L30: Introduction To Skin

Question 1

3 layers of skin

Answer 1

1. Epidermis (Keratinized stratified squamous epithelium, contains keratinocytes, 30-day cycle)
   - Stratum corneum
   - Stratum granulosum
   - Stratum spinosum
   - Stratum basale
2. Dermis (Dense irregular connective tissue)
3. Subcutis (Fat, Skin appendages)

Underlying: muscle, fascia

Question 2

Function of Dermo-epidermal junction (DEJ)

Answer 2

Basement membrane between stratum basale and superficial dermis

1. Adhesion
2. Cellular migration (wound healing)
3. Cellular signalling (epithelial-mesenchymal)

Question 3

Describe Dermis

Answer 3

• Connective tissue ECM:
  —> fibrous substance (85% Collagen fibre: tensile strength + Elastic fibre: elasticity)
  —> ground substance (Hyaluronic acid: water-binding)
• Function: strength + water retention
• Rich in blood supply
• Contains Adnexal structure: pilosebaceous unit, merocrine, apocrine gland

Question 4

Dermis collagen type

Answer 4

Type I, III: Dermal interstitium

Type IV: Basement membrane

Question 5

Subcutis

Answer 5

Adipose tissue: contains arterioles, venules, lymphatics
Function:
- Calorie reserve
- Cushion
- Insulation

Question 6

Skin appendages

Answer 6

1. Hair
2. Nail
3. Adnexal structure
   - pilosebaceous unit (Terminal, Vellus, Apopilosebaceous, Sebaceous)
   - sweat gland (eccrine gland + apocrine gland)

Question 7

Pilosebaceous unit

Location of Terminal, Vellus, Apopilosebaceous, Sebaceous gland

Answer 7

Terminal (largest follicles, extend into subcutis): scalp, beard
Vellus (small follicles): majority of skin
Apopilosebaceous: axilla, groin
Sebaceous: face, chest, back

Hair follicles no. remain unchanged until middle life, Terminal-Vellus ratio may change

Question 8

Hair growth phases

Answer 8

ACT:
Anagen (90%, 3 years)
Catagen (1%, 3 weeks)
Telogen (10%, 3 months, shedding phase, 100 per day, unless telogen effluvium)

1cm/month

Question 9

Sebaceous gland

Answer 9

• Rapidly reduction in size after birth

- Regain of function during puberty

Question 10

2 types of human skin

Answer 10

1. Glabrous skin
No hair follicles and sebaceous gland
Palms, soles
Compact stratum corneum
Encapsulated sense organ (dermis)

2. Hair-bearing skin
   Lack encapsulated sense organ

Question 11

2 types of sweat gland

Answer 11

1. Eccrine
   - Bullous secretory coil
   - Secretory duct
   - Opening pore
2. Apocrine
   - Secretion by decapitation
   - Low secretory output
   - Lipid rich
   - connected to hair follicles
   - Axilla, genitalia

Question 12

2 types of perspiration

Answer 12

1. Active

2. Insensible

Question 13

Nerve innervation in sweat gland

Answer 13

Sympathetic and cholinergic in character

Pilocarpine: Cholinergic agonist (stimulate sweating)
Atropine: Anti-cholinergic (inhibit sweating)

Question 14

Nail anatomy

Answer 14

1. Nail plate
2. Proximal nail fold
3. Nail matrix
4. Nail bed
5. Hyponychium

Question 15

Function of nails

Answer 15

1. Protection
2. Sensory discrimination
3. Dexterity e.g. scratching
4. Cosmetic

Question 16

Embryonic debvelopment of skin

Answer 16

Ectoderm: epidermis + nervous system
Mesoderm: dermis + skin appendages

Hair follicles, nails: 9 wks
Sweat gland: 9 wks (palms and soles); others: 15 wks
Sebaceous gland: 15 wks

Question 17

Function of skin

Answer 17

1. Mechanical barrier
   - Stratum corneum: insoluble —> prevent passage of water and electrolytes
2. UV Protection
   - Stratum corneum, keratinocytes, melanocytes (transfer melanin to keratinocytes)
   - UV absorption
3. Sensation
   - specialised sensory receptors (Meissner’s corpuscles, Merkel’s receptors)
4. Thermo-regulation
5. Immunity
   - Innate: antimicrobial peptides, alarmins (chemotactic), phagocytosis (dermal dendritic cells)
   - Adaptive: APC (Langerhans’ cells, dendritic cells), Cellular (Th1), Humoral (Th2)
6. Endocrine
   - Vitamin D3 (cholecalciferol) production
7. Communication

Question 18

Stems cells in skin

Answer 18

1. Bulge area of follicles
2. Basal area of inter-follicular epidermis
3. Base of sebaceous gland