Structure, function and disorders of the skin

Question 1

What are the main macroscopic variations in human skin?

Answer 1

Colour - ethnicity, site, UV
Hair- site, sex, age, ethnicity
Laxity/wrinkling - site, age/UV

Question 2

What are some example skin conditions that have a psychosocial impact?

Answer 2

Vitiligo - autoimmune depigmentation
= if it affects visible areas in dark-skinned races its much more noticeable than in whites

Alopecia areata - autoimmune hair loss= effects scalp, especially in women

Question 3

What are UV induced abnormalities?

Answer 3

Sunburn causes aging of the skin in white people but doesn’t occur in black people
- skin cancer: basal cell carcinoma, malignant melanoma

Question 4

How does UV light cause skin ageing?

Answer 4

UV induces damage to dermal collagen and elastin causing “photo ageing”

Question 5

What is the epidermis of the skin made up of ?

Answer 5

stratified squamous keratinised epithelium, mainly made up of keratinocytes and their products

Question 6

What are the layers of the epidermis?

Answer 6

Stratum corneum (horny layer)
Stratum lucideum (only in hard skin)
Stratum granulosum (granular layer)
Stratum spinousum (prickle cell layer)
Stratum basale (basal layer)

Question 7

Which layer of the skin does keratinocyte mitosis occur in mainly?

Answer 7

basal layer

Question 8

What happens to the daughter cells produced in the basal layer?

Answer 8

Move upwards to form the prickle cell layer, where terminal differentiation begins and keratinocytes lose ability to divide

Question 9

What do keratinocytes produce?

Answer 9

keratins (heterodimeric fibrous proteins) which contribute to the strength of the epidermis
Keratins = main constituent of hair and nails

Question 10

Why is the stratum spinsosum called the “prickle cell layer”?

Answer 10

prickle cells joined by prickle like desmosomes (intercellular junctions)

Question 11

What happens to keratinocytes in the stratum granulosum?

Answer 11

abrupt changes

• lose their plasma membrane
• begin differentiating into corneocytes= main cells of stratum corner

Question 12

What is present in the granular layer?

Answer 12

Keratohyalin granules = aggregations of

• keratins
• fibrous proteins (filaggrin, involucrin)
• enzymes (which degrade plasma membrane; cross link proteins = fillaggrin and involucrin)

Question 13

What are the roles of filaggrin and involucrin?

Answer 13

Filaggrin: aggregates keratins
Involucrin: forms a major part of corneocyte envelope

Question 14

What is the stratum corneum made up of?

Answer 14

layers of flattened corneocytes - skin barrier function

Question 15

What is the transit time of a keratinocytes from basal layer to horny layer?

Answer 15

30-40 days

Question 16

What are melanocytes and where are they found?

Answer 16

Dendritic cells of neural crest origin
Occur at intervals along basal layer
Produce melanin
In black or tanned skin, they produce more melanin but there are not increased numbers of them

Question 17

What are langerhan cells and where are they found?

Answer 17

Dendritic cells of bone marrow origin
Scattered throughout prickle cell layer
Specialised at presenting antigens to T lymphocytes
Mediate immune reactions - e.g. allergic contact dermatitis

Question 18

What is psoriasis?

Answer 18

abnormal epidermal growth and differentiation

Question 19

How common is psoriasis and what causes it?

Answer 19

2% of the population

cause is unknown but runs in families and thus is influenced by genetic factors

Question 20

What happens in psoriasis ?

Answer 20

Extreme proliferation of the epidermal basal layer, causing gross thickening of the prickle cell layer and production of excessive stratum corner cells - clinically manifesting as excessive scaling

Question 21

What is allergic contact dermatitis?

Answer 21

mediated by langerhan cells - these cells are responsible for presentation of antigens to T lymphocytes and for cutaneous delayed type hypersensitivity reactions

Question 22

What can cause allergic contact dermatitis?

Answer 22

Nickel (10% of women) - earrings

hair spray

Question 23

What is malignant melanoma?

Answer 23

malignant growth of melanocytes

• most common primary site is in the skin
• retention of tumour cells above the epidermal basement membrane is associated with a good prognosis
• more penetrating nodular melanomas may have a more poor prognosis

Question 24

What is vitiligo?

Answer 24

autoimmune destruction of melanocytes - immune system attacks melanocytes, usually in symmetrical localised areas of skin, causing well-demarcated pigmentation

• much more visible in dark skin
• no clear explanation for the curious symmetrical nature of vitiligo
• it can sometimes affect the whole body

Question 25

What happens to melanin?

