Week 1 Flashcards
Which germ layers do epidermis and the dermis come from?
ectoderm cells - epidermis
mesoderm - dermis
What type of epithelium is the epidermis?
stratified epithelium
What are the layers of the skin?
epidermis keratin layer granular layer prickle cell layer basal layer dermis
Where are melanocytes found in the skin and where did they migrate there from?
basal epidermis or in the matrix of hair during embryological development - migrated from neural crest
How is the neural crest formed?
during the formation of the neural tube (precursor to spinal cord) embryological cells are pinched off = neural crest
What happens during epidermis differentiation? How long does it take?
Keratinocytes migrate from the basement membrane to the surface of the epidermis = continuous regeneration of the epidermis.
Takes 28 days.
How many weeks into foetal development does the epidermis comprise 4 layers?
16 weeks
Name the layer of epidermis: one cell thick small cuboidal lots of intermediate filaments (keratin) highly metabolically active
basal layer
What are corneocytes and which epidermis layer has them?
overlapping non-nucleated remnants of terminally differentiated keratinocytes
therefore found in keratin layer
What are the features of the keratin layer?
corneocytes insoluble cornified envelope 80% keratin & filaggrin lamellar granules release lipid tight waterproof barrier
Which layer: 2-3 layers of flatter cells large keratohyalin granules Odland (lamellar) bodies high lipid content cell nuclei lost
granular layer
Which layer is the origin of the ‘cornified envelope’?
granular layer - granules burst and release contents in layer, left over lipids and proteins come together to form an evelope
Which layer:
larger polyhedral cells
lots of desmosomes
intermediate filaments (connect desmosomes)
prickle cell layer
Describe melanocytes.
melanin (pigment) producing dendritic cells
contain organelles called melanosomes
form protective cap over nucleus
Which chemical conversion occurs in melanocytes?
tyrosine to melanin pigment;
eumelanin and phaeomelanin
Which type of melanin pigment is brown/black?
eumelanin
which type of melanin pigment is red/yellow?
phaeomelanin
What is the function of melanin and melanin granules?
melanin absorbs light and therefore a natural density filter (sun cream)
full melanosomes (‘melanin granules’) are transferred to adjacent keratinocytes via dendrites (bud off)
What is the correct name for the smooth muscle fibres attached to hair follicles?
arrector pili muscles
What type of unit is a hair follicle?
pilosebaceous unit
What is the name for the ‘natural moisturiser’ that is continuously secreted? Which gland secretes it?
sebum from sebaceous gland
What are the 3 phases of growth?
angen
catagen
telogen
Angen phase takes place during which years of life and producing what percentage of hairs?
3-7 years, 90%
angen = growing
Catagen phase occurs for how long?
3-4 weeks, 10% hairs
catagen = involuting
Telogen phase also known as what phase? Occurs when?
shedding phase, each day <1% hairs
telogen = resting
What is the growth rate of nails?
0.1mm per day
Toe nails grow faster than finger nails?
False, fingers > toes
summer > winter
Nail plate sits on top of ?
nail bed
White area at base of nail plate?
lunula
What secures the free nail?
hyponychium
What cellular processes occur in the nail matrix?
cells divide and then produce hard keratin
What is a cuticle?
an extension of free skin fold covering the nail root
What is the interface between the epidermis and the dermis?
the dermo-epidermal junction
What are the key roles of the DEJ?
support, anchorage, adhesion, growth and differentiation of basal layer
semi-permeable membrane acting as barrier and filter
Name the condition where antibodies are formed against the DEJ.
bullous pemphigoid
Babies with a ‘mitten deformity’
epidermolysis bullosa
Rash and large itchy blisters found on the arms, legs and middle of body…
bullous pemphigoid
A group of genetic skin disorders that make skin very fragile - any trauma or friction to the skin can cause painful blisters…
epidermolysis bullosa
What do fibroblasts do?
collagen and extracellular matrix synthesis
Where are retentions ridges found and what is their role?
papillary dermis (top layer) - epithelial extensions that project into the underlying areolar connective tissue
What is the layer of dermis below papillary dermis?
reticular dermis - dense irregular connective tissue featuring densely packed collagen fibres.
