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Anatomy and Physiology Chapter 5 Etymological Breakdown of the Term Integumentar y System: • Integument-: Derived from the Latin root integumentum, which means "a covering," "disguise," or "cloak" (stemging from integere, meaning to cover or protect). • -ary: A standard adjectival suffix meaning "pertaining to" or "relating to.” • System: Derived from the Greek systēma, meaning a "organized whole" or a "combination of parts" working together. Put it all together, and the integumentary system literally translates to the system relating to the body's covering (the skin, hair, nails, and associated glands that protect the body as an organized unit). Overview of the Integumentary System The Skin and Beyond: • While commonly called the skin, the integumentary system is actually a complex organ system. • Includes the skin (cutaneous membrane) plus its accessory structures: hair, nails, and sweat and sebaceous (oil) glands. Scale & Importance: • The skin is the largest organ of the body, accounting for about 16 percent of body weight (16 to 20 pounds average adult) and covering a surface area of 1.5 to 2 square meters. Primary Functions: • Acts as the immediate barrier protecting the body from pathogens, chemicals, and mechanical injury. • Prevents fluid loss and regulates body temperature and sensation. Clinical Significance: • Often reflects overall health; changes in color, texture, or integrity can indicate underlying systemic diseases (e.g., cardiovascular, respiratory, or liver conditions). https://www.researchgate.net/ Overview of Skin Layers Dual-Layered Organ: • The skin consists of two main, distinct layers resting on a supportive subcutaneous layer. 1. Epidermis: • The superficial, outermost layer of the skin. • Composed of keratinized stratified squamous epithelium. • Avascular (receives nutrients via diffusion from the dermis below). 2. Dermis: • The deeper layer lying directly beneath the epidermis. • Composed of connective tissue (areolar and dense irregular). • Vascularized; houses blood vessels, lymphatic vessels, nerves, hair follicles, and sweat glands. Overview of Skin Layers 3. Hypodermis (Subcutaneous Layer / Superficial Fascia): • Technically not part of the skin itself, but closely associated. • Composed of loose areolar and adipose tissue; anchors skin to underlying muscle and bone while providing insulation and cushioning. https://quizlet.com/ Thick Skin vs. Thin Skin (Epidermal Layers) Classification Criteria: • Skin is categorized as either "thick" or "thin" based on the number of epidermal layers and the depth of the stratum corneum, not the total thickness of the skin organ as a whole. Thin Skin: • Contains four layers (stratum basale, spinosum, granulosum, and corneum). NOTE: These are listed from deep to superficial • Lacks the stratum lucidum. • Covers the vast majority of the body surface and contains hair follicles and sebaceous glands. Thick Skin: • Contains five layers (features the translucent stratum lucidum). • Found only on areas subject to heavy friction and abrasion: the palms of the hands and the soles of the feet. • Features a much thicker stratum corneum and lacks hair follicles and sebaceous glands. https://med.libretexts.org/ Cells of the Epidermis 1. Keratinocytes: • The most abundant cells in the epidermis (approx. 90%). • Synthesize keratin, a tough, fibrous protein that gives skin its hardness, durability, and water-resistant properties. • Continuously produced by stem cells in the deepest layer, pushing upward and eventually shedding. 2. Melanocytes: • Located in the deepest epidermal layer. • Produce the pigment melanin, which absorbs UV radiation and protects deeper cell DNA; transferred to keratinocytes. 3. Langerhans Cells: • Dendritic cells functioning as macrophages in the epidermis. • Engulf bacteria, foreign particles, and damaged cells to trigger an immune response. 