13.4 Wound healing and skin disorders
4 min read•august 14, 2024
Wound healing is a complex process involving four stages: , , , and . These stages work together to repair damaged skin, with each phase playing a crucial role in restoring the skin's protective barrier.
Skin disorders can be classified by their causes: infectious, inflammatory, neoplastic, or congenital. Understanding these disorders and their treatments is essential for maintaining healthy skin and addressing various skin conditions effectively.
Wound Healing Stages and Processes
Hemostasis and Inflammation
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- Wound healing is a complex process that involves four overlapping stages: hemostasis, inflammation, proliferation, and remodeling
- Hemostasis occurs immediately after injury and involves vasoconstriction, platelet aggregation, and formation of a fibrin clot to stop bleeding
- The inflammatory phase begins within hours of injury and is characterized by vasodilation, increased vascular permeability, and the recruitment of neutrophils and to the wound site
- Neutrophils remove debris and bacteria (dead cells, foreign particles)
- Macrophages secrete growth factors (PDGF, TGF-β) and cytokines (IL-1, TNF-α) to stimulate the proliferative phase
Proliferation and Remodeling
- The proliferative phase begins within days of injury and involves the formation of granulation tissue, , and
- migrate into the wound and produce collagen and other extracellular matrix components (glycosaminoglycans, proteoglycans) to form granulation tissue
- Endothelial cells form new blood vessels (angiogenesis) to supply the granulation tissue with oxygen and nutrients
- migrate from the wound edges to re-epithelialize the wound surface
- The remodeling phase begins weeks to months after injury and involves the reorganization of collagen fibers, contraction of the wound, and maturation of the scar tissue
- Collagen fibers align along lines of tension to increase wound strength
- Myofibroblasts contract the wound to reduce its size
- Scar tissue becomes less cellular and vascular over time
Factors Affecting Wound Healing
Factors Impairing Wound Healing
- Factors that can impair wound healing include age, nutritional deficiencies (protein, vitamin C, zinc), smoking, diabetes, obesity, and certain medications (corticosteroids, chemotherapy)
- Chronic diseases such as diabetes and peripheral vascular disease can impair blood flow and to the wound, leading to delayed healing and increased risk of
- Immunocompromised states, such as those caused by HIV/AIDS or immunosuppressive medications, can impair the inflammatory response and increase the risk of infection
- Impaired neutrophil and macrophage function reduces the ability to clear bacteria and debris
- Reduced growth factor and cytokine production delays the proliferative phase
Factors Promoting Wound Healing
- Factors that can promote wound healing include proper , adequate hydration, and maintaining a moist wound environment
- Adequate protein intake is necessary for collagen synthesis and tissue repair
- Vitamin C is essential for collagen cross-linking and enhances immune function
- Zinc plays a role in collagen synthesis, immune function, and epithelialization
- Wound that maintain a moist environment, such as hydrocolloids and hydrogels, can promote re-epithelialization and reduce scarring
- Moist environments prevent cell desiccation and promote migration
- Occlusive dressings (film, foam) maintain moisture and protect the wound from contaminants
- Growth factors, such as platelet-derived growth factor (PDGF) and epidermal growth factor (EGF), can stimulate cell proliferation and migration to promote wound healing
- PDGF attracts and activates macrophages and fibroblasts
- EGF stimulates keratinocyte migration and proliferation
Skin Disorder Classification
Etiology-based Classification
- Skin disorders can be classified based on their etiology into four main categories: infectious, inflammatory, neoplastic, and congenital
- Infectious skin disorders are caused by bacteria (cellulitis, impetigo), viruses (herpes simplex), fungi (tinea), or parasites (scabies)
- Inflammatory skin disorders are characterized by an abnormal immune response and include conditions such as acne, , , and contact
- Neoplastic skin disorders involve the abnormal growth of skin cells and include benign conditions (seborrheic keratosis) and malignant conditions (basal cell carcinoma, melanoma)
