Lesson 1 Flashcards
Ranges in skin thickness
0.5 to 6.0mm
weighs 4-5 kg
How much cardiac output does skin receive?
1/3 resting cardiac output
Skin function:
Thermoregulation Sensation Metabolism of vitamin D Protection from Shear Protection from Water Loss Body image, expression
3 main layers:
Epidermis
Dermis
Subcutaneous
How often is epidermal renewal?
every 45 to 75 days.
Layers of epidermis:
startum corneum stratum lucidum stratum granulosum statum spinosum statum basale
How does epidermins receive nutrients?
diffusion from dermis
Thickness of epidermis?
.06-.6 mm thick
Keratinocytes
Are the majority of epithelial cells (90%).
Make up the layers of the epidermis, lining of various body organs, sebaceous glands, hair follicles, and sweat glands
What attracks keratinocytes?
Attracted by neutrophils, macrophages, and the current of injury and advance in a sheet to resurface injured area.
Also advance from dermal appendages
What stimulates growth of keratinocytes?
Growth stimulated by moist environment and oxygen
Corneocytes
Differentiated keratinocyte surrounded by a cornified envelope
Langerhans Cells
Dendritic clear cells containing distinctive granules
Probably monocytic in origin
What are Langerhan cells necrosed by?
UV rays
Location of Melanocytes:
Between or beneath the deepest layer of epithelium (Basal layer).
Function of melanocytes:
Synthesize melanin (pigment) from amino acids Tyrosine with enzyme tyrosinase.
How do melanocytes pigment the cell?
Have branching processes by which melanosomes (pigment granules) are transferred to epidermal cells, pigmenting epidermis.
Cells involved in hypersensitivity and skin graft rejection?
Langerhans Cells
Merkel Cells/Discs
Mechanoreceptors attached to keratinocytes by desmasomes that provide sensation of light touch
Epidermal functions
Protective layer to the more fragile dermis and its structures
Prevents water loss (90% keratinocytes)/regulates fluid
Synthesizes vitamin D
Provides pigmentation (melanocytes)
Protect from shear, friction and toxins
Important role for body image, expression
Assists with excretion
Light touch sensation
Thermoregulation
Starum Corneum:
25- 30 rows of flat dead cells filled with Keratin
Flattened cells, no nuclei
Continuously shed and replaced, barrier to heat, light, bacteria and some chemicals
Stratum Lucidium
only present in palms of hands and soles of feet
Appearance of stratum lucidium under microscope:
Clear flat dead cells that appear clear under microscope
Stratum Grannulosum (grannular layer)
3-5 rows of flattened cells
What does stratum grannulosum contain?
Keratohyalin which is precursor to waterproofing protein Keratin which is found in the top layer
Stratum Spinosum
Multiple rows of polyhedral cells
What does stratum spinosum contain?
More mature rows of keratinocytes appear “spiny” due to keratin filament formation
Langerhan cells
What is the stratum spinosum attached together by?
desmosomes
Stratum Basale/Germinativum
Cuboidal/Columnar Cells
Site of new cell production
What are keratoncytes connected by in the stratum basale?
connected to the basement membrane by hemadesmosomes, and to each other by desmosomes
Which layer doe nails arise from?
stratum basale
What else is in stratum basale?
merkel discs (nerve endings/mechanoreceptors) melanocytes
Basement Membrane
Attaches the epidermis to the dermis via rete ridges(rete pegs)
Acts as a scaffold for the epidermis
Filters substances moving from dermis to epidermis
What compromised basement membrane?
type IV collagen fibers
What does dermis house?
Sensory organs
Vasculature- Provides nourishment to epidermis and thermoregulation
Dermal appendages
Protects against infection
Thickness of dermis:
2-4mm
thickest layer of skin
Dermal appendages
hair follicles
sebaceous glands
sudoriferous glands
nails
Where are sudoriferous glands?
everywhere but lips and ears secrete sweat
Dermis cell types
Fibroblasts produce collagen and elastin Macrophages White blood cells Mast cells- produce histamines Sensory receptors
Papillary region
Top 1/5 is the dermal papillae- which are finger-like projections into concavities of the epidermis and attach to the Rete ridges of the epidermis
What does the papillary region allow?
capillaries to come close to the epidermis for nutrient and O 2 exchange
Reticular Region
Dense irregular connective tissue, collagen, elastin
Contains adipose, follicles, nerves, oil glands, ducts of sweat glands
Provides strength and elasticity to skin
Subcutaneous/Endodermal Layer/Hypodermis
Fibers extend from the dermis into this layer to anchor the skin
Superficial fascia (fibrous in appearance)
Contains deep blood vessels and nerve endings
Adipose or fatty layer
What does the adipose or fatty layer do?