4. Merkel Cells: • Receptor cells located in the deepest layer that function as touch receptors, associating with sensory nerve endings. Cells of the Epidermis Layers (Strata) of the Epidermis Layers (Strata) of the Epidermis 1. Stratum Basale (Basal Layer / Stratum Germinativum): • Deepest single layer; attached to the basement membrane and underlying dermis. • Forms a wavy boundary by interlocking with upward projections of the dermis called dermal papillae, increasing surface area and strengthening the epidermal-dermal bond to prevent shearing (enhancing grip). • The stratum basale is a single layer of cells primarily made of basal cells. • Site of continuous mitotic cell division (cuboidal stem cells) that continually produce new keratinocytes. • Houses melanocytes (pigment producers) and Merkel cells (touch receptors). 2. Stratum Spinosum ("Spiny Layer"): • 8 to 10 layers of keratinocytes connected by strong desmosomes, giving a spiny appearance under a microscope. • Contains maturing keratinocytes and Langerhans cells. • Keratinocytes in the stratum spinosum begin the synthesis of keratin and release a water-repelling glycolipid. https://www.flickr.com/photos/187096960@N06/51172620298 Layers (Strata) of the Epidermis 1. Stratum Basale (Basal Layer / Stratum Germinativum): • Deepest single layer; attached to the basement membrane and underlying dermis. • Forms a wavy boundary by interlocking with upward projections of the dermis called dermal papillae, increasing surface area and strengthening the epidermal-dermal bond to prevent shearing (enhancing grip). • The stratum basale is a single layer of cells primarily made of basal cells. • Site of continuous mitotic cell division (cuboidal stem cells) that continually produce new keratinocytes. • Houses melanocytes (pigment producers) and Merkel cells (touch receptors). 2. Stratum Spinosum ("Spiny Layer"): • 8 to 10 layers of keratinocytes connected by strong desmosomes, giving a spiny appearance under a microscope. • Contains maturing keratinocytes and Langerhans cells. • Keratinocytes in the stratum spinosum begin the synthesis of keratin and release a water-repelling glycolipid. https://www.flickr.com/photos/187096960@N06/51172620298 Layers (Strata) of the Epidermis 3. Stratum Granulosum ("Granular Layer"): • 3–5 layers deep; cells flatten and fill with keratin, keratohyalin granules, and lamellar granules (waterproofing glycolipids). • Organelles disintegrate and cell death occurs as cells are pushed further from the blood supply. 4. Stratum Lucidum ("Clear Layer"): • Thin, translucent layer of dead, flattened cells packed with eleidin. • Found only in thick skin (palms of hands and soles of feet). 5. Stratum Corneum ("Horny Layer"): • Superficial layer consisting of 15–30 layers of flat, dead, keratin-filled cells. • Provides a durable, waterproof barrier against microbes, dehydration, and mechanical abrasion; continuously sloughed off. Layers (Strata) of the Epidermis The Dermis: Regions & Structure General Characteristics: • The "core" of the cutaneous system; houses blood vessels, sweat glands, oil glands, hair follicles, and nerve endings. • Consists of two layers of connective tissue that compose an interconnected mesh of elastin and collagenous fibers, produced by fibroblasts. 1. Papillary Layer: • Upper 20% of the dermis; composed of loose areolar connective tissue with a loose meshwork of collagen and elastic fibers. • Features dermal papillae that project upward into the epidermis, forming unique epidermal ridges (fingerprints) that enhance grip. • Contains rich capillary loops that nourish the avascular epidermis via diffusion and help regulate body temperature and lymphatic capillaries. • Packed with sensory nerve endings, including Meissner corpuscles (receptors sensitive to light touch) and free nerve endings that detect pain and temperature. • 2. Reticular Layer: • Deeper, thicker 80% of the dermis; composed of dense irregular connective tissue. • Packed with thick bundles of collagen fibers (for structural strength and tensile resilience) and elastic fibers (for skin stretch and recoil). • Contains larger blood vessels, sweat/sebaceous glands, and Pacinian corpuscles (deep pressure receptors). Papillary layer also contains fibroblasts, some fat cells (adipocytes), and phagocytes. Meissner corpuscles https://neuroscientificallychallenged.com/glossary/meissners-corpuscles