Classification Of Epithelial Tissues:
Epithelial cells can be Classified on the basis of Number of cells in layers and on the basis of Shape
Classification On basis of number of cells layer
there are three types of epithelial tissues on basis of number
Simple epithelia:
single layer of cells that functions in diffusion, osmosis, filtration, secretion, or absorption
Stratified epithelia:
consists of two or more layers of cells that protect underlying tissues
Pseudo stratified epithelia:
Appears to have multiple layers of cells because the cell nuclei lie at different levels not all cells reach the apical surface but all cells rests of basement membrane. Cells that do extend to the apical surface may contain cilia; others secrete mucus
Classification on basis of shape
Squamous epithelium
are thin, which allows for the rapid passage of substances through them.
Cuboidal epithelium
are as tall as they are wide and are shaped like cubes or hexagons.
They may have microvilli at their apical surface and function in either secretion or absorption.
Columnar epithelium
are much taller than they are wide, like columns, and protect underlying tissues.
Their apical surfaces may have cilia or microvilli, and they often are specialized for secretion and absorption.
Transitional epithelium
change shape, from squamous to cuboidal and back, as organs stretch to a larger size and then collapse to a smaller size.
Types Of Epithelial Tissues
Combining all the classification of epithelial tissues, following 8 (eight) Types of epithelial tissues are present in bodytypes of epithelium are individually elaborated..
- Simple squamous epithelium
- Simple cuboidal epithelium
- Simple columnar epithelium (nonciliated and ciliated)
- Pseudostratified columnar epithelium (nonciliated and ciliated)
- Stratified squamous epithelium : keratinized, when surface cells are dead and become hardened, and nonkeratinized,when surface cells remain alive.
- Stratified cuboidal epithelium
- Stratified columnar epithelium
- Transitional epithelium
now we are moving toward a little detailed classification.
Simple squamous epithelium:
its characteristics are :
- Single layer of flat cells that resembles a tiled floor when viewed from apical surface.
- Has centrally located nucleus
- Present at sites of filtration, diffusion or at site of secretion of serous membrane.
- lines the cardiovascular and lymphatic system
endothelium.
prevent abnormal blood clotting because of smooth surface and in capillaries it facilitates exchange of fluidmesothelium
- forms the epithelial layer of serous membranes.
- reduce friction
- simple squamous epithelium is Found in Bowman’s capsule of kidney, inner surface of ear drum and air sacs of lungs
areas where epithelial tissues are present
Simple cuboidal epithelium:
it has the following features:
Single layer of cube-shaped cells. Has round, centrally located nucleus.- Its main functions are secretion and absorption.
- It has abundance of organelles to facilitate active transport frequently found in glands, such as salivary glands, the thyroid gland, and the pancreas, where its function is secretion.
- Simple cuboidal epithelium also covers the ovaries and lines most of the kidney tubules. In one part of the kidney tubule, it absorbs substances from the tubule, and in another part it secretes substances into the tubule.
areas of presence of simple cuboid epithelium in the body
NON-CILIATED SIMPLE COLUMNAR EPITHELIUM :
- Single layer of non-ciliated column like cells with oval nuclei near base of cells
- More tall than wide
- Some of them are goblet cells - modified columnar epithelial cells that secrete mucus at their apical surfaces. Before release, mucus accumulates in upper portion of cell, causing it to bulge and making the whole cell resemble a goblet or wine glass.
- Also has microvilli to increase surface area for absorption
Function of non ciliated simple columnar tissue
larger columnar cells contain more organelles and are capable of higher level of secretion andabsorption. secrets mucous which lubricates linings of digestive tract, which helps prevent
destruction of stomach lining by acidic gastric juice secreted by stomach.
Lines gastrointestinal tract (from stomach to anus), ducts of many glands, gallbladder
non ciliated simple columnar tissues
CILIATED SIMPLE COLUMNAR EPITHELIUM:
Single layer of ciliated column like cells with oval nuclei near base of cellsSome of the cells are goblet cells Located in bronchioles of respiratory tract, uterine
tubes, uterus, central canal of spinal cord and ventricles of brain
Their unique function is because of cilia which beat and move mucus, foreign particles and other
secretions for clearance and swallowing
ciliated simple columnar tissues.
