Introduction to Skin Flashcards
What are the 2 main functions of skin?
- protection
- insulation
How does skin offer protection?
- physical trauma
- infection
- penetration of drugs and chemicals
- UV radiation
- water loss
How does skin allow function?
- sensory information
- vitamin D synthesis
- heat insulation
What are the 2 layers of the skin?
- epidermis (protection)
- dermis (strength and elasticity)
- also contains glands, hair follicles, arterioles
What is the epidermis?
- stratified squamous epithelium
- outermost, protective
- keratinocyte is main cell
- 4 main layers
- includes and hair and sebaceous gland
What are keratinocytes?
produces keratins:
- intermediate size (larger than microfilament but smaller than microtubule)
- keratin = most abundant proteins in stratum, corneum, hair and nails
- alpha = soft/loose, coiled
- beta = hard, beta sheets, cross by disulphide and hydrogen bonding
- generally acidic or basic in pH and pair up accordingly so whole structure is neutral
- K5 and K14 always pair up so neutral
- expression pattern specific to epidermal layer
What are the 4 main layers of the epidermis?
- Stratum corneum (outermost part of skin)
- stratum lucidum
- stratum granulosum (dark purple, flattened)
- stratum spinosum (spiny processes)
- stratum basale (bottom)
What are the features of the stratum corneum?
- main protective skin barrier
- thick cornified envelope
- cross linked by enzymes
- dead cells
- intracellular lipids containing moisture
What are the features of the stratum granulosum?
- 2-3 cell layers
- large granules of kertohyalin (filaggrin, involucrin, loricrin)
- nucleus breaks down
What are the features of the stratum spinosum?
- 3-4 layers thick
- desmosomes giving spiny appearance
What occurs in the straum basale?
- proliferation
- adult stem cells maintaining epidermis = self-renewal, terminal differentiation, long lived
What is the basement membrane?
- basal cells adhere to ECM
- laminin 332, collagen IV, collagen VII
- hemidesmosomes link keratin cytoskeleton(inside) to basement membrane (outside)
- cell polarity, regulating basal function, anchor epidermis to dermis
What are the types of cell-cell adhesions?
- adherens junctions = cadherin receptor linked to actin cytoskeleton
- desmosomes = cadherin receptor linked to keratin cytoskeleton
- tight junction = claudin and occludin seal IC space
- gap junctions = intercellular pores made up of connexins
What is the dermis?
- provides strength and elasticity
- macromolecule mix
- vascularised and innervated
- fibroblast main cell
- 3 layers=
- papillary
- reticular
- adipose
What is the papillary layer of the dermis?
- beneath epidermis and basement membrane
- many blood capillaries
- fine randomly organised collagen III
- elastin
What is the reticular layer of the dermis?
- large and densely packed collagen fibres
- mechanical strength of skin
What is the adipose layer of the dermis?
- strength and elasticity
- macromolecule complex mix
- vascularised and innervated
What is a fibroblast?
- in the dermis
- most abundant cell in dermis
- mesenchymal origin
- synthesises collagen, elastin and proteoglycans
What is a pilosebaceous unit?
- hair follicle and associated sebaceous gland
What is a hair follicle?
- part of epidermis
- 2 types -> vellus body hair (fine and non-pigmented) and terminal scalp/secondary sexual hair (pigmented)
- produced by matrix keratinocyte
- dermal papilla fibroblasts control hair growth
What are hair follicle stem cells like?
- localised to bulge region
- express keratin 15
- slow cycling
- give rise to hair cells under normal conditions
How do hair follicle stem cells differentiate?
- migrate own from bulge to bulb of follicle
- receive signal from dermal papilla to rapidly proliferate
- differentiation depends on spatial location
What are the 3 stages of the hair growth cycle?
- anagen = active
- catagen = regressive
- telogen = resting
What is a sebaceous gland?
- exocrine gland
- androgen sensitive
- enlarges at puberty
- mature sebocytes contain sebum
- cell ruptures and sebum released into sebaceous duct onto skin
- infection = acne
What are the 2 types of sebaceous glands?
- eccrine sweat gland
- apocrine gland
What is an eccrine sweat gland?
- allows thermoregulation
- 2 components = excretory duct and secretory coil
What is an apocrine gland?
- sweat glands associated with hair follicles
- in axilla and pubic region
- secretion is odourless
- sweat broken down on skin by bacteria
- release volatile fatty acids
What are melanocytes?
- dendritic cell
- epidermis on basement membrane and hair matrix
- produce melanin protecting against UV
What are langerhan cells?
- dendritic
- in basal and spinous layer
- APC
- first line of defence
- presents antigens to T lymphocytes
What are merkel cells?
- in stratum basale
- sensory perception
- primary communication between epidermis and sensory nerve endings below
What are mast cells?
- in dermis
- immune response
- secretes histamine
What are the 3 wound types?
- superficial = epidermis
- partial thickness = epidermis and dermis
- full thickness = epidermis and dermis hypodermis
What are the 3 stages of normal wound healing?
- inflammation (minutes up to 6 days)
- proliferation (several days to weeks)
- maturation/remodelling (weeks to months)
What does inflammation in would healing involve?
- haemostasis (endothelial cells and platelets, within minutes)
- minutes to days T cells, macrophages, lymphocytes etc
- interleukin mediated, TNFa
What does proliferation in wound healing involve?
- keratinocyte migrate into wound, proliferation and differentiated (mediated by GF) and new vascularisation angiogenesis, fibroblasts produce new collagen, granulation tissue
What are the 4 main types of skin diseases?
- Cancer = malignant melanoma
- Inflammation = Psoriasis
- Wounds = diabetic ulcer
- Genetic diseases = epidermolysis bullosa
What are the 2 types of melanin?
- eumelanin (brown)
- pheomelanin (red)
What does the maturation phase in wound healing involve?
- collagen deposited broken down and remodelled to form normal tissue structure
What are the main complications of wound healing?
- infection
- chronic wounds (not healed >6 weeks due to pressure sores, diabetic ulcers)
- scarring extreme so wound process does not stop
