Integumentary System: Skin Structure and Function

Integumentary System Overview

• The integumentary system is the largest organ, comprising 16% of body weight.
• It protects against external stimuli, aids in metabolic functions, and maintains homeostasis.
• The skin has five body cavities that open to the exterior of it: oral, nasal, orbital, anal, and vaginal cavities.
• Skin thickness ranges from 0.5 to 6 mm, varying by body location, and dorsal surfaces are generally thicker than ventral.
• The skin consists of the epidermis and dermis.

Epidermis

• The epidermis is composed of tough stratified squamous epithelium and lacks blood vessels.
• Functions of the epidermis include protection from chemicals and harmful microorganisms.
• Regulates body fluid volume and temperature, and eliminates wastes.

Epidermis Layers

• Stratum Corneum: It is up to 75% of the epidermal thickness, composed of keratinized dead squamous epithelial cells that are flat, lack nuclei, and tightly bonded to prevent water loss and maintain hydration.
• Stratum Lucidum: It's a thin, translucent layer in thick skin (lips, palms, soles), lacking nuclei and organelles, and containing desmosomes and Eleidin gives it a translucent look.
• Stratum Granulosum: It is composed of three to four layers of flattened cells with irregular keratohyalin granules.
• Stratum Spinosum: It consists of several layers of polygonal cells with large oval nuclei undergoing occasional mitosis, spiny projections form intercellular bridges, and lymph fluid provides nourishment and immunity here.
• Stratum Basale: It is the basal layer and has a single layer of columnar epithelial cells on the dermis and it contains keratinocytes, melanocytes, tactile cells (Merkel cells), and nonpigmented granular dendrocytes (Langerhans cells).

Dermis

• Dermis is composed of two layers:
  • Stratum Papillarosum: The upper layer below the epidermis is loose connective tissue that accounts for 1/5 of the dermis.
  • Stratum Reticularosum (Reticular Layer): This is the thicker, deeper layer with dense irregular connective tissue containing collagen and elastin.
• Nerves and blood vessels are widely distributed in the dermis. It nourishes the stratum basale.
• Blood vessels play a vital part in controlling body temperature and blood pressure.

Subcutaneous Tissue

• Subcutaneous tissue consists of loose connective tissue, blood vessels, and adipose cells.
• Adipose cells act as a buffer for bones and tissues.
• This tissue attaches the skin loosely to underlying organs and muscles, allowing it to slide.

Skin Appendages

• Skin appendages include hairs, nails, sweat glands, sebaceous glands, mammary glands, and ceruminous glands.
• Appendages are developed from the embryonic epidermis.
• Integumentary glands play a vital part in body protection and homeostasis maintenance.
• Hair: It is produced by hair follicles and is a thin, flexible filament. Consisting of keratinized dead cells, contributing to temperature maintenance and touch sensations.
• Fingernails and Toenails: They are firm plates formed in the stratum corneum, nails consist of compressed and keratinized dead cells grow at 1 mm/week, protecting sensitive fingertips & toes and aiding accurate movements.
• Sebaceous Glands: They are developed from from follicular epithelium, secreting serum, and found in all skin except palms and soles
• Sweat Glands: They are distributed over the skin except for lips, nipples, and external genital organs, secreting sweat, classified as eccrine and apocrine.
• Mammary Glands: They are modified sweat glands located in female breasts.
• Ceruminous Glands: They are modified sweat glands in the external auditory canal, secreting cerumen for lubrication and protection.

Cutaneous Sensation and Innervation

• Cutaneous sensation involves sensory receptors for warmth, cold, touch, vibration, and pain distributed in the dermis.
• Face, palms, fingers, soles, and genitals have high sensory neuron concentration.
• Thinner skin is generally more sensitive.

Sensory Receptors

• Free Nerve Endings: They are unencapsulated and are the simplest receptors, nociceptors beneath the epidermis, and those wrapped around hair follicles sense touch and pressure.
• Meissner's Corpuscles: Located in the stratum papillarosum, they are encapsulated nerve endings sensing light touch and low-frequency vibrations, abundant in hairless skin.
• Pacinian Corpuscles: Encapsulated nerve endings and mechanoreceptors in superficial fascia, stimulated by quick movements, play a role in sensing deep touch and vibration.
• Ruffini's Corpuscles: Mechanoreceptors similar to Merkel's disks, also nerve endings are surrounded by a sheath, respond to continuous pressure and stretching, and detect stimulus intensity and speed.
• Krause's End Bulbs: Widely distributed and considered small Meissner's corpuscles and cold receptors in the dermis.
• Merkel's Disks: They are typical speed sensors beneath fingertip ridges, responding to light touch and constant pressure.
• Muscle Spindles and Golgi Tendon Organs: They are deep sensory receptors for proprioception, located in muscles and tendons.
• Golgi Tendon Organs: They work as tension detectors providing information about tension applied to tendons.

