Basics: Anatomy, physiology (incl pigment), wound healing, scars Flashcards
List the functions of the skin
1) Barrier - to environment extremes, thermal injury, pathogens, UV light 2) Thermoregulation 3) Immune function 4) Vitamin D metabolism 5) neurosensory 6) cosmetic / social function
List the ways that skin is involved in thermoregulation
1) Vaso-motor: i) hypothalamus control of periperhal vasoconstriction and vasodilation AND ii) superficial (hot, radiation) vs. deep (cool) venous shunting AND iii) glomus bodies AV shunts 2) Sweating (evaporation) 3) Subcutaneous fat insulation 4) Sebum prevents water loss 5) Other ? not skin - piloerection and shivering
What skin structures arise from the ectoderm?
Epidermis Epidermal appendages: pilosebaceous unit, eccrine and apocrine sweat glands Keratinocytes Nail unit
What skin structures arise from the mesoderm?
Dermis Macrophages, langerhaan’s cells, mast cells, fibroblasts Adipocytes vessels
What skin structures arise from neuroectoderm
Melanocytes Nerves, nerve endings Merkel cells
What are the epidermal appendages? When do they develop?
Pilosebaceous unit: hair follicle, sebaceous gland, arrector pilli muscle Eccrine sweat gland Apocrine (odour) gland Develop 9-16 weeks
What is a keratinocyte and what are the layers in the epidermis and their function?
Keratinocyte is the primary cell type of the epidermis, produces keratin Stratum basale - for replicating Stratum spinosum - for Stratum granulosum - for storing melanosomes and contains granules to produce keratin Stratum lucidum (only palm, sole) - non viable, extra protection Stratum corneum - non-viable, for protection
What is a melanocyte and what is its function
a melanocyte is a specialized cell of neuroectodermal origin (neural crest cell) located along basal layer- function is to produce melanin, stored in melanosomes, transferred to keratinocytes, in order to protect DNA from UV radiant damage
What is a langerhan’s cell, it’s function and locaiton?
A langerhaan’s cell is located in the papillary epidermis malphigi layer (also: appendages in dermis, oral/vag muscosa, LN, tymus ) and it’s function is as a specialized antigen presenting cell to TH cells for immunie function
Describe the anatomy of the dermis
Located below the epidermis, the epidermal rete ridges interdigitate with the dermal papillae. The epidermis and dermis are adherent via hemi-desmosomes. The dermis has 2 layers: papillary (superficial, loosely less organized collagen) and reticular (deeper, densely organized collagen and vessels)
What are the functions of the dermis?
1) Nourish the epidermis 2) Protection of deeper structures 3) Provide strength, pliability and elasticity to skin 4) Wound healing
Compare and contrast eccrine and apocrine glands
Function
- eccrine - secrete sweat, thermal control
- apocrine - secrete odour, activated by bacteria, vestigial sexual function
Location
- eccrine - most concentrated palms/soles/axillae but cover most of body except mucous membranes, lips, glans penis, labia minora and clitoris
- apocrine - anogenital region, axilla, areola
Excretion promoted by:
- eccrine: cholingeric stimulation
- apocrine: adrenergic stimulation
Release to:
- eccrine - direct to skin
- apocrine - to hair follicle
Describe the phases of wound healing, dominant cell type, dominant cytokines, duration
Inflammatory - 0 - 5 days
- Overall: hemostasis and acute inflammatory infiltrate
- 5 processes occur: vasoconstriction (including platelet plug and coagulation cascade and fibrin production), vasodilation, chemotaxis, cell migration and cellular response
- Dominant cells: neutrophils (phagocytosis, bacterial killing) and macrophages (critical for inflammatory phase; phagocytosis, bacterial killing, antigen presentation, cytokine release critical for next phases)
- Cytokines: PDGF, EGF, IL-1
Proliferative - 5 days to ~ 3 weeks
- Overall: fibroplasia, granulation, epithelialization, angiogensis, contraction
- 4 major processes occur:
- Connective tissue framework by fibroblasts: collagen synthesis and production, elastin synthesis and production, extracellular matrix production (chondroitin sulfate, heparain sulfate, dermatin sulfate)
- Granulation: occurs in open wounds
- Epithelialization: mobilization, migration, mitosis, maturation
- Angiogenesis
- Contraction
- Dominant cell type: fibroblast, other cells = myofibroblast
- Dominant cytokines: TGF-b, VEGF, TNF
Maturation - 3 wks - 1 yr
- Overall: movement neutral collagen balance and reorganization
- Major process is collagen reorganization to more parallel, organized fibres to reach mature wound levels of type I and type III (from immature wound at I:III of 2:1 to normal of 4:1)
- 50% tensile strength @ 3 wks and 80% by ~ 60 days
- Dominant cell: decreasing cellular populations
- Dominant cytokine: TGF-b
What is granulation tissue?
Granulation tissue is formed in open healing wounds due to the process of neovascularization - capillaries, macrophages, fibroblasts, embeded in loose matrix of HA, collagen, fibronectin
List local factors that modify wound healing
- oxygen tension
- infection
- foreign body
- radiation
- chronic wound
- malignancy
- moisture
- temperature
- iatrogenic (surgical technique and wound mechanism)
- fistula/sinus tract
- Mechanical stress
- Denervation
- Edema
List systemic factors that modify wound healing
- Genetic: age, skin type, sebaceous quality / thickness, inherited disorders
- Nutrition: macro (caloric, protein malnutrition), anemia, micro (Fe, Cu, Zn, Vit C, Vit E)
- Comorbidities: DM, PVD, CAD, ESRD, cirrhosis, obesity
- Immunosuppression
- Drugs:
- immunosuppressants: chemotherapy, steroids
- smoking
- alcohol
- Psychosocial
List medications & toxins that impair / influence wound healing
- Anti-inflammatories: NSAIDs, colchicine - decrease collagen synthesis
- Steroids: decrease angiogensis, wound contraction, macrophage activation
- Chemotherapeutics
- Smoking
- Lathyrogens
Describe the location and function of melanocytes
- Derived from NCCs and migrate to epidermis week 10
- Located basal layer epidermis, also appendages (hair follicles), uveal tract, leptomeninges, mucous membranes
- Function: produces tyrosinase (only cell) to synthesize melanin, package in melanosomes, transfer to keratinocytes
- Function of melanin is to prevent DNA damage from radiant UV light (repair DNA damage and scavenge free radicals)
Describe and classify melanin
- High molecular weight pigmented polymer synthesized by melanocytes and stored in melanosomes
- Melanin is synthesized from tyrosine (+/- cysteine) using tyrosinase, via intermediate DOPA.
- Produced in ER, packaged into melanosomes in golgi, transferred via dendrites to keratinocytes
- 3 types: eumelanin, pheomelanin, neuromelanin
- Eumelanin: brown/black, found in skin/hair, synthesized from tyrosine and tyrosinase
- Pheomelanin: yellow/red, found in blond/red hair; synthesized from tyrosine & cysteine by tyrosinase
- Neuromelanin: black, in neural tissue, exact role uncertain
Compare melanocytes, nevus cells, melanoma cells
- Melanocytes become nevus cells when they leave the epidermis and go to dermis
- Both produce melanin via similar mechanisms, but they do differ on the following:
- Shape:
- Melanocytes: dendritic
- Nevus cells: round
- Melanoma: round
- Grouping
- Melanocytes: solitary
- Nevus cells: clusters
- Melanoma: clusters or sheets
- Nucleai
- Melanocytes: Small, regular
- Nevus cells: small, regular
- Melanoma: large, irregular, hyperchromatic
- Mitoses
- Melanocytes: rare
- Nevus cells: rare
- Melanoma: common
What are the 4 pigments in control of skin colour?
- Melanin - from melanocytes - brown/black
- Oxyhemoglobin - from intravascular RBCs and iron breakdown prods - red
- Deoxyhemoglobin - intravascular - blue
- Carotin - dietary sources - orange
- Note that bile is a pigment not responsible for skin colou
Describe skin colour
- Skin and hair colour is determined by the size and number of MELANOSOMES within keratinocytes
- # melanocytes is constant and does not affect pigment
- Factors that influence melanin production (and therefore size/# of melanosomes) are:
- Genetic determinants
- Hormonal: melanocyte stimulating hormone, ACTH, liptropin - not major influence in healthy adults
- Paracrine - melanotropins are secreted by keratinocytes and act locally on melanocytes
- UV radiation stimulates melanotropin release
- Skin colour can be constitutive (genetically pre-determined colour or facultative (genetically pre-determined response to UV radiation - UV dependent)
DEFINE TISSUE EXPANSION
- process of using an inflatable (usually silicone) device to provide donor tissue that maintains qualities of donor site such as colour, sensation, hair-bearing, thickness
LIST ADVANTAGES IF TISSUE EXPANSION
- follows principle of reconstructing like with like
- can be hair-bearing, similar colour, similar thickness, sensate
- reliable
- minimal donor site morbidity
- can be repeated
LIST DISADVANTAGES OF TISSUE EXPANSION
- takes time - preliminary operation, multiple expansions
- not immediately available
- requires multiple stages
- some morbidity - scarring or pressure alopecia, scars, contour defect (skeletal), forms capsule
- some operative risks of placement and expansion - hematoma, seroma, infection, exposure, skin necrosis
- aesthetically displeasing while TE in situ
LIST CONTRAINDICATIONS TO TE PLACEMENT
- infection
- malignancy
- radiation
- unstable soft tissue
- poor compliance
describe the physiologic property of skin that is employed for TE
- utilizes the visco-elastic property of “creep”
- mechanical creep is 70% of expansion - whereby tissue is expanded by water displacement from cells and ground substance, increased inter-cellular space in gap junctions, cellular stretch (hypertrophy)
- biological creep is 30% of expansion - whereby reorientation of existing tissue and regeneration of new tissue including cellular hyperplasia
describe the histological changes that occur to each tissue layer during tissue expansion
- epidermis - increased thickness - hypertrophy, acanthosis, hyperkeratosis
- dermis - changes occur at reticular dermis - hypoplasia, atrophy (thinner), increased space between NV structures, reorientation of collagen fibres parallel, elastic may rupture of fibrose
- subcutaneous fat - atrophy (thinner)
- muscle - atrophy, may fibrose
- vasculature - capillary dilatation (in reticular dermis), Increased vessel number, length, calibre; increased VEGF, increased blood flow (especially in capsule) - regarded as delay
- bone: resporption of outer cortex (especially children)
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WHAT ARE THE 4 ZONES OF TISSUE EXPANDER CAPSULE?
- INNER ZONE: macrophages and fibrin
- CENTRAL ZONE: elongated fibroblasts and myofibroblasts
- TRANSITION ZONE: loose collagen
- OUTER ZONE: blood vessels and collagen
WHAT ARE PRINCIPLES OF PRE OP PLANNING OF TE PLACEMENT?
- choose the expander: round, rectangular, crescent
- aim for length of TE = length of defect; width of TE = 2-2.5x width of defect; area of TE = > 2x area of defect
- for advancement, arc of circumference needs to be length of defect + length of TE
- rectangular ~ 38% increase; crescent ~ 32% increase; round = ~ 25% increase
- plan in reverse
- choose skin/tissue to be expanded
- choose scars / incision placement - radial, border, remote
- orient TE parallel to long axis of defect
describe fundamentals of operative procedure OF TE
- prophylactic antibiotics,
- TE pocket dissection following prophylactic hemostasis
- irrigation of pocket w/ bacitracen
- soaking of TE in bacitracen
- single touch technique of TE placement
- use of closed-suction drains
- 2 layer close
- expansion of 10-20% TE volume
list reasons to pause TE and reasons to stop or remove TE
- pause
- pain, neurapraxia, seroma, pressure on underlying non-critical structures, spread scar
- Stop / remove
- infection, hematoma, dehiscence, exposure, skin ischemia, pressure on underlying critical structures
