Introduction to Skin Flashcards
what is the largest organ in the body
skin
how much does skin weight
12-15% body weight
what is the most common reason for visiting a GP
Skin - 42%
name some skin diseases
Cancer - malignant melanoma
inflammation - e.g.Psoriasis
genetic diseases
wounds - diabetic ulcers
What is the function of skin
Protection
- Physical trauma
- Infection
- Penetration of drugs and chemicals
- UV radiation
- Water loss
- insulation
- provides sensory information
- vitamin D synthesis
what are the two layers of the skin
epidermis - barreie function of the skin
dermis - made up of a large amount of collagen and connective tissue therefore responsible for the strength of the skin
describe the epidermis
- epithelium
- major cell type
- what it also includes
Stratified Squamous Epithelium
Major cell type the keratinocyte
Also includes hair and sebaceous gland
what are the four main layers of the epidermis
- Stratum basale (basal layer) - have dark nuclei
- Stratum spinosum (spinous layer) - become more round and nuclei become lighter so not as prominent
- Stratum granulosum (granular layer) - contains keratinohylaine granules
- Stratum corneum (cornified layer)- become very flattened
What is the most abundant cell type in the skin
- Keratinocytes
describe keratinocytes and what they produce
- epithelial cell type
- produces keratins
describe the structure of keratin
intermediate filament
Mol Wt. 40-50,000 kD
Exist as acidic and basic pairs (e.g. K5/K14)
Expression pattern is specific to epidermal layer
where is keratin abdunant in
Most abundant proteins in stratum corneum, hair and nails
how many types of keratin are there
54
what are the two categories of keratins
Depends on their secondary structure
- alpha type - soft
- beta type - hard, beta sheets that cross over together by disulphide and hydrogen bonding which makes them harder
can classify according to there pH
- pair together with acidic or basic pairing so the structure is normal
- these pairing is specific to each other and to a location
what is the epidermis maintained by
Maintained by a population of adult stem cells
- Long lived and slow cycling
- Capable of self-renewal and terminal differentiation
where does proliferation occur in the epidermis
basal layer
what are the basal keratinocytes attached to
Basal cells adhere to ECM rich basement membrane
- helps attach the epidermis to the underlying dermis
what is does the basement membrane consist of
Consists of Laminin 332, Collagen IV, and Collagen VII
how are basal cell anchored to the basement membrane
Hemidesmosomes (integrin receptors) link keratin cytoskeleton to basement membrane
what is the basement membrane essential for
Essential for cell polarity, regulating basal cell function, and anchoring epidermis to dermis
describe the structure of the stratum spinosum
3-4 cell layers thick
Numerous desmosomes give cells spiny appearance
what is terminal differentiation in the keratinocytes
keratinocytes stop proliferating and start producing keratin
describe the stratum granulosum
2-3 cell layers
Characterised by large granules of keratohyalin
- Filaggrin
- Involucrin
- Loricrin
describe the stratum corner
Main protective barrier of skin
Have a thick cornified envelope
Cross-linked by enzymes
Cells in cornified layer are dead
Intercellular lipids (ceramides) maintain moisture
keratinocytes ave complexity lost there nuclei
what are adherent junctions
Cadherin receptor linked to actin cytoskeleton
what are adheres and desmosomes made up of
Cadherin receptor
describe desmosomes
Cadherin receptor linked to keratin cytoskeleton
describe tight junctions
- between cells and form a tight seal and prevent the movement of water between cells
- Claudin and occludin seal intercellular space
describe gap junctions
- pores between two adjacent cells allowing nutrients and materials to reach from the bottom to the top of the epidermis
- Intercellular pores made up of connexins
what are the three layers of the dermis
Three layers
- Papillary
- Reticular
- Adipose
what is the role of the dermis
Provides strength and elasticity to skin
what is the structure of the dermis
Complex mix of macromolecules
Vascularised and innervated
What is the most abundant cell in the dermis
fibroblast
where does a fibroblast originate from
Mesenchymal origin
what does a fibroblast synthesis
Collagen
Elastin
Proteoglycans
describe the papillary layer of the dermis
- Directly beneath epidermis and BM
- Contains many blood capillaries
- Fine, randomly oriented collagen
- Type III Collagen
- Elastin
what collagen is the papillary layer of the dermis made up of
Type III Collagen
Elastin
where does the papillary layer of the dermis sit
- right below the epidermis
describe the reticular dermis