Primary location of dermal elastic fibres
What is elastin?
the protein which allows skin to be pinched and return back to its normal position
Name the sweat glands active only upon puberty. Where are they found and what do they secrete? Which hormone are they dependent on?
Apocrine sweat glands
develop as part of pilosebaceous unit - produce oily fluid -> odour after bacterial decomposition
axillae, nipples, perineum
androgen dependent
What are holocene secretions?
produced in cytoplasm and released by the rupture of the plasma membrane which destroys the cell and results in the secretion of the product into the lumen.
Which sweat gland utilises holocrine secretions? Where are they found & what is their function?
sebaceous glands - holocrine secretions opening into pillary canal
widely distributed - largest glands in face and chest
lobulated masses in dermis which secrete sebum into hair follicle to coat hair and skin
control moisture loss, protection from fungal infection
Where are sebaceous glands not found?
palms and sole skin
When are sebaceous glands dormant?
pre-puberty (hormone sensitive)
Which sweat glands are found on the whole skin surface, except lips & genitalia?
eccrine sweat glands
found on palms, soles and axillae in particular
What is the stimulation of eccrine sweat glands? What are their functions?
sympathetic cholinergic nerve supply - mental, thermal & gustatory stimulation
Coiled tubular structure which regulate heat & salt loss; cooling by evaporation; moisten palms/soles to aid grip
Which sweat gland has the best filtration rate?
eccrine
ultrafiltration: can be >10L per day
NaCl + HCO3 reabsorbed - hypotonic fluid
Name conditions that occur if the skin barrier function is lost.
dehydration hypoalbuminaemia steroid-sulphatase deficiency x-linked ichthyosis cumulative irritant hand dermatitis ulcer following compound fracture
Erosions on fingertips; redness and scaling in-between fingers - type IV hypersensitivity
cumulative irritant hand dermatitis
condition characterised by loss of barrier function due to no normal lipids present in keratin layer…
steroid-sulphatase deficiency x-linked ichthyosis
Which sweat gland type is triggered in thermoregulation?
eccrine
What cell types are found in the dermis and involved in sensation?
pacinian corpuscles
meissner’s corpuscles
Which structure is involved in deep pressure sensation?
pacinian corpuscles
Which structure is used for tactile sensation?
messier’s corpuscles
Pain is detected by free nerve endings found in which layer of skin?
basal layer of epidermis
Define stigma.
the term describes the situation of an individual who is disqualified from full social acceptance
Skin is metabolically active in which metabolisms?
vitamin D and thyroid hormone
Skin absorbs which frequency of UV light to cause which conversion in vitamin D synthesis?
290-320nm
cholecalciferol (7-dehydrocholesterol) converted to vitamin D3
Vitamin D3 is stored by the liver as which compound?
hydroxycholecalciferol
What conversion does the kidneys do in vitamin D synthesis?
hydroxycholecalciferol -> 1,25-dihydroxycholecalciferol
What is the effect of 1,25-hydroxycholecalciferol on the bowel?
increased calcium absorption
What is the role of skin in thyroid hormone metabolism?
80% of the conversion of T4 -> T3 occurs in peripheral (to thyroid) tissues including the skin;
remaining 20% occurs in thyroid gland
What is PVL?
Panton Valentine Leukocidin is a cytotoxin associated with highly virulent strains of Staph aureus causing necrolytic skin infections by directly killing leucocytes.
Which virulence factor causes damage to the host directly?
Aggressin
Which virulence factor enables the organism to invade a host tissue?
Invasin
Which virulence factors enables binding of the organism to host tissue?
Adhesin
Which virulence factor enables the organism to avoid host defence mechanisms?
Impedin
Which virulence factor causes damage to the host indirectly?
Modulin
3 y/o boy presents on sunny day, mother reports crying & rubbing skin when outside. Skin sometimes red but no rash, clear now. Skin type 1 with few freckles.
erythropoietic protoporphyria
deficiency of which enzyme causes erythropoietic protoporphyria (EPP)?
ferrochelatase
What accumulates due to the enzyme deficiency in erythropoietic protoporphyria?
protoporphyrin IX in RBCs (erythrocytes), plasma, skin, and liver.
What is impaired in acute intermittent porphyria?
porphobilinogen - results in acute neurotoxic reaction in many tissues