https://histology.siu.edu/intro/Meissners2.htm The Dermis: Regions & Structure • Papillary layer also contains fibroblasts, some fat cells (adipocytes), mast cells, and phagocytes. https://www.enhance-me-training.com/topic/the-dermis/ The Hypodermis (Subcutaneo us Layer) Position & Anatomy: • Located directly beneath the reticular layer of the dermis. • Technically not part of the skin proper, but rather a connective tissue layer that anchors the skin to underlying bone and muscle. • Composed primarily of loose areolar connective tissue and adipose tissue (fat cells). Vascular Supply: • Highly vascularized; contains large blood vessels that supply the skin and serve as a common site for subcutaneous injections (hypodermic needles). Primary Functions: • Energy Storage: Adipocytes store triglycerides as an energy reserve. • Insulation & Protection: The fat layer provides thermal insulation against heat loss and acts as a shock-absorbing cushion to protect underlying structures from mechanical trauma. Skin Pigmentation & Color Determinants 1. Melanin: • Produced by melanocytes; primary pigment determining skin color. • Exists in two primary forms: eumelanin (brown/black) and pheomelanin (red/yellow). • UV exposure stimulates tyrosinase enzyme activity, increasing melanin production (tanning) to shield cell nuclei from DNA damage. • Freckles and moles represent localized accumulations of melanin. 2. Carotene: • A yellow-orange pigment obtained from plant-based foods (e.g., carrots, sweet potatoes) that can accumulate in the stratum corneum and hypodermis. 3. Hemoglobin: • The red oxygen-transporting protein in red blood cells. • Imparts a pinkish or red tint to the skin as blood flows through the dermal capillaries, particularly visible in lighter-skinned individuals when oxygenated. Carotenodermia https://www.nejm.org/doi/abs/10.1056/NEJMicm950425 https://en.wikipedia.org/wiki/Jaundice https://www.azolifesciences.com/ Integumentary System Disorders Overview of Accessory Structures Definition: • Structures that originate from the epidermis and extend down into the dermis or hypodermis. Key Components: • Hair • Nails • Sweat (Sudoriferous) Glands • Sebaceous (Oil) Glands General Function: • While embedded in the skin, these structures play critical roles in protection, sensory input, thermoregulation, and excretion. https://www.mayoclinichealthsystem.org/ https://www.harleystreethairtransplants.org/ Hair Structure and Growth Anatomy of a Hair: • Shaft: The portion of the hair exposed above the skin surface (completely dead, keratinized cells). • Root: The portion of hair anchored within the follicle below the skin surface. • Hair Bulb: The expanded base of the root surrounding the hair papilla (which contains blood vessels and nerves). Layers of the Hair: • Medulla: The central core of the hair. • Cortex: The middle layer providing strength and pigment. • Cuticle: The outermost layer of overlapping, single cells protecting the inner layers. Follicle & Arrector Pili: • Surrounded by a root sheath and connected to an involuntary smooth muscle called the arrector pili, which contracts to pull hair upright ("goosebumps" in response to cold or fear) and is controlled by the sympathetic nervous system. • This traps a layer of air to add insulation https://www.toppik.com/ Internal Root Sheath Layers of the Hair Follicle External Root Sheath • Structure: Surrounds the growing hair root up to the hair shaft. • Origin: Derived from the basal cells of the hair matrix. Wall • Structure: Encloses the hair root as a direct extension of the epidermis. • Characteristics: Composed of basal cells at the base; becomes increasingly keratinous toward the upper regions. Glassy Membrane • Structure: A thick, clear connective tissue sheath covering the hair root. • Function: Connects the hair follicle directly to the surrounding dermal tissue. Root Hair Plexuses (Hair Follicle Receptors) • Histological Definition: Specialized networks of unmyelinated sensory nerve fibers that wrap intricately around and entwine within the external root sheath of hair follicles. • Anatomical Position: Located in the dermal portion of the hair follicle wall, typically