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HISTOLOGY
Topic: EPITHELIUM
Clinical Instructor/s: Dr. Antonette A. Baes
Layout by: Alyssa Gayle Garcia
INTRODUCTION TO TISSUES
● Tissue is group of cells that perform a similar functions
● Parenchymal cells are specific cells that is responsible for the
function of the organ
o E.g., The parenchymal cells of the liver that
produces bile are the hepatocytes
● Stroma are connective tissues were the parenchymal cells are
located
Figure 1. Four Basic Types of Tissues
CHARACTERISTICS OF EPITHELIUM
● Closely aggregated usually polyhedral
● Only a small amount of extracellular matrix; has a few
connective tissues
● Strong intracellular adhesion
● Avascular
o no blood vessels, gets nutrition from the
connective tissue
o The connective tissues’ blood vessels diffuse the
nutrients and oxygen to supply the cell
● All epithelial cells rest on basal lamina
o Basal lamina is the reason for its polarity; meaning
it has an apex and a base
▪ Base is the part of the cell attached to the
basal lamina
▪ Apex is the part of the cell facing the
lumen
o Basal lamina is composed of lamina densa and
lamina lucida
▪ Lamina densa - electron dense layer;
composed of type IV collagen fibers
▪ Lamina lucida - electrolucent; type III
collagen fibers
o Basement membrane is composed of basal
lamina
o Under the light microscope, only the basement
layer is visible since it is thick
o However, under the electron microscope, we can
delineate the basement membrane (lamina lucida
and densa)
FUNCTIONS
● Covering and protecting surfaces and body cavities
o Is skin equivalent to epithelium?
▪ Skin is an organ, epithelium is a tissue
▪ Epidermis = epithelium; stratified
squamous keratinized
● Absorption
● Secretion
● Contraction
o Myoepithelial cells - covering the secretory portion of
gland. Singular cells that has contractile “tentacles”
that helps in secretion
● Sense of taste and smell - the neuroepithelial cells present in
eyes and ears
MAJOR CLASSIFICATION OF EPITHELIUM
● Covering Epithelium
o Lines all external (skin), internal surfaces (lumen of
blood vessels: endothelium) and body cavities
(mesothelium - simple squamous)
o All substances entering and leaving the organ
passes through it
o How to name an epithelial lining?
▪ Shape of topmost cell
● Squamous - flattened
● Cuboidal - square
● Columnar - rectangular
▪ Number of cell layers
● Simple - one layer
o The cells are attached
to the basement
membrane
o Generally, contains the
following:
▪ Lamina
Propia:
OUTLINE
I Introduction to Tissues
II Characteristics of Epithelium
III Functions of Epithelium
IV Major Classification of Epithelium
● Function of the Major Classification of Epithelium
V Cell Surface Modifications
VI Glandular Epithelium
VII Classification According to How Secretory Products Leave
The Cells
VIII Classification Based On Consistency Of Secretion
IX Clinical Significance
FOUR BASIC TYPES OF
TISSUES
EPITHEL
IUM
CONNEC
TIVE
MUSCUL
AR
NERVOU
S
