Dermatology: Anatomy & Physiology (incomplete)

Question 1

What is the epidermis?

What layers does it have?

Answer 1

Stratified squamous epithelium consisting of 4-5 layers:

1. Stratum corneum: outer layer of dead cells and keratin - barrier to bacteria/toxins
2. Stratum lucidum: palms and soles only
3. Stratum granulosum
4. Stratum spinosum
5. Stratum basale (basal cell layer) - source of new epidermal cells

The squamous shape means skin resistant to mechanical trauma and allows shedding without disruption of the whole surface

Question 2

How do cells of the epidermis become squamous?

Answer 2

Elongated flattened cells formed by filling of cytoplasm with proteins (esp. keratin), and cross-linking these polymer fibres into strong stable networks.

Question 3

What are desmosomes?

Answer 3

Cell adhesion structures that are especially prominent in the epidermis and mucous membranes

Desmosomes are organelles that hold together keratinocytes (epidermal cells).

Question 4

What four cell types make up the epidermis?

Answer 4

Keratinocytes
Melanocytes
Merkel cells (contain specialised nerve endings for cutaneous sensation)
Langerhans cells (present antigens and active T lymphocytes)

Question 5

What do keratinocytes do

Answer 5

produce keratin and lipids as a protective barrier, daughter cells move to the surface to form the cornified layer (stratum corneum)

Question 6

What do melanocytes do?

Answer 6

Produce melanin (pigment to skin and protects against UV induced DNA damage - physical barrier that scatters UV and reduces its penetration through epidermis). The damage and/or repair produces initiating signals that induce an increase in melanogenesis.

Question 7

How does melanogenesis occur?

Answer 7

In specific ovoid organelles (melanosomes) - which are produced in dendritic melanocytes

Melanin is then transported via dendrites to adjacent keratinocytes and melanocytes in the perinuclear areas

Question 8

What is an epidermal melanin unit?

Answer 8

Each melanocyte is associated with ~36 keratinocytes and one Langerhans cell

Question 9

What is epidermal turnover time?

Answer 9

Migration of cells from stratum basale to stratum corneum

Question 10

What is the function of the dermis?
2 components that provide this?

Answer 10

Provide structural stability and elasticity to skin

Fibrous component (mainly collagen and elastin) 
Ground substance (glycosaminoglycans)

Question 11

What are the layers of the dermis?

Answer 11

Papillary dermis

Reticular dermis

Also contains vascular plexus (supplied by vessels in the SC fat), lymphatic system and nerve system

Question 12

What is the hypodermis?

Answer 12

Loose tissue layer, attaches dermis to underlying tissues
Contains variable amounts of adipose tissues

Question 13

What is a pilosebaceous unit?

Answer 13

Sebaceous gland + hair follicle
Most concentrated on face/scalp
Stimulated by androgens and become active at puberty

Question 14

How can sweat glands be categorised?

Answer 14

Eccrine - palms, soles, axillae, forehead (regulate body temperature)

Apocrine - axillae and perianal regions (open into pilosebaceous follicles and produce body odour)

Question 15

What is hair comprised of?

Answer 15

Modified keratin

The cortex is produced from the medulla within the hair bulb, cortex contains densely packed keratin and surrounded by single layer of cells called cuticle

Hair colour depends on amount of melanin within cortex

Question 16

What are the 3 main types of hair?

Answer 16

Lanugo - fine long hair on fetus
Vellus - fine short hair on all body surfaces
Terminal hair - course long hair on scalp, eyelashes, eyebrows, pubic areas.

Question 17

What are the 3 phases in terminal hair cycle?

Answer 17

Growth phase (anagen) - lasts several years 
Short involutional phase (catagen) 
Resting phase (telagen) - lasts several months 

In an adult, approximately 85-90% hairs are in anagen, 10-15% in telogen and <1% in catagen

Question 18

What is the course of hair growth at birth?