positioned just inferior to the entrance of the sebaceous gland ducts. • Functional Role: Act as rapid-adapting mechanoreceptors (tactile receptors) responsible for detecting fine, light-touch stimuli. • Mechanism of Action: • Deflection of the hair shaft (from wind, clothing, or a crawling insect) acts as a mechanical lever. • Movement physically shifts the follicular wall and deforms the entwined nerve endings. • Mechanical deformation opens mechanically- gated ion channels, triggering action potentials that travel via sensory neurons to the central nervous system. • Clinical/Physiological Significance: Highly sensitive to initial directional movement, providing early cutaneous awareness of external environmental contact before deeper touch receptors are engaged. https://quizlet.com/ca/443370620/hair-and-nails-flash-cards/ https://www.nisenet.org/catalog/scientific-image-human-hair Hair Growth Cycle & Dynamics • Anagen Phase (Growth): Rapid cell division at the root pushes the hair shaft upward at ~0.3 mm/day; lasts 2 to 7 years. • Catagen Phase (Transition): A brief 2 to 3 week transitional period marking the end of active follicular growth. • Telogen Phase (Resting): Lasts 2 to 4 months with no new growth, culminating in a new anagen phase that sheds the old hair. • Shedding & Loss: Average daily loss is 50 hairs; excessive loss exceeding replacement results from aging, hormonal fluctuations, or dietary changes. https://www.pinterest.com/pin/halloween-hair--417638565445540250/ Sweat (Sudoriferous) Glands Function: • Produce sweat to cool the body via evaporative cooling and excrete metabolic wastes. 1. Eccrine (Merocrine) Sweat Glands: • More common; distributed across nearly the entire skin surface (especially palms, soles, and forehead). • Produce a hypotonic fluid (water, salts, metabolic wastes) released via exocytosis directly onto the skin surface for thermoregulation. 2. Apocrine Sweat Glands: • Confined to areas with hair follicles (e.g., armpits and genital regions). • Larger glands that release a thicker, organic-rich (in addition to water and salts) secretion into hair follicles, which is metabolized by bacteria to produce body odor; become active starting at puberty. • The release of this sweat is under both nervous and hormonal control https://en.wikipedia.org/wiki/Apocrine_sweat_gland Sebaceous (Oil) Glands Definition: • Exocrine glands associated with hair follicles found all over the body except on the palms and soles. Secretion (Sebum): • Produce sebum, a mixture of lipids, cholesterol, and proteins. Functions of Sebum: • Lubricates and waterproofs the skin and hair, preventing them from drying out. • Possesses antibacterial properties to inhibit the growth of microorganisms on the skin surface. Mode of Secretion: • Holocrine secretion: cells accumulate sebum until they rupture and destroy themselves, releasing their product (replaced by mitotic division of basal cells). https://quizlet.com/ca/443370620/hair-and-nails-flash-cards/ Nails Structure & Composition: • Specialized accessory structures composed of densely packed, dead, heavily keratinized epidermal cells. Key Anatomical Features: • Nail Body (Plate): The visible hard plate covering the dorsal surface of the fingertip/toe. • Nail Bed: The specialized skin underlying the nail body, richly supplied with blood vessels (giving it a pink color). • Nail Root: The deep epidermal fold under the skin where nail production begins. • Eponychium (Cuticle): The fold of epithelial tissue that overlaps the proximal edge of the nail body. • Lunula: The thick, crescent-shaped whitish area at the base of the nail body overlying the thick nail matrix. Primary Functions: • Protects the distal tips of fingers and toes from trauma and enhances precision grip for picking up small objects. Overview of Integumentary Functions Primary Role: • The skin and its accessory structures function as an integrated organ system that maintains homeostasis and protects the body. Core Physiological Functions: • Protection: Acts as a physical and chemical barrier against external elements. • Sensation: Detects environmental stimuli via specialized receptors. • Thermoregulation: Modulates body temperature through sweat and blood vessel adjustments. • Vitamin D Synthesis: Produces a crucial hormone essential for calcium absorption. Protection (The Body's Armor) Physical & Chemical Barrier: • Protects underlying vital organs from mechanical injury, UV radiation, wind, and water. Dehydration Prevention: • Layers of tough keratin and water-resistant glycolipids in the stratum corneum prevent excessive fluid loss. Microbial Defense: • Acts as a first line of defense against pathogens, abrasive grit, and harmful chemicals. • Sweat contains dermcidin, which possesses antibiotic properties to deter microbe over-colonization. Immune Protection: • Langerhans (dendritic) cells patrol epidermal layers to intercept foreign invaders and trigger immune responses. https://uen.pressbooks.pub/anatomyphysiology/chapter/epidermis/ Langerhan s (Dendritic) Cells (APC’s) https://courses.lumenlearning.com/wm-biology2/chapter/antigen-presenting-cells/ Sensation (Sensory Function) Environmental Awareness: • The integumentary system contains a rich network of specialized nerve endings and receptors across the epidermis, dermis, and hypodermis. Key Sensory Receptors: • Meissner (Tactile) Corpuscles: Highly concentrated in fingertips; respond to light touch. • Pacinian (Lamellated) Corpuscles: Detect deep pressure and vibration. • Merkel Cells & Hair Root Plexuses: Detect fine touch and minor hair disturbances (e.g., sensing an insect crawling on the skin). Pain & Temperature: • Free nerve endings distributed throughout the skin monitor noxious stimuli, temperature shifts, and physical trauma. Sensation (Sensory Function) • Merkel cells (Tactile discs): Located in the deep layer of the epidermis (stratum basale), these are slow-adapting receptors that excel at detecting sustained touch, fine detail, texture, and edges. When pressed, they release signaling molecules that excite adjacent nerve endings, providing high-resolution tactile feedback (like reading Braille or feeling a smooth surface). • Meissner corpuscles (Tactile corpuscles): Situated in the dermal papillae of hairless (glabrous) skin, such as your fingertips and lips, these are rapid-adapting receptors. They fire intensely when skin first makes contact with an object and when it loses contact, making them exceptionally sensitive to light touch, low-frequency vibration, and slippage (helping you adjust your grip on a moving object). • Pacinian corpuscles (Lamellar corpuscles): Found deep in the dermis and subcutaneous layer, these large, onion-shaped receptors are rapidly adapting and exquisitely sensitive to deep pressure and high-frequency vibration. Because of their layered capsule, steady pressure is filtered out, allowing them to fire only when vibration or sudden mechanical shifts occur (such as feeling a drill vibrate or walking on a rough surface). • Hair root plexus (Hair follicle receptors): A web of sensory nerve fibers wrapped around the base of hair follicles. These rapid-adapting mechanoreceptors detect the bending or movement of hairs. Even a light breeze or an insect crawling across your arm displaces a hair, triggering the surrounding nerve plexus and providing an early warning system for tactile movement across hairy skin. Pacinian Corpuscle (Sensory Organ) Pacinian Corpuscle Anatomy: Encapsulated, onion-like mechanoreceptor for deep pressure and vibration. • The Capsule & Outer Lamination: Dense connective tissue outer envelope and flattened lamellar cells that filter out steady pressure. • Viscous Gel: Interstitial fluid between layers that shifts hydraulically to dampen sustained forces, driving rapid adaptation. • Inner Lamination: Tightly packed, specialized modified Schwann cells forming a core around the central nerve terminal. • Terminal Non-Myelinated Axon: Bare, uninsulated nerve tip at the center with stretch-sensitive channels that trigger action potentials when compressed. • Myelinated Axon: Insulated nerve fiber exiting the corpuscle to rapidly transmit electrical impulses toward the central nervous system via saltatory conduction. Thermoregulation Sympathetic Nervous System Control : The integumentary system works