Epithelium Tissue or Epithelial Tissue – Types and Function
Epithelial tissue is also referred to as epithelium tissue. It forms sheets
of cells that cover surfaces of the body, lines internal cavities, hollow
organs, and passageways, and forms ducts and certain glands.
Epithelial tissue -
1. Cover’s body surfaces
2. Lines hollow organs, body activities, and ducts
3. Forms ducts and certain glands
Check out here the embryonic origin of epithelial tissue.
Epithelial tissues originate from the ectoderm,
mesoderm, and endoderm of the embryo. Epithelium tissues form the protective
covering and inner lining of the body and organs.
Epithelial tissue is formed of a single layer of epithelium cells, called simple
epithelium tissue, or formed of multiple layers of epithelial cells, called
stratified epithelium tissue.
Surfaces of Epithelium Tissue
Epithelium
cells forming a single layer of epithelial tissue consist of three surfaces;
these surfaces have a distinct function -
1.
Apical surface
The apical surface of epithelial
cells is allowed for exchanging material passing in and out of the cell.
2.
Basal surface
The basal surface of epithelial
cells serves to connect the bottom layer of epithelial tissue to a basement
membrane.
3.
Lateral surface
The lateral surface of epithelial cells mediates the intracellular connections among epithelial cells.
What are connective
tissue and the types and functions of connective tissue?
Classification of Epithelial Tissue
Epithelial tissues are classified
according to the number of their cell layer formed, the shape of the cells, and the function of the cells.
Epithelial tissues are
classified into –
1. Membranous Epithelial tissues
2. Glandular Epithelial tissues
1. Membranous Epithelial Tissue
The membranous epithelium is composed of one or more layers of cells that form covers and lines the internal and external surface of the body and its organs. Such as lining all
internal cavities, organs, tubes, and passageways.
Types of Membranous Epithelial Tissues
Membranous Epithelial tissues are categorized into –
1. Simple Epithelial
Tissue (Single layered)
2. Stratified Epithelial
Tissue (Multi-layered)
Simple Epithelial Tissue
Simple epithelial tissue consists of a single layer
of epithelial cells. It is usually found on the absorptive or
secretory surfaces, but never found on surfaces subjected to wear and tear and
stress.
Classification of Simple epithelial tissue
Simple epithelial tissues are classified by both the number of cells and shape of
their cells, divided into main 4 types-
1. Simple squamous epithelial
tissue
2. Simple cuboidal epithelial
tissue
3. Simple columnar epithelial
tissue
a. Non-ciliated
b.
Ciliated
4. Simple pseudostratified epithelial tissue
1. Simple Squamous Epithelial
Simple squamous epithelial tissue is composed of a single
layer of flattened cells. These cells fit closely together like a flat stone,
forming a thin and smooth membrane across which diffusion easily occurs.
Location
1. Lines heart (endocardium)
2. Lines the endothelium (inner surface of a blood vessel)
3. Lines lymph vessel known (endothelium)
4. Forms the wall of alveolar sacs in the lung
5. Lining of collecting ducts of nephrons in the kidney
6. Lines the body cavities (mesothelium)
7. Inner surface of eardrum and membranes of the inner ear
Functions of Simple Squamous Epithelium
The primary function of simple squamous epithelia is -
1. Diffusion
2. Osmosis
3. Filtration
4. Protection against friction
5. Secretion
6. Absorption
2. Simple Cuboidal Epithelium
The simple cuboidal epithelium consists of a single layer of cube-shaped cells fitting
closely together lying on a basement membrane.
All epithelia rest on a basement membrane,
which provides structural support and integrity to epithelia by the
framework of proteins to which epithelial cells adhere.
Location
1. Lines collecting ducts and tubes - Kidney tubules
2. Gland and their ducts
3. Lining of terminal bronchioles
4. Surface of ovaries
5. Choroid plexus of the brain
6. Inner surface of the eye lens
7. Pigmented epithelium of eye, retina
Functions of Simple Cuboidal Epithelium
1. It involves absorbing or secreting
material into the tubes or ducts.
2. Secretion (production and release by cell fluid; mucus,
perspiration, enzyme).
3. Absorption (intake of fluid or substance by cell)
4. Excretion
3. Simple Columnar Epithelium
Simple Columnar Epithelium formed by a single layer of the cell,
rectangular in shape on the basement membrane.
Types of Simple columnar epithelium
The simple columnar epithelium is two types –
A. Non-ciliated simple columnar epithelium
B. Ciliated simple columnar epithelium
A. Non-ciliated simple columnar epithelium
Non-ciliated simple columnar
epithelium cells are a single layer with oval nuclei near the base of cells.
Non-ciliated simple columnar epithelium cells don’t contain or bear any
cilia.
The layer of cells contains columnar epithelial cells with
microvilli and goblet cells.
Microvilli
Specialized for absorption
(absorptive cells). It is finger-like projection serve to increase the surface area of the plasma membrane and allow a larger amount of absorbed digested nutrients from the lumen of the small intestine and
fluids to be absorbed into the body.
Goblet cell
It secretes thick
sticky material mucus. Secreted mucus helps in lubricant and protects the lining of
various body systems.
For example,
digestive system, respiratory system
Location
1. Lining organs of the alimentary canal
2. Goblet cells - Secrete mucus
3. Glands and some duct (gall bladder)
4. Cell with microvilli - absorb product of digestion
5. In the stomach where
it secretes acid, digestive enzymes, and mucus.
Functions of Non- ciliated simple columnar epithelium
1. Secretion and absorption in the alimentary canal
2. Secretion by cells of glands
3. Simple columnar epithelia lines with microvilli
secrete digestive enzymes, where nutrients are absorbed from the lumen of the
intestine.
