular junctions. They are not vascularisés with the exception of vascular streaks (cochlea, the production of endolymph). The input of nutrients and export of waste is done in conjunction with connective tissue underlying through a basement membrane, which rests epithelium (if a fabric has joined cells but not basal, this is not an epithelium, such épendymocytes). In this type of tissue, cells are often polarized (the two opposite ends are different morphologically and biochemically), although there are some epithelia where this polarity is difficult to distinguish (liver tissue). There are the apical region of the cell and basal region which is attached to the basal lamina.

They meet two physiological functions not exclusive of each other: function coating and glandular function.

The presence of specific intermediate filament Cytokeratin allows their identification by immunohistochemical methods.

Ciliated Columnar Epithelium

Ciliated Columnar Epithelium These are simple columnar epithelial cells, but in addition, they posses fine hair-like outgrowths, cilia on their free surfaces. These cilia are capable of rapid, rhythmic, wavelike beatings in a certain direction. This movement of the cilia in a certain direction causes the mucus, which is secreted by the goblet cells, to move (flow or stream) in that direction. Ciliated epithelium is usually found in the air passages like the nose. It is also found in the uterus and Fallopian tubes of females. The movement of the cilia propel the ovum to the uterus.

Squamous (pavement) epithelium

Squamous cells have the appearance of thin, flat plates. The shape of the nucleus usually corresponds to the cell form and help to identify the type of epithelium. Squamous cells, for example, tend to have horizontall flattened, elliptical nuclei because of the thin flattened form of the cell. They form the lining of cavities such as the mouth, blood vessels, heart and lungs and make up the outer layers of the skin.
Priority of this kind of tissue is to allow rapid exchange by diffusion or filtration


Simple Cuboidal Epithelium:
As their name implies, cuboidal cells are roughly square or cuboidal in shape. Each cell has a spherical nucleus in the centre. Cuboidal epithelium is found in glands and in the lining of the kidney tubules as well as in the ducts of the glands. They also constitute the germinal epithelium which produces the egg cells in the female ovary and the sperm cells in the male testes.
Most cuboidal cells in this kind of tissue are involved in secretion, filtration and absorption


Simple Columnar Epithelium:
Columnar epithelial cells occur in one or more layers. The cells are elongated and column-shaped. The nuclei are elongated and are usually located near the base of the cells. Columnar epithelium forms the lining of the stomach and intestines. Some columnar cells are specialised for sensory reception such as in the nose, ears and the taste buds of the tongue. Goblet cells (unicellular glands) are found between the columnar epithelial cells of the duodenum. They secrete mucus or slime, a lubricating substance which keeps the surface smooth.

Many columnar cells in this kind of tissue are involved in secretion and absorption
Those that are ciliated are involved in movement of particles

Simple epithelium

Simple epithelium can be subdivided according to the shape and function of its cells.


1. Shape of the cells “Squamous”
Cells are thin and flat
Often display many angular outlines when viewed from above
“Cuboidal”
Cells are approximately as tall as wide
“Columnar”
Cells are definitely more taller than wide
2. The number of cell layers present “Simple”
Only one layer of cells
All cells touch the basement membrane
“Stratified”
There is more than one layer of cells
Only the lowest cells rest on the basement membrane
Other cells are stacked upon each other in various configuration making up the "layers"
All cells arise from cell division by the lowest cells
Depending on the number of layers, displacement of the cells upwards into the different layers causes them to change shape

Types of Epithelial Tissue

Epithelial tissue can be divided into two groups depending on the number of layers of which it is composes. Epithelial tissue which is only one cell thick is known as simple epithelium. If it is two or more cells thick such as the skin, it is known as stratified epithelium.

Epithelium: Surface and Glandular

Epithelium is one of the primary tissues. Typically it consists of cells that are closely opposed to one another and occur in various morphological types, thus producing tissues with rather scanty intercellular substance. The epithelial tissues are divided into two major groups: namely, the covering and lining epithelial membranes and second the glandular epithelium.

Maximum cell-to-cell contact; minimum extracellular material; cell junctions; supported by basement membrane (basal lamella); not penetrated by blood vessels; derived from all embryonic germ layers, including mesoderm (endothelia and mesothelia)

Polarity: basal vs apical (luminal); lateral; specialized plasmalemma, appendages and junctional complexes

glycocalyx (apical) vs basement membrane (bm: basal lamina secreted by epithelium + lamina reticularis secreted by connective tissue)

Epithelia: thelia = nipple; epithelia = upon the nipple (convex [surface layer: epidermis, intestinal lining]); endothelia = within the nipple (concave [lining blood and lymph vessels and heart; cornea]); mesothelia = epithelia derived from splanchnic and somatic mesoderm lining body cavity (peripheral serosa) and covering organs (visceral serosa) within peritoneal, plural- and cardiac cavities.