Epidermis
Made up of four layers that gradually become more and more keratinized as you move up. Basal cells at bottom have stem cells (maybe). 10-30 cell layers. From bottom to top its the sensory neuron attached to the merkel cell , the melanocyte, and then the keratinocytes.
Keratinocyte
Makes keratin until the cell does a special apoptosis.
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Structure, Function, Conditions, Burn Classification, Thermoregulation, and Biomechanics
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Epidermis
Made up of four layers that gradually become more and more keratinized as you move up. Basal cells at bottom have stem cells (maybe). 10-30 cell layers. From bottom to top its the sensory neuron attached to the merkel cell , the melanocyte, and then the keratinocytes.
Keratinocyte
Makes keratin until the cell does a special apoptosis.
Epidermis Main Layers
Bottom to top: stratum basal (replicating cells), stratum spinosum (connected by desmosomes instead of connective tissue), stratum granulosum (“granules of keratin), lucidum, and corneum (dead cells, no organelles, fully keratinized).
Basement Membrane
Connects the epidermis to the dermal layer and the waves in the structure help with mechanical stability and SA. It’s the lining under the bottom layer of the epidermis, the stratum Basale. It’s connective tissue.
Dermis
75% collagen by dry weight and has the epidermis on one side and the hypodermis on the other. Contains the papillary and reticular dermises as well as the dermal papillae which is the bumps/humps in the bottom of the basement membrane. Contains the free nerve endings for pain, touch, temperature.
Papillary Dermis
Thin upper layer containing the meissener’s corpuscles (mechanoreceptor).
Reticular Dermis
Dense lower layer made of connective tissue. It contains the glands and receptors.
Sebaceous Gland
Makes sebum and is connected near the top of the hair follicle.
Hypodermis
Bottom layer with subcutaneous fat that helps with heat insulation and acts as an energy source.
Arrector Pili
Muscle that moves the hair follicle so hairs stand on end.
Keratin
In human air, nails, skin, horns, claws, and scales. It’s an intermediate filament. So the alpha helical region, into the coiled dimer, into the staggered tetramer of two dimers, two tetramers together, and then 8 tetramers in a hollow tube for whole fiber.
Vitamin D
AKA cholecalciferol and a hormone. 7-dehydrocholestorol broken by UV rays and vitamin D increases calcium absorption from intestines.
Melanin
Melanocytes make melanin. Melanocyte concentration changes based on signaling factors (MSH expression) released from UV exposure. Melanocortin 1 receptor (MCR1) regulates quantity and quality of melanin.
Skin Barriers
Microbiome barrier, chemical barrier, physical(epidermal), immune barrier once you’re in the body (probs dermis).
Skin Permeability
Dermis is permeable so some burn ooze. Stratum corneum/top epidermal layer is mostly impermeable water and polar substances.
Burn
Could be a thermal, chemical, radiation, or electrical burn. Heat based burns can cause coagulation so that the burn depth is limited.
Superficial/1st Degree
Vasodilation, damage localized to epidermis, nerve stimulation results in pain, heals quickly.
Capillary Vasodilation
Redness and some swelling because heat is sensed and then dilation occurs so that heat loss is increased.
Partial Thickness/2nd Degree
Epidermis fully damaged, partial damage to dermis w/underlying structures, likely to result in scarring, blistering and major inflammation, extremely painful because nerves are exposed. It’s also shiny because of dermis fluid loss.
Deep Partial Thickness/2nd Degree
Damage reaches the reticular dermis so nerves are destroyed and you can’t feel the pain in the burned area (although surrounding areas probably feel it). Stem-cell containing follicles are lost and fibroblasts (unable to make new skin matrix) are damaged. It’ll heal through contraction with major hypertrophic (raise) scarring. They qualify for skin grafting.
Healing by Contraction
The skill/cells pull themselves together so healing can start and it results in raised scarring.
Full Thickness/3rd Degree
Damage goes down to the subcutaneous level and all sensation is lost because the nerves have been destroyed. Requires debridement to remove dead cells and a full thickness graft to try to have blood vessels. Merkel cells won’t come bac but some nerves might depending on the damage.
Blanching
The whitening and then flushing as a result of the application of pressure. If there’s no blood flow then this won’t occur.
Jackson’s Concentric Zones of Burn Tissue
From center to outside, zone 1 is coagulation, 2 is stasis, and 3 is hyperemia. The coagulation is the dead/burned cells (turns green), stasis is the white area that is potentially viable but lacking blood flow, and hyperemia shows a reversible increase in blood flow.
Inhalation Injury
Lung injury from smoke or heat.
Burn Physiological Impact
Scarring, fluid loss, nutrient loss, burn shock.
Severe Scarring can lead to…
Mobility problems. These can be relieved through escharotomy which is an incision through the burn tissue to relieve compression on the tissue underneath.
Nutrient Loss Details
A hypermetabolic state after the injury, as the wound exudates (leaks) there’s protein loss so a protein infusion is necessary to stop the body from breaking down the muscles and other organs for nutrients.
Burn Shock
Hypervolemia (too much fluid in the blood), edema (swelling), massive inflammatory response, immunosuppression which leads to infection, and decreased cardiac input which can lead to heart failure.
Diabetic Ulcers
Caused by high pressure and reduced sensation. Exacerbated by impaired immunity and reduced blood flow.
Diabetes is linked to
Heart disease, kidney disease, retinopathy (vision issues), neuropathy (nerve damage), chronic wounds, and lower limb amputation.
Psoriasis
A chronic skin condition with plaques that become dry and cracked. As the top scaly layer cracks, the layer beneath is exposed which causes discomfort and irritation.
Metabolic Processes that produce heat
Basal metabolism of cells, muscle activity, extra b/c of hormonal or chemical impacts, digestion and food absorption
Convection
Air currents impact on heat transfer
Skin Heat Maintenance
Vasoconstricted (reduce blood flow near surface) to hold onto heat and vasodilated to release heat.
Piloerection
Goosebumps, pilo muscles activate, the muscle activation releases heat the body needs.
Thermogenesis
Heat production. There’s a core body temp sensor in the brain that’ll involuntarily begin shivering.
Eccrine Sweat Gland
Present in most of the skin and opens directly to skin surface.
Apocrine Sweat Gland
Opens into hair follicles so its density increases in areas of high hair concentration. When the sweat mixes with sebum and is degraded by bacteria, people smell.
Sweat Gland
Has sympathetic nerve attached at coiled region. The coil is at osmotic equilibrium so as sweat moves up, sodium and chloride ions are reabsorbed to reduce the salt concentration that reaches the surface. When it’s greatly stimulated more fluid is lost as the salt can’t be reabsorbed.
Sweating is induced by
Hypothalamus stimulation, epinephrine, nore
pinephrine, or nerves that secrete accetylcholine.
Dermis Contents
Elastin (amorphous w/hydrophobic regions to make it recoil) which provides recoil strength and collagen (triple helix)that provides tensile strength (there’s more of both at joints).
Older people have looser skin because…
Collagen breaks down but elastin does not.
Mechanically, skin is…
Viscoelastic
Langer Lines
Tensions follows these, it’s the average of collagen orientation in the body, is important for surgery and wound healing. If you cut perpendicular to the lines then tension keeps the wound open and is more likely to have a scar.
Wound Contraction
Fibroblasts differentiate into myofibr
oblasts to pull on the newly formed matrix so that the wound closes. Immune cells also enter the wound for clean up.
Scar Tissue
As the wounded matrix is broken down, it’s replaced with collagen and with less elastin resulting in a scar.