This document provides an overview of epithelial tissues. It defines tissues and discusses the four main types: muscular, nervous, epithelial and connective tissues. Epithelial tissue forms coverings and linings. There are several types of epithelial tissue classified by cell shape and layer, including simple squamous, simple cuboidal, simple columnar, pseudostratified columnar, stratified squamous, transitional and glandular epithelium. Each type has distinct characteristics and locations in the body where they perform important protective, secretory, absorptive and other functions.

1. Section 1, Chapter 5
Introduction to Tissues
& Epithelial Tissues

2. Tissues
A Tissue is to a group of similar cells that carries out a specialized function.
Histology is the science of tissues.
examples of tissues

3. There are four broad categories of tissues
Muscular tissue – specialized to contract
Nervous tissue – conducts, senses, and stores information
Epithelial tissue – forms coverings (skin) & linings (blood vessels)
Connective tissues – support, transport, protect

4. Intercellular junctions
Cells may be separated by a matrix or connected together by cellular junctions.
1. Tight Junction
A tight junction fuses the cell membranes of adjacent cells together so
molecules cannot move between the cells. Instead, they must move
through the cells.
Tight junctions prevent the passage of unwanted & harmful substances
Examples: Blood Brain Barrier & Digestive Tract
Cell 1
Interlocking membranes form
tight junction between two cells
Cell 2

5. Cellular Junctions
2. Desmosome
desmosomes form “spot welds” between cells
Provides structural support
Examples of desmosomes are in the epidermis of the skin
Cells connected by desmosomes

6. Cellular Junctions
3. Gap Junction
Gap Junctions connect cells by protein ion channels that
allow for cell-to-cell diffusion of ions
Example of gap junctions are within the intercalated
discs of cardiac muscle
Intercalated discs of cardiac muscle
are one type of gap junction.

7. Types of Tissues: Epithelial Tissue
Epithelial Tissue:
Epithelial tissue lines cavities, such as the digestive & respiratory tracts
It also forms coverings, such as the skin
Functions include protection, secretion, absorption, excretion

8. Epithelium: structure
Epithelium is anchored to a layer of connective tissue, called the
basement membrane.
Epithelium has a basal surface that faces the basement membrane
The free (apical) surface is exposed to the open space (lumen)
Open space = lumen
Basement membrane

9. Characteristics of Epithelial Tissue
Epithelium consists of tightly packed cells
They lack a blood supply, instead they receive nutrients by diffusion
Epithelium readily divide, so they are continually replaced = rapid healing

10. Classifications of Epithelial Tissues
Epithelium are classified by the layer of cells
1. Simple = Single layer of epithelial cells
2. Stratified = two or more layers of cells
And they’re classified by the shape of cells
1. squamous = scale-like
2. cuboidal = cube-like shape
3. Columnar = tall cells

11. Simple Squamous Epithelium
Single layer of flattened cells
Functions include diffusion, filtration, and secretion
Locations include:
air sacs of lungs (alveoli)
lining of capillaries and the walls of blood vessels
glomerulus of kidneys.
surface view of simple squamous ep.
alveoli of lung

12. Simple Cuboidal Epithelium
Single layer of cube-shaped cells
Functions include secretion and absorption
Locations include
the lining and the ducts of some glands
tubules within kidneys
lumen
cross-section of tubules in kidneys

13. Simple Columnar Epithelium
Single layer of elongated cells and their nuclei appear as a single row
Functions include absorption, secretion, or transport
Often contain goblet cells
Goblet cells secrete mucus onto apical surface
may be ciliated, or have microvilli, or have no modifications on apical surface.
columnar cells
goblet cell
microvilli “brush border”

14. Simple Columnar Epithelium
Some simple columnar epithelium are covered with cilia on
their free surface.
Cilia beat constantly in a rhythmic motion to propel
substances across the cell surface.
Cilia propels the egg through uterine tube

15. Simple Columnar Epithelium
Some simple columnar epithelium are covered with
microvili on their free surface.
Microvilli are extensions of the cell membrane that increases the
surface area of a cell.
Example of microvilli include the intestinal epithelium, where they
increase the amount of contact each cell makes with food.
Microvilli greatly enhance absorption of nutrients.

16. Pseudostratified Columnar Epithelium (PSCE)
PSCE appear striated, but each cell touches the basement membrane.
Usually ciliated
Most PSCE contain goblet cells that secrete mucus
Locations of PSCE include the lining of the
respiratory tract: nasal cavity, pharynx,
trachea, bronchi
Functions: Mucus from goblet cells traps
debris & cilia moves the mucus (and trapped
debris) away from the lungs

17. Stratified Squamous Epithelium
Several layers of cells = thick tissue
Primary function is to protect underlying tissues from abrasion
Superficial cells are squamous but the deeper cells are cuboidal or
columnar
May be keratinized or non-keratinized

18. Keratinized Stratified Squamous Epithelium
Keratinized epithelium is found in the epidermis (outer layer) of skin
Keratin is an insoluble protein that hardens and forms a protective coating.
Cells accumulate keratin over time, so the older outermost cells of the
epidermis are keratinized
Stratified squamous epithelium of epidermis

19. Non-keratinized Stratified Squamous Epithelium
Non-keratinized (moist) stratified squamous epithelium
lines the esophagus, oral cavity, vagina, and anal canal.
Apical surface
Stratified squamous epithelium of vagina

20. Transitional Epithelium
Transitional epithelium forms an expandable lining (Function: permit expansion)
Locations include the inner layer of the urinary bladder & ureters
The lining is several layers thick and the cells appear cuboidal when the urinary bladder
is contracted, but only a few layers thick when the urinary bladder is distended and the
cells appear squamous.
empty urinary bladder
distended urinary bladder

21. Glandular Epithelium
Glandular epithelium is specialized to produce & secrete substances
Glandular epithelium form glands
Exocrine Glands
Exocrine glands secretes substances
through ducts onto an open surface
Examples includes goblet cells, sweat
glands, and mammary glands
Duct of a
sweat gland

22. Glandular Epithelium
Endocrine Glands
Endocrine glands secretes substances (hormones) directly into the blood
stream.
Examples includes the thyroid gland, pituitary gland, adrenal glands, ect.
Follicles of thyroid gland are
composed of simple cuboidal
epithelium
End of Section 1, Chapter 5