Types of Epithelial Cells

Question 1

What are epithelial cell cancers called?

Answer 1

Carcinomas.

Question 2

What are the two main ways we classify epithelial cells?

Answer 2

Their shape and how they are layered.

Question 3

What are simple squamous epithelia?

Answer 3

Flat, square-shaped epithelia in a single layer.

They allow exchange of substances to occur.

Question 4

Where are single squamous epithelia found?

Answer 4

Lining blood vessels, lung alveoli, and mesothelia.

Question 5

What are single cuboidal epithelia?

Answer 5

A single layer of cuboidal shaped epithelia.

Question 6

Where are single cuboidal epithelia found?

Answer 6

Typically found in the lining of ducts such as those lining the kidney collecting ducts.

Question 7

What are simple columnar epithelia?

Answer 7

A single layer of column-shaped epithelia.

Question 8

Where are simple columnar epithelia found?

Answer 8

These epithelial cell arrangements are typical of surfaces involved in absorption and secretion of molecules, e.g. enterocytes lining the gut, involved in the take up and breakdown of products of digestion.

Question 9

What are stratified squamous epithelia and where are they found?

Answer 9

Multiple layers of flat, square-shaped epithelia.
There are two main types:

Keratinising - produce keratin and in doing so die and thicken. They form protecting structures such as skin epithelia (epidermis) and lose their cellular organelles and nuclei making them invisible under light microscopy. They can form thick layers that protect underlying tissues from physical and chemical damage.

Non-keratinising - do not undergo keratinization and retain their nuclei and organelles, forming the epithelium lining the mouth, oesophagus, anus, cervix and vagina.

Question 10

What are pseudostratified epithelia, where are they found?

Answer 10

They appear to be multi-layered epithelial cells but in reality, are not. Examples include the airway and various ducts in the urinary and reproductive tracts.

Question 11

What makes an epithelial type single-layered?

Answer 11

All cells must have contact with the basal lamina.

Question 12

Epithelial cells can be split into what two domains?

Answer 12

The apical domain at the top and the basolateral domain at the bottom.

Question 13

What are the two cell domains separated by and what else do they do?

Answer 13

Cell junctions, which also generate cell polarity.

Question 14

What is the name for the part of the membrane opposing adjacent cells?

Answer 14

Lateral membrane (hence basolateral domain which comprises the basal membrane and the lateral membrane).

Question 15

How can epithelial cell functions achieve directionality?

Answer 15

Cell polarity due to discretely organized cellular components.
Transporters must be polarised to allow a net directional flow of secretion.

Question 16

How many cell-cell junction types are there?

Answer 16

4

Question 17

What are tight junctions for?

Answer 17

Sealing gaps between cells.

Question 18

What controls the formation of other junctions?

Answer 18

Adherens junctions.

Question 19

What do desmosomes do?

Answer 19

Form mechanically tough junctions that are important in tissues that need to resist mechanical stress.

Question 20

What do gap junctions do?

Answer 20

Form pores between cells, allowing for the exchange of materials. This allows cells to form communities and synchronize a number of activities.

Question 21

What are the three main epithelial functions?

Answer 21

Transportation, absorption, secretion.

Question 22

In transporting epithelia, what do the plasma membranes contain high concentrations of?

Answer 22

Ion transporters.

Question 23

Why might there be lots of mitochondria associated with transporting epithelia?

Answer 23

To provide the ATP required for active transport across the membrane.

Question 24

How do transporting epithelia increase the amount of ions they can transport?

Answer 24

Infoldings of the membrane increase the amount of basal membrane to pump ions across.

Question 25

Where are the mitochondria of transporting epithelia most concentrated?

Answer 25

Mitochondria are concentrated in the basal aspect of the cell, close to the basal infoldings which contain the active transporters.

Question 26

What is the purpose of having most active transport occur only at the basal membrane?

Answer 26

It achieves directionality by inducing a cell polarity.

Question 27

How are the intestines adapted to increase the amount of absorption?

Answer 27

Increased surface area with finger-like folds called villi.

Question 28

What does the brush border contain?

Answer 28

Large amounts of active transporters and channels for the uptake of nutrients from the lumen of the gut.

Question 29

How do nutrients leave the absorptive epithelia?

Answer 29

As the concentration of nutrients increases in the cytoplasm of the absorptive cells, it diffuses down its concentration gradient into the basal interstitial space to be collected in the capillaries and distributed in the circulation.

Question 30

What are the two main types of secretion?

Answer 30

Exocrine and endocrine.

Question 31

What is exocrine secretion?

Answer 31

Secretion into a duct or lumen.

Question 32

What is endocrine secretion?

Answer 32

Secretion into the blood stream.

Question 33

How do endocrine and exocrine cells differ?

Answer 33

Different arrangements of cell organelles. For example, exocrine cells have secretory vesicles closer to the blood circulation.

Question 34

Apart from exocrine vs endocrine secretion, how else can we classify secretory cells?

Answer 34

Based on the way they secrete.

Constitutive cell’s secretory vesicles move directly to the plasma membrane and release their contents upon formation.

Stimulated cell’s secretory vesicles are stored in the cytoplasm and only fuse with the plasma membrane to release their contents when stimulated.

Question 35

Many epithelial cells are constantly turning over, they are replaced by the proliferation of stem cells. Give two examples of this.

Answer 35

Cells in intestinal crypts replacing cells lost from the tips of intestinal villi.

Cells of the basal layer of stratified squamous epithelia dividing to replace cells lost from the surface.

Question 36

How are cells replaced in the villus tips in the small intestine?

Answer 36

The cells are formed by the crypt stem cells and migrate up the villus epithelium. New cells are constantly being produced by the crypt stem cells to replace cells constantly being lost from the villus tip.

Question 37

How does chemotherapy result in gastro-intestinal disturbances?

Answer 37

Inhibition of the proliferation of intestinal crypt cells, e.g. in cancer chemotherapy, results in loss of the finger-like intestinal villi and flattening of the intestinal mucosa.

Question 38

How can hyperproliferation in the skin occur (non-pathogenically) and what can this cause?

Answer 38

In response to repeated or constant pressure. If the increase in cell production is greater than the cell loss from the surface, cells will accumulate creating an increased thick hard layer e.g. pressure and abrasion to areas of the skin results in local hyperproliferation leading to “hard skin” or “corns”.

Question 39

How can pathogens cause hyperproliferation?

Answer 39

Infectious agents such as papilloma virus can also induce hyperproliferation. They do this by hijacking the cellular machinery of stratified squamous epithelia and inducing increased cell proliferation, which results in a surface growth, e.g. a wart.