Epidermis Layers and Functions

Anatomy and Physiology

• Skin consists of two main layers: epidermis and dermis

Epidermis

• Divided into 5 strata composed of keratinocytes

Epidermis Strata

• Stratum corneum is the outermost layer
• Stratum lucidum is a clear layer
• Stratum granulosum has a granular appearance
• Stratum spinosum has a spiny appearance
• Stratum basale/germinativum is the base layer where cell division occurs
• Avascular nature, meaning it lacks blood vessels
• Regenerates every 6-8 weeks
• Contains melanin, which produces skin color, carotene and hemoglobin also contribute
• The basement membrane zone (BMZ) divides the epidermis from the dermis
• Risk of skin injury increases when aging causes the basement membrane to flatten, decreasing contact between the epidermis and dermis
• Partial thickness wounds involve the epidermis and superficial dermis only
• Blisters, superficial skin tears, and abrasions are considered partial thickness wounds
• Dermal appendages facilitate healing in partial thickness wounds

Dermis

• Papillary dermis is the upper layer
• Reticular dermis is the lower layer

Stratum Corneum

• The outermost skin layer is composed of mature keratinocytes called corneocytes
• Consists of 20-30 cell layers and has a 2-week lifespan
• Functions to create the outer barrier, defending against dehydration, toxins, and bacteria, known as the brick wall
• Protects the other layers of epidermis

Stratum Lucidum

• Thin, clear layer of epidermis, only 2-3 cell layers consisting of dead cells
• Found in thicker skin areas such as palms, soles, and digits
• Provides an additional barrier to water

Stratum Granulosum

• It's only 3-5 cells thick and contains diamond-shaped cells.
• Dense basophilic keratohyalin granules accumulate in its cells
• The waterproof barrier is formed and fluid loss is prevented by lipids in keratohyalin granules

Stratum Spinosum

• Known as the prickle cell layer
• It contains 8-10 layers of irregular, polyhedral cells with cytoplasmic processes or "spines"
• Skin flexibility and strength are promoted by it
• The layer contains Langerhans cells, sentinel cells, which monitor for unwanted intruders

Stratum Basale/Germanitivum

• A single row of cuboidal or columnar cells rests on the BMZ
• Most of the cells consist of constantly reproducing keratinocytes replenishing the epidermal layers
• Melanocytes are also present in this layer

Dermis

• Thickest layer of skin, averaging 2mm in thickness, but varying throughout the body

Papillary Dermis

• It is composed of collagen and reticular fibers
• High vascularity and water content characterize it
• Fingerlike projections, papillae, project into the epidermis
• Pain and touch receptors, Pacinian and Meissner's corpuscles, are located within

Reticular Dermis

• Collagen bundles anchor the skin to the subcutaneous tissue
• Collagen fibers provide strength and flexibility

Reticular Dermis Structures

• The reticular dermis contains sweat glands and hair follicles
• Multipotent stem cells are sourced from within the reticular dermis, allowing it to regenerate
• Sebaceous glands, nerves, and blood vessels are all found in this layer

Dermis Components

• Fibroblasts, migratory cells, produce and degrade the extracellular matrix (ECM)
• Lymphocytes, macrophages, mast cells
• Collagen and elastin

Collagen Functions

• Collagen functions to give tissue integrity, facilitate tissue repair, migration, and adhesion, to facilitate tissue morphogenesis and platelet aggregation
• Essential for epidermal adherence to the dermis
• Gives skin its tensile strength

Elastin Functions

• Provides skin's elasticity

Full Thickness Wounds

• Full thickness wounds affect the epidermis and dermis, involving the subcutaneous tissue, and may expose underlying organic structures

Subcutaneous Tissue (Hypodermis)

• It attaches the dermis to the underlying structures and is not part of the integument
• It promotes blood supply to the dermis and insulates the body
• Soft support is provided between skin layers, muscles and bones by it
• Mobility is promoted in the skin and body contours are molded by it
• Contributes in the prevention of pressure injuries

Skin Appendages

• Eccrine sweat glands originate and are transported to epidermis, serving as the body's cooling system
• Apocrine sweat glands originate in dermis and release sweat into hair follicles, located in axilla, eyelids, pubic area, and genitals, remaining inactive until puberty, and responsible for body odor
• Hair follicles, hair made up of keratin, located everywhere except hands and soles

Hair Follicle Types

• Vellus-light/fine
• Terminal-dark/thick
• A sebaceous gland attached to each hair follicle secretes sebum (oil) to the hair follicle surface
• Sebum provides an acidic protective skin barrier
• Present on the scalp, face, and upper trunk
• Increased production during androgen increase during adolescence

Nails

• The only appendage not in the dermis, found at the end of digits
• The nail plate consists of dead keratin to form a hard, protective structure
• The nail bed, the epidermal layer tightly attached under the nail plate
• Blood vessels give nails their pink color

