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Systems composed of Organs
Organs composed of Tissues
Tissues composed of Cells

Tissues - major components of
systems and organs

http://www.anselm.edu/homepage/jpitocch/genbio/organizationnot.html

VC Supplementary Lesson: Tissues

Types of Tissue:
Muscular tissue: Muscular tissues make
up the major part of the soft tissues of
the body & by means of its contraction
power helps in locomotion. e.g. – Skeletal
muscle, cardiac muscle.

Nervous tissue: Nervous tissue is highly
specialized tissue which controls & co-
ordinates the body functions by forming
nervous system. e.g – Neuralgia, White
matter, Grey matter.

Connective tissue: Connects
different structures of the body &
also helps to provide framework of
the body. e.g. – Blood, Bones.

Epithelial tissue: are formed of cells
that line the cavities in the body and
also cover flat surfaces. Of the four
major tissue types found in the
human body epithelial cells are by far
the most prolific.

The muscular, connective and
nervous tissues mentioned on
the previous slides will be
discussed further in the
Organ System discussion for
that particular organ.

The succeeding slides will
focus on Epithelial tissues.

Special types of tissues
Epithelial tissue: Covering the external &
internal body surfaces. e.g. – Skin,
internal covering of (Gastro-intestinal
Tract) GIT.
1) Epithelial - linings and coverings
a) simple - single layer (found in the
intestine
b) stratified - multiple layers
c) cuboidal - cube shaped (secretory)
d) columnar - column shaped (found in
the intestine)
e) squamous - flat for diffusion (found in
the lungs)

An epithelium may be one or more
cells thick and the cells may be of
very different shapes and sizes.
Some are thin and flat. They form
pavement or squamous epithelium
which is found, for example, in the
lining of parts of the kidney tubes.

Where Are Epithelial Cells Found?

Epithelial cells line the major cavities of
the body.
Epithelia form the structure of the lung,
including the alveoli or air sacs where gas
exhange occurs.
• Cells line most organs, such as the
stomach and small intestine, kidney, and
pancreas. They also line the esophagus.
• Cells are also found in ducts and
glands, like the bile duct and sailvary
glands.

•The skin is made of epithelial cells.
Its striated layers demonstrate the
extensive morphology of epithelia.
•Capillary beds are made of
epithelium.
•Epithelia is the first type of cell to
differentiate in the embryo. This
occurs during the eight-cell stage.

•Epithelia can specialize to act as
sensory receptors. They form taste
buds, line the nose, and are in the ear.
They are also found in the eye.
•Female reproductive organs are lined
with ciliated epithelial cells.

How Do Epithelial Cells Differ From Other Cells?
Avascular
•Capillaries do not reside within
epithelial cell tissues.
Sensory
•Endings of neurons are present within
epithelial cell tissues
•Perceive external stimulus (i.e.
Tactile)

Gliding surface layer
•Epithelial cells slough off and glide in
order to replace dead cells.
•This function allows epithelial cells to
maintain a closed barrier to the external
environment.

Transitional
•Multi-layered epithelia are able to
stretch
•Allows the urinary bladder to distended
or contracted without compromising it
Tight barrier
•tight junctions
•Epithelium is held together more tightly
than other cells
•Aids cells in withstanding mechanical
stress

Different from endothelial cells
•Endothelial cells line the insides of
structures that aren’t exposed to the
“outside”
•Ex. Blood vessels

Structure of Epithelial Tissue
Epithelial cells are bound together in
sheets of tissue called epithelia. These
sheets are held together through several
types of interactions, including tight
junctions, adherence, and gap junctions.

One type of junction found only in
epithelium is the tight junction, which is
considered by most scientists as the
closest junction in the world.
http://www.bio.davidson.edu/people/kabernd/BerndCV/Lab/EpithelialInfoWeb
/index.html

Tight junctions act as the delineation
between the apical (upper) and basal
(lower) regions of an epithelial cell in
conjunction with polarization between
the two regions. Epithelium is
supported on the basal side by a
basement membrane called the basal
lamina.

Below the basal lamina lies the capillary
bed, which provides epithelia with
required nutrients and disposal of waste
products. In addition, the nucleus in the
epithelial cell is usually found closer to
the basal surface than the apical
surface.

