Epithelia

Question 1

What is epithelia ?

Answer 1

It is the lining and covering of all body surfaces
- it is a completely cellular layer
- they are avascular (the blood supply comes from underneath)
- sit on top of a basement membrane
- usually over a vascular connective tissue
- control the entry and exit of all materials to and from bodily tissues

Question 2

How are glands formed ?

Answer 2

They are formed from epithelial cells

Question 3

What are some of the general functions of epithelial cells ?

Answer 3

• protection
• secretion
• absorption
• dialysis (filtration)
• sensation

Question 4

How are epithelial cells classified ?

Answer 4

1) number of layers -
• simple = 1 layer
• stratified = more than 1 layer
2) shape of the TOP layer -
• squamous = thin and flat
• cuboidal = same width and height
• columnar = tall and thin

Question 5

What are the 2 types of stratified squamous epithelial cells ?

Answer 5

1) keratinised
2) non keratinised

Question 6

What is pseudostratified epithelia ?

Answer 6

• there are some tall cells and some short cells all in one layer touching the basement membrane
• it doesn’t fit the classification

Question 7

What is transitional epithelium ?

Answer 7

• epithelium that lines the bladder and constantly shifts from collapsed epithelial to stretched epithelial when the bladder empties and fills
• it doesn’t fit the classification

Question 8

What are some features that are common to all epithelial cells ?

Answer 8

1) all epithelial cells are entirely cellular
- separate the internal and external environments
- cells control the entry and exit of materials into and out of bodily tissues

2) they are specialised intercellular contacts (cell junctions)

3) the bottom and top surfaces are different due to different polarities
- the top surface contacts the external environment
- the bottom surface touches the basement membrane and body
- the surfaces may be modified with cilia, microvilli, basal striations

4) all are above a basement membrane

Question 9

Describe the structure of the basement membrane

Answer 9

There are 2 layers -
Top layer - basal lamina (made from epithelium)
Bottom layer - reticular fibres = collagen (made from connective tissue)

Question 10

What is the function of stratified epithelia ?

Answer 10

• stratified epithelia is the most common (specifically stratified squamous)
• provide protection from damage
• the surface cells can be lost and replaced by stem cells from underneath
• the toughest is stratified squamous keratinised epithelium
• the next toughest is stratified squamous non-keratinised epithelium

Question 11

What is keratinised epithelium ?

Answer 11

When the surface cells die and fill up with keratin to form a tough and waterproof covering

Question 12

What is non - keratinised epithelium and where is it found ?

Answer 12

The cells are alive all the way to the surface
Found in inner body surfaces such as the oral cavity, oesophagus and vagina
They are not waterproof so kept moist by glandular secretions

Question 13

What is the function of the simple epithelia ?

Answer 13

• they are found where substances must be transported across the epithelium
• the simple squamous cells act as filters for water and ions
• the simple columnar and cuboidal cells have roles in active transport and modification of materials that pass through them e.g gut cells

Question 14

Which other cell types may be found in columnar epithelia ?

Answer 14

• goblet cells (in simple columnar and pseudostratified columnar)
• lymphocytes

Question 15

How many layers of epithelial cells are in the oesophagus and classify the epithelium

Answer 15

~ 30
Stratified squamous non keratinised epithelium

Question 16

Classify the epithelium found in the Bowman’s capsule of the kidney

Answer 16

Simple squamous epithelium

Question 17

Classify the epithelium found in the thyroid gland

Answer 17

Simple cuboidal epithelium

Question 18

Classify the epithelium found in the small intestine

Answer 18

Simple columnar epithelium

Question 19

What type of cell junctions are found between epithelial cells and why ?

Answer 19

Tight junctions because they prevent leakage between cells
We don’t want any material which has been actively transported to diffuse back again

Question 20

What is the function of basal cells ?

Answer 20

They act as stem cells to replace the surface cells of the epithelium

Question 21

Why do different cells have different epithelia ?

Answer 21

Different cells have different functions and so have different epithelia
- simple squamous epithelium is present when a thin diffusion barrier is needed
- columnar epithelium is used when active transport takes place because they contain lots of cytoplasm and therefore lots of mitochondria

Question 22

What are the structural and cytoskeletal differences between tracheal epithelial cells and the intestinal epithelial cells ?

Answer 22

Trachea = cilia - waft mucus over the epithelial surface and supported by microtubules
Intestine = microvilli - increases surface area for absorption and supported by actin filaments

Question 23

What type of epithelium is found in the lining of the stomach ?

Answer 23

Simple columnar epithelium