- Congenital skin disorders are present at birth and include conditions such as epidermolysis bullosa and ichthyosis
Clinical Presentation
- Clinical presentation of skin disorders can vary widely and may include symptoms such as erythema, edema, vesicles, bullae, scales, plaques, and ulcers
- Erythema is redness of the skin caused by dilation of blood vessels (cellulitis, eczema)
- Edema is swelling caused by fluid accumulation in the skin (angioedema, contact dermatitis)
- Vesicles are small, fluid-filled blisters (herpes simplex, chickenpox)
- Bullae are large, fluid-filled blisters (pemphigus, bullous pemphigoid)
- Scales are flakes of dead skin cells (psoriasis, seborrheic dermatitis)
- Plaques are raised, flat-topped lesions (psoriasis, lichen planus)
- Ulcers are open sores that extend into the (venous ulcers, pressure ulcers)
Pathophysiology and Treatment of Skin Disorders
Acne and Eczema
- Acne is a chronic inflammatory disorder of the pilosebaceous unit characterized by the formation of comedones, papules, pustules, and nodules
- The pathophysiology of acne involves increased sebum production, abnormal keratinization of the follicular epithelium, colonization by Propionibacterium acnes, and inflammation
- Treatment options for acne include topical retinoids (tretinoin, adapalene), benzoyl peroxide, antibiotics (clindamycin, erythromycin), and oral medications (isotretinoin)
- Eczema, also known as atopic dermatitis, is a chronic inflammatory skin disorder characterized by pruritic, erythematous, and scaly lesions
- The pathophysiology of eczema involves a complex interplay between genetic susceptibility, immune dysregulation, and environmental triggers
- Treatment options for eczema include emollients, topical corticosteroids (hydrocortisone, triamcinolone), topical calcineurin inhibitors (tacrolimus, pimecrolimus), and systemic immunosuppressants (cyclosporine, methotrexate)
Psoriasis
- Psoriasis is a chronic autoimmune disorder characterized by the formation of well-demarcated, erythematous plaques with silvery scales
- The pathophysiology of psoriasis involves hyperproliferation and abnormal differentiation of keratinocytes, as well as infiltration of inflammatory cells (T cells, dendritic cells) into the skin
- Treatment options for psoriasis include topical corticosteroids, vitamin D analogs (calcipotriol), phototherapy (UVB, PUVA), and systemic medications (methotrexate, cyclosporine, biologic agents)
- Biologic agents target specific cytokines (TNF-α, IL-17, IL-23) involved in the inflammatory cascade of psoriasis
- Examples of biologic agents include etanercept, adalimumab, ustekinumab, and secukinumab
Key Terms to Review (26)
Angiogenesis: Angiogenesis is the physiological process through which new blood vessels form from existing ones. This process is essential for growth, development, and wound healing, as it ensures that tissues receive an adequate supply of oxygen and nutrients. In the context of healing and skin disorders, angiogenesis plays a critical role in repairing damaged tissues and facilitating recovery by delivering necessary components to the affected areas.
Biofilm: A biofilm is a complex community of microorganisms that adhere to surfaces and are embedded within a self-produced extracellular matrix. These structures can form on various surfaces, including living tissues and medical devices, and can play a significant role in wound healing and the development of skin disorders by affecting the healing process and potentially leading to infections.
Debridement: Debridement is the medical process of removing dead, damaged, or infected tissue from a wound to promote healing. This technique is essential in managing wounds effectively, as it helps to clear the wound bed of any necrotic material that can impede healing and serve as a breeding ground for infection. The goal is to prepare the wound for further treatment and to enhance the body’s natural healing processes.
Dermatitis: Dermatitis is a general term for inflammation of the skin, often characterized by red, itchy, and swollen skin. It can be triggered by various factors such as allergens, irritants, and underlying health conditions, and it directly impacts the skin's barrier function and overall health. Understanding dermatitis is essential for grasping how the skin responds to injury or irritation and how it can affect the wound healing process.
