Session 4 - Integrating cells into tissues, organs and tissues (plus epithelial tissue)

Question 1

How cells are held together at the molecular level? List the 4 main ways in which cells are held together

Answer 1

Cell are held at the lateral surface to other cells and to the basal lamina

1. Cell-cell adhesion molecules
2. Extracellular matrix proteins (fibres) e.g. collagen fibres
3. Internal scaffolding
4. Close proximity (pressure effects holding layers together)

Question 2

Describe the 4 layers of the mucosal membrane present in the gastrointestinal system

Answer 2

1. Mucosa (containing epithelial cell lining, lamina propria and the muscularis mucosa)
2. Submucosa
   - Connective tissue layer containing blood vessels
3. Muscularis externa
   - Smooth muscle layer containing (inner) circular and (outer) longitudinal muscle going in opposite directions
4. Serosa/Adventitia
   - Another connective tissue layer with smaller blood vessels and some nerves

Question 3

List the 4 proteins that hold cells together laterally and briefly describe their main feature

Answer 3

Tight junctions:

• Prevents substances from moving across between cells
• Can also open to allow paracellular transport

Adhesion molecules:
- Very strong so is a stabilising factor

Desmosomes:
- Strongest feature so prevent mechanical strength

Gap junctions:
- Quickly communicate intracellular changes (have pores)

Question 4

List the 4 proteins that hold cells to the basal surface and briefly describe their main feature (all have the same main feature)

Answer 4

Hemi-desmosome:
- Anchors to the basal lamina

Focal adhesions:
- Anchors to the basal lamina

Integrins
- Anchors to the basal lamina

Question 5

Describe the 3 layers of the mucosal membrane present in the respiratory system and the role of each of the layers

Also, which part of the respiratory tract is missing a layer and what does it have instead?

Answer 5

1. Mucosa (containing epithelial cell lining, lamina propria and the muscularis mucosa)
   - Epithelium has stratified squamous non-keratinised cells that withstand abrasion
2. Submucosa
   - Connective tissue layer containing mucus secreting glands
3. Muscularis externa
   - Contains smooth muscle layers which moves bolus of food by peristalsis

(in the bronchi, there is no musclaris externa but there is C-shaped hyaline cartilage)

Question 6

Describe the 4 layers of the mucosal membrane present in the urinary system

Answer 6

Ureter!

1. Mucosa
   a. Urothelium (transitional epithelium) - produce mucus
   b. Lamina propria
   c. Muscularis mucosa
2. Muscularis externa
   - Smooth muscle layers: (inner) longitudinal muscle and (outer) circular muscle layers

Bladder!
Has above layers but ALSO muscular layer which is the detrusor muscle and the adventitia

Question 7

List the ways in which epithelia are classified

Answer 7

Squamous
Cuboidal
Columnar
Transitional (exception)

Simple
Stratified/Compound
Pseudostratified

Question 8

For the following types of surface specialisation found in epithelial tissues, describe how their structure is related to their function (relate to clinical conditions) and where they are found

List: keratin, non-keratinised, microvilli, stereocilia, M-cells, Clara cells, mucus secreting cells and cilia

Answer 8

Keratinised surface (dead layers of squamous epithelial cells):

• Protects against abrasion
• Found in skin

Non-keratinised (living layers of squamous epithelial cells):

• Keeps surface moisture and protects against abrasion
• Found in vagina/oesophageous

Microvilli:

• Increases surface area for absorption
• Also damaged/impaired in cystic fibrosis
• Found in upper respiratory tract

Stereocilia:

• Converts pressure waves into electrical signals
• Found in ears

M-cells

• Can sample the lumen for pathogens and present to lymphocytes
• Can be evaded by salmonella (M-cells are how it enters the cells)
• Found ONLY in small intestine

Clara/club cells

• Protect the bronchiolar epithelium and detoxify harmful substances
• Damaged by heavy smoking and can’t be regenerated!
• Found in terminal bronchioles

Mucus secreting cells/goblet cells

• Produces mucus
• All tissues with mucus secreting cells affected in cystic fibrosis (CFTR mutation)
• Found in

Cilia

• Involved in mucociliary escalator
• Damaged as well by smoking

Question 9

Explain the reasons for the different rates of renewal of each type of epithelium (relate to clinical conditions)

Answer 9

It depends on the level of use/exposure/abrasion experienced by the tissue

In psoriasis, this regeneration occurs to fast (from 8-9 days) to only 1-3 days which results in scaly like silverly patches

In the bronchi, club cells that are damaged cannot be replaced therefore there is no regeneration if this is the case (they act as stem cells)