White or pale yellow when healthy Insulates Energy reserve Cushioning Storage of vitamin A, D, E, & K
Deep Tissue Layer
muscle
tendon
ligament/joint capsule
bone
Effects of aging on skin:
decreases: Dermal thickness Fatty layer Collagen and elastin Sensation and metabolism Sweat glands Circulation Epidermal regeneration
Superficial Wounds effect:
epidermis
Examples of superficial wound:
abrasion
first degree burn
Partial thickness would affects:
epidermis
dermis
Examples of partial thickness wounds:
blister
second degree burn
stage II pressure ulcer
wagner grade I ulcer
Full thickness would affects:
epidermis
dermis
subcutaneous tissue
may extend deeper
Examples of full thickness wounds:
3rd degree burns
4th degree burn
stage II pressure ulcer
wagner grade 2-5 ulcer
Types of Full Thickness Wound Closure
primary intention
secondary intention
delayed primary/tertiary intention
Primary intention:
wound edges are approximated and closed
Secondary intention:
allow wound to heal without surgical closure. Heals with scar tissue replacement. Infection risk or unable to approximate edges
Delayed primary/ tertiary intention:
The wound is allowed to heal secondarily, then primarily closed for final healing. Done to resolve infection, allow contracture of wound or granulation base prior to grafting.
Wound should be closed within 1–2 weeks of suturing
How long does primary closure (intention) take?
1-14 days
edges are approximated
How long does secondary closure (intention) take?
follows 3 phases of normal wound healing
How long does an acute wound take in secondary closure?
within 2 weeks
How long does chronic wound take in secondary closure?
within 30 days
Phases of Wound Healing
Hemostasis
Inflammation
Epithelialization/Proliferation
Remodeling
Hemostasis
Immediate after injury
Vasoconstriction
Platelet aggregation-Platelets adhere to vascular endothelium and each other
What is released as platelets adhere?
albumin, fibrinogen, fibrinectin, coagulation factors, and growth factors including PDGF, TGF-, FGF-2 (cytokines and chemotactic agents)
Fibrin deposition, clot is end product
Cardinal Signs of Inflammation
Swelling Redness Warmth Pain Decreased function
How long does inflammation last?
start at time of injury and lasts 3-7 days
Margination
A phenomenon that occurs during the early inflammatory phase. As a result of capillary dilation and slowed blood flow, Leucocytes tend to occupy the periphery and adhere to the endothelial cells that line the blood vessels
Cellular response of inflammation:
Platelets PMNs Fibroblasts Macrophages Mast cells
Polymorphonuclear Leukocytes:
Margination, diapedesis, chemotaxis First cells to site of injury Scavengers Kill bacteria Clean wound Secrete inflammatory mediators and MMPs
What do Granular (polymorphonuclear leukocytes- PMN’s) neutrophils do?
cleanse wound of microorganisms
release lysozyme
migrate to wound space
phagocytotic
What is lysozyme?
an enzyme that produce free radicals to destroy bacteria
Who do PMNs eosinophils do?
Larger nucleii than neutrophils.
Motile phagocytes with distinctive anti-parasitic function
What do PMNs basophils do?
release histamine which cause vascular dilation
stimulates migration of enothelial cells
What to basophils promote?
fibroblast proliferation and mitosis by release of a mitogen TNF alpha
Macrophages:
type of monocyte from bone marrow
ingest bacteria
clean up debris after infection
What do macrophages excrete?
ascorbic acid, Hydrogen peroxide, & Lactic Acid which attract more Macrophages and intensify inflammatory response.
Parts of proliferation:
angiogenesis
granulation tissue formation
wound contraction
Goal of proliferation phase?
in wound defect with new tissue, and restore skin integrity
When does proliferation phase begin?
Overlaps and follows the inflammatory Phase beginning 3-5 days post-injury and continuing for 3 weeks in healing by primary intention
Angiogenesis
Capillary buds extend into the wound bed.
Endothilial cells fill wound space creating capillaries with loose junctions and gaps in enothelial lining causing edematous look.
Capillary loops look like small granules: Granulation. Granulation tissue is delicate and needs protection.
Collagen synthesis by fibroblasts
Chronic wound:
Fibronection composition, Chronic wound fluid-inhibiting factors, delayed re-epithelialization due to non-productive wound edges, protracted inflammatory and proliferative responses
Goal of epithelization:
wound closure
When does epithelization begin?
Starts immediately after trauma as protection from organisms
Occurs concurrently with other phases
Function of angioblast:
forms new blood vessels
Function of fibroblast:
builds granulation tissue
Function of myofibroblast:
causes wound contraction
Function of keratinocyte
reepithelialize wound surface
Maturation and Remodeling
New collagen synthesis
Old collagen is broken down by collagenases
Reorientation of collagen fibers
May continue up to 2 years after wound closure
When does remodeling being?
Begins as Granulation tissue is formed and continues for 1-2 years post injury until it reaches maturation
Strength after remodeling?
Will not exceed 70-80% tensile strength of original. At closure tensile strength 15% normal
Chronic remodeling:
imbalance in collagen synthesis and lysis, dehiscence, keloids
