Epithelial Tissue

Question 1

Define epithelial tissue in simple terms.

Answer 1

The epithelium is a type of body tissue that forms the covering on all internal and external surfaces of your body, lines body cavities and hollow organs and is the major tissue in glands.

Question 2

What features are common in all epithelia?

Answer 2

1. Totally cellular
2. No blood vessels (avascular)
3. Stem cells lie within the epithelium (self-regenerating)
4. Separated from underlying tissues by a basal lamina
5. Always supported by an underlying layer of connective tissue containing blood vessels

Question 3

What does totally cellular mean?

Answer 3

No connective tissue fibres holding the cells together; integrity depends on cell junctions.

Question 4

Name and describe the two types epithelia can be divided into.

Answer 4

1. Simple (single layer of cells)
2. Stratified (multiple layers of cells)

Question 5

What are the four types of simple epithelia?

Answer 5

• Squamous
• Cuboidal
• Columnar
• Pseudostratified

Question 6

Where are simple epithelia found?

Answer 6

Internal protected surfaces

Question 7

What is the appearance of simple squamous tissue?

Answer 7

• Extremely flattened cells
• The region containing the nucleus bulges from the cell like the yolk of a fried egg, and has a thin layer of cytoplasm.

Question 8

Where can simple squamous epithelium be found?

Answer 8

• Lining the exchange area of the lung
• Lines pleural cavities
• Covers the gastrointestinal tract

Question 9

Describe the appearance of simple cuboidal.

Answer 9

The cells look like cubes (as wide as they are tall), with a central nucleus, giving the appearance of beads on a necklace.

Question 10

Describe the function of simple cuboidal epithelium.

Answer 10

They commonly act as simple building blocks; e.g., forming
the walls of ducts.

Question 11

Describe the appearance of simple columnar.

Answer 11

In longitudinal section, these cells are columnar in shape, with all the nuclei lying at the same level towards the base of the cells.

Question 12

Describe the function of simple columnar epithelium.

Answer 12

Involved in absorption, secretion and moving material over the surface of the epithelium e.g. found in small intestine with microvilli.

Question 13

Describe the appearance of pseudostratified columnar.

Answer 13

In longitudinal section, the cells have an apparently columnar shape similar to that of simple columnar,
but the nuclei clearly lie at different levels in the lower half of the cells, suggesting that this epithelium is stratified and therefore should not be classified as simple. However, with the EM, it can be seen that this is a true simple epithelium, a single layer of cells, all of which make contact with the basal lamina (and this is your clue for correct identification), but not all reaching the free surface.

Question 14

Where can pseudostratified columnar epithelium be found?

Answer 14

Respiratory epithelium

Question 15

Name the two stratified epithelium divisions.

Answer 15

Squamous and transitional

Question 16

What 3 subtypes can stratified squamous be divided into?

Answer 16

Stratified squamous epithelium, keratinised stratified squamous epithelium and parakeratotic stratified squamous epithelium.

Question 17

Describe the appearance of stratified squamous epithelium.

Answer 17

This subtype is composed of multiple layers of cells. The cells in the basal layer are roughly cuboidal in appearance! Cells take on a flattened squamous appearance only as they move up through the layers.

Question 18

What is the function of stratified squamous epithelium and where is it found?

Answer 18

• Form a thick layer which provides defence against mechanical damage.
• Line the oral cavity and
  oesophagus so that these can withstand shearing forces from coarse food materials.

Question 19

How is integrity of stratified squamous epithelium maintained?

Answer 19

Many desmosomes between cells and attachment to underlying connective tissue via rete pegs.

Question 20

Describe the appearance of keratinised stratified squamous epithelium.

Answer 20

As the cells move up through the layers of this epithelium, they become more squamous in shape and accumulate granules of keratohyalin, which stain dark blue with H&E. Abruptly, in the adjacent more superficial layer, all cellular detail is lost, no nuclei or cell membranes can be seen, and the blue-staining granules disappear to be replaced by a layer of red-staining keratin.

Question 21

What is the function of keratinised stratified squamous epithelium and where is it found?

Answer 21

Forms the epidermis (epithelial layer of the skin) where it protects from mechanical damage, chemical damage and desiccation.

Question 22

Where is parakeratotic stratified squamous epithelium found?

Answer 22

Compartments of the ruminant forestomach.

Question 23

Describe the appearance of parakeratotic stratified squamous epithelium.

Answer 23

It is similar to stratified squamous, but the superficial layer of cells shows cellular detail and keratinisation.

Question 24

Describe the appearance of transitional epithelium.

Answer 24

Variable; composed of multiple layers of cells. As the cells move up from the base of the epithelial layers, they get fatter and rounder. Some may contain two nuclei. They do not contain keratin.

Question 25

Where is transitional epithelium found and why?

Answer 25

In the urinary system - the balloon shape of the cells allows for great lateral stretching of the epithelium when the bladder fills.

Question 26

What is the difference between a desmosome and hemidesmosome?

Answer 26

Desmosomes are junctions involved in intercellular adhesion of epithelial cells and hemidesmosomes are junctions involved in adhesion of epithelia to basement membranes.

Question 27

What is cornification?

Answer 27

A layer of dead cells filled with keratin that form a protective barrier over a layer of
cells. Seen with stratified squamous epithelium.