Intro to Dermatology Flashcards
1
Q
What is the Epidermis?
A
- Outermost layer of skin
- Primary defense layer to the external environment
- 85% keratinocytes, also melanocytes, Langerhans’ cells, and Merkel’s cells
- Layers: (deep to superficial)
- Stratum Basale
- Stratum spinosum
- Stratum granulosum
- Stratum lucidum
- Stratum Corneum
2
Q
What are Keratinocytes? Funtion?
A
- Contain keratin
- Produce cytokines - cutaneous immune response, inflammation, wound healing
- Produce lipids
- capable of phagocytosis
- Held together by desmosomes
3
Q
What is a Melanocyte? Function?
A
- Found in the basal layer of the epidermis, outer root sheath of hair follicles, hair matrix, sebaceous and sweat gland ducts
- Melanocytes produce melanin pigments
- Photoprotective function
- Scavenging free radicals
4
Q
What are Langerhans’ Cells? Function?
A
- Dendritic cells located in the basal layer or suprabasally
- Antigen presenting cells
- antigen specific T-cell activation
- Produce cytokines
5
Q
What is a Markel Cell? Function?
A
- Located int he stratum basale, tylotrich pads, and hair follicle epithelium
- Slow-adapting mechanoreceptors
6
Q
What is the Stratum basale?
A
- Basal layer
- Deepest layer of the epidermis
- Area of active mitosis
- consists of a single keratinocyte cell layer that is in direct contact with the basement membrane zone
7
Q
What is the Stratum spinosum?
A
- Spinous layer
- Cells arise from the basal layer and have prominent intracellular attachment sites called “desmosomes”
- Lipid synthesis occurs
- dispersed into intercellular spaces and a lipid layer surrounds each corneocyte
8
Q
What is the Stratum granulosum?
A
- Granular layer
- Cells are flattened and contain keratohyalin granules
- Granules release profilaggrin, cleaves to filaggrin
9
Q
What is the function of filaggrin
A
- Necessary for organization of keratin intermediate filaments
- Required for effective epidermal barrier function
10
Q
What is the Stratum lucidum
A
- Thin layer of fully keratinized cells
- Present only in footpads and nasal planum
11
Q
What is the Stratum corneum
A
- Most superficial layer
- Fully keratinized cells
- End product of epidermal differentiation where cells lose their mitotic activity and undergo gradual desquamation (constantly shed)
- Cells have cornified cellular envelope that connects the intracellular keratin matrix with the intercellular lipids
- Cells are anucleate, flattened cells that form layers that are permeated by sebum, sweat and lipids
- Impedes external movement of water and electrolytes and serves as a barrier to the entrance of external substances.
- decreases in stratum corneum lipids result in defective barrier function ⇢ increased transepidermal water loss (TEWL)
- Antimicrobial peptides ae a component
12
Q
What is the function of the cornified cellular envelope
A
- Structural support and protection
- Resistance to microorganism invasion
13
Q
What is the Basement Membrane Zone (BMZ)?
A
- The interface between the epidermis and dermis in the BMZ
- Complex structure that has several layers
- Functions of the BMZ:
- Anchors the epidermis to the dermis and maintains a functional epidermis
- Maintains tissue architecture and structural support
- Barrier and wound healing functions
- The site of injury/attack in certain autoimmune disorders ⇢ blister formation
14
Q
What is the Dermis?
A
- Provides tensile strength, elasticity and structural support
- Water and electrolyte storage
- Made up of Fibers, ground substance, cells, appendages and arrector pili muscles, vessels, and nerves
15
Q
What are dermal fibers?
A
- Formed by fibroblasts
-
Collagen (collagenous fibers)
- comprised of multiple protein fibrils
- Main component responsible for skin tensile strength
- 90% of dermal fibers are collagen
- Several types of collagen (most is type I collagen)
-
Elastic fibers
- comprised of protein (cross-linked amino acids) and microfibrils
- Visualized microscopically with special elastin stains
-
Reticular fibers
- similar to collagen
16
Q
What is Dermal Ground Substance?
A
- Interstitial substance of fibroblast origin
- Comprised of glucosaminoglycans and proteins (proteoglycans)
- Water storage
- glucosaminoglycans and proteoglycans bind water
- Passage of electrolytes, nutrients and cells from vessels to the epidermis
- Maintenance of dermal structure
- Fibronectins are glycoproteins that modulate cell interactions, vascular permeability, wound healing
17
Q
What are Dermal Cells
A
- Fibroblasts and dermal dendrocytes
- Mast cells (small #)
- Melanocytes may be present around vessels and hair bulbs
- Sparse neutrophils, lymphocytes, plasma cells, macrophages, eosinophils
- Normally, there are few cells in the dermis
18
Q
What appendages are in the dermis?
A
- Hair follicles
- Hair shafts
- sebaceous glands
- apocrine sweat glands
- Eccrine sweat glands
- Tail gland (supracaudal gland)
19
Q
What are hair follicles?
A
- These are compound in the dog and cat (large primary hairs and smaller secondary hairs all exit through a common opening)
- Outer layer (outer root sheath) is a downward extension of the epidermis
- Hair matrix cells, at the base of the follicle, give rise to the hair
20
Q
What are hair shafts
A
- Comprised of protein
- Primary (guard), Secondary (undercoat) and tactile (whiskers)
- Medulla - cells, glycogen vacuoles, and air
- Cortex - pigmented cells
- Cuticle - outermost layer of flattened cells
21
Q
What are sebaceous glands?
