Kufa University
Dentistry College
First Year
Lect. Dr. Dheyaa S.A. Al-Hissnawy
Medical Biology
Primary Tissues
Lec. 1
Epithelial Tissue
Epithelial tissues are found on surfaces as either coverings (outer surfaces) or linings (inner
surfaces).
GENERAL FEATURES
A. Because they have no capillaries of their own, epithelial tissues receive oxygen and nutrients
from the blood supply of the connective tissue beneath them.
B. Many epithelial tissues are capable of secretion and may be called glandular epithelium, or
more simply glands.
C. Highly cellular (sparse intercellular space).
D. Numerous intercellular junctions for attachment and anchorage.
E. High regenerative capacity, especially in epithelial membranes, to replace continual sloughing of
cells from free surface.
F. Most rest on a basement membrane that provides support and attachment for the epithelial cells
and serve as a selective diffusion barrier.
CLASSIFICATION
Classification of the epithelial tissues is based on the type of cell of which the tissue is made. There
are three distinctive cell shapes:
1) squamous cells are flat,( width much wider than tall), resembling a “fried egg." and Nucleus
is highly flattened
2) cuboidal cells are cube shaped(equal height and width), nucleus is spherical.
3) columnar cells are tall and narrow, Nucleus is oval shaped, generally located toward the base
of the cell.
As well to the number of layers of cells which either “Simple” is the term for a single layer of cells,
and “Stratified” means that many layers of cells are present.
TYPES OF EPITHELIAL TISSUES
a. Simple squamous—one layer of flat cells; thin and smooth. Sites: alveoli (to permit diffusion of
gases); capillaries (to permit exchanges between blood and tissues).
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Kufa University
Dentistry College
First Year
Lect. Dr. Dheyaa S.A. Al-Hissnawy
Medical Biology
Primary Tissues
Lec. 1
b. Stratified squamous—many layers of mostly flat cells; mitosis takes place in lowest layer.
Divided into two types:
i.
Nonkeratinized (moist). Lining of wet cavities, including the mouth, esophagus,
rectum, and anal canal; surface cells are nucleated and living.
ii.
Keratinized (dry). Epidermis of the skin (a barrier to pathogens); surface cells are
nonliving.
c. Transitional—stratified, yet surface cells are rounded and flatten when stretched. Site: urinary
bladder (to permit expansion without tearing the lining).
d. Simple cuboidal—one layer of cube-shaped cells. Sites: thyroid gland (to secrete thyroid
hormones); salivary glands (to secrete saliva); kidney tubules (to reabsorb useful materials back
to the blood).
e. Simple columnar—one layer of column-shaped cells. Sites: stomach lining (to secrete gastric
juice); small intestinal lining (to secrete digestive enzymes and absorb nutrients— microvilli
increase surface area for absorption).
f. Stratified cuboidal / columnar. Lines the larger ducts of exocrine glands.
g. Pseudostratified: Cells are of various heights. All cells rest on the basement membrane, but
only the tallest cells reach the free surface. Variation in height of the cells and the location of
nuclei give the appearance of a stratified epithelium. Frequently ciliated. Provides protection.
Forms the lining of much of the respiratory tract and much of the male reproductive system.
FIGURE (1-1): Types of lining and covering epithelia.
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Kufa University
Dentistry College
First Year
Lect. Dr. Dheyaa S.A. Al-Hissnawy
Medical Biology
Primary Tissues
Lec. 1
SURFACE SPECIALIZATION
A. Microvilli
a. Finger-like extensions from the free surface of the cell, about 1 micron in height.
b. Present in large numbers on each cell and, collectively, are called a brush or striated border.
c. Contain a core of actin microfilaments.
d. Are relatively nonmotile.
e. Increase surface area for absorption.
f. Prominent on cells lining the digestive tract and proximal tubules in the kidney.
B. Stereocilia
a. Large, nonmotile microvilli; not cilia.
b. Contain a core of actin microfilaments.
c.
Increase surface area.
d. Present on cells lining the epididymis and ductus deferens in the male reproductive tract.
C. Cilia
a. Multiple hair-like extensions from free surface of the cell; 7–10 microns in height.
b. Highly motile; beat in a wave-like motion
c.
Function to propel material along the surface of the epithelium (e.g., in the respiratory
system and the oviduct of the female reproductive system)
d. Core of a cilium is called the axoneme, in which nine pairs of microtubules surround a
central pair of microtubules (9 + 2 arrangement).
e.
The axomene of each cilium originates from a basal body that is located at the apex of the
cell and is composed of nine triplets of microtubules.
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