Skin

Question 0

Describe the mechanism of psoriasis.

Answer 0

Extreme proliferation of the epidermal basal layer, causing gross thickening of the stratum spinosum and excessive production of the stratum corneum (scaling)

Disrupted barrier -> loss of fluid, protein, nutrients, heat, & excessive absorption of exogenous agents (topical drugs).

Question 1

Describe the mechanism of vitiligo.

Answer 1

Autoimmune depigmentation = immune system attacks melanocytes (symmetrical/localised areas)

Question 2

Describe the mechanism of allergic contact dermatitis.

Answer 2

Langerhan’s cells in the stratum spinosum bind to allergens and present them to T lymphocytes -> stimulates inflammatory reaction

Question 3

Describe the mechanism of alopecia areata.

Answer 3

Autoimmune destruction of hair follicles, causing inflammation and hair loss -> bald patches, loss of eyebrow hair and eyelashes

Question 4

How can damage to collagen and elastin manifest?

Answer 4

UV damage -> SOLAR ELASTOSIS (yellow, wrinkled, thickened skin)

Stretch marks -> STRIAE

Question 5

What are some of the different types of skin cancer?

Answer 5

BASAL CELL CARCINOMA (common) = cancer of basal cells -> ulcerate. Metastasis rare.

MALIGNANT MELANOMA (rare) = neoplasm of melanocytes.

Retention of tumour cells above the epidermal basement membrane (superficial spreading).

Penetrates basement membrane -> metasis (poor prognosis)

Question 6

What are the layers of the skin above the basal layer?

Answer 6

STRATUM CORNEUM 	(dead keratinocytes) 
STRATUM LUCIDUM (thin clear layer of keratinocytes) 
STRATUM GRANULOSUM (keratinocytes without plasma membrane + granules) 
STRATUM SPINOSUM (keratinisation begins, keratinocytes no longer divide - spiny appearance due to desmosomes, contains Langerhan's cells)
MELANOCYTES (dendritic cells producing melanin on top of basal layer)
BASAL LAYER (keratinocyte mitosis)

Question 7

How do keloids form?

Answer 7

Excessive scar tissue formation after wounding.

More common in dark-skinned people.

Question 8

What is a port wine stain?

Answer 8

Congenital malformation of dermal blood vessels (the interconnecting vessels leading to blood vessels in the superficial dermis are always dilated -> skin appears red)

Question 9

Describe the mechanism of immediate hypersensitivity reaction.

Answer 9

Histamine released -> increased vascular permeability -> leakage of plasma into extravascular sites -> oedema (angio-oedema or urticaria)

ANGIO-OEDEMA = swelling of subcutaneous tissues due to degranulation of mast cells

URTICARIA = dermal oedema due to increase in capillary permeability

Question 10

Describe the mechanism of acne.

Answer 10

Abnormal differentiation of sebaceous gland ducts -> obstruction of glands -> increased sebum production -> infection with normally commensal bacteria

Occurs during puberty.

Question 11

What is the mechanism of hyperhidrosis?

Answer 11

Increased sweating -> apocrine sweat glands produce odourless, protein-rich secretion -> digestion by cutaneous microbes -> body odour

Question 12

What are the main functions of the skin?

Answer 12

Barrier = stratum corneum prevents percutaneous absorption of exogenous substances 
Sensation = see effects of damaged nerves in leprosy and diabetic sensory neuropathy 
Thermoregulation = vascular (constriction/dilation) & eccrine sweating (evaporation of sweat)

Question 13

What do Langerhan’s cells do and where are they found?

Answer 13

Dendritic cells (bone marrow origin)
Stratum spinosum
Antigen-presenting cells (present to T-lymphocytes)