KEY NOTES CHAPTER 1: GENERAL PRINCIPLES (A) Embryology, structure and function of skin.

Question 0

What does skin give rise to?

Answer 0

Teeth and hair follicles (derived from epidermis and dermis)

Fingernails and toenails (derived from epidermis)

Question 1

Where does skin differentiate from and when?

Answer 1

Ectoderm and mesoderm

4th week

Question 2

What are epidermal appendages?

Answer 2

They are all ingrowth of epidermis into dermis

• hair follicles
• sebaceous glands
• sweat glands
• apocrine glands
• mammary glands

Question 3

What are the functions of skin?

Answer 3

1. Physical protection
2. UV protection
3. Microbiological invasion
4. Prevent fluid loss
5. Regulation of body temp
6. Sensation
7. Immunological surveillance

PUMPSIT

Question 4

Draw the layers of the skin and a hair follicle

Answer 4

.

Question 5

How does epidermis develop?

Answer 5

It derives from ectoderm, and is composed of stratified squamous epithelium.
Keratinisation: epidermal cell’s cytoplasm is replaced with keratin as the cell dies and becomes more superficial.
Rete ridges: epidermal thickenings that extend downward b/t dermal papillae.

Question 6

What are the layers of the epidermis? (Deep to superficial)

Answer 6

1. Stratum germinativum (basal layer) - only proliferating layer, contains melanocytes.
2. Stratum spinosum (prickle cell layer) - contains keratinocytes.
3. Stratum granulosum - contains mature keratinocytes, main protein synthesis site (keratin).
4. Stratum lucidum - clear layer, only in glaborous skin.
5. Stratum corneum - contains non-viable keratinised cells.

Question 7

What cells are present in the epidermis? *

Answer 7

Keratinocytes
Langerhans cells - APC
Merkel cells - mechanoreceptors of neural crest origin
Melanocytes - melanin, melanosomes, cap over nucleus, protects DNA from UV

Question 8

How does dermis develop?

Answer 8

Derived from mesoderm, 95% of skin’s thickness.
Papillary - superficial, more cells, finer collagen fibres.
Reticular - deeper, less cells, coarser collagen fibres.

Question 9

What is the dermis composed of?

Answer 9

1. Collagen fibres (type 1:3 = 5:1, fibroblasts)
2. Elastin fibres (fibroblasts)
3. Ground substance (fibroblasts, GAGs)
4. Vascular plexus (b/t papillary and reticular layers)

Question 10

Tell me about the structure of hair follicles

Answer 10

Hair - composed of medulla, cortex, outer cuticle.
Hair follicle - inner (derived from epidermis) and outer (dermis) root sheath.
Sebaceous glands drain into it.
Arrector pili muscles.

Question 11

What are the phases of hair growth?

Answer 11

Anagen (growth) - <90%
Catagen (regressing) - 1%
Telogen (resting) - 10%

Question 12

What are the different sweat glands?

Answer 12

Eccrine glands - odourless, all over body.
Apocrine glands - axilla and groin, mammary gland (specialised), ear, eyelid.
Hidradenitis suppurativa = disease of apocrine glands.
Sebaceous glands - holocrine glands, drain into pilosebaceous unit, produce sebum.

Question 13

What are epidermoid cysts?

Answer 13

aka sebaceous cysts, but not entirely correct as they are not caused by sebaceous glands necessarily.

Question 14

What do the following terms mean?
Acanthosis
Papillomatosis
Hyperkeratosis
Parakeratosis
Pagetoid
Palisading

Answer 14

Acanthosis - epidermal hyperplasia.
Papillomatosis - increased depth of corrugations in dermoepidermal junction.
Hyperkeratosis - increased thickness of keratin layer.
Parakeratosis - nucleated cells at skin surface
Pagetoid - cells invade upper epidermis from below.
Palisading - cells orientated perpendicular to surface.