Chapter 4.2.1 Introduction to Epithelial Tissues BIO201

Summary

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Outlines

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Keywords

💡Epithelial tissue

Epithelial tissue, also known as epithelium, is a type of tissue composed of cells that are tightly bound together to form a sheet. It plays a crucial role in covering body surfaces and lining cavities, such as the skin and the respiratory and digestive tracts. In the video, epithelial tissue is the central theme, with its functions and characteristics being the main focus of discussion.

💡Covering and lining epithelia

Covering and lining epithelia refer to the types of epithelial tissues that cover the body's external surface, like the skin, or line the internal surfaces of cavities, such as those in the respiratory and digestive tracts. The script explains that these tissues serve protective roles and are essential for maintaining the body's integrity.

💡Glandular epithelia

Glandular epithelia are specialized epithelial tissues that line the ducts of glands, such as the salivary glands and pancreas. They are involved in the secretion process, contributing to the production and transport of glandular secretions. This concept is important for understanding how epithelial tissues contribute to gland function.

💡Polarity

Polarity in epithelial tissues refers to the distinct differences between the apical (upper free side) and basal (lower attached side) surfaces of the cells. The apical surface is involved in secretion, protection, and absorption, while the basal surface is involved in attachment and transportation. This concept is crucial for understanding the specialized functions of epithelial cells.

💡Avascular

Avascular means lacking blood vessels. Epithelial tissues are avascular, which is why they rely on underlying connective tissue for support and nourishment. The video explains that this characteristic necessitates the diffusion of nutrients from the connective tissue to the epithelial cells.

💡Innervated

Innervated refers to the presence of nerve supply within a tissue. Epithelial tissues are innervated, meaning they contain nerve fibers that play a role in receiving and transmitting sensory information. This is important for the tissue's ability to respond to stimuli.

💡Regenerative capacity

Regenerative capacity refers to the ability of epithelial tissues to regenerate and replace damaged cells. This is particularly important because these tissues are often exposed to damaging factors and need to be frequently replaced. The video highlights this as a key characteristic of epithelial tissues.

💡Basal lamina

The basal lamina is a thin layer that attaches epithelial cells to the underlying connective tissue. It is part of the basement membrane, which also includes the reticular lamina. The script mentions that the basal lamina, along with the reticular lamina, provides support and helps to resist stretching and tearing of the epithelial sheet.

💡Connective tissue

Connective tissue is the tissue that supports epithelial tissues by providing a base for attachment and a means for nutrient delivery. Since epithelial tissues are avascular, they depend on the underlying connective tissue for nourishment and support. The video explains the role of connective tissue in maintaining the health of epithelial tissues.

💡Intercellular junctions

Intercellular junctions are the points of contact between adjacent epithelial cells, such as tight junctions and desmosomes. Tight junctions prevent the passage of substances between cells, while desmosomes hold cells tightly together. These junctions are essential for the integrity and function of epithelial tissues, as discussed in the video.

💡Classification of epithelial tissues

The classification of epithelial tissues is based on the number of cell layers and the shape of the cells. The video describes simple (single layer) and stratified (multiple layers) epithelia, as well as the shapes such as squamous (flattened), cuboidal (cube-like), and columnar (taller than wide). This classification system helps in understanding the diversity and specialized functions of epithelial tissues.