Answer 18

Most infants at term have full head of terminal hair
Shortly after birth, undergo brief period of shedding where pattern of synchronous hair growth shifts to dyssynchronous like in adults.

Question 19

What can cause alopecia?

Answer 19

Vascular compromise secondary to perinatal trauma
Hamartomous malformation
Development of naevi such as epidermal naevus and sebaceous naevus
Aplasia cutis

Question 20

What can cause generalised sparse hair?

Answer 20

Inherited structural hair defect or genodermatosis

Question 21

What are congenital causes of diffuse hair loss?

Answer 21

Congenital hypotrichosis

Hair shaft anomalies (commonly associated with genetic syndromes) e.g. Netherton syndrome, Menkes kinky hair syndrome

Question 22

What is congenital hypotrichosis?

Answer 22

Most = autosomal dominant
Usually no internal abnormality
Ectodermal dysplasias = genodermatoses characterised by absent or inadequate development of one or more epidermal appendages e.g. hair, sweat glands, nails, teeth

Question 23

What is Netherton syndrome?

Answer 23

Autosomal recessive - ichthyosis associated with bamboo hair (ball-and-socket hair shaft), erythroderma and atopy

Question 24

What is Menkes kinky hair syndrome?

Answer 24

X linked recessive - copper metabolism
microcephaly, brittle silvery hair, pale skin, neurological abnormalities

Question 25

What are acquired causes of diffuse hair loss? (non-scarring)

Answer 25

Telogen effluvium - excessive loss of telogen hair, can be physiological in newborn, or triggered by illness, stress, surgery, iron and protein deficiency

Anagen effluvium - abrupt loss of anagen hairs, triggered by radiotherapy (can cause scarring), systemic chemotherapy and any toxic agents

Question 26

What are congenital causes of focal hair loss? (scarring)

Answer 26

Aplasia cutis

Naevus sebaceous

Inflammatory skin disorders e.g. morphoea

Question 27

What is aplasia cutis?

Answer 27

Eroded area of scalp which presents at birth and heals over time as a patch of scarring hair loss. Can be associated with or without developmental abnormalities.

Question 28

What is naevus sebaceous?

Answer 28

Type of epidermal naevus, presents early in life as waxy hairless rough plaque on head/neck

Question 29

What is morphoea?

Answer 29

Localised scleroderma on frontal scalp

May present as shiny plaque of firm skin with scarring hair alopecia

Question 30

What are acquired causes of focal hair loss? (non-scarring)

Answer 30

Alopecia areata

Tinea capitis

Trichotillomania - compulsive habit, pull out hairs, bizarre pattern of loss with twisted and broken off hairs on otherwise normal scalp

Question 31

What is tinea capitis

Answer 31

Common cause of patchy hair loss in children, especially developing countries

Represents fungal infection (scalp) by dermatophytes, most often Trichophyton tonsurans in the UK. Positive culture requires systemic antifungals

Question 32

What is alopecia areata?

Answer 32

Chronic autoimmune disease, usually presenting with focal smooth patches of hair loss on scalp or other hair bearing areas (typically eyelashes, eyebrows)

May be associated with other autoimmue conditions e.g. thyroid

Most children - full regrowth within 1 year

Question 33

What is clubbing?

Answer 33

Thickening of soft tissue beneath proximal nail plate causing widening of angle between proximal nail fold and nail plate (>180 degrees)

Normal is <160 degrees

Hereditary causes - primary hypertrophic osteoarthropathy

Acquired - AV malformations, lung disease, congenital heart disease, cirrhosis, IBD.

Question 34

What is kolionychia

Answer 34

-

Question 35

What is Beau’s lines

Answer 35

-

Question 36

What is splinter haemorrhages

Answer 36

-

Question 37

What is pitting

Answer 37

-

Question 38

What is onycholysis?

Answer 38

-

Question 39

Why are newborns more suspectible to skin infection than older infants?

Answer 39

Skin pH less acidic than children and older adults