Skin Functions - Protection

• Normal skin pH is 4-6.5, with a mean of 5.5
• The acid mantle protects skin from bacteria and fungal infections
• Loss of the acid mantle increases susceptibility to infection and damage
• Frequent soap use and overwashing can cause loss of protective barrier of Stratum corneum
• Certain skin conditions and systemic disorders like diabetes, kidney failure and stroke, can increase the pH of the skin

Skin Functions - Sensation

• Fingertips are most sensitive to touch
• Tactile corpuscles are at the base of hair follicles, shaving reduces sensibility
• Meissner's corpuscles are hairlike tactile corpuscles

Skin Functions - Pain

• Rapid A-delta fibers transmit superficial pain, which tends to be sharp
• Smaller, thinly myelinated C fibers transmit deep, chronic pain
• Diffuse pain lasts longer and remains

Skin Function - Temperature Regulation

• Thermoregulation is controlled by the hypothalamus
• Dilation and constriction of blood vessels
• Overheated: red, moist skin
• Cold: pale, dry skin

Skin Function - Metabolism

• Sunlight allows the skin to synthesize D
• Assists in excreting metabolism byproducts and prevents excessive fluid loss
• Macrophages and Langerhans digest bacteria and mast cells

Skin Function - Psychosocial Communication

• Allows to communicate feelings
• Sensation of touch conveys feelings

Changing Anatomy in the Elderly

• Higher risk of skin tears due to flattening of dermal-epidermal junctions
• Decreased sweat glands cause dry skin
• Decreased elastin fibers cause easier stretching without recoil
• Blood vessels become more fragile due to lower protein levels, leading to senile purpura
• 20% loss in dermal thickness
• Reduced subcutaneous fat leads to a decrease in protective functions
• Less vitamin D made from sun exposure
• Reduced immune function from mast cell and Langerhans decline

Cellular Function

• Cells types involved in wound healing
• Cell adhesion molecules (CAMs)
• Recognize and bind similar proteins on cells or ECM components
• Critical to leukocyte extravasation and cellular migration in wound healing
• The 5 main CAM Classes are Cadherins, Immunoglobulin superfamily, Mucins, Integrins, Selectins
• Every cell and chemical mediator is programmed in the endogenous fluids to act when needed
• The body heals when conditionals are normal

Leukocytes

• White blood cells
• Platelets secrete cytokines leading to neutrophil recruitment, which in turn characterizes the inflammatory phases of healing
• Primary job is to kill microbes through phagocytosis and lysosomal degradation
• Macrophages are professional phagocytes that induce inflammation

Neutrophils

• Most abundant WBCs in circulation
• First line of immune defense and recruited to the site within hours
• Chemokines enhance recruitment of cell death after bacterial phagocytosis
• Primary component of pus is "dead white blood cells"

Lymphocytes

• Main type of cell found in the lymph
• Migrate from the bone marrow to the thymus
• Acquires surface proteins for specific antigens
• 3 functions
  • Directly target and kill antigen-bearing cells (cytotoxic T cells)
  • Activate macrophages (helper T cells)
  • Regulate inflammation as the wound closes
  • Arrive during proliferative phase and peaks at day 7

Macrophages

• Macrophages originate from monocytes in bone marrow when called to the wound by cytokines, chemokines and neutrophils.
• Removes debris and regenerate continuously at the wound site.
• Predominant cell population at the wound site.
• Respond to hypoxic wound environments

Wound Properties

• Wound exhibit hypoxic environments from damage or intense activity
• Hypoxic locations lead to macrophages that aid angiogenesis

Langerhans Cells

• Resident macrophages living in epidermis and papillary dermis among vessels
• Immune system sentinels
• Watches the skin for antigens and send to lymph nodes to T-lymphocytes
• Internalize antigens and process for lymph nodes
• Immune response

Mast Cells

• Resident defense cells living within tissues
• The 2 types of mast cells are connective tissue and mucosal
• Connective issue mast cells live in the skin, perivascular areas, and peritoneal cavity
• Mucosal cells live in the gut and respiratory system
• Respond to protein tissues from immediate vasospasm and vasodilation.

Fibroblasts

• Fibroblasts build building fibrous tissues and fibers
• Living in the dermis, once an injury happens, they move to the damage
• Attracted to platelet secretion (PDGF)
• Migration is mediated by integrins on the fibroblast to CAMs in the ECM
• Deposition begins once arriving in ECM

Keratinocytes

• Greek for "horn"
• Scales, nail, and hair is made with keratin
• Form for skin integrity
• Migrate and mark final repairs

Melanocytes

• Greek for black (color)
• Functions to produce pigmentation
• Located in receptors and responds through receptor radiation
• Protects from UV radiation

Myofibroblasts

• Form of muscle
• Aids in fibers with contractile abilities
• Secretes collagen
• Present in wounds 3-5 days
• Participates in contraction