Sensory Conduction Pathways

• Somatosensory Stimuli: The four types of stimuli received and perceived by the cortex are touch, proprioception, pain, and temperature.
• Conscious Sensory Pathways: The pathways from the spinal cord to the cortex include the posterior white column, medial lemniscal pathway and relays for discriminate touch.
• The Spinothalamic Tract: It conveys pain and temperature information.

Skin Types

• Skin type classifications: normal, dry, oily, and combination, based on sebum, they are also affected by psychological, environmental, and pathological factors.

Normal Skin

• Ideal skin has balanced keratinization, desquamation, water loss, sebum excretion, and sweating, soft, elastic, and well-moisturized.
• This type of skin needs sustained care.

Dry Skin

• Dry skin lacks oil, leading to moisture loss.
• It has a rough surface and is frequently accompanied by erythema and can be caused by external factors such as dry air, wind, detergents, chemicals, excessive bathing, UV rays and physical stimulation.
• Other causes are aging, atopic dermatitis, and chronic renal failure, resulting from lack of natural moisturizing factors (NMF) and reduced epidermal lipids.

Oily Skin

• Oily skin has excessive sebum from overactive oil glands that forms an oily film, blocking pores and inducing pimples.
• Excessive sebum can alkalize the epidermis, increasing bacterial infection risk.
• Major causes include genetics, puberty hormones, digestive issues, diet, vitamin deficiencies, and hot, humid conditions.

Combination Skin

• Presents both dry and oily characteristics due to regional sebum differences. It's sensitive and prone to infection.
• Typically, the T-zone (nose, chin, forehead) is oily, while cheeks are dry/normal.
• This condition is common in middle age due to lifestyle, environmental factors, skincare habits, and hormones.

Integumentary Physical Therapy for Skin Types

• Dry skin care: Appropriate moisture and cleansing, preventing additional drying.
• Oily skin care: Mainly focus on sebum removal.
• Combination skin care: Needs antibacterial, hypoallergenic cleansing.

Wounds

• A wound is the destruction of normal skin structure.

Classification of Wounds

• Classified by depth into epidermis, dermis, subcutaneous tissue.
• Wounds are called erosions if only the epidermis is affected and are called ulcers if there is breakage of the epithelium.
• Partial-Thickness Wounds (Erosion): Only the superficial dermis is involved and structures are intact, aiding epidermis restoration.
• Full-Thickness Wounds (Ulcer): Involves epidermis, dermis and often underlying structures, it requires epidermis movement to cover the area since appendages are lost, as well as contraction which diminishes wound size.

Other Wound Classifications

• Stab wounds, incised wounds, lacerations, and abrasions.

Causes of Wounds

• Causes determine risks and treatments, classified by forces like shearing, tension, and compression.
• Shearing Wounds: Caused by sharp objects, minimal damage, low inflammation risk, and treatable by primary suture.
• Tension Wounds: Due to blunt objects hitting diagonally, creating a triangular flap thus leading to possible ischemia and necrosis due to blood supply obstruction, this leads to more cell damage & inflammation.
• Compression Wounds: Caused by perpendicular blunt force, and are characterized with bumpy, fragmented texture with dead tissue and are high inflammation risk, requiring thorough cleansing/excision.

Wound Healing

• A complex process influenced by health, knowledge of phases, and requires healthcare skills.
• Wound Healing Phases: Hemostasis, inflammation, granulation and maturation .

Hemostasis Phase

• Platelets act as utility workers to seal off damaged blood vessels.
• Blood vessels constrict after injury, then relax.
• ADP aids platelet aggregation and adhesion to exposed collagen.
• Platelets secrete vasoconstrictors to stabilize the clots.
• Platelets stimulate the intrinsic clotting cascade via thrombin, fibrin formation.
• Fibrin strengthens the platelet aggregate into a haemostatic plug and secrete cytokines like Platelet-Derived Growth Factor (PDGF).
• Hemostasis completes within minutes of injury unless there are clotting disorders.

