Epithelial Tissue The Outer Shell. Epithelial Tissue Take a look at your right hand Describe what you see Now feel your hand Note the thickness and elasticity.

Epithelial TissueThe Outer Shell

Epithelial Tissue

• Take a look at your right hand• Describe what you see

• Now feel your hand• Note the thickness and elasticity

of your hand• Finally use your other hand to

pinch, poke and prod your hand

Epithelial Tissue

• Everything that you have been feeling on your hand is epithelial tissue• Epithelia are layers of cells that

cover internal or external surfaces• The epithelia that you have been

feeling is commonly referred to as skin

Epithelial Tissue

• Epithelia tissue are often mixed with glands• Glands are organs that secrete

liquid• These secretions can vary in

many different forms• However, all glands are part of or

derive from epithelial tissue

• Understanding how the epithelial tissue in your body works is often the first step in anatomy• This is because it is the most

visible• It is also because it is the part of

the body that protects and supports many other organs

Epithelial Tissue

Features of Epithelial Cells

• Epithelial cells have several key features that make them effective at what they do• These features create the

properties that you see in epithelial cells• They allow for the properties

that you see in organs• Skin is an excellent example

Features of Epithelial Cells

• Epithelial cells are tightly packed together• They are most commonly

connected together by cell junctions• Cell junctions are

interconnections that bind cells together• When cells are packed together

this closely they are said to have cellularity

Features of Epithelial Cells

• Epithelial cells have two different sides• The exposed surface of a layer of

epithelial cells is called the apical surface• The base surface of a layer of

epithelial cells is called the basal surface• Since there are two different sides

to epithelial tissue it is said to be polar

Features of Epithelial Cells

• Epithelial cells are attached to other layers of the body• This allows them to be anchored

to particular parts of the body• The basal layer of cells is

attached to a basement membrane (also called a basal lamina)• This connects the epithelium to

the underlying connective tissue

Features of Epithelial Cells

• Have you ever noticed that small cuts that do not penetrate far into your skin do not bleed?• This is because your epithelial

cells are avascular• Avascular tissues obtain their

nutrients from diffusion or absorption, but not from blood• They must gain nutrients from

other cells or their environment

Features of Epithelial Cells

• Epithelial cells are constantly damaged and lost• Think about every single time you

wash in the shower• Epithelial cells are experts at

regeneration• Regeneration is the ability to

replace dead cells by stem cell division• Epithelial cells have some of the

highest regeneration rates in the body

Types of Tissue

• There are many different types of epithelial tissue• However, we can quickly

quantify them into groups based on their structure• This is similar to soccer players • There are many similar types of

soccer players, however they can be quantified into different positions

Types of Tissue

• Any type of epithelial tissue that has only one layer of cells that cover the basement membrane is called simple epithelial tissue• These types of tissue do not

provide as much support or protection as layered types of tissue• Generally they are in protected

places where secretion or absorption are important

Types of Tissue

• You can expect to find these types of tissue in the lining of the intestines, covering the internal surface of the lungs and in all glands of the body• These are places where being

thin is an advantage due to absorption and secretion time being minimized

Types of Tissue

• Stratified epithelium is several layers of cells that cover the basement membrane• The actual definition is when the

nuclei are at different lengths from the basement membrane• These types of epithelial tissue are

most often exposed to chemical, physical or environmental stresses• These provide more protection to

the underlying structures

Types of Tissue

• You can expect to find these types of cells in the mouth and the skin• The mouth is routinely burned,

bitten, subjected to acids, subjected to bases and more• This means that it needs a strong

protective barrier that will hold up to the stress of the environment

Squamous Epithelium

• Not all “cells” are cell like in shape • In fact several cells in the human

body have highly irregular shapes that seem to have no consistency• Many cells that are directly next

to each other might have different shapes

Squamous Epithelium

• Squamous epithelium are cells that are thin, flat and irregular in shape• Often times they are layered in

any formation where there is space• You can think of them like jigsaw

puzzle pieces

Squamous Epithelium

• Simple squamous epithelium is the most delicate type of tissue in the body• They are located in absorption or

secretion parts of the body• Many have a fluid outer coating

to protect from harm• Examples are the alveoli of the

lungs and the linings of vascular tissue

Squamous Epithelium

• Stratified squamous epithelium is a much tougher type of tissue that can hold up to high amounts of mechanical stresses• The irregular layers of cells stack

on top of each other to form a tough outer layer• Surface of the skin, lining of the

esophogus and the lining of the mouth are places where you would expect to find these tissues

Squamous Epithelium

• Stratified epithelium is made even tougher by a protein called keratin• Keratin is a tough waterproof

protein that exists in several different types of epithelial tissues• Keratin stimulates and is

increased in places where there is a lot of stress• This allows for a tougher layer of

cells

Columnar Epithelia

• Some cells do have a defined shape• Their shape is important for their

structure and their function• These defined shapes can give

the cells different properties and different jobs

Columnar Epithelia

• Columnar epithelial cells commonly look like a tall and skinny column• This is only because we see the

cells from the side• Columnar cells actually have a

hexagonal structure that is tough to see in a side view

Columnar Epithelia

• Simple columnar epithelium is one cell layer thick above the basement membrane• This is seen in areas where there

is abortion and secretion• These are the types of cell that

line the intestines• They allow rapid extraction of

nutrients from different foods

Columnar Epithelia

• Stratified columnar epithelia are groupings of cells that often contain stratified columnar cells• It is easy to confuse them with

other cells, because not all of the cells will appear to be columnar• These cells are rare but can be

found providing protection in the pharynx, epiglottis and urethra

Columnar Epithelia

• Some portions of the respiratory tract contain cells that are hard to visually identify• Pseudostratified columnar epithelial

cells have one layer of cells with nuclei that are at different distances from the basement membrane• This gives them the look of a stratified

layer of cells, but they are all attached to the basement membrane• Most of these cells have cilia that

help move fluids on their apical surface

Cuboidal Epithelia

• The cells that have a district box-like or cube structure are called cuboidal epithelium• This is because… they appear

like they are cubes• They are scientifically identified

because the distance between nuclei are relatively the same

Cuboidal Epithelia

• Simple cuboidal epithelia mostly occur where absorption and secretion take place• They have one layer of cells that

provide very limited protection• Simple cuboidal epithelia are

commonly seen in the linings of the kidney tubules

Cuboidal Epithelia

• Stratified cuboidal epithelia are cells that are multilayered cubes• Generally the layering is not overly

thick• These types of cells are mostly

used for areas where there is a large amount of regular secretion • The large ducts of the mammary

glands and the sweat glands are made from stratified cuboidal epithelium

Transitional Epithelium

• One type of epithelial cells does not get classified based on their appearance• These cells are classified based

on their job in the body• The reason we do not classify

them on their appearance is because their appearance is constantly changing

Transitional Epithelium

• Transitional epithelium is a type of tissue that is designed to stretch and return to a normal state without damage• The cells in this stratified section of

cells will change shape while stretched• Transitional is a reference to them

changing shape

• These cells line the bladder and other parts of the urinary system where changes in volume are common place