Answer 25

it is produced in the melanocytes and fed out to the surrounding keratinocytes through dendrites

Question 26

What happens to melanocytes in hair follicles as we age?

Answer 26

they stop functioning and this causes greying (but not in the epidermis)

Question 27

Where is the epidermal basement membrane ?

Answer 27

at the derma-epidermal junction below the basal layer = best seen with PAS stain

Question 28

What are the characteristics of the dermis?

Answer 28

tough, fibrous and vascular layer - main component of leather

Question 29

What makes up the main part of the dermis and what is it made up of?

Answer 29

extracellular matrix - includes collagens (esp. type 1 collagen), elastin and other ECM components

Question 30

What synthesises the ECM?

Answer 30

Fibroblasts - spindle shaped cells scattered throughout the dermis

Question 31

Other than the ECM, what other dermal components are there?

Answer 31

Blood vessels
Lymphatic vessels
Mast cells
Nerves

Question 32

What is “solar elastosis”?

Answer 32

damage to collagen and elastin due to excessive UV exposure

Question 33

What is another name for stretch marks?

Answer 33

striae

Question 34

What are keloids?

Answer 34

Traditional skin markings

- Scars following wounding and comprise mainly of collagen synthesised by fibroblasts

Question 35

Where are the blood vessels located in the skin?

Answer 35

Smaller blood vessels are found in the superficial dermis (mainly capillaries, small venues and arterioles)

Interconnecting vessels

Larger blood vessels in the deeper dermis

Question 36

What is a port wine stain?

Answer 36

it is a birthmark = congenital malformation of dermal blood vessels

Question 37

Where are mast cells located ?

Answer 37

they are distributed around dermal blood vessels and contain histamine

Question 38

What happens when mast cells are activated?

Answer 38

During a type 1 immediate hypersensitivity reaction, histamine is released causing increased vascular permeability and leakage of plasma into extravascular sites = local oedema
- in the skin = urticaria and angio-oedema

Question 39

What are the skin appendages?

Answer 39

hair follicles 
Sebaceous glands 
- hair follicles + sebaceous glands = pilosebaceous unit 
sweat glands = eccrine and apocrine
nails

Question 40

What happens if the sebaceous duct can no longer communicate with the hair follicle?

Answer 40

if it can’t communicate any longer because it becomes obstructed acne can occur - this causes holocrine secretion

Question 41

What causes acne?

Answer 41

Skin disease affecting the sebaceous glands

• abnormal differentiation of sebaceous gland ducts which become obstructured
• infection with normally harmless skin bacteria
• changes in these glands occur at puberty

Question 42

What is hyperhidrosis?

Answer 42

increased sweating cause is usually unknown - may affect only palms and soles
- embarrassing wet hands, - wet, malodorous feet

Question 43

What are apocrine sweat glands?

Answer 43

large sweat glands most abundant in axillae, genital and submammary areas

• no function of value
• produce odourless, protein rich, apocrine secretion
• digestion of this by cutaneous microbes produces body odour

Question 44

What are the main functions of the skin?

Answer 44

• barrier function
• sensation
• thermoregulation
• psychosexual communication

Question 45

How does the skin act as a barrier?

Answer 45

Outer epidermis forms a major barrier preventing percutaneous absorption of exogenous substances

• studied a lot as it has to be overcome during percutaneous drug delivery
• can be seriously disrupted in many diseases = e.g. psoriasis

Question 46

What does poor barrier function lead to?

Answer 46

• loss of fluid
• loss of protein
• loss of other nutrients
• loss of heat

Could lead to excessive absorption of potentially harmful exogenous agents

Question 47

What are some disorders of skins sensory function?

Answer 47

• leprosy

- diabetic sensory neuropathy

Question 48

How is the skin involved in thermoregulation?

Answer 48

vascular thermoregulation and thermoregulatory eccrine sweating are both critically important in the maintenance of body temp
- failure of either may have serious consequences

Question 49

What is involved in vascular thermoregulation?

Answer 49

• dilation of skin blood vessels = heat loss

- constriction of skin blood vessels = pallor and heat conservation

Question 50

What happens if vascular thermoregulation fails?

Answer 50

widespread vasodilation or erythrodermic psoriasis and inability to vasoconstrictor in a cold environment = heat loss - patients are often shivery and may become hypothermic

Question 51

What is thermoregulatory eccrine sweating?

Answer 51

evaporation of eccrine sweat causes cooling - critically important in the maintenance of body temp

Question 52

What is psychosexual communication?

Answer 52

skin itself and its appendages are manipulated in many ways as a means of communication and expression