Skin

Question 1

Describe how vitiligo is caused

Answer 1

Autoimmune destruction of melanocytes at basal layer of the skin resulting in depigmentation (usually symmetrical however the cause is unknown, possibly neurological?)

Question 2

Where do melanocytes originate from?

Answer 2

Dendritic cells of the neural crest origin

Question 3

What is ALOPECIA?

Answer 3

Autoimmune destruction of hair follicles that results in hair loss

Question 4

Explain the effects of UV light on the skin

Answer 4

• 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)

Question 5

Describe the layers of the epidermis

Answer 5

• 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

Question 6

How many days does it take for cells from the basal layer to reach the stratum corneum?

Answer 6

30-40 days

Question 7

What is the role of keratinocytes?

Answer 7

Synthesise KERATINS which are fibrous proteins that contribute to the strength of the epidermis

Question 8

Name the major cell types present in the epidermis

Answer 8

• Keratinocytes
• Corneocytes
• Melanocytes
• Langerhans cells

Question 9

What is the role of melanocytes?

Answer 9

• Produce MELANIN which give skin its pigmentation and colour
• Melanocytes in black skin secrete MORE MELANIN (do NOT have more melanocytes)

Question 10

Where are melanocytes situated?

Answer 10

Occur at intervals along the BASAL LAYER of the epidermis

Question 11

Where do Langerhans cells originate from?

Answer 11

Dendritic cells of bone marrow origin

Question 12

What is the role of Langerhans cells?

Answer 12

• Specialised antigen presenting cells which can present antigens to T lymphocytes
• Mediate immune reactions such as ALLERGIC CONTACT DERMATITIS

Question 13

Where are Langerhan cells located?

Answer 13

Scattered throughout the PRICKLE CELL LAYER of the epidermis

Question 14

What is psoriasis and how does it occur?

Answer 14

• 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

Question 15

How is allergic contact dermatitis mediated?

Answer 15

LANGERHAN CELLS detect foreign antigens and present them on their cell membranes for recognition by T lymphocytes, stimulating immune response

Question 16

What is a malignant melanoma?

Answer 16

• Aggressive malignant tumour of melanocytes

- RETENTION OF TUMOUR CELLS TO THE EPIDERMAL BASEMENT MEMBRANE IS A GOOD PROGNOSIS SIGN

Question 17

Describe the structure of the dermis

Answer 17

• 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

Question 18

How does the arrangement of fibres in the dermis assist its function?

Answer 18

• 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

Question 19

Explain how the dermis connected to the epidermis and how this is visible

Answer 19

• EPIDERMAL BASEMENT MEMBRANE at the dermal-epidermal junction (stains with PAS)
• Interdigitation of dermis to epidermis prevents slippage of layer under friction

Question 20

What are keloids?

Answer 20

Result from grossly excessive scar tissue production from fibroblasts

Question 21

How are port wine birthmarks formed?

Answer 21

Congenital malformation of dermal blood vessels

Question 22

What is the role of mast cells in the dermis?

Answer 22

• 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

Question 23

What does the PILOSEBACEOUS unit consist of?

Answer 23

• Hair sheath
• Hair shaft
• Arrector pili muscle
• Sebaceous gland

Question 24

Name 4 appendages of the skin

Answer 24

• Sweat glands (eccrine and apocrine)
• Hair
• Sebaceous glands
• Nails

Question 25

How is acne caused?

Answer 25

• Abnormal differentiation of sebaceous glands causing obstruction
• Increased sebum production
• INFECTION by harmless skin bacteria

Question 26

How do sebaceous glands secrete sebum into hair follicles?

Answer 26

HOLOCRINE SECRETION (involves disintegration of cell and release of entire cell contents)

Question 27

What are apocrine sweat glands and where are they located?

Answer 27

• Large sweat glands that produce odourless, colourless secretion (merocrine) rich in proteins
• Located at AXILLE, GENITAL and SUBMAMMARY regions
• Digestion of secretion by microbes causes body odor

Question 28

What are the main functions of the skin?

Answer 28

• BARRIER FUNCTION to protect against water loss and absorption of toxins
• SENSATION as dermis contains many nerves
• THERMOREGULATION by vasodilation/vasoconstriction of arterioles or by thermoregulatory eccrine sweating
• PSYCHOSEXUAL COMMUNICATION by means of tattoos and piercings

Question 29

List 3 variations in the macroscopic structure of the skin

Answer 29

• COLOUR (ethnicity, site, UV light)
• HAIR (site, age, sex, ethnicity)
• LAXITY/WRINKLING (age, UV exposure)