Skin

Question 0

Describe the macroscopic structure of human skin (i.e. as determined by the naked eye) and how this large and highly visible organ varies with site, sex, age, ethnicity and exogenous influence

Answer 0

Colour - ethnicity, site (lips, areolae), UV light
Hair - site, sex, age, ethnicity
Laxity/wrinkling - site, age/UV

Question 1

Describe how some of these variations influence the susceptibility to and/or the manifestations of skin disease

Answer 1

Vitiligo (autoimmune depigmentation) - more noticeable in dark skin
Alopecia areata (autoimmune hair loss) - psychosocial impact if affects scalp (especially women)
UV induced abnormalities - sun burn doesn't occur in black skin, skin aging and cancer in white skin (basal carcinoma, malignant melanoma)

Question 2

Describe the microscopic and molecular structure of human skin including the different regions of the epidermis (horny layer, granular layer, prickle cell layer, basal layer), the process of keratinocyte differentiation, epidermal dendritic cells and melanocytes

Answer 2

Epidermis - stratum corneum (horny layer), stratum granulosa, stratum spinosa (prickle cell layer), stratum basale
Keratinocyte differentiation - transit time = 30-40 days
Melanocytes - neural crest origin, intervals along basal layer, produce melanin (darker skin = more production)
Langerhans - bone marrow origin, scattered in prickle cell layer, mediate immune reactions and present antigens to T lymphocytes, difficult to see without special stains

Question 3

Describe the dermo-epidermal junction, dermis and it’s constituents, skin appendages, the immediate subcutaneous fat

Answer 3

Dermo-epidermal junctions - between epidermal basement membrane and dermis, best seen with PAS stain
Dermis - dense irregular CT, fibroblasts + ECM, blood vessels, lymphatic vessels, mast cells, nerves
Skin appendages - hair follicles, sebaceous glands (branched, acinar, holocrine), sweat glands (merocrine controlled by hypothalamus), nails

Question 4

Describe the main functions of the skin

Answer 4

Barrier - poor barrier function leads to loss of fluid, protein, nutrients, heat, excessive absorption of harmful agents
Sensation - leprosy, diabetic sensory neuropathy
Thermoregulation - dilation/constriction of skin blood vessels, sweating
Psycho-sexual communication - a means of communication and expression

Question 5

Briefly describe the following diseases, which arise as a result of disordered structure and/or function of selected skin components: psoriasis, malignant melanoma, vitiligo, alopecia areata

Answer 5

Psoriasis - patchy lesions on skin form increased proliferation of keratinocytes
Malignant melanoma - malignant growth of melanocytes
Vitiligo - autoimmune depigmentation
Alopecia areata - autoimmune attack on hair follicles