Structure and Functions of Epithelial Tissues

Structure and Functions of Epithelial Tissues

EPITHELIAL TISSUE

What is epithelial tissue?

EPITHELIAL TISSUE

Epithelial tissues are linings of the various passages inside the body.

Structure of Epithelial Tissues

General Structure of Epithelial Tissues Epithelium is a group of closely associated cells with scanty intercellular materials that cover external and internal surfaces of the body They form the covering of all body surfaces, line body cavities and hollow organs, and are the major tissue in glands Epithelial tissues are widely spread throughout the body The cells in epithelial tissue are tightly packed together with no intercellular material between the cells or very little intercellular materials

It also forms all glands including endocrine and exocrine glands

The cells are attached to the underlying connective tissue known as the basement membrane The basement membrane is a connective tissue structure where the epithelial cells are attached Cells of epithelial tissue appear in different shapes and structure These differences reflect the functions of the epithelium

Classification of Epithelial Tissues

what are the classes of epithelial tissue?

Classification of Epithelial Tissues

Classification according to the cell shape Squamous epithelia:cells are flat cells with an irregular flattened shape (fish-scale appearance) Cuboidal eithelia:cells have a shape similar to a cube, meaning its width is the same size as its height Columnar epithelia: cells are taller than they are wide Classification based on number of cell layers (Stratification) Simple epithelia

• Stratified epithelia
• Pseudostratified epithelia

Transitional epithelia

Simple Epithelium

Cells are organized in a single layer and therefore all cells are attached to the basement membrane Because the shapes of the cells include possible function, they are found in different organs depending on their function:

There are three types of simple epithelium: Simple squamous epithelium, Simple cuboidal epithelium, Simple columnar epithelium

Simple Squamous Epithelium

• All Squamous cells are flat cells with an irregular flattened shape

It is a one-cell layer of simple squamous epithelium Forms a thin membrane and therefore it is found in places where exchange of material from one compartment to the other occurs.

Squamous cells can be found in the heart, blood vessels, lymph vessels and alveoli of the lung.

They allow free diffusion

Simple Cuboidal Epithelium

This consists of cube-shaped cells fitting closely together lying on a basement membrane.

Forms secretory cells, lining of the small ducts of the glands and it covers the outer surfaces of organs such as the ovaries and in the kidney tubules Are actively involved in secretion, absorption and excretion

Simple Columnar Epithelium

This is formed by a single layer of cells, rectangular in shape lying on a basement membrane.

It is found lining the organs of the alimentary tract.

Consists of mixture of cells, some absorb the products of digestion and others secrete mucus.

Stratified Epithelia

• Consists of several layers of cells of various shapes
• The superficial layers grow up from below
• Basement membranes are usually absent
• The main function of compound epithelium is to protect underlying structures

There are two types: Stratified and transitional

Stratified squamous epithelium

• Consists of several layers of cells of different shapes

The cells are arranged into superficial, intermediate and basal (deep) layers In the deepest layers the cells are mainly columnar and, as they grow towards the surface, they become flattened.

It is the main protective epithelium of the body external surface for example in the skin it forms the epidermis,some parts of tongue, hard palate There are two types: Non keratinized stratified epithelium and Keratinized stratified epithelium Keratinized stratified epithelium

Refers to cells that has become hardened and died.

The cells have a tough fibrous protein called keratin that helps protect the skin and underlying tissues from heat, microbes and chemicals.

It is found on dry surfaces that are subject to wear and tear such as skin, hair and nails.

Non keratinized stratified epithelium

Does not contain keratin and consists of cells which are not dead It is found on wet surfaces that may be subjected to wear and tear but are protected from drying, for example conjunctiva of the eyes, and lining of the mouth, pharynx, the oesophagus and vagina. It provides mechanical protection from injury

Transitional Epithelia

Transitional epithelium: A transitional epithelium (also known as urothelium) is made up of several layers of cells that become flattened when stretched. It lines most of your urinary tract and allows your bladder to expand.

General Functions of Epithelial Tissues

What are the functions of epithelial tissues?

General Functions of Epithelial Tissue

Protection

Epithelial cells from the skin protect underlying tissue from mechanical injury, harmful chemicals, invading bacteria and from excessive loss of water Sensation

Sensory stimuli penetrate specialized epithelial cells Specialized epithelial tissue containing sensory nerve endings is found in the skin, eyes, ears, nose and on the tongue

Secretion

In glands, epithelial tissue is specialized to secrete specific chemical substances such as enzymes, hormones and lubricating fluids Absorption

Certain epithelial cells lining the small intestine absorb nutrients from the digestion of food Excretion

Epithelial tissues in the kidney excrete waste products from the body and reabsorb needed materials from the urine Sweat is also excreted from the body by epithelial cells in the sweat glands Diffusion

Simple epithelium promotes the diffusion of gases, liquids and nutrients

summary

• The term "epithelium" refers to layers of cells that line hollow organs and glands
• It is also those cells that make up the outer surface of the body.

Cells of epithelial tissue appear in different shapes and structure.

General functions of epithelial tissue include signal transduction, protection, secretion, absorption ,excretion, filtration, diffusion and sensory reception

assignment

Explain the structure of epithelial tissue

reference

National Cancer Institute. SEER Training Modules. Retrieved From:http://training.seer.cancer.gov/anatomy/cells_tissues_membranes/tissues/epithelial.html . September 2015