Inflammatory Phase

• Inflammation presents as redness, swelling, warmth, and pain.
• Lasts 3-5 days post-injury, longer with infection.
• Neutrophils clean up debris as non-skilled laborers.
  • Vascular Response: Prostaglandins, bradykinin, leukotriene and histamine dilate vessels and increase vascular permeability and congestion.
  • Vascular Response: Blood vessels release plasma and PMNs, resulting in exudate, erythema, edema, pyrexia, pain, or dysfunction.
  • Cellular Response: Neutrophils, macrophages, and monocytes eliminate bacteria by phagocytosis and purification.
• Macrophages: Serve as the "contactor" in wound healing, aiding phagocytosis and defense.
• Inflammatory mediators: Fibroblast growth factor (FGF), epidermal growth factor (EGF), transforming growth factor beta (TGF-β) and interleukin-1 (IL-1).
• Without interference, the inflammatory phase lasts 3--5 days.
• Ongoing contamination: it continues monocytes and neutrophils activation, and it hinders resolution, prolonging the phase.

Proliferative Phase

• Granulation starts 4-5 days post wounding until day 21.
• Red pebbled tissue replaces dermal tissues, involves sub-dermal tissues for deep wounds, as well as wound bed contraction.
• Granulation Tissue Formation:
  • Vascularization/Angiogenesis: Endothelial cells near necrotic tissue proliferate and grow to the damaged tissue within two days, providing oxygen and nutrients.
  • Collagen Synthesis: This happens when cellular regeneration is difficult, vascular cells proliferate with fibroblasts, lymphocytes, mastocytes, and macrophages, capillaries cause edema due to permeability and water leaks.
• Contraction: Myofibroblasts pull wound edges together, and decrease defect size.
• Epithelization: Closes the wound by epithelial cell migration and replication. Collagen, elastin and glycoproteins are synthesized, with scar tissue formation. Unremoved scar tissue leads to granulation tissue and keloid development,.

Maturation Phase

• In Maturation, fibroblasts and capillaries reduce, scar tissue is replaces with soft, dense tissue for protection. Scar tissue is still 20-30% less elastic than normal tissue.

Wound Healing and Chronic Wounds

• Over-abundant neutrophil infiltration causes chronic inflammation, and it must be reduced for healing.
• Neutrophils release collagenase and elastase, which destroys tissue and healing.

Wound Symptoms

• General signs include erythema, swelling, burning, pain, pus, hardness, tense skin, red lines, fever, discoloration, itchiness.

Wound Complications

• Wound Infection: Topical harm is caused by bacterial growth and pathogens, the occurrence depends on bacterial count, pathogenicity & host resistance.
• Infected wounds result in more bacteria which consume oxygen and nutrients so cells lose function and toxins destroy cells, which causes delayed repair because it gets stuck in the inflammation phase. Awareness of signs like discomfort, discharge, reddening, and lymph node issues is important.

Hypertrophic vs Keloid Scars

• Hypertrophic Scars: Raised, thick scars are an abnormal response, occur on stressed sites.
• Keloids: Excessive scar tissue extending beyond injury margins, in dark skinned people often, and are prone to ears, arms, lower abdomen and breastbone.

Suture Marks

• Suture marks are caused by unpleasant complications.

Causes of Suture Marks

• Location is vulnerable in back, chest, arms, and nose, not the eyelids, palms, or soles.
• Keloid Tendencies: Those with keloid tendencies are prone to suture marks.
• Suture Tension: Caused by knotting resulting in skin contraction and clear marks.
• Suture Abscesses: Small abscesses develop around sutures, silk sutures cause inflammation more easily compared to nylon sutures or staplers.
• Duration of Sutures: There will be marks if sutures are not removed within 14 days.

Burns

• Burns are injuries that cause skin cell destruction or necrosis from heat sources.
• Burns can severely damage physiological functions, which results in scarring and life-threatening complications.

Histology of the Skin

• The skin consists of two layers: epidermis and dermis.
• The epidermis is comprised of stratified squamous epithelium.
• The dermis consists of connective tissue.
• The skin appendages arise from the epidermis.

Functions of the Skin

• Creates a barrier against microorganisms and prevents water loss. It also helps regulate body temperature.