closely with the autonomic nervous system (involuntary bodily control) to continuously monitor and adjust core body temperature. Response to Overheating (Cooling): • Sweating: Eccrine sweat glands secrete water and electrolytes; evaporative cooling dissipates body heat. (Note: insensible perspiration secretes ~500 mL/day even without noticeable sweating). • Vasodilation: Dermal blood vessels dilate to bring warm blood closer to the body surface, releasing heat into the environment. Response to Cold (Heat Retention): • Vasoconstriction: Dermal arterioles constrict to minimize blood flow to the skin surface, trapping core heat internally (can cause a pale/whitish hue). • Shivering: Involuntary muscle contractions generate metabolic heat (assisted by the contraction of arrector pili muscles). Vitamin D Synthesis The Pathway: • 1. Skin Activation: When epidermal cells are exposed to ultraviolet (UV) radiation, a cholesterol derivative in the skin converts into cholecalciferol (Vitamin 3). • 2. Liver Processing: The liver converts cholecalciferol into an intermediate compound called calcidiol. • 3. Kidney Activation: The kidneys convert calcidiol into calcitriol, which is the active, functional hormone form of Vitamin D. Physiological Importance: • Calcitriol is essential for the normal intestinal absorption of calcium and phosphorus, which are strictly required for bone health, growth, and remodeling. https://www.researchgate.net/ Effects of Aging on the Integumentary System Epidermal & Dermal Changes: • Mitotic activity in the stratum basale slows down, causing the epidermis to thin. • The dermis exhibits a reduced ability to regenerate, leading to a loss of structural elasticity and flexibility (manifesting as wrinkles). • Fibroblast activity declines, resulting in decreased production of collagen and elastic fibers. Vascular & Glandular Decline: • Blood supply to the skin decreases, reducing the skin's capacity to heal quickly and impairing thermoregulation (leading to increased sensitivity to cold). • Functional activity of sweat (sudoriferous) and sebaceous (oil) glands drops, causing dry, scaly skin and a reduced ability to sweat effectively. Subcutaneous & Accessory Alterations: • The hypodermis loses fat storage over time, contributing to a loss of padding, insulation, and a sunken appearance. • Melanocyte and hair follicle activity slows down, resulting in graying or thinning hair and a reduced capacity to protect against UV radiation. • Immune responsiveness declines as the number of Langerhans cells drops, increasing susceptibility to skin infections and damage. Overview of Skin Cancer Definition & Cause: • Cancer caused by abnormal, uncontrollable cell division in the skin. • Primary culprit is overexposure to ultraviolet (UV) radiation from the sun or tanning beds, which damages cellular DNA. The Danger of Metastasis: • Metastasis is the process where cancer cells break away from the primary tumor, enter the bloodstream or lymphatic vessels, and spread to secondary sites (such as lymph nodes, lungs, or liver), making treatment significantly more difficult. Types of Skin Cancer: • Basal Cell Carcinoma (BCC): Starts in the stratum basale and spreads along that boundary; the most common form of skin cancer, highly curable with early treatment (common in areas exposed to the sun). • Treatments include surgery, freezing (cryosurgery), and topical ointments • Squamous Cell Carcinoma (SCC): Affects keratinocytes of the stratum spinosum; presents as lesions on the scalp, ears, and hands; more aggressive than BCC and can metastasize if left untreated. • Surgery and radiation are used to cure SCC • Melanoma: Uncontrolled growth of melanocytes, typically developing from a mole; the most fatal form of skin cancer due to high rates of metastasis. • Treatment typically involves surgical excision and immunotherapy Basal Cell Carcinoma Squamous Cell Carcinoma Melanoma Early Detection of Melanoma (The ABCDE Rule) Clinical Screening Guidelines: • A – Asymmetry: The two sides of the mole or lesion do not match. • B – Borders: The edges are irregular, ragged, notched, or blurred. • C – Color: The color is not uniform