Skin Flashcards
Describe how vitiligo is caused
Autoimmune destruction of melanocytes at basal layer of the skin resulting in depigmentation (usually symmetrical however the cause is unknown, possibly neurological?)
Where do melanocytes originate from?
Dendritic cells of the neural crest origin
What is ALOPECIA?
Autoimmune destruction of hair follicles that results in hair loss
Explain the effects of UV light on the skin
- Damage to collagen and elastic fibres which leads to skin wrinkling
- Skin cancer (malignant melanoma) due to increased UVB exposure
- Sunburn and freckling (particularly in fair skin)
Describe the layers of the epidermis
- STRATUM BASALE (basal layer) where keratinocyte mitosis occurs
- STRATUM SPINOSUM (prickle cell layer) where terminal differentiation of keratinocytes occurs and they lose their ability to divide
- STRATUM GRANULOSUM (granular layer) where keratinocytes differentiate into corneocytes, contains keratohyalin granules
- STRATUM CORNEUM (horny layer) composed of flattened corneocytes
How many days does it take for cells from the basal layer to reach the stratum corneum?
30-40 days
What is the role of keratinocytes?
Synthesise KERATINS which are fibrous proteins that contribute to the strength of the epidermis
Name the major cell types present in the epidermis
- Keratinocytes
- Corneocytes
- Melanocytes
- Langerhans cells
What is the role of melanocytes?
- Produce MELANIN which give skin its pigmentation and colour
- Melanocytes in black skin secrete MORE MELANIN (do NOT have more melanocytes)
Where are melanocytes situated?
Occur at intervals along the BASAL LAYER of the epidermis
Where do Langerhans cells originate from?
Dendritic cells of bone marrow origin
What is the role of Langerhans cells?
- Specialised antigen presenting cells which can present antigens to T lymphocytes
- Mediate immune reactions such as ALLERGIC CONTACT DERMATITIS
Where are Langerhan cells located?
Scattered throughout the PRICKLE CELL LAYER of the epidermis
What is psoriasis and how does it occur?
- EXTREME PROLIFERATION OF BASAL CELL LAYER (cause unknown but possibly genetic)
- Causes thickening of prickle cell layer and growth of stratum corneum
- Causes SCALING of the skin
How is allergic contact dermatitis mediated?
LANGERHAN CELLS detect foreign antigens and present them on their cell membranes for recognition by T lymphocytes, stimulating immune response
What is a malignant melanoma?
- Aggressive malignant tumour of melanocytes
- RETENTION OF TUMOUR CELLS TO THE EPIDERMAL BASEMENT MEMBRANE IS A GOOD PROGNOSIS SIGN
Describe the structure of the dermis
- DENSE IRREGULAR CONNECTIVE TISSUE
- Contains TYPE I COLLAGEN, ELASTIC FIBRES, blood/lymph vessels and nerves
- Cells include fibroblasts, mast cells, mesenchymal cells, and nerve cells
How does the arrangement of fibres in the dermis assist its function?
- IRREGULAR ARRANGEMENT of type I collagen bundles allows skin to resist forces in multiple directions, preventing TEARING
- Elastic fibres allow restoration of skin after it has been bent or stretched
Explain how the dermis connected to the epidermis and how this is visible
- EPIDERMAL BASEMENT MEMBRANE at the dermal-epidermal junction (stains with PAS)
- Interdigitation of dermis to epidermis prevents slippage of layer under friction
What are keloids?
Result from grossly excessive scar tissue production from fibroblasts
How are port wine birthmarks formed?
Congenital malformation of dermal blood vessels
What is the role of mast cells in the dermis?
- Contain many cytoplasmic granules of HISTAMINE
- STIMULATE HYPERSENSITIVITY REACTIONS
- Histamine increases the permeability of blood vessel walls causing local oedema
- Causes URTICARIA and ANGIO-OEDEMA
What does the PILOSEBACEOUS unit consist of?
- Hair sheath
- Hair shaft
- Arrector pili muscle
- Sebaceous gland
Name 4 appendages of the skin
- Sweat glands (eccrine and apocrine)
- Hair
- Sebaceous glands
- Nails
