Epithelial Tissue
Key Terms
Histology:
– the study of tissues.
Tissues:
– Simply groups of similar cells that work
together performing the same task
– Greatest form of teamwork in the body
Where are tissues found?
With few exceptions, organs are composed
of four basic tissue types:
– Epithelial Tissue
– Connective Tissue
– Muscular Tissue
– Nervous Tissue
Why Study Histology?
Knowing the difference between normal
and abnormal tissue is the first step in
diagnosis and treatment of patients.
Skin, our largest organ
* made of all four tissue types
Epithelial Tissue
Makes up 3% of your body weight
They don’t move
They don’t send messages
Their cells are all touching one another
Of all tissues, they are the most widely
varied in structure and function
Locations of Epithelial Tissues
Covers the body (epidermis)
Found on the inside of hollow organs and
the outside of all organs
Found above a connective tissue layer
(epi = above)
Lines the cavities, tubes, ducts, and blood
vessels inside the body
Epithelial Anatomy
Apical surface – upper surface that is free or
exposed to the “exterior”
Basal surface – attached surface (below)
Microvilli – small fingerlike extensions that
increase the surface area allowing for more work
to be done
Functions of Epithelial Tissue
– Protects from physical & chemical injury
– Protects against microbial infection
– Contains nerve endings which respond to
stimuli
– Filters, secretes & reabsorbs materials
– Secretes fluids to lubricate joints
Three Basic Shapes
Squamous – like scales, or
pancakes (“being squashed
like a pancake”)
Cuboidal – looks like cubes
Columnar – longer and look
like columns
Cell Organization
Simple – single layer of cells; typically found
where absorption and filtration occur or a single
layer of epithelial is needed
simple squamous
simple cuboidal
simple columnar
Stratified – layers of cells; common in areas
where protection is needed like the skin
stratified squamous
stratified cuboidal
stratified columnar
Two Types of Stratified Columnar
Ciliated
cilia
Unciliated
No cilia
Squamous Epithelium
Simple – one cell thick
Forms solid layer of cells
which line blood vessels,
body cavities and covers
organs in body cavities
Stratified – multiple layers
Forms epidermis
Cuboidal Epithelium
Cuboid Cells
Simple – one cell thick
Duct
Roughly cube shaped
Cuboid Cells
Duct
Line ducts in kidneys
where re-absorption and
secretion activities take
place.
Columnar Epithelium
Simple – one cell thick
Column shaped
(long and narrow)
Lines digestive tract
where re-absorption &
secretion occurs.
Confusing Epithelial Tissue
Transitional Epithelium – stratified tissue
that can’t make up its mind as to whether it
is squamous or cuboidal
Shape of cells depends upon the amount
of stretching (ex: bladder)
Confusing Epithelial Tissue Continued…
“Pseudostratified Columnar Epithelium”
Looks like it has more than one layer
because of the position of the nucleus
Nuclei are positioned at differing levels
Cells narrow in the area without the
nucleus
Epithelial Tissue in Review…
Types of Epithelial Membranes
Mucous or mucosa– lining of tubes; moistens
and protects from enzymes (stomach,
trachea, and vagina)
Serous or serosa – outside of organs;
lubricates (all thoracic, abdominal and pelvic
organs)
Cutaneous or skin – body surface; protection
Synovial – synovial joints; lines and protects
synovial cavities (elbow, knee, hip, etc.)