B. Ciliated Simple Columnar Epithelium
Ciliated simple columnar epithelial cells contain or bear cilia (having hair-like projections called cilia) on their surfaces. Wave-like movement of many cilia propels the content of tubes, which line in one direction only.
Location
1. Lining uterine tubes
2. Respiratory passage
3. Uterus
4. Paranasal sinus
5. Central canal of spinal cord
6. Ventricles of the brain
7. Fallopian
tubes
Functions of Ciliated Simple Columnar Epithelium
1. Moves mucus and other substances via cilia
2. Movement of “oocyte” through the uterine tube
3. Movement of particles out of respiratory passage by
ciliated cells
4. Cilia waves move with mucous with any foreign particles
towards the throat, where they can be swallowed or spit out.
4. Simple Pseudostratified Columnar Epithelium
Composed of a single layer of irregularly shaped and
differently sized columnar cells, attached to the ment membrane.
Found on cells surface either with mucus or bear cilia that
sweep away mucus trap foreign particle for eliminating from body.
Cilia and mucus secretions help collect foreign materials
and they can be coughed or sneezed out.
Location
1. Lining of the l cavity
2. Nasal sinus
3. Auditory tube
4. Pharynx
5. Trachea and bronchi of lungs
6. Male reproductive tract
7. Parts of the ear cavity
Functions of Simple Pseudostratified Columnar Epithelium
1. Movement of a substance across the surface
2. Protection
3. Secretion
Stratified Epithelium Tissue
There are mainly four types of Stratified epithelium tissue-
1. Stratified squamous epithelium tissue
a. Non-keratinized
b. Keratinized
2. Stratified cuboidal epithelium tissue
3. Stratified columnar epithelium tissue
4. Stratified transitional epithelium tissue
1. Stratified Squamous Epithelium
Stratified squamous epithelium is composed of a number of layers of cells, only one layer is in contact with the basement membrane.
In the superficial layer, cells are
made up of squamous (flattened) epithelial cells. The deepest layers of the cell vary in shape from cuboidal to columnar.
Basal or bottom cells are continually replaced by new cells that grow through mitosis. New cells
grow, cells of basal layer continually shift upward surface maturing and then degenerating and become
dehydrated, shrunken and hardened.
Epithelial tissues have a nerve supply, but they do not have
a blood supply. So, they receive
nourishment via the diffusion of substances from the underlying connective
tissue, through the basement membrane.
Types of Stratified squamous epithelium
Stratified squamous epithelium is divided into two types –
A. Non keratinized stratified squamous epithelium
B. Keratinized stratified squamous epithelium
A. Non keratinized stratified squamous epithelium
Non-keratinized
epithelium is found on wet surfaces that may be
subjected to wear and tear, which serves as a protective and lubricating layer of
the epithelium. It covers the lining mucosa, such as-
1. Layer conjunctiva
2. Vagina, anus
3. Inferior urethra
4. Cornea of eye
5. Pharynx and esophagus
6. Rectum
7. Larynx
8. Lining of mouth
B. Keratinized stratified squamous epithelium
Keratinize epithelium surface layer
consists of the dead epithelial cells to which protein keratin K has been added.
They form, tough, moisture resistance, protective layer that
prevents drying of underlying live cells. It is primarily involved providing protection against abrasion.
Keratinized stratified squamous epithelium is found on dry
surfaces that are subjected to wear and tear, such as skin, hair, nails.
Location found stratified squamous epithelium
Found in where the body comes into close contact with the outside
environment.
Such as skin, respiratory, digestive, reproductive system,
excretory system
Functions of Stratified Squamous Epithelium
1. They protected the body from desiccation (becoming completely
dry) and water loss.
2. Protection against abrasion and infection
3. Protective and lubricating layers
2. Stratified Cuboidal Epithelium
Stratified cuboidal epithelium tissue
is cube-shaped epithelial cells composed of more than two layers, arranged in multiple layers.
Location
1. Ducts of sweat gland
2. Sebaceous glands
3. Salivary gland
4. Ovarian follicular cells
5. Developing epithelium in testes
Functions of Stratified Cuboidal Epithelium
1. Secretion
2. Protection against infection
3. Absorption
3. Stratified Columnar Epithelium
A rare type of epithelial tissue composed of column-shaped cells arranged in multiple
layers. Only superficial cells are columnar in form. They are
ciliated in the larynx.
Location
1. Mammary gland duct
2. Male urethra
3. Larynx
4. Conjunctiva
5. Anus
Functions of Stratified Columnar Epithelium
1. Protection
2. Secretion
4. Transitional Epithelium
Transitional epithelium is composed of multiple layers of
pear-shaped cells, which can contract and expand.
It is found lining the urinary bladder and allows for stretching
as the bladder fills. It lines the urinary bladder and ureters, a structure in which
considerable expansion can occur.
Location
1. Lining of the urinary bladder
2. Ureters
3. Superior urethra
Functions of Transitional Epithelium
1. Accommodates fluctuations in the volume of fluid in an organ or tube
and prevents rupture of this organ.
2. Protect against caustic (infection or burning) effect of
Urine.
Get here
details on muscle
tissue and nervous tissue.
2. Glandular Epithelium
Glands are secretory organs, most glands
are composed primarily of epithelium. It
produces and releases substances that perform a specific function in the body.
Secretion - Secrete substance into a duct, onto a surface, or into the blood. Production of such substance required active work by
cells and results in an expenditure of energy. It regulates various physiological
activities and regulates metabolism controlling activities.
For example; Pituitary gland
Check out here types of glandular epithelium.
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