What is the primary function of the stratum basale?
Consists mainly of keratinocytes that are constantly reproducing and pushing upward
Keratin expression: Primarily K5 and K14 (also K15 and K19).
A defect in keratin 5 causes which condition?
Bovine epidermolysis bullosa simplex
This condition is characterized by fragile skin that blisters easily.
What keratin types are expressed in the lower stratum spinosum?
K1 and K10
Clinical relevance: Norfolk Terriers have a defect in K10 leading to decreased keratin synthesis.
What is the stratum granulosum characterized by?
Flattened keratinocytes containing keratohyalin granules
The final stage of granular cell differentiation involves programmed destruction of the nucleus.
What is the stratum corneum also known as?
Horny layer
It consists of terminally differentiated keratinocytes known as corneocytes.
What does the ‘brick and mortar’ model refer to?
Corneocytes suspended in an extracellular lipid matrix
This model describes the structural organization of the stratum corneum.
What is the epidermal turnover rate for dogs?
22 days
For comparison: Humans: 14 days, Horses: 17 days.
Define keratinization.
Process by which living keratinocytes produce large amounts of keratin
Keratinization and cornification are distinct but essential processes for a functioning epidermis.
What are the four key processes of keratinization?
- Synthesis of principal fibrous proteins
- Keratohyalin granule synthesis
- Formation of cornified cell envelope
- Generation of neutral lipid-enriched intercellular domains
These processes are crucial for the development of the stratum corneum.
What is the role of transglutaminases in keratinization?
Mediates cross-linking of CCE precursor scaffold proteins
Important for apoptosis, keratinization, and hair follicle formation.
What is the significance of filaggrin in the epidermis?
Bundles keratin intermediate filaments together
It also plays a role in maintaining epidermal hydration and UV photoprotection.
What condition is associated with a mutation in the ASPRV1 gene?
German shepherd ichthyosis
This mutation affects profilaggrin processing to filaggrin.
What stimulates keratinocyte proliferation?
- Keratinocyte growth factor (KGF)
- Insulin-like growth factor 1 (IGF-1)
KGF is produced by dermal fibroblasts.
What is the function of keratin in the epidermis?
Provides a major barrier between the animal and the environment
It also offers mechanical support and regulates hair follicle cycling.
What are the three types of cytoplasmic filaments in keratinocytes?
- Cytokeratin
- Actin microfilaments
- Microtubules
These filaments provide mechanical strength, motility, and intracellular transport.
True or false: Keratinization and cornification are the same processes.
FALSE
Keratinization is the production of keratin, while cornification is the terminal differentiation of keratinocytes.
What is the role of caspase-14 in the epidermis?
Involved in the degradation of filaggrin
This degradation is key to epidermal barrier function.
What mutation is implicated in canine atopic dermatitis?
FLG loss of function mutation
Similar to mutations observed in human atopic dermatitis (Combarros 2020).
Name a factor that stimulates keratinocyte proliferation.
- Keratinocyte growth factor (KGF)
- Insulin-like growth factor 1 (IGF-1)
- Epidermal growth factor (EGF)
- Transforming growth factor-α (TGF-α)
- Zinc
- Calcium
- Vitamin A/retinoids
- Copper
- Ornithine decarboxylase
- Cytokines (e.g., IL-17, IL-6, IL-1β)
- Fibroblast growth factor (FGF)
- Granulocyte macrophage-colony stimulating factor (GM-CSF)
- Vascular endothelial growth factor (VEGF)
- Platelet-derived growth factor-BB (PDGF-BB)
These factors promote keratinocyte growth and proliferation.
What is the role of calcium in keratinocyte proliferation?
Low calcium promotes proliferation; high calcium promotes proper differentiation
Calcium levels influence keratinocyte behavior and function.
What do desmosomes do in the epidermis?
Provide anchor for intermediate filaments, stabilize structure of epidermis, distribute physical stress
Major cell adhesion junction of epithelial tissues.
What are hemidesmosomes primarily responsible for?
Epidermal-dermal adhesion
They link cytokeratin to the basal lamina portion of the extracellular matrix.
What proteins are involved in corneodesmosomes?
- Dsg1
- Dcl1
- Corneodesmosin
These proteins play a role in adhesion between corneocytes in the stratum corneum.
What are the main components of tight junctions?
- Claudins
- Occludins
- JAM proteins
Tight junctions form a permeability barrier in the granular layer of the epidermis.
