Lecture 8 Integumentary System 1

Structure, Function, Conditions, Burn Classification, Thermoregulation, and Biomechanics

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.