Dermatology: Anatomy & Physiology (incomplete) Flashcards
What is the epidermis?
What layers does it have?
Stratified squamous epithelium consisting of 4-5 layers:
- Stratum corneum: outer layer of dead cells and keratin - barrier to bacteria/toxins
- Stratum lucidum: palms and soles only
- Stratum granulosum
- Stratum spinosum
- 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
How do cells of the epidermis become squamous?
Elongated flattened cells formed by filling of cytoplasm with proteins (esp. keratin), and cross-linking these polymer fibres into strong stable networks.
What are desmosomes?
Cell adhesion structures that are especially prominent in the epidermis and mucous membranes
Desmosomes are organelles that hold together keratinocytes (epidermal cells).
What four cell types make up the epidermis?
Keratinocytes
Melanocytes
Merkel cells (contain specialised nerve endings for cutaneous sensation)
Langerhans cells (present antigens and active T lymphocytes)
What do keratinocytes do
produce keratin and lipids as a protective barrier, daughter cells move to the surface to form the cornified layer (stratum corneum)
What do melanocytes do?
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.
How does melanogenesis occur?
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
What is an epidermal melanin unit?
Each melanocyte is associated with ~36 keratinocytes and one Langerhans cell
What is epidermal turnover time?
Migration of cells from stratum basale to stratum corneum
What is the function of the dermis?
2 components that provide this?
Provide structural stability and elasticity to skin
Fibrous component (mainly collagen and elastin) Ground substance (glycosaminoglycans)
What are the layers of the dermis?
Papillary dermis
Reticular dermis
Also contains vascular plexus (supplied by vessels in the SC fat), lymphatic system and nerve system
What is the hypodermis?
Loose tissue layer, attaches dermis to underlying tissues
Contains variable amounts of adipose tissues
What is a pilosebaceous unit?
Sebaceous gland + hair follicle
Most concentrated on face/scalp
Stimulated by androgens and become active at puberty
How can sweat glands be categorised?
Eccrine - palms, soles, axillae, forehead (regulate body temperature)
Apocrine - axillae and perianal regions (open into pilosebaceous follicles and produce body odour)
What is hair comprised of?
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
What are the 3 main types of hair?
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.
What are the 3 phases in terminal hair cycle?
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
What is the course of hair growth at birth?
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.
What can cause alopecia?
Vascular compromise secondary to perinatal trauma
Hamartomous malformation
Development of naevi such as epidermal naevus and sebaceous naevus
Aplasia cutis
What can cause generalised sparse hair?
Inherited structural hair defect or genodermatosis
What are congenital causes of diffuse hair loss?
Congenital hypotrichosis
Hair shaft anomalies (commonly associated with genetic syndromes) e.g. Netherton syndrome, Menkes kinky hair syndrome
What is congenital hypotrichosis?
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
What is Netherton syndrome?
Autosomal recessive - ichthyosis associated with bamboo hair (ball-and-socket hair shaft), erythroderma and atopy
What is Menkes kinky hair syndrome?
X linked recessive - copper metabolism
microcephaly, brittle silvery hair, pale skin, neurological abnormalities
What are acquired causes of diffuse hair loss? (non-scarring)
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
What are congenital causes of focal hair loss? (scarring)
Aplasia cutis
Naevus sebaceous
Inflammatory skin disorders e.g. morphoea
What is aplasia cutis?
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.
What is naevus sebaceous?
Type of epidermal naevus, presents early in life as waxy hairless rough plaque on head/neck
What is morphoea?
Localised scleroderma on frontal scalp
May present as shiny plaque of firm skin with scarring hair alopecia
What are acquired causes of focal hair loss? (non-scarring)
Alopecia areata
Tinea capitis
Trichotillomania - compulsive habit, pull out hairs, bizarre pattern of loss with twisted and broken off hairs on otherwise normal scalp
What is tinea capitis
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
What is alopecia areata?
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
What is clubbing?
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.
What is kolionychia
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What is Beau’s lines
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What is splinter haemorrhages
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What is pitting
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What is onycholysis?
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Why are newborns more suspectible to skin infection than older infants?
Skin pH less acidic than children and older adults
