Intro: Skin Structure Flashcards
List some causes of skin disease
-genetics -irritants -allergens -drugs -sunshine -temperature/humidity -infections
What are the two main layers of the skin?
- epidermis: outer layer: stratified cellular epithelium
- dermis: under epidermis: connective tissue
What does epidermis derive from?
Ectoderm
What does ectoderm become by week 4 ?
-periderm -basal layer -dermis
By 16 weeks what layers of skin have developed?
-keratin layer -granular layer -prickle cell layer -basal layer -dermis
What are Blaschko’s lines and what does skin disease along these lines mean?
-developmental growth pattern of skin -that disease is due to genetic error
What are 5 components of skin?
-epdermis -appendages: nails, hair, glands, mucsoae -dermo-epidermal junction -dermis -sub-cutis
What is skin scar defined by?
lack of appendages (nails, hair, glands, mucosae)
Pilum
hair
pilosebaceous unit
relating to gland/hair
Epidermal cell layers
-keratin layer -granular layer -prickle cell layer -basal layer
Why called prickle cell?
because held together by desmosomes that look like prickles
Label this diagram.
What cells make up 95% of the epidermis?
Keratinocytes
What are 4 layers of the epidermis?
- keratinous layer
- granular layer
- prickle cell layer
- basal layer
What 3 factors control epidermal turnover?
- growth factors
- cell death
- hormones
What 2 skin diseases are a result of loss of control of epidermal turnover?
- psoriasis
- skin cancer
What are 4 cells in the epidermis?
- keratinocytes
- Langherhans
- Merkel cells
- melanocytes
Where do keratinocytes orginate from and what happens as they migrate to surface?
- Basal layer
- differentiate as they migrate
What is significance of desmosomes holding together prickle cells?
desmosomes allow both stability and some flexibility
What are rete ridges in the skin?
Downward projections of the epidermis into the dermis
What do keratinocytes synthesise in the basal layer?
keratin filaments and desmosomal proteins
What do keratin filaments and desmosomal proteins make up in the cell?
What is synthesised in the granular layer and what cells secrete them?
- lipid & lipid hydrolases
- secreted by lamellar bodies
What do lipid and lipid hydrolases form?
a water-tight intercellular lipid bilayer
What secretes pro-filaggrin and where is it converted to filaggrin?
- lamellar bodies in granular layer
- in the stratum corneum (AKA keratinous layer)
What are the 2 functions of filaggrin?
- holds moisture within cells (natural moisturising factor)
- forms part of tough cell envelope i.e. water barrier, binds keratin filaments and lipid filaments
Which layer provides most of the barrier function of the epidermis?
outer stratum corneum
What can filaggrin deficiency lead to?
Leaky skin that allows entry of allergens causing an immunological response e.g. Ichthyosis vulgari, eczema
Where do melanocytes originate from?
Neural crest
Where do melanocytes reside?
Basal layer
What amino acid is melanin a product of?
tyrosine
What is the function of melanin?
Thick brown coloured cap over the nucleus that won’t let UV light penetrate to protect stem cells (basal cells)
Variation in what causes the difference in skin colour?
variation in melanin production not the number of melanocytes
What are the organelles in melanocytes called and what do they do?
- Melanosomes
- convert tyrosine to melanin pigament
What is the name of the melanin pigment of brown/black skin?
Eumelanin
What is the name of the pigment associated with red/yellow skin?
phaeomelanin
What are Merkel cells, where are they numerous and where exactly in the skin do they sit?
- cells that play a role in sensation
- numerous in fingertips and oral cavity
- sit in the basal layer between keratinocytes and nerve fibres
What is the mortality rate of Merkel cell cancer and what is a cause?
- Very high
- viral infection
How does melanin get into keratinocytes?
By travelling in melanosomes across dendrites extended by the melanocytes
What is the pathophysiology behind vitiligo?
autoimmune disease with loss of melanocytes
What is pathophysiology of albinism?
genetic partial loss of pigment production
What is Nelson’s syndrome and how does it present in dermatology?
- disorder characterised by abnormal hormone secretion and enlargement of pituitary gland
- melanin stimulating hormone produced in excess by pituitary and so there is hyperpigmentation
Where are Langerhan cells derived from?
Bone marrow
What type of cell are Langerhan cells and what do they form?
- dendritic cells
- network across the supra basal layer
Where do Langerhan cells sit in the epidermis and where else are they found?
- In the prickle cell layer in epidermis
- also in dermis and lymph nodes
What is the function of Langerhan cells?
-play a role in immunoregulation through picking up antigen and transporting them to lymph nodes via lymphatic system
What is the dermo-epidermal junction?
Describe pathology of bullous pemphigoid and describe blisters.
-antibody attack dermo-epidermal junction
BP 20 and PB 240
- tense blisters
- generally old people
- biopsy and stain to diagnose
epidermolysis bullosa
- rare
- tends to be in babies
- abnormalities in proteins in dermo-epidermal junction, collagen 7
- can affect trachea etc
- chronic scarring
What is dermis made up of?
- ground substance: polysaccharides, water-based, helps with solute transfer
- cells: fibroblasts(make collagen, elastic fibres), mast cells, lymphocytes, Langerhan cells
- fibres (collagen, elastin)
- muscles, blood vessels, lymphatics, nerves
urticaria and nettle rash
wheals
mast cells pop
- release histamine
- so antihistamines for these
Describe collagen arrangement across dermis?
more horizontal and condensed further down you go
What does it mean to have horizontal plexuses?
blood vessels run parallel to skin surface and then branch off
What is angioma?
disorganised large arterioles and vessels that grow abnormally in the skin
What do lymphatic vessels in the skin drain?
- plasma proteins
- extravasated cells
- excess interstital fluid
What can cause chronic lymphoedema?
damage to lymph vessels so lymph cant drain e.g. from athletes foot (fungal)
What are pacinian corpuscle responsible for?
sensing pressure on skin
What nerves innervate the sweat glands?
motor nerve fibres by autonomic nervous system
Nerves in the skin
pilosebaceous unit
epidermal component + dermal papilla (papilla is hair root)
-specialised keratins, sebaceous gland with it
-
label this imagine
What are the 3 phases of hair growth?
anagen = growing
catagen = involuting
telogen = resting
What is the involuting phase?
dying phase, hair root shortens, come out naturally, new hair pushes out, embedded but not growing
What are hormonal influences on hair
thyroxine
androgen
what is alopecia areata?
autoimmune condition where body attacks alogen hair follicle
hirsutism
too much hair growing in inappropriate areas
What are 3 skin glands
sebaceous (present everywhere but mostly in face, chest and upper back, very hormone sensitive, produce sebum (squalene, wax esters, TG and FFA)
apocrine (armpits + groin, feed into hair follicles, linked to pheromones)
eccrine( sweat glands on hands and feet, face also, autonomic nervous system, help with thermoregulation)
acute skin failure
e.g. toxic epidermal necrolysis
functions of the skin
- barrier function
- metabolism and detoxification
- thermoregulation
- communication
- immune defense
-
barrier:
- physical (UV, trauma)
- chemical
- pathogens
skin metabolic actions examples
vitamin D metabolism
-thyroid hormone metabolism
wyatbis Hansen’s disease
tuberculoid leprosy
eczema herpeticum
disseminated herpes simplex virus infection
What is this autoimmune disease?
chronic discoid lupus erythematous
What is this?
self harm burns, scratching
What is this an example of?
neuropathic ulcer e.g. leprosy
