Pseudostratified epithelium

Pseudostratified epithelium - basic histology Intermediary between simple and stratified epithelium. Consists of one layer of irregularly shaped and sized cells attached to a basement membrane. Because these cells vary in height, their nuclei are at different levels, giving the appearance (under the microscope) of more than one layer of cells. Found in lining of the trachea, bronchi, pharynx, nasal cavity, and urethra in basic histology blog

Stratified Epithelium

Stratified epithelim in basic histology Where body linings have to withstand wear and tear, the epithelia are composed of several layers of cells and are then called compound or stratified epithelium. The top cells are flat and scaly and it may or may not be keratinised (i.e. containing a tough, resistant protein called keratin). The mammalian skin is an example of dry, keratinised, stratified epithelium. The lining of the mouth cavity is an example of an unkeratinisied, stratified epithelium.

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.

Germ Cell Origin: Epithelial tissues are derived from all three primary germ cell layers.

Ectoderm: The epithelial cells of the skin and oral cavity (epidermis) are derived from ectoderm. Epithelial cells covering the cornea and lens, as well as sensory receptors of the eyes, ears, and nose, are also ectodermal in origin.
Mesoderm: The epithelial lining of blood vessels (endothelium) is derived from mesoderm. The epithelial lining of the pleural and peritoneal cavities (mesothelium) also originate from mesodermal cells.
Endoderm: The epithelial lining of the respiratory system and digestive tracts - as well as the functional cells (parenchyma) of the liver, pancreas, gallbladder, thyroid, and parathyroid, are derived from endoderm.