Highlights

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Transcripts

okay in this video we're going to talk

about the epithelial tissue so

epithelial tissue also called epithelium

is basically a sheet of cells that are

all tightly bound together

and these cover body surfaces or

cavities there's two major forms we have

covering and lining epithelia that you

find let's say

you know covering your whole body like

skin or lining the internal surfaces of

your body like

all on your respiratory tract or all

along the inside of your digestive tract

these would form the walls

of those spaces now the glandular

epithelia

are involved with lining the the

ducts of a gland things like salivary

glands or pancreas

have epithelial tissues that line those

ducts and they even

make part of this secretion that we'll

talk about here in a minute

some of the major functions of

epithelial tissues are to protect

absorb to filter to excrete

an excretion is elimination of wastes to

secrete

you know saliva obvious secretion and

some epithelia are involved with sensory

reception so they're used to pick up

information in your body

now the epithelial tissues of our body

have five distinguishing characteristics

we say they have polarity

specialized contacts they're supported

by connective tissue

and this is because epithelial tissues

are avascular so a meaning lacking

vascular means blood

blood vessels so avascular means that

epithelial tissues do not have blood

vessels within them

this is why they're supported by an

underlying connective tissue

that's because the connective tissues

can bring in the blood vessels and

nutrients that can

basically nourish those epithelia but

epithelial tissues are

innervated which means they get nerve

supply so that you do find nerves within

epithelial tissues

also epithelial tissues need have a high

regenerative capacity

um this is because they're involved with

protection and

uh they're you know exposed to a lot of

damaging factors so they need to be able

to regenerate pretty frequently

so polarity refers to the fact that

epithelial tissues have a top and a

bottom

the top is what we refer to the apical

surface surface now the apical surface

is this

upper free side or you can also call

this the side that's exposed to your

surface or cavity

so an example of where you'd find this

would be if you look at your skin

the side of the cells you're looking at

when you're viewing your skin

externally is the apical surface of

those epithelial cells

and then deeper those epithelial cells

would be attached by their basal surface

to an underlying basal lamina of

basement membrane

and then that would be attached to an

underlying connective tissue

now both surfaces differ in their

structure and function because the

apical surface is involved with

secretion and protection and absorption

whereas the basal surface is involved

with attachment

and also transportation of certain

materials

epithelial tissues need to have lots of

specialized contacts

so going back to when we talk about the

intercellular junctions of chapter three

we said we had tight junctions and

desmosomes remember tight junctions were

involved with waterproofing so that

water can't pass between cells

and desmosomes were involved with very

strongly holding cells together

so we find that epithelial tissues have

a lot of these because we really need

those

cells to be tightly bound together and

not pass

substances between them now connective

tissues all

support epithelial tissues and

what we find is that the epithelial

sheets are basically these long mats of

cells that are all interconnected

are supported by an underlying

connective tissue at some point

now uh we have this reticular lamina

that's deep to the basal lamina and it's

basically a network of collagen fibers

that

these epithelial cells attach to this is

part of the basement membrane so the

basement membrane is made of the basal

and reticular laminas

it's basically something that reinforces

the epithelial sheet

think of this as like the velcro for the

cells to attach to

this base membrane also resists

stretching and tearing and it defines

the epithelial boundary

because just deep to basement membrane

that's when you have the underlying

connective tissue

that would basically help to support and

nourish the epithelium

now we need an underlying connective

tissue because epithelial tissues are

avascular

which means that they don't have blood

vessels within them but they do have a

lot of nerve supply

so because of the fact that epithelial

tissues don't have blood vessels within

them

they need to be nourished by diffusion

or you know sort of

movement of particles from an underlying

connective tissue

now these epithelial do have nerve

fibers and these are involved with

receiving information in different areas

of your body

now epithelial tissues also have a high

regenerative capacity

this is because they are exposed to

friction

or hostile substances which can result

in damage

and therefore must be replaced and it

requires an adequate amount of nutrients

as well as cell division to adequately

replace those epithelia

what something else that stimulates the

regeneration of epithelial tissues is

this

loss of apical basal polarity or broken

lateral contacts that way the tissue

knows that

um you know there are spaces that need

to be filled in

with new cells now what we'll do next is

move on and talk about the

classification of epithelial tissues

so all epithelial tissues have two names

the first part of the name

indicates the number of cell layers so

if we say it's a simple epithelial

tissue it means it has a single layer of

cells

if it's a stratified epithelial tissue

it has two or more cell layers thick

an example this would be skin where you

have you know probably over

30 cell layers thick so we would call a

stratified epithelium

you'd find an example of simple

epithelium like in your respiratory path

uh passages specifically the alveoli

where you need to absorb rapid

absorption of gases

now another name here would indicate the

shape of the cells

so squamous means that the cells look

kind of flattened or scale like

cuboidal means they look box like like a

cube and columnar means they're taller

than they are

wide or column like so we do that is we

can mix

these the combinations of these words

here so we can have simple

squamous epithelium or stratified

cuboidal epithelium

and that tells you basically the number

of cells and the shape of those cells

in the stratified epithelia the shape

can vary in each layer so

ultimately we classify the stratified

epithelium

based on the shape of the cells at the

apical surface

of the epithelium and i'll give you guys

an example here in a minute

so you can see here is a classic example

of simple squamous epithelium

we can tell it's simple squamous because

you have one layer of cells here

and they're flattened which means

they're squamous so we said it's a

simple squamous

now we can compare this down here to a

stratified epithelium

and if you look first of all you can

tell this is stratified because you have

many cell layers that are stacked

upon each other now you might wonder

okay well these cell shapes can kind of

vary the closer you get to the surface

and you might say okay these ones kind

of look cube shape so then you might be

inclined to say stratified cube oil

where you have

you know many layers of cube shaped

cells however the stratified epithelial

tissues

uh that are named for the shape of the

cells

at the apical surface you can see that

apically we see that these cells are

more flattened

so we would call this type of epithelium

actually stratified squamous which is

basically like what you'd find in your

skin

now remember squamous is flattened

cuboid is cube shaped and columnar is

more column shaped

you'll find that when you look in a

microscope

they're not going to be in their

three-dimensional views they're going to

see more two-dimensional like this

so we start looking at microscopy images

here pretty soon

you'll see cells that are shaped like

this we see there's squamous or

cube shaped cuboidal or columnar down

here which are more column shaped

but in reality they're actually

three-dimensional structures here