Dermatology: Structure & Function

Question 1

Dermatophagoides farinae

Answer 1

Feed on dead skin cells – “house mites”

Question 2

Bacterial Dysbiosis

Answer 2

when there is a shift in skin microbiome, favoring opportunistic bacteria leading to atopic dermatitis (allergic rxns)

Question 3

Epidermis

What are the 4 layers of the epidermis layer of the skin? What is the importance of knowing these different layers?

Answer 3

Different conditions affect different layers of the epidermis (e.g., Pemphigus foliaceus => SG & SS)

Question 4

Epidermis

Function of Stratum Basal

Answer 4

skin cell regeneration

Question 5

Epidermis

Function of stratum spinosum

Answer 5

thickest layer (squamous cell layer – keratinocytes and Langerhans cells)

• thicker at the footpads, nose and mucocutaneous junction

Question 6

Epidermis

Components / function of Stratum granulosum

Answer 6

Dense packing of basophilic keratohyalin granules (lipids + desmosomal interactions) – help to form a waterproof barrier that functions to prevent fluid loss from the body.

Question 7

Epidemis

Composition and function of Stratum corneum

Answer 7

• Terminally differentiated (dead, low-nutrient, anucleated) keratinocytes that are constantly being shed
• Layers of corneocytes - function as a physical, chemical and immunological barrier

Question 8

Epidermis

Function of the corneocyte layers in Stratum Corneum

Answer 8

the corneocyte layers are like bricks, mortared together by lipids/desmosomes, creating the water impermeability of the epidermis

Question 9

Epidermis

Define cornification and epidermal cell renewal time

Answer 9

The process in which the stratum basale cells differentiates into stratum corneum via an active process (requires ATP!!)

Epidermal cell renewal time = time it takes for SB cells to differntiate into SC cells

Turnover requires a delicate balance of replacement & replenishment
- if too many daughter cells being replenished, but not enough being shed, -> thicker skin
- if too much shedding but not enough replenishment, -> thin, raw skin

Question 10

Epidermis

Desmosomes - functions

Answer 10

Structures that keep the keratinocytes (cells within the epidermis) strong and keep the skin intact

Question 11

Epidermis

What are the 3 junctions of the epidermis and their functions?

Answer 11

Adherence, tight, and gap junctions

Question 12

Epidermis

What is the importance of the Basement Membrane Zone?

Answer 12

Region that allows for the basal cells to anchor to the basement membrane and keeps the epidermis intact. If this didn’t occur, the whole epidermis would fall apart!

Question 13

Dermis

Fibroblasts - function

Answer 13

Produce the ECM (proteoglycans, HA,, etc.) and collagen fibers => structural components of skin!

Question 14

Dermis

What are the epidermal appendages?

Answer 14

Sebaceous glands, hair follicles

Question 15

Type of hair follicle?

Answer 15

Simple
Only one hair follicle emerging from one opening

Question 16

Type of hair follicle?

Answer 16

Compound
>1 hair follicles emerging from one opening

Question 17

What are the 3 phases of the hair cycle?

Answer 17

1. Anagen (growing phase)
2. Catagen (transition phase, signals end of active growth phase)
3. Telogen (resting phase)

Some breeds have shorter / longer phases than others

Poodles: long anagen phases
Bulldogs: long telogen phases

Question 18

Identify the regions of the nasal planum

Answer 18

Question 19

Functions of the Foot Pad

Answer 19

Copious blood & nerve supply++

Question 20

Functions of the claw

Answer 20

Prehensile (gripping)
Locomotion
Defense and offensive apparatus

Question 21

Canine Symmetric Lupoid Onychodystrophy (SLO)
- definition
- why is it called “lupoid”

Answer 21

• immune-mediated disease that ONLY affects the claws/nails
• Lupoid = “lupus-like” –> biopsy of the affected nail beds revealed histological features seen in cutaneous lupus erythematosus

Symmetrical lupoid onychodystrophy (SLO) is the most common inflammatory disease to cause abnormal nails in dogs. The etiology of this condition is unknown, but it is suspected to be hereditary or immune-mediated. SLO normally involves multiple nails on all four paws. It’s most commonly seen in middle-aged dogs, around 3 to 8 years of age, but has been seen in both puppies and older dogs. Predisposed breeds include German shepherds, Rottweilers and Gordon setters, but it has been seen in other breeds as well.

The disease often starts as an acute onset of nail loss. Because SLO often starts with a single abnormal nail, it can often take owners a while to realize there is a more generalized nail problem. It may take several months for other nails to be affected or slough off. Nails can also present as dry, distorted claws that do not slough on their own.

One or more of the following abnormalities are typically seen over time:

Onychogryphosis: abnormal curvature of the claws
Onychomadesis: sloughing of claws
Onychorrhexis: fragmentation of the claws
Onychoschizia: splitting of the claws
In some cases (although less commonly), significant inflammation (paronychia) or purulent discharge from the nail bed may be present if there is a secondary bacterial infection. Dogs with this disease may by asymptomatic, but many can have associated discomfort or lameness. SLO is not typically seen with other skin abnormalities or systemic illnesses.

Cutaneous lupus erythematosus (LE) is a diverse group of autoimmune connective tissue disorders localised to the skin that can be associated with systemic lupus erythematosus (SLE) to varying degrees.

Question 22

Signalement, clinical signs and treatments of Canine Symmetric Lupoid Onchyodystrophy (SLO)

Answer 22

Treatment: doxy + niacinamide (immunomodulatory action); oral-modified cyclosporine (atopica); fatty acid supplmentation; analgesis PRN

Question 23

How do claws / nails heal in Canine SLO?

Answer 23

Affected dogs heal with abnormal claw formation (onchodystrophy)