Wound Physiology

• Any cut in skin disrupts the blood supply to the dermis

Wound Classification

• Acute Vs. Chronic
• Partial thickness Vs. Full thickness

Wound Healing

• Primary
• Secondary
• Tertiary=Delayed healing

Wound Phase

• Initial injury/Hemostasis
• Inflammatory
• Proliferative
• Remodeling
• Repair will be short with less tissue loss
• Don't let scabs forms to ensure healing

Initial Wound Stage

• Hemostasis occurs immediately upon injury
• Prevents hemorrhage with damaged blood vessels
• Uses fibrin and platelets to plug injured vessel

Clots

• Help wound heal and acts a matrix for it
• Platelets release growth factors to stimulate fibroblasts to produce collagen, proteoglycans and GAGs
• Platelets start plugging to strengthen
• Blood flow cuts off oxygen delivery (creates hypoxia)

Inflammation

• Lasts from Day 0-7
• the body's immune system reaction to help heal
• Characterized by leukocyte infiltration
• Cytokines help activate leukocytes, like Mast cells and platelets
• Classical signs include the following
• redness
• temperature
• edema
• pain
• loss of function

Inflammation Specifics

• Acute inflammation sets biological events
• Provide Hemostasis
• Remove debris from restoration(Neutrophils 6 hours- several days)
• Initiates repair and responder cells

Following Damage

• wound space becomes hypoxic
• Hypoxia key in healing cascade
• Hypoxia releases growth factors (AGFs) by macrophages

Macrophages Action

• Release AGF- signals source to damage vessels
• Re-establish blood supply for nutrients
• Induce proliferation during chemotaxis

Chronic Wounds

• Wounds lack any type of wound injury stimulation
• Must be debrided to restart inflammatory cascade
• Usually the result of vascular insufficiency
• The hemostasis is muted after response

Proliferative

• 5 days to 3 weeks
• Overlaps inflammation
• Achieve the following
  • Fill in wound
  • Restore integrity of the skin

Processes

Angiogenesis: Collagens contraction

Angiogenesis/Neovascularization- New buds form intact vessel

Endothelial cells proliferate

Nutrients reach wound for help

Granulation tissue forms

Hallmark sign

New blood vessels that are bright and beefy

Remodeling

• Final phase of wound healing, begins in the proliferation phase and ends 1-2 years after
• Rebuilds strength
• Type 3 collagens forms
• In maturation phase, it's replaced with a thinker collagen- for strength!
• Decreases baselines
• Innervation lasts to arrive

Wound Intention

Primary Intention: Surgical Surgically closed No granulation Little contraction

Secondary Intention Not surgically closed Heals contraction Most effective when all skin layers are extended

Involves steps and uses special help

Wounds

-Should be covered, moist and heated

• Dry wounds are hostile to healing -Epithelial cells can't migrate

Intrinsic Issues

• Age, disease and or suppressed immunity
• Slows down maturation and change
• Causes less oxygen perfusion

Extrinsic Issues

• Compression
• Poor diet
• Radiation

Brain stops function due to high stress or high injury from scar

Scarring

• Hypertrophic
• Keloid
• Pathergy

Hypertrophic

• Excess growth within the wounds margins
• Time closure takes
• Color
• Genetics
• High Tension

Keloid

• Extends beyond edges
• Normally in trunk, face, back and ears
• Genetics
• Younger people and or pregnant people

Pathergy

High response to trauma with lesions

• Treat with disease

Wound Causes

• Acute/Partial - Epidural tissue to dermis, heals quickly

Wound Type

• Ful- skin, tissue and exposure
• Won't heal fast

Chronic

• Slow to heal
• Cellular abnormalities
• Sensitivity and slow repair cause: -Low activity -High inflammation

Injuries Causes

• Pressure Areas of tissue and high pressure can cause Almost always over bony prominences High pressure on issues leads to damage

Injury Factors

• Friction
• Shear
• Temp

High staging is need for these injuries Don't close back

Assessment

• Assess mobility, activity

Venous Wounds

• Superficial/Deep/perforation
• Flow from systems that only have one valve
• Causes reflux Leads to low blood Pressure occurs

Conditions

Edema heavy Discoloration- Due to leaking iron Usually medial side

Treatment

• gradient compression with corner stone treatment
• Treatments needs to happen

Lymphedema

• Causes issues from returning the lymph and fluid to tissue
• From blockage
• Is chronic
• Check for Venous Issues Stemmer test- skin wont pinch Send expert to treat- due to wrapping

Arteriole Issues

• Normally on legs
• Causes with bumping shins
• High pain with hanging legs
• Has issues with poor circulation

Testing

• Check for a pulse and test with legs
• Rubor will show dark red for blood

Neuropathic Wounds

• Happens with the case by diabetes
• Leading from poor nutrition
• From poor shoes

Signs

• Heat and cold with be absent
• Ulceration is at 71%
• Affecting great toe
• Diabetes open sore at 15%

Offload when necessary

###Wound assessment

• Size and location

Measure amount of tissue type -Slough

• Drainage

Take picture, measure, and do plan