Characteristic Features of Epithelial Tissue在线视频

Hi every one,

welcome to the clinical histology world.

We will divide this chapter into three parts:

covering epithelium,

characteristic features,

and specialized structures.

Today we will introduce the characteristic

features of epithelial tissue.

Here are the objectives of this section.

First,

we are going to list the principal functions

and types of epithelial tissue.

Second,

we will state the characteristic features of

epithelial tissues

and explain the associations

of these features and functions.

The last objective will be

to use the features of

epithelial tissue to explain the key

points of skin grafting.

Let's first review the previous contents.

There are four basic tissues in our body,

including epithelial, connective,

muscular, and nervous tissues.

Connective tissue is characterized by cells

producing extracellular proteins,

e.g. collagen and fibronectin;

muscle tissue is composed of elongated cells

specialized for contraction and movement;

and nervous tissue consists of cells with long,

fine processes specialized to receive,

generate, and transmit nerve impulses.

Lastly we have epithelial tissue,

our focus for today.

Look at these pictures.

Can you identify which one is epithelial tissue?

Is it A, B, or C ?

Okay, the answer is A.

Did you get it right?

But why is it A?

How did you identify it?

To answer this question,

you need to know

what are the unique features of epithelial tissues.

The principal functions of epithelial tissues

include the following:

Covering, lining, and protecting surfaces

(e.g, epidermis, the skin that covers our body)

Absorption (e.g, the intestinal or gut lining)

Secretion (e.g, sweat glands)

Other:

specific cells of certain epithelia may be contractile

(e.g, myoepithelial cells,

epithelial cells that act like muscles)

or specialized sensory cells,

such as those of taste buds

or olfactory epithelium (for smell)

According to function,

epithelia can be divided into two main groups:

1) covering (or lining) epithelia and

2) secretory (glandular) epithelia.

This is a loose functional division

for we do have lining epithelia,

in which the cells also secrete

(e.g, the lining of the stomach);

and lining epithelium with glandular cells

(e.g, mucous cells in the small intestine and trachea).

Specialized epithelial cells are all categorized

under the category of "others" in the last slide.

They all have the following common features:

The first one is avascular,

the prefix 'a' means "no",

vascular is blood vessel.

So it means there is no blood vessel

in the epithelial tissue.

This picture shows

what the esophageal lining looks like.

It contains stratified squamous epithelium.

This protects the underlying tissues

and prevents the entry of harmful substances.

The second feature is that epithelial cells

are arranged tightly with only

a little intercellular substance stained in black,

again offering protection to the underlying tissue.

The last feature is polarity.

What is polarity?

Just like my skirt it has its top and bottom.

Or as the cell model shows,

regions of cuboidal or columnar cells that

are situated next to each other

form the lateral surfaces;

cell membranes here often have numerous folds

which increase the area and functional

capacity of that surface.

The part of the cell next to the ECM

and connective tissue is called the basal pole

and the top surface,

usually facing a space,

is the apical pole,

with the two poles differing significantly

in both structure and function.

for example:

growth factors are released from the basal surface

where as growth factor receptors are located

on the apical surface,

so when the epithelium is injured,

the lateral surfaces are damaged

and growth factors can leak

to the apical side and stimulate growth

and wound healing

Let me give you a clinical example.

I was a doctor in the Burn Department 17 years ago.

My daily work was to treat patients with skin loss.

Skin grafting is often used to burn patients.

Skin is removed from one area of the body

and transplanted to another,

for example,

from the scalp as shown in this picture.

The wound site is often much larger than the skin graft,

so it is necessary to cut the graft

into small pieces and try to cover more

area of the wound.

So, my question is,

when you put the graft onto the wound,

which side should be up?

We will discuss this in the next lecture.

So, to summarize:

there are 3 features of epithelial tissue

which could help us identify the epithelial tissue

under the microscope.

Try it!

That's all. Thank you!