Epidermis

Question 1

Which layer is the main barrier to physical insult, such as mechanical injury or UV radiation? And what other type of barrier protection does it provide?

Answer 1

The Stratum Corneum

Permeability barrier (1st line of defence) This is due to the corneocytes themselves as well as the lipid ECM consisting of ceramides, free fatty acids and cholesterols.

Question 2

What do the cells undergo to become squams? And what are the stages to this?

Answer 2

Cornification

1. Lipid extrusion and bilayer formation
2. Cornified envelope formation (protein coats from the inside of the cell membrane)
3. Keratin deposition

n.b. all of these can occur at the same time.

Question 3

Describe the relationship between cells of the stratum corneum

Answer 3

Corneocytes connected by corneodesmosomes. Lipid-rich ECM between them. Transition desmosome links corneocytes to stratum cranulosum cells.

Question 4

How is desquasmation achieved and what factors can affect it?

Answer 4

It is the hydrolytic dissolution of corneodesmosomes. It can be affected by:

• washing
• hydration
• pH

Question 5

How does the nucleated epidermis act as a barrier?

Answer 5

Permeability barrier - tight and adherens junctions + keratins

2nd level of immune defence - microbe receptors, antimicrobial peptides and inflammatory mediators

Question 6

How is damage to the epidermis sensed by the deeper layers?

Answer 6

A change in the Ca2+ gradient.

Question 7

Briefly describe the events that occur after damage.

Answer 7

Injury or pertubation of the barrier (could be caused by stress) leads to cytokine release which leads to increased lipid synthesis and release of lamellar bodies which should result in barrier repair. If damage is extensive then hyperplasia and inflammation of the dermis may also result.

Question 8

What are the two categories under which skin disease could occur?

Answer 8

A primary dysfunction(intrinsic)

A secondary dysfunction (caused by inflamamtion/external damage)

Question 9

What things can cause scale?

Answer 9

Metabolic causes (endocrine/nutritional defects)
External assault (parasites, infections and adverse environmental conditions)
Internal inflammatory (hypersensitivity reactions and immune-mediated diseases)
Genetic problems (desquamation or any of the stages of cornification may be affected)

Question 10

Define parakeratosis

Answer 10

Persistance of nucleated cells into the stratum corneum. This represents abnormal cornification.

Question 11

How can skin be sampled for diagnosis?

Answer 11

Using sticky tape.