and may include different shades of brown or black, or patches of pink, red, white, or blue. • D – Diameter: The lesion is larger than 6 mm (about the size of a pencil eraser), though melanomas can sometimes be smaller. • E – Evolving: The mole is changing in size, shape, color, or elevation, or begins to bleed/itch. Common Skin Disorder s Introduction to Skin Disorders: • Skin disorders range from minor localized irritations to chronic systemic conditions, often involving inflammation, immune responses, or blocked glands. • Disorders include psoriasis, cold sores, impetigo, scabies, hives, and warts. Eczema: • An inflammatory, allergic condition that presents as dry, red, itchy patches resembling rashes. • Often accompanied by swelling, flaking, and skin cracking; managed with moisturizers, corticosteroid creams, and immunosuppressants. Acne: • A skin disturbance involving the overproduction of sebum and keratin that blocks hair follicles. • Most common during puberty due to hormonal surges (androgens) that stimulate sebaceous glands, leading to bacterial infection and inflammation. Skin Injuries & The Healing Process Types of Injuries: • Cuts, punctures, scrapes, and burns caused by physical trauma, heat, chemicals, or electricity. • Step-by-Step Wound Healing Stages: 1. Hemostasis & Clotting: A blood clot forms immediately to stop bleeding and eventually dries into a protective scab. 2. Inflammation: White blood cells (macrophages) clear out debris and fight potential infection. 3. Proliferation: Fibroblasts migrate into the wound bed to produce new collagen and blood vessels (granulation tissue). 4. Remodeling & Scarring: Epithelial cells regenerate across the wound under the scab, while scar tissue (dense collagen) replaces normal tissue depending on the depth of the injury. https://www.shieldhealthcare.com/ https://jetem.org/thermal_burns/ Burns and Classification s Nature of Burns: • Caused by intense heat, radiation, electricity, or chemicals, resulting in massive cell death and fluid loss. Severity Classifications: • First-Degree (Superficial): Affects only the epidermis; results in redness and minor pain (e.g., mild sunburn) that heals within days. • Second-Degree (Partial-Thickness): Damages both the epidermis and upper dermis; results in blistering and significant pain. • Third-Degree (Full-Thickness): Destroys the full thickness of the skin (epidermis and dermis), charring tissue and destroying nerve endings (often requiring skin grafts). • Fourth-Degree (Full-Thickness with Deep Tissue Damage): Extends completely through the skin down to underlying muscle, tendons, and bone; requires extensive surgical intervention and often amputation. Major Systemic Risks: • Severe dehydration, electrolyte imbalance, renal/circulatory failure, and rampant secondary infections due to lost skin barrier function. Fourth degree Burn https://burncenters.com/burns/evaluate-a-burn/ Common Integumentary Abnormalities and Injury Responses Scars & Keloids: • Scars: Formed when the skin repairs deep dermal damage using collagen-rich connective tissue rather than regenerating normal tissue. • Lacks accessory structures (e.g., hair follicles, sweat glands, and sebaceous glands) • Keloids: Result from an overproduction of scar tissue (collagen) that extends beyond the original boundaries of the wound. Bedsores (Decubitus Ulcers): • Caused by constant, long-term pressure on bony areas that cuts off blood supply to the skin, leading to tissue necrosis and breakdown. Stretch Marks (Striae): • Occur when the dermis is stretched beyond its elastic limits (e.g., during rapid growth, weight gain, or pregnancy), causing collagen and elastin fibers to tear. Calluses & Corns: • A protective response where the stratum basale increases mitotic activity in areas subjected to constant friction or pressure, resulting in a thickened, hardened layer of dead cells. https://www.healthline.com/health/keloid-ear https://www.mayoclinic.org/diseases-conditions/corns-and- calluses/multimedia/callus/img-20007285 https://myexpertmidwife.com/blogs/my-expert-midwife/stretch-marks-101 https://blog.xoxoday.com/empuls/get-to-know-you-questions-for-coworkers/