When the cells of squamous
epithelium have wavy outlines (e.g.,
cells lining the blood vessels) they are
said to be tessellated. Other cells are
approximately as wide as they are tall.
These form cuboidal or cubical
epithelium which is found in many
glands (e.g., the liver).
In columnar epithelium the cells are
tall and column-shaped. Such
epithelium lines most of the gut.

If columnar cells bear cilia the
epithelium is known as ciliated
columnar epithelium. Ciliated cells
occur in the lining of the trachea
(windpipe). The cilia beat to help
remove dirt particles.

The outer cells of the skin and the
lining of the cheek form stratified
squamous epithelium. It is also found
in the front, transparent layer of the
eye (cornea).

A layer or sheet of cells that lines a
body cavity; they show an unusually
high cell-turnover rate. Epithelial cells
are held together by a small amount
of cementing substance. The outer
covering of the body (the skin), the
lining of the gastrointestinal
tract and other organs, such as
the lungs and blood vessels, and the
inner lining of the ducts in glands are
examples.

Below most epithelia is a thin sheet
of connective tissue, the basement
membrane. The free surface of most
types of epithelium (the surface that is
not attached to other tissue) may have
on it short hair-like structures
called cilia.

The ones forming the outer
covering of the skin are mainly
protective and water-resistant,
while the cells of the lung lining
produce the wet mucusin which
oxygen dissolves before passing to
the blood.

When the epithelium is several layers
of cells thick it is said to stratified.

The cells of epithelia may serve very
different purposes. Those lining
the salivary glands, and the glands in
the intestine for example, produce
the enzymes that digest food.

http://www.daviddarling.info/encyclopedia/E/epithelium.html

Functions
Boundary & Protection

Epithelial cells cover the inner and
outer linings of body cavities, such as
the stomach and the urinary tract. As
the barrier between the outside
world’s contaminants and the body,
these cells replicate often to replace
damaged or dead cells.

Many layers provide better
protection, meaning if one layer is
lost, the underlying tissue is still
protected. Tight junctions, are
very difficult to alter or break and
create a semi-permeable seal that
few macromolecules or microbes
can penetrate.

Sensory
Although epithelial cells are
avascular, they are innervated. These
nerve endings provide signals for
sensory sensations such as taste,
sight, and smell. These cells exhibit
specialized structure to fulfill their
function.

Absorption
The ability of certain epithelial cells to
use active-transport systems, as
discussed above, enables them to
absorb filtered material, such as
glucose from the lumen of the
intestine, which can then be circulated
to the rest of the body. Cells are also
able to endocytose other materials that
are necessary for cell growth and
signaling. For more information,
see transcytosis.

Tranportation
Some epithelial cells, such as the ones found
on the intestinal lining, aid in the
transportation of filtered material through
the use active-transport systems located on
the apical side of their plasma
membranes. For example, the glucose-Na+
pump located within certain domains of the
plasma membrane of epithelial cells lining the
intestine enable the cells to generate Na+
concentration gradients across their plasma
membranes, which provides the energy
needed to uptake glucose, from the lumen of
the intestine.

The glucose is then released into the
underlying connective tissues and is
transported into the blood supply
through facilitated diffusion down its
concentration gradient.

Secretion & Lubrication
Some epithelial cells, such as the goblet
cells, secrete fluids that are necessary for
other processes such as digestion,
protection, excretion of waste products,
lubrication, reproduction, and the
regulation of metabolic processes of the
body. As part of its excretory role, certain
epithelial cells secrete mucus, which
lubricate the body cavities (i.e. peritoneum,
pericardium, pleura, and tunica vaginalis)
and passageways that they line.

In the trachea, goblet epithelial cells
secrete mucous which provides the
lubrication to aid ciliated epithelial
cells in sweeping bacteria and dust
away from the lungs. In addition, type
II alveolar cells excrete pulmonary
surfactant, which decreases surface
tension, allowing for normal lung
function.

Movement

Some epithelial cells have cilia,
which aid in moving substances
in the lumen by creating a
current via coordinated
"sweeping" of the cilia.

For instance, ciliated columnar
epithelial cells are instrumental
in the movement of the ovum
through the Fallopian tubes to
the uterus.

1. What are the four major classification of
tissues?
2. For each kind of tissues give at least three
organs where it can be found.

http://www.anselm.edu/home
page/jpitocch/genbio/organiza
tionnot.html

http://www.bio.davidson.edu/
people/kabernd/BerndCV/Lab/
EpithelialInfoWeb/index.html

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VC Supplementary Lesson: Tissues

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