Large and densely packed collagen fibres
Provides much of mechanical strength of skin
in the dermis what layer provides much of mechanical strength of the skin
reticular dermis
what are the two different types of pilosebaceous unit
- hair follicle
- sebaceous gland
what are the two sweat glands
- eccrine sweat gland
- apocrine gland
where is the cells in the hair follicle derived form
the epidermis
what are the two types of hair follicle
- Vellus-body hair
- Terminal-scalp and secondary sexual hair
where is the hair follicle found
- found over the entree body
What produces hair
Matrix keratinocytes produce hair
what function does hair have
- they all have a sensory function
what controls hair growth
Dermal papilla fibroblasts control hair growth
describe the lifecycle of hair production
- Hair follicles start form the bulge
- At some point they are pushed out of the bulge region and migrate down the outermost part of the hair
- When they get to the bottom of the hair they encounter dermal papilla
- The dermal papilla causes a signal that leads to proliferation
- And this leads to differentiation and production of the hair
- Once the differentiation is complete the hair cells die and they are pushed through the surface of the skin as a hair
where are hair follicular stem cells
Hair follicle stem cells are in the bulge region
Express keratin 15
describe hair follicular stem cells
Slow cycling
Give rise to hair cells under normal conditions
Contribute to SG and epidermis upon wounding
what are the three phases of hair cycle
Anagen = active
Catagen = regressive
Telogen = resting
after telongen the hair follcile re enters anlagen
How long is the hair cycle phase in human
whole thing is 3 months
where is the sebaceous gland
attaches to the hair follicle
what do sebaceous glands produce
Mature sebocytes contain sebum = produce an oily substance which provides moisture and lubrication for the hair
- Cell ruptures and sebum released into sebaceous duct and onto skin
what does infection of Sebaceous Gland result in
acne
describe sebaceous gland
Exocrine gland
Androgen sensitive
Enlarges at puberty
what is the eccrine sweat gland responsive for
Thermoregulation and sweat
what are the two main components of the eccrine sweat gland
Excretory duct
Secretory coil - where the sweat is produced
how much of water is sweat
Sweat 99% water
what sweat gland is associated with hair follicles
apocrine gland
- secretion is odourless
Where are apocrine glands found
Axilla and pubic region
what do apocrine glands do when they are broken down by
Broken down on skin by bacteria
Release volatile fatty acids
What are other cell types associated with the skin
Melanocytes
Langerhans cell
Merkel cell
Mast cell
what do melanocytes protect against
Protect against UV
where are melanocytes
- Dendritic cell
- Epidemis on basement membrane and hair matrix
what do melanocytes produce
Produce melanin which is packaged into melanosomes
- eumelanin
- pheomleanin
- melanosomes are then injected into keratinocytes
What are the two main types of melanin
- Eumelanin
- Pheomelanin
describe the langerhan cell and where it is found
Dendritic cell
Basal and spinous layers
what does the langerhan cell do
Antigen presenting cell
First line of defence
Presents antigen to T lymphocytes
describe where Merkel cells are and what they do
Stratum basale
Sensory perception
Describe where mast cells are and what they do
Dermis
Immune response
Secretes histamine
name the types of wound and what layers of the skin it involves
Superficial – epidermis
Partial thickness – epidermis and dermis
Full thickness – epidermis, dermis, hypodermis
what are the three phases of wound healing
Inflammation
Proliferation
Maturation
describe the three phases of wound healing
Inflammatory response
– minutes to a few days,
- respond vascularly, haemostasis happens involving endothelium and platelets in the blood vessel
- then have response of the immune cells such as neutrophils, macrophages and then lymphocytes
- this is regulated by factors such as IL-1. IL-6 and TNF alpha
Proliferation
– matter of days
- Keratinocytes which need to migrate into the wound and increase proliferation and undergo differentiation to reform the barrier
- regulated by fibroblast growth factors and TGF beta
- At the same time there is formation of a new vascular site – angiogenic
- Fibroblasts need to migrate into this area
Maturation
– last weeks and months
- Carried out by the fibroblasts and there contractile version of the myofibroblasts
- The collagen that would have been quickly deposited is broken down and remodeled to form a more normal tissue structure
What are the complications of wound healing
- infection
- chronic wounds - not healed greater than 6 weeks = venous, pressure, diabetic ulcer
- scarring
