Epithelial Cells and Tissues

Question 1

• What are the 5 main cell types?

Answer 1

Connective cell tissue - fibroblasts

Contractile tissue - skeletal, cardiac and smooth muscle

Haemopoietic cells - blood cells, tissue-resident immune cells

Neural cells - cells of nervous system; neurones and glial cells

Epithelial cells - cells forming continuous layers, lining surfaces and separate tissue compartments

Question 2

• How are epithelial cells organised?
• What are carcinomas?
• What are sarcomas?

Answer 2

Stable cell-cell junctions to form continuous, cohesive layers

Epithelial cancers 

Mesenchymal (connective tissue and muscle) cancers

Question 3

• How are epithelial cells classified?

Answer 3

Shape:

- Squamous (flattened plate-shape)
- Cuboidal
- Columnar

Layering:

- Single - simple
- Multi-Layer - stratified
- Pseudostratified- single layer but looks like more than one layer

Question 4

• How are simple squamous epithelial cells adapted to their function?

Answer 4

Found in lung alveolar epithelium

Form thin epithelium that allows gas exchange to occur

Question 5

• Where are simple cuboidal epithelial cells found?

- How are simple columnar epithelial cells adapted to their function in the gut?

Answer 5

Linings found in ducts e.g. kidney collecting ducts

In enterocytes lining gut Absorption and secretion of molecules increased through microvilli found on their apical surface

Question 6

• What is pseudo-stratified epithelium and where is it found?

Answer 6

Epithelium that appears to be multi-layered but is only single-layered

The surface cells all have contact with the basal lamina

Found in airway epithelium, various ducts in urinary and reproductive tracts

Question 7

• What is epithelial polarity?

Answer 7

Different regions of cell-surface being different from one another, with discretely organised cellular contents

Allowing secretion to only occur in one direction and absorption to occur either apically or basolaterally

Question 8

• What are the 2 domains in epithelial cell polarity?

- Why is epithelial polarity essential?

Answer 8

Apical and basolateral

To give directionality needed for epithelial function

Question 9

• What would happen if there was no epithelial polarity?

Answer 9

Epithelial cells would end up in the basolateral domain and you’d end up digesting your own tissue

Question 10

• Describe the 4 main types of junctions between epithelial cells

Answer 10

Tight junction - sealed gaps between cells

Adherens junction - Controls formation of other junctions

Desmosomes - Restrict mechanical stresses

Gap junction - Allow cells to exchange and share materials (form pores between cells)

Question 11

• What characteristic do transporting-epithelial cells have that adapts it to its function?

Answer 11

Mitochondria lie close to the basal lamina to provide ATP required for active transport at these membranes

Because active transport is mainly confined to the basal membranes, ion and water transport will have directionality

Question 12

• Where are absorptive epithelial cells found?

- How are absorptive epithelial adapted to their function?

Answer 12

Surface of small intestine and have microvilli (small projections found on membrane of villi which are found on surface of folds on small intestine)

They contain large amounts of active transporters and channels for uptake of nutrients from the lumen of the gut
As concentration of nutrients increase in cytoplasm of these cells, it diffuses down concentration gradient into basal interstitial space to be collected in capillaries and distributed into circulation

Question 13

• What are the secretory cells on microvilli called?

- Describe the 2 main types of secretion

Answer 13

Goblet cells

Exocrine (into duct or lumen)
Endocrine (into bloodstream)

Question 14

• How are exocrine secretory cells adapted for their function?
• How are endocrine secretory cells adapted for their function?

Answer 14

Secretory granules in apical cytoplasm as secretion will occur through the apical plasma membrane

Secretory granules found along the basal aspect of the epithelium (opposite side to those in exocrine secretory cells)

Question 15

• What is the difference between Constitutive and Stimulated secretion?

Answer 15

Constitutive - Secretory vessels fuse with plasma membrane to release contents as soon as they are formed

Stimulated - Secretory vessels are stored in cytoplasm and only fuse with plasma membrane to release contents when stimulated by release of hormone, such as adrenaline

Question 16

• How are new epithelial cells formed in the villi?

- How might chemotherapy treatments be responsible for gastro-intestinal disturbances?

Answer 16

New cells constantly being produced by crypt stem cells, to replace cells constantly being lost from villus tip

Inhibition of proliferation of intestinal crypt cells
Results in loss of intestinal villi
Flattening intestinal mucosa

Question 17

• How are epithelial cells in the epidermis replaced?

Answer 17

By stem cells in the dermis migrating towards the epidermis whilst differentiating from one cell layer to the next

The epidermis cells eventually die in one layer, allowing the next layer to be exposed

Question 18

• What occurs as a result of hyperproliferation of epithelial cells?

Answer 18

Increase in cell production not balanced out by cell death

Cells accumulate creating an increased thick hard layer, 'hard skins' or 'corns'