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
