Hello and welcome to a brand-new topic in Histology. today we will try to cover the following topics and I hope that it becomes useful to all of you, if there is any suggestion please tell me in the comments.

What is epithelial tissue?

Functions of epithelial tissue?

Classification of epithelial tissue?

Simple epithelium definition and kinds of simple epithelium?

Epithelium:

It is one layer or more than one layer of cells which covers the outer surface of the body (like skin) or it covers the inner (luminal surface) of tubular organs like (stomach, intestine, and more).

 Characteristics of epithelium:

1: Usually without blood vessels.

2: it has a membrane under it which is called (basement membrane).

3: it has very little intercellular space.

Functions of epithelium:

1: Protection of the body.

2: helps in Absorption.

3: helps in exchanging.

4: Secretion.

Classification of epithelium:

If an epithelium is made of one layer of cells it is called simple Epithelium.

If an epithelium is made of more than one layer of cells it is called Stratified Epithelium.


Basement membrane:

Epithelium cells lie on a membrane that is called the basement membrane and it is also called (Lamina propria) In stratified or epithelium that has more than one layer of cells the deepest layer lies on this membrane.

Functions of basement membrane:

It gives support to epithelial tissue on one side and also provides support to connective tissue which is located under epithelial tissue. It has a vital role in the diffusion and provides nutrition to epithelial tissue.

It also plays a vital role in cell shapes or organization of cells and regeneration of epithelial cells.

Simple epithelium:

Its also called unilayerd epithelium and it is made of one layer of cells which has a basement membrane under it. Generally, it is divided into 3 kinds.

Squamous epithelium:

The cells of this kind are flat and the height is very less when it's compared to its width.

From a surface view, it has polygonal shapes. In section view, the height of cells is much less than its width. The cytoplasm of cells makes a thin layer and the nuclei make a bulging point in the surface.

Examples: Pleura, the peritoneum. Alveoli of the lung, inside heart, lymphatics, vessels.

Cuboidal epithelium:

When the heights of the cells are similar or equal with widths of the cells it is called cuboidal it has a hexagonal shape from the surface view and the nuclei are round. It helps in the secretory and absorptive functions of the epithelium.

Examples: the surface of the ovary, the inner surface of the eye lens.


Columnar epithelium:

The cells are taller when it is compared to their width. Nuclei are placed at the lower half of the cells and all nuclei are at the equal or same level in cells. On surface view, the cells look like polygonal shapes.

This epithelium is located on the inner surface of the stomach, the large intestine. Also ciliated columnar is seen in the respiratory system. Some columnar cells have a secretory function, some of them secrete enzyme in an intestinal tube and also it has microvilli in the intestine. In the respiratory system, it has cilia and provides a defensive function.

Pseudostratified epithelium:

It appears as a multilayered epithelium but it is not stratified in fact. If the nuclei in columnar epithelium locate at different levels it appears like two or three layers of cells and cells are different in height some of them are tall and some of them are short in size.

The taller cells have secretory function while the short cells are stem cells in this kind of epithelial tissue.