Epithelia
Epithelia are tissues consisting
of closely apposed cells without intervening intercellular substances.
Epithelia are avascular, but all epithelia "grow" on an underlying
layer of vascular connective tissue. The connective tissue and the epithelium
are separated by a basement membrane. Epithelium
covers all free surfaces of the body. Epithelium also lines the large internal
body cavities, where it is termed mesothelium.
Furthermore, the internal surfaces of blood and lymph vessels are lined by
epithelium, here called endothelium.
Epithelia
are classified on the basis of the number of cell layers and the shape of the
cells in the surface layer.
- If there is only one layer of cells in the epithelium, it is
designated simple.
- If there are two or more layers of cells, it is termed stratified.
- Cells in the surface layer are, as a rule, described
according to their height as squamous
(scale- or plate-like), cuboidal or columnar.
Simple Epithelia
Simple squamous
epithelium
This type is
composed of a single layer of flattened, scale- or plate-like cells. It is
quite common in the body. The large body cavities and heart, blood vessels and
lymph vessels are typically lined by a simple squamous epithelium. The nuclei
of the epithelial cells are often flattened or ovoid, i.e. egg-shaped, and they
are located close to the centre of the cells.
Simple cuboidal
epithelium
Cells appear
cuboidal in sections perpendicular to the surface of the epithelium. Viewed
from the surface of the epithelium they look rather like small polygons. Simple
cuboidal epithelium occurs in small excretory ducts of many glands, the follicles of the thyroid gland, the tubules of the kidney
and on the surface of the ovaries.
Simple columnar
epithelium
The cells
forming a simple columnar epithelium are taller than they are wide. The nuclei
of cells within the epithelium are usually located at the same height within
the cells - often close to the base of the cells. An example is the simple
columnar epithelium which lines the internal surface of the gastrointestinal tract (GIT) from the cardia of the
stomach to the rectum.
simple squamous epithelium: any section
containing blood vessels, sections of organs which
include an outer lining (or serosa) of the organs, or sections of kidney
(parietal blades of Bowman's capsules) - H&E,
trichrome
simple cuboidal epithelium: sections of ovaries (epithelium lining the
surface), thyroid gland (follicles), kidney (tubules) or large glands (e.g.
parotid gland) with well preserved small ducts
simple columnar epithelium: sections of the small
intestine (duodenum, jejunum or ileum), uterus (uterine glands), liver (large bile ducts)
or gall bladder - H&E, trichrome
Epithelia
Epithelia are tissues consisting
of closely apposed cells without intervening intercellular substances.
Epithelia are avascular, but all epithelia "grow" on an underlying
layer of vascular connective tissue. The connective tissue and the epithelium
are separated by a basement membrane. Epithelium
covers all free surfaces of the body. Epithelium also lines the large internal
body cavities, where it is termed mesothelium.
Furthermore, the internal surfaces of blood and lymph vessels are lined by
epithelium, here called endothelium.
Epithelia
are classified on the basis of the number of cell layers and the shape of the
cells in the surface layer.
- If there is only one layer of cells in the epithelium, it is
designated simple.
- If there are two or more layers of cells, it is termed stratified.
- Cells in the surface layer are, as a rule, described
according to their height as squamous
(scale- or plate-like), cuboidal or columnar.
Simple Epithelia
Simple squamous
epithelium
This type is
composed of a single layer of flattened, scale- or plate-like cells. It is
quite common in the body. The large body cavities and heart, blood vessels and
lymph vessels are typically lined by a simple squamous epithelium. The nuclei
of the epithelial cells are often flattened or ovoid, i.e. egg-shaped, and they
are located close to the centre of the cells.
Simple cuboidal
epithelium
Cells appear
cuboidal in sections perpendicular to the surface of the epithelium. Viewed
from the surface of the epithelium they look rather like small polygons. Simple
cuboidal epithelium occurs in small excretory ducts of many glands, the follicles of the thyroid gland, the tubules of the kidney
and on the surface of the ovaries.
Simple columnar
epithelium
The cells
forming a simple columnar epithelium are taller than they are wide. The nuclei
of cells within the epithelium are usually located at the same height within
the cells - often close to the base of the cells. An example is the simple
columnar epithelium which lines the internal surface of the gastrointestinal tract (GIT) from the cardia of the
stomach to the rectum.
simple squamous epithelium: any section
containing blood vessels, sections of organs which
include an outer lining (or serosa) of the organs, or sections of kidney
(parietal blades of Bowman's capsules) - H&E,
trichrome
simple cuboidal epithelium: sections of ovaries (epithelium lining the
surface), thyroid gland (follicles), kidney (tubules) or large glands (e.g.
parotid gland) with well preserved small ducts
simple columnar epithelium: sections of the small
intestine (duodenum, jejunum or ileum), uterus (uterine glands), liver (large bile ducts)
or gall bladder - H&E, trichrome
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Title:
Epithelia are
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2013-02-15T02:42:00+07:00
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Epithelia are