1. Epithelial Tissue
The Outer Shell

2. 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

3. 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

4. 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

5. 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

6. 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

7. 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

8. 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

9. 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

10. 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

11. 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

12. 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

13. 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

14. 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

15. 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

16. 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

17. 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

18. 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

19. 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

20. 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

21. 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

22. 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

23. 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

24. 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

25. 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

26. 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

27. 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

28. 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

29. 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

30. 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

31. 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