Dermis: The dermis is the thick layer of living tissue located beneath the epidermis, playing a crucial role in skin structure and function. It contains connective tissue, blood vessels, hair follicles, and various glands that contribute to thermoregulation, sensation, and overall skin health. The dermis supports the epidermis and serves as a critical barrier against external threats while facilitating essential physiological processes.
Diabetes mellitus: Diabetes mellitus is a chronic metabolic disorder characterized by high blood sugar levels due to insulin resistance or insufficient insulin production. This condition can lead to various complications, especially affecting wound healing and skin integrity, as high glucose levels impair the body’s natural healing processes and increase the risk of infections.
Diabetic foot ulcer: A diabetic foot ulcer is a sore or wound that occurs on the foot of a person with diabetes, often resulting from a combination of neuropathy, poor circulation, and skin integrity issues. These ulcers are common complications of diabetes and can lead to serious infections, amputations, and other severe health problems if not treated properly. Understanding the mechanisms behind diabetic foot ulcers is crucial for effective prevention and management strategies.
Dressings: Dressings are sterile pads or compresses applied to a wound to promote healing and protect it from infection. They come in various types and sizes, tailored to different wound conditions and stages of healing, and play a crucial role in wound management.
Eczema: Eczema is a chronic skin condition characterized by inflammation, redness, and itching, often leading to dry and scaly patches on the skin. It can significantly impact the healing process of the skin and is commonly associated with other skin disorders, making it an important topic in understanding skin health.
Epidermis: The epidermis is the outermost layer of skin, acting as a protective barrier that shields underlying tissues from environmental hazards such as pathogens and chemical irritants. It is primarily composed of keratinocytes, which produce keratin, a protein that helps maintain the skin's integrity and resilience. The epidermis plays a crucial role in processes like skin pigmentation and wound healing, making it vital to overall skin health.
Fibroblasts: Fibroblasts are specialized cells within connective tissue that are responsible for producing and maintaining the extracellular matrix, which provides structural support to tissues and organs. They play a crucial role in wound healing by synthesizing collagen and other fibers that help to repair damaged tissues and maintain skin integrity.
Hemostasis: Hemostasis is the process that prevents and stops bleeding, ensuring that blood remains within a damaged vessel. This complex mechanism involves a series of steps, including vascular spasm, platelet plug formation, and coagulation, which work together to seal wounds and restore blood flow. It is essential for maintaining the integrity of the circulatory system and plays a critical role in wound healing and recovery from injuries.
Hypodermis: The hypodermis, also known as the subcutaneous layer, is the innermost layer of skin that lies beneath the dermis. It plays a crucial role in connecting the skin to underlying tissues, providing insulation, cushioning, and energy storage through adipose tissue. This layer also contains larger blood vessels and nerves, making it vital for skin health and overall body function.
Infection: An infection occurs when harmful microorganisms, such as bacteria, viruses, fungi, or parasites, invade and multiply within the body, leading to tissue damage and immune response. This process can disrupt normal bodily functions and may lead to a range of symptoms, varying in severity depending on the type of pathogen and the individual's health status. In the context of wound healing and skin disorders, infections can complicate recovery by introducing additional inflammation and delaying the healing process.
Inflammation: Inflammation is a biological response of body tissues to harmful stimuli, such as pathogens, damaged cells, or irritants. It serves as a protective mechanism, promoting healing and facilitating the repair of tissue. However, when inflammation becomes chronic, it can lead to various disorders and negatively impact overall health.
Keloid: A keloid is a type of raised scar that forms due to an overproduction of collagen during the healing process following an injury to the skin. Keloids extend beyond the original wound area and can vary in size, shape, and color. They often occur in individuals with darker skin tones and can be itchy or painful, making them a significant concern in the context of wound healing and skin disorders.
Keratinocytes: Keratinocytes are the predominant cell type in the epidermis, the outermost layer of the skin, responsible for the synthesis of keratin, a key structural protein that provides strength and resilience to the skin. These cells undergo a process of differentiation as they migrate from the deeper layers of the epidermis to the surface, ultimately forming a protective barrier against environmental damage, pathogens, and water loss.