A
- Holocrine
- open through a duct into the hair follicle
- More numerous on dorsal neck, rump, tail, chin, interdigital regions, and mucocutaneous junctions
- Production of oily sebum (triglycerides, cholesterol, phospholipids, fatty acids)
- Sebum has antimicrobial properties
- Sebum-sweat emulsion retains moisture, softens skin, produces sheen, provides physical and chemical barrier
- Androgens cause hypertrophy of sebaceous glands
- Estrogens and glucocorticoids cause atrophy of sebaceous glands
22
Q
What are apocrine sweat glands
A
- Open through a duct into the hair follicle
- Sweat has antimicrobial and pheromonal properties and functions in excretion of waste products
23
Q
What are Eccrine sweat glands
A
- Found only in footpads
- Duct opens onto footpad surface
- May see eccrine seating of footpads in nervous animals
24
Q
What are tail glands?
A
- Dog - oval area on the dorsal tail surface, about 5 cm distal to the anus
- Cat - all along the dorsal tail surface
25
Q
What are arrector pili muscles
A
- smooth muscle with vacuoles
- Largest in dorsal neck and rump skin
- Contraction causes piloerection (hair stands up)
26
Q
What are the function of blood vessels in the dermis?
A
- Arise form superficial, middle and deep plexus of arteries and veins
- Supply hair follicles, glands, arrector pili muscles and the epidermis
27
Q
What is the function of lymph vessels in the dermis?
A
- drain away tissue debris, protein, cells, fluid and have an immunoregulatory function (via linking the skin and regional lymph nodes)
28
Q
What is the function of nerves in the dermis?
A
- Innervate the blood vessels, hair follicles, glands and arrector pili muscles
- Ara of skin supplied by branches of one spiral nerve is called a dermatome
- Nerves function in sensory perception and maintenance of epidermal viability
29
Q
How does the nervous system sense an ‘Itch’?
A
- Itch is received by free nerve endings near the dermal-epidermal junction
- Specialized afferent neve fibers transmit the itch sensation to the central nervous system
- Tertiary neurons relay the itch to the level of conscious perception in the cerebral cortex
30
Q
What is the Subcutis?
A
- Panniculus
- Consists of fat lobules separated by fibrous bands
- Functions:
- Protective cushion
- Structural support
- Energy reserve (steroid reservoir)
- Insulation
- Capillary walls are thinner as compared to those in the dermis and there are no lymphatics present in fat lobules
- fat is susceptible to disease processes from injury because of an inefficient system for removal of damaged tissue
39
Q
what is a papule
A
- pinkish/red, raised, solid, circumscribed elevation of the skin
- 1mm to a few mm in diameter
- Indicative of cellular infiltrate and usually represents an inflammatory lesion
- Common causes in dogs:
- bacterial skin disease (pyoderma)
- ectoparasitism (scabies ,demodicosis, flea bite hypersensitivity
- Common causes in cats:
- hypersensitivity/allergic dermatitis
- infected feline acne
40
Q
What is a pustule
A
- small, round, epidermal elevation containing pus
- “white head”
- Usually contains neutrophils
- eosinophilic pustules are less common
- Often indicate bacterial infection
- can be sterile ⇢ pemphigus foliaceus
- Fragile and rupture easily
41
Q
What is a Vesicle?
A
- Small (<1cm) epidermal elevation containing clear fluid ( ~blister)
- Rarely seen ⇢ occur infrequently and rupture easily
- Causes:
- autoimmune skin diseases
- irritant reactions
- burns
- Vesicular lesions >1cm = “bulla”
42
Q
What is a Wheal
A
- Raised, well-circumscribed, edematous lesion
- “hives”, urticaria)
- Overlying skin usually normal
- Persist for minutes to hours (short lived)
- Uncommon in dogs, rare in cats
- Causes:
- insect bites
- hypersensitivity reactions
43
Q
What is a nodule?
A
- Well-circumscribed, solid lesion that usually occurs deep within the skin
- Numerous causes including inflammatory or neoplastic cellular infiltration
44
Q
What is a Macule
A
- Circumscribed flat, nonpalpable, small (<1cm) spot of color change
- A patch is a macule >1cm
- Can be hyperpigmented, hypopigmented, erythematous, hemorrhagic
- Common in dogs as a post-inflammatory hyperpigmented change
45
Q
What is a cyst
A
- Epithelium-lined cavity that is filled with fluid or solid material
- Can be soft/fluctuant or firm (follicular cysts are often firm)
47
Q
What is an epidermal collarette
A
- Circular ring of scale/peeling keratin
- Often a remnant of a papule or pustule
48
Q
What is Lichenification
A
- A rough appearance of the skin, usually thickened
- generally from friction and is indicative of chronicity
49
Q
What is a callus
A
- A thickened, rough, alopecic hyperkeratotic plaque-like lesion
- Commonly seen over bony areas and caused by pressure and friction
- elbow calluses are protective to the underlying bone
50
Q
what is a Fissure
A
- A linear cleavage into or through the epidermis
- a ‘crack’ in the skin
- Sites include:
- footpads
- ear margins
- nasal planum
- mucocutaneous junctions
51
Q
What is an erosion or ulcer?
A
- Erosion - epidermal defect that does not penetrate the BMZ and heals without scarring
- Ulcer - Epidermal defect that is deeper than an erosion ⇢ exposes the dermis
- often heals with scarring
- Causes:
- self-trauma
- infection
- neoplasia
- vasculitis
- autoimmune skin diseases
- burns
52
Q
What is a scar
A
- Fibrous tissue replacement of normal epidermis, dermis, or subcutis
- May result from burns or deep infection