Etiology of Burns

• Thermal Burn:
  • Flame Burn: Caused by fire or gas explosion, mainly in confined areas, it causes severe respiratory damage due to gas inhalation.
  • Hot Fluid Burn (scald): It is caused by hot liquids or steam, often occurring in children and elder people.
• Chemical Burn: Caused by contact with acids/alkalis, severity depends on the exposure type.
• Electrical Burn: It Is caused by electricity exposure (500-1000v). Electrical shocks lead to damage through the body, particularly affecting internal organs.
• Inhalation and Respiratory Burns: It is caused by smoke damaging airways, also early intubation, high-flow oxygen, ventilatory support are needed.

American Burn Association Classification

• Assessment: The depth AND area of a burn is related to the location, patient's age and burn cause.
• Severity: The American Burn Association has classified burns into minor burn, moderate burn, and major burn.

Burn Classifications

• First-Degree Burn: Superficial, damaging the epidermis, leading to erythema as illustrated by sunburns.
• Second-Degree Burn: It is partial-thickness, classified as superficial or deep based on damage to the epidermis and dermis.
  • Superficial burns damage the epidermis and papillary layer, involving blisters, erythema, edema, and pain.
  • Deep burns destroy formed blisters, and burnt areas may be red or white.
• Third-Degree Burn: It is a full-thickness burn, destroys the epidermis and dermis.
• Fourth-Degree Burn: subcutaneous burn, it destroys fatty tissues, tendons and muscles, which is caused by electrical, hot fluid, and flame accidents, extensive skin grafts are required in order to treat a fourth-degree burn.

Third Degree Appearances

• Flame: formation of blisters surrounded by erythema, The surface is mottled red and is usually moist due to exudation of plasma.
• Electrical and Chemical: Area is dry and it has a white or black eschar, possible visible thrombosed subcutaneous.

Burn Healing

• Rate of heat: Depends on the quantity of adnexal epithelial structures remaining inside the dermis. Separation of eschar occurs, leaving clear granulation tissues in 3-4 weeks .
• In partial thickness burn: It is healing achieved by epithelialization within 3 weeks without any surgical intervention
• Full Thickness: Skin becomes barren, dry, and burnt, as it also starts damaging osseous so the bones may be exposed and amputation is needed.

Jackson's Thermal Wound Theory

• Three zones in thermal wounds include coagulation, stasis, and hyperemia.

1. Central Zone of coagulation ( Inner zone): Forming the visible burn eschar which can separate on three to four week if left.
2. The second Zone of Stasis( intermediate zone): It surrounds coagulation zones.
3. Hyperemia's Zone (outer zone): It contains inflammatory mediators which contribute to tissue edema and it recovers after a week if there are no other infections sustained.

Test and Assessment (Body Surface Area)

• The Rule of Nines assists in assessing the damaged skin area in burns following the pattern of 9% or its multiples.
• It is calculated by 9% for the head and neck, 18% for the front and back of the body, 9% for each arm, and 1% for the genitals per leg.
• The Lund-Browder Chart is used on young adults as it is made especially for children because their skin condition is unique compared to adults.

Recovery Stages

• Shock Phase: The phase where Burn victims fall in shock over 2 to 3 days since they are severely injured.
• Eschar Detachment: The layer of damaged or burned tissue is replaced with new healthy skin around 3-4 weeks.

Compartimental syndrome

• Pathophysiological changes: Pathophysiological changes on the skin happens due to lack of heat or loss on body fluids and immunity from the body.
• Systematic symtoms in the shock phase: In the phase, patient will be restless as they lack blood or because the injury is still recent.

Systemic Complications

• Complications may occur because of: Inhalation injury: Asphyxia, atelectasis, pneumonia, pulmonary emboli, emphysema and pulmonary edema, respiratory failure, Neurogenic shock.

Prognosis

• Can be determined based on amputation in case of deep second or severe burns. Amputation may be needed do to dysfunction or social handycappedness.
• Factors that affect prognosis. -The percentage of the Total Burn Surface Area and inhalation burn patients must be treated in the intensive care unit.

Initial emergency steps

• In the situation of being on fire, one of the first things to do is remove the victim safely and wash with water to help hydrate and avoid possible irritations such as the metallic zips.

Medical Treatment

• To help the victim: Medical assistance must be provided to help avoid sharp increased of fluids is sharply increased in the early days. In cases of 20%, Parkland Formula must be supplied.

Physical Therapy Intervention

• During the burn, it can be hard to swallow the food: the intervention during physical therapy would be the levin tube by providing protien since that will provide and increase the caloric flow with heat.
• The burns can affect or cause infections: To avoid the damage done by burn and maintain the hygiene with proper hygiene and cleaning method, infection may be prevented.