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EPITHELIUM
By
Dr. Mudassar Ali Roomi(MBBS, M.Phil)
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Four basic types of tissues?
1. Epithelium
2. Connective tissue
3. Muscular tissue4. Nervous tissue
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EPITHELIUM
DEFINITION: It is made up ofclosely packed cells and arrranged in one or
more layers with almost no intercellular spaces and only a small amount of
intercellular substance.
This tissue is specialized to form the covering or lining of all internal and
external body surfaces. Epithelial tissue covers the whole surface of thebody.
Epithelial tissue that occurs on surfaces on the interior of the body is known
as endothelium.
Epithelial tissue, regardless of the type, is usually separated from the
underlying tissue by a thin sheet of connective tissue; basement
membrane. The basement membrane provides structural support for the
epithelium and also binds it to neighbouring structures.
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Types of Epithelial Tissue
Epithelial tissue can be divided into two
groups depending on the number of layers of
which it is composes.
Epithelial tissue which is only one cell thick is
known as simple epithelium.
If it is two or more cells thick such as the skin,
it is known as stratified epithelium.
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Types of simple epithelium
Simple epithelium can be subdivided according to the shapeand function of its cells.
1. Simple Squamous (pavement) epithelium:
Squamous cells have the appearance ofthin, flat plates.
The shape of the nucleus usually corresponds to the cellform and help to identify the type of epithelium.Squamous cells, for example, tend to have horizontallflattened, elliptical nuclei because of the thin flattenedform of the cell.
They form the lining of cavities such as the mouth, bloodvessels, heart and lungs and make up the outer layers ofthe skin.
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1. Simple Squamous (pavement)
epithelium:
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2. Simple Cuboidal Epithelium:
As their name implies, cuboidal cells are roughly
cuboidal in shape.
Each cell has a spherical nucleus in the centre.
Cuboidal epithelium is found in glands and in thelining of the kidney tubules
Also found in the small ducts of exocrine glands. Surface epithelium of ovary (germinal
epithelium).
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3. Simple Columnar Epithelium: The cells are elongated and column-shaped.
The nuclei are elongated and are usually located near thebase of the cells.
Columnar epithelium forms the lining of the stomach andintestines and gallbladder.
Some columnar cells are specialized for sensory receptionsuch as in the nose, ears and the taste buds of the tongue.
G
oblet cells (unicellular glands) are found between thecolumnar epithelial cells of the intestine. They secretemucus or slime, a lubricating substance which keeps thesurface smooth.
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Simple columnar epithelium with goblet
cells
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Ciliated Columnar Epithelium:
These are simple columnar epithelial cells, but in addition,
they posses fine hair-like outgrowths, cilia on their free
surfaces. These cilia are capable ofrapid, rhythmic, wavelike beatings
in a certain direction. This movement of the cilia in a certain
direction causes the mucus, which is secreted by the goblet
cells, to move (flow or stream) in that direction.
Ciliated epithelium is usually found in the air passages like the
nose.
It is also found in the uterus and Fallopian tubes of females.
The movement of the cilia propel the ovum to the uterus.
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Pseudostratified epithelium
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