PT 531 Wound healing

What are the 3 layers of the skin?

Epidermis, dermins, subcutis

How much of the cardiac output does the skin receive?

1/3

Basement Membrane

• semipermeable and scaffolding layer between epidermis and dermis

Where does the skin form blisters?

basement membrane, friction or damage detaches the connection

Where does a callus form?

Stratum corneum = too many dead keratinocytes

What are some epidermal appendages?

• Appendages originate in the dermis and extend into the epidermis

• Nails (from stratum basale); hardened keratin

• hair (soft keratin)

• sebaceous glandsm - skin oil

• sudoriferous glands- sweat

Functions of the epidermis

• provides a physical and chemical barrier

• fluid regulation

• assists with excretion

• assists thermoregulation

• Provides light touch sensation

• endogenous vit D production

• cosmesis

Blood supply of the epidermis?

NONE, it is avascular

2 parts of the dermis?

• Papillary dermis (20%), loosely woven fibers in gelatinous matrix

• Reticular dermis (80%), dense irregularly arranged connective tissue, provide structural support to skin

Functions of the dermis

• supports and nourishes the epidermis

• houses epidermal appendages

• assists with infection control

• assists with thermoregulation

• provides sensation

cells of epidermis

cells of dermis

Dermal cells:

Fibroblasts (primary cells) - produce collagen and elastin

Macrophages and WBC - fight infection

Mast cells (secretory) - produce chemical mediations for inflammation including histamine, stimulate vasodilation and attract other cells to the wounded area

Sensory receptors: touch, pressure, temperature, pain

Where to find subcutaneous tissue?

below the dermis

How does viable tissue appear?

shiny and white

Describe Superficial wounds

involve the epidermis only and heal by cell division

Describe partial thickness wounds

involves the epidermis, and part of the dermis but not completely through the dermis

Describe Full-thickness wounds

involve the epidermis, dermis, and into the subcutaneous level

How do superficial wounds heal?

healing occurs by cell proliferation - no scar formation

What is primary closure?

wound is cleansed and edges are approximated, then stitch,

staple, glue, or tape

What is delayed primary closure?

Clean a wound, then wait a while before surgical closure

What is secondary closure?

Healing by granulation and scar tissue production

How long does dealing take for primary closure?

should be closed within 7-14 days

An acute wound that is healing through secondary intention should take approx how long?

follow a predictale progression; closure within 2 weeks / as fast as possible

Describe the progression of a chronic wound

Progression will be prolonged or delayed, stuck between inflammatory and proliferative

>6 weeks

In what tissue does inflammation NOT occur?

dead tissue, tissue with poor blood flow; if systemic suppression is present

What stage of healing will you find transudate?

Inflammatory, early vascular response

What is transudate?

fluid that leaks from damaged blood vessels’ produces localized edema, clear and watery

What occurs during the later response of inflammation?

Vasodilation occurs within 30 min, bringing more blood cells to the area and increase growth factors and inflammatory cells, histamine release by mast cells, prostaglandin release

Exudate formation

What is exudate?

wound drainage that is slightly viscous; yellow or creamy color (contains proteins, debris and macrophages)

Cardinal signs of inflammation

Swelling (tumor)

Redness (rubor)

Warmth (calor)

Pain (dolor)

Decreased function (functio laesa)

What are polymorphonuclear neutrophils?

First cells to the site of injury - secrete MMP’s, inflammatory mediatiors and enzymes

stimulate fibronlasts migration and new vascular growth

What cells arrive later to site of injury?

Macrophages (attract inflammatory cells), mast cells (accelerate lysis, produce histamine and enzymes)

What are the 4 critical events of proliferation?

1. Angiogenesis - formation of new vessels , edema subsides

2. granulation tissue formation - temporary new lattice work of connective tissue, MMP’s degrade the derbis

3. Wound contraction - myofibroblasts reduce size of defect

4. Epithelialization - keratinocytes at wound edges + epithelial appendages grow to cover wound

When is epithelialization complete?

When the wound is completely covered, cannot occur over non-viable tissue

When does epithelialization start?

when the defect is filled

What are cells of the proliferative phase?

Angioblasts, fibroblasts, myofibroblasts, kertinocytes

What is epibole?

non advancing wound edge - rolled under or closed wound edge; like a pothole

What are 3 treatments for hypergranulation?

Pressure

silver nitrate stick to cauterize abnormal tissue

surgical excision

Maturation and remodeling is characterized by:

New collagen synthesis

Old collagen broken down

Reorientation of collagen fibers

Remodeling can occur up to ______ after wound closure until complete

2 years

What is needed for a functional scar to develop?

Appropiate tissue tension

A fully remodeled scar only has ___ % of tensile strength and elasticity of skin

80%

What is dehiscence?

primary closure wound edges become separated

What causes dehiscence?

1. Lack of collagen formation

2. infection

3. abnormal stresses

4. systemic factors like DM

What are keloids?

Out of control healing, too much scar tissue that raises above the skin, scar is BIGGER than original wound

Describe and acute wound

injury induced by surgery or trauma in an otherwise healthy individual, progressed through normal phases of healing in predictable time and manner

Describe a chronic wound

a wound whose progression through the phases of wound healing is prolonged or arrested due to underlying conditions

occurs in individuals with wounds related to systemic disease or co-morbidities

What are deterrents that affect wound healing?

inappropiate wound management

patient adherence

systemic factors

local factors

What are systemic factors that affect wound healing?

Age, inadequate nutrition, comorbidities, medication (steroids >30 mg)

behaviorial: alcohol abuse, smoking

How much oxygen do wounds require to heal?

3 x O2

What are local factors that affect healing?

Circulation, sensation, tissue trauma (mechanical stress/moisture)

What is desiccation?

Wound bed is too dry - dry wounds heal slower

What is maceration?

Wound bed is too wet - damage to periwound

What factors affect the RATE of wound healing?

Mechanism of onset, time since onset, location, dimensions, hydration, chronic inflammation

chronic inflammtion: presence of necrotic tissue or foreign bodies, presence of infection

What are things to consider based on wound location?

vascularity, bony prominences, presence of epidermal appendages, skin thickness

Describe how necrotic tissue / foreign bodies affect wound healing

promotes an environment conducive to infection, prolongs inflammatory process

What is slough?

Stringy, adherent, dead tissue

What is Eschar?

dead skin that is often dry and black, becomes gray and soft with deterioration

What is colonization?

Presence of microbes, normal skin microflora

describe how infection is different than inflammation

culture with >10^5 microbes per g/tissue

signs and symptoms are similar but disproportionate in area relative to size of the wound the time post injury