Question

Classify and derive epithelium tissue on basis of structure,modification of cell

Answer 1

Epithelial tissue: characteristics and classification scheme and types

epithelial tissue

An epithelium is a sheet of cells that covers a body surface or lines a cavity.Epithelium forms the coverings of surfaces of the body such as Skin, Mouth, Nasal cavity (Ectodermal), Lines internal body surface such as GI tract, Lungs, Urinary bladder and vagina (Endodermal) and Lining of blood vessels, lymphatic and heart (Endothelial cells derived from Mesoderm).It serves many purposes, including protection, adsorption, excretion, secretion, filtration, and sensory reception.Epithelium also serves as glandular epithelium.There are two functional types of epithelium:lining epithelium and glandular epithelium.

Characteristics of epithelium tissue

Polarity- Epithelium is arranged so there is one free surface (apical surface) and one attached surface (basal surface)Cellular nature– Cells in epithelium fit closely together side by side and sometimes atop each other to form sheets of cells. These sheets are held together by specialized junctions.Supported by connective tissue– Attachment to a layer of connective tissue at the basal surface forms a layer called thebasement membrane, an adhesive layer formed by secretions from the epithelial cells and the connective tissue cells.Avascular– Epithelium typically lacks its own blood supply.Regeneration– Epithelium cells can regenerate if proper nourished.Absence of nerves (except for a few axons in the deeper layers)

Classification scheme of epithelial tissue:

Typically epithelial tissue is classified on the basis of arrangement and shape of cells. For naming the tissue types, the arrangement of the cells is stated first, then the shape, and is followed by “epithelium” to complete the naming. For example; Simple Squamous Epithelium.



1. Classification scheme of epithelial tissue on the basis of arrangement of cells

i. Simple epithelium:

Cells are found in a single layer attached to the basement membrane.

ii. Compound or Stratified epithelium:

Cells are found in 2 or more layers stacked atop each other.

iii. Pseudo-stratified epithelium:

Pseudo-stratified epithelium appears to be more than one cell thick since the nuclei lie at different heights, but in fact it is single layer of cells, in contact with the basement membrane

iv. Transitional epithelium:

cells are rounded and can slide across one another to allow stretching

 

2. Classification scheme of epithelial tissue on the basis of shape

i. Squamous epithelium: (Latin, squama- scale)

flat, thin, scale-like cells,eg. Endothelium, mesothelium, pericardium, peritonium

ii. Cuboidal epithelium:

cells that have a basic cube shape.Typically the cell’s height and width are about equal.Eg. Kidney tubules, thyroid glands, duct of sweat gland

iii. Columnar epithelium:

tall, rectangular or column shaped cells.Typically cells are longer than width.Eg. Intestinal lining, gall bladder, ducts of glands

Types of epithelium tissue:

simple epithelium tissuecompound epithelium tissueSpecialized Epithelium

Simple epithelium tissue

Simple squamous epitheliumSimple cuboidal epitheliumSimple columnar epitheliumPseudo-stratified epithelium

Compound or Stratified epithelium:

Stratified squamous epitheliumStratified cuboidal epitheliumStratified columnar epitheliumTransitional epithelium

Specialised Epithelium

Glandular epitheliumGerminal epitheliumSensory epitheliumCiliated epithelium

Answer 2

Epithelium is one of the four basic types of animal tissue, along with connective tissue, muscle tissue and nervous tissue. Epithelial tissues line the outer surfaces of organs and blood vesselsthroughout the body, as well as the inner surfaces of cavities in many internal organs. An example is the epidermis, the outermost layer of the skin.

Epithelium

Types of epithelium
There are three principal shapes of epithelial cell: squamous, columnar, and cuboidal. These can be arranged in a single layer of cells as simple epithelium, either squamous, columnar, or cuboidal, or in layers of two or more cells deep as stratified (layered), either squamous, columnar or cuboidal. In some tissues, a layer of columnar cells may appear to be stratified due to the placement of the nuclei. This sort of tissue is called pseudostratified. All glands are made up of epithelial cells. Functions of epithelial cells include secretion, selective absorption, protection, transcellular transport, and sensing.

Epithelial layers contain no blood vessels, so they must receive nourishment via diffusionof substances from the underlying connective tissue, through the basement membrane.Cell junctions are well employed in epithelial tissues.