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HISTOLOGY NOTES
NOTES ON EPITHELIAL TISSUES
CHARACTERISTIC FEATURES OF EPITHELIAL TISSUE
One of the four basic tissues in the human body.
The tissue that covers the body surfaces and lines most body cavities.
Made up of closely aggregated polyhedral cells with their edges
connected by tight junctions.
All epithelia are supported by a basement membrane of variable
thickness.
The basement membrane separates the epithelial cells from the
underlying supporting tissues
The tissue is avascular never penetrated by blood vessels.
There are no capillaries among the epithelial cells
Dependent on diffusion of oxygen and metabolites from
adjacent supporting tissues.
CLASSIFICATION OF EPITHELIAL TISSUE :
Based on three morphological characteristics:
1. Number of cell layers:
A single layer of cells is called a Simple epithelium:
Two or more layers in thickness it is called stratified epithelia
Pseudostratified epithelium: some cells reach the surface others only
part of the way to surface from the basement membrane
2. Shape of the cell:
• Squamous cell- Flat cell- height is less than diameter
• Cuboidal cell is- cube shaped- height and diameter is similar
• Columnar epithelial cell is a tall cell- height is greater than diameter.
3. Surface specialisations: simple epithelia may exhibit a variety of surface
specialisations such as microvilli and Cilia.
FUNCTIONS OF EPITHELIAL TISSUE:
Protection
Secretion
Absorption
Exchange or diffusion
, 2
A.SIMPLE EPITHELIUM
1) SIMPLE SQUAMOUS EPITHELIA:
Composed of: flattened, irregularly shaped cells forming a continuous
surface. It is also sometimes called pavement epithelium. They look like
scales of a fish hence the name. The height of the cells is less as compared to
the width.
Function: The tissue is found lining surfaces involved in passive
transport( diffusion) of gases or fluids.
Distribution:
Aveoli of lungs
Lining of blood vessels (endothelium)
Lining of body cavities –pleural,pericardial and peritoneal
( mesothelium)
2) SIMPLE CUBOIDAL EPITHELIUM:
In a section perpendicular to basement membrane: epithelial cell appears
square or cuboidal in shape. Height of cells same as width of cell.On
surface view they are polygonal in shape.
The nucleus is round and centrally placed.
Function: secretory and absorptive
Distribution:
Follicles of thyroid gland
Surface of ovary
Ducts of many glands
Inner surface of lens
Pigment cell layer of retina
Proximal convoluted tubules of kidneys (with prominent brush
border)
3) SIMPLE COLUMNAR EPITHELIUM:
Cells are taller compared to their width. The nucleus is elongated and
located in lower half of cells, in the same level as in other cells.
Types and distribution:
There are different types of columnar cells in different locations.
Simple columnar cells with no specialisation on surface
Seen lining the mucous membrane of stomach and large intestine
Ciliated columnar cells with cell surface bearing cilia are seen in
Respiratory tract,Uterine tubes,Efferent ductules of testis,Parts of middle ear
and Auditory tube,Ependymal lining of central canal of spinal cord and
HISTOLOGY NOTES
NOTES ON EPITHELIAL TISSUES
CHARACTERISTIC FEATURES OF EPITHELIAL TISSUE
One of the four basic tissues in the human body.
The tissue that covers the body surfaces and lines most body cavities.
Made up of closely aggregated polyhedral cells with their edges
connected by tight junctions.
All epithelia are supported by a basement membrane of variable
thickness.
The basement membrane separates the epithelial cells from the
underlying supporting tissues
The tissue is avascular never penetrated by blood vessels.
There are no capillaries among the epithelial cells
Dependent on diffusion of oxygen and metabolites from
adjacent supporting tissues.
CLASSIFICATION OF EPITHELIAL TISSUE :
Based on three morphological characteristics:
1. Number of cell layers:
A single layer of cells is called a Simple epithelium:
Two or more layers in thickness it is called stratified epithelia
Pseudostratified epithelium: some cells reach the surface others only
part of the way to surface from the basement membrane
2. Shape of the cell:
• Squamous cell- Flat cell- height is less than diameter
• Cuboidal cell is- cube shaped- height and diameter is similar
• Columnar epithelial cell is a tall cell- height is greater than diameter.
3. Surface specialisations: simple epithelia may exhibit a variety of surface
specialisations such as microvilli and Cilia.
FUNCTIONS OF EPITHELIAL TISSUE:
Protection
Secretion
Absorption
Exchange or diffusion
, 2
A.SIMPLE EPITHELIUM
1) SIMPLE SQUAMOUS EPITHELIA:
Composed of: flattened, irregularly shaped cells forming a continuous
surface. It is also sometimes called pavement epithelium. They look like
scales of a fish hence the name. The height of the cells is less as compared to
the width.
Function: The tissue is found lining surfaces involved in passive
transport( diffusion) of gases or fluids.
Distribution:
Aveoli of lungs
Lining of blood vessels (endothelium)
Lining of body cavities –pleural,pericardial and peritoneal
( mesothelium)
2) SIMPLE CUBOIDAL EPITHELIUM:
In a section perpendicular to basement membrane: epithelial cell appears
square or cuboidal in shape. Height of cells same as width of cell.On
surface view they are polygonal in shape.
The nucleus is round and centrally placed.
Function: secretory and absorptive
Distribution:
Follicles of thyroid gland
Surface of ovary
Ducts of many glands
Inner surface of lens
Pigment cell layer of retina
Proximal convoluted tubules of kidneys (with prominent brush
border)
3) SIMPLE COLUMNAR EPITHELIUM:
Cells are taller compared to their width. The nucleus is elongated and
located in lower half of cells, in the same level as in other cells.
Types and distribution:
There are different types of columnar cells in different locations.
Simple columnar cells with no specialisation on surface
Seen lining the mucous membrane of stomach and large intestine
Ciliated columnar cells with cell surface bearing cilia are seen in
Respiratory tract,Uterine tubes,Efferent ductules of testis,Parts of middle ear
and Auditory tube,Ependymal lining of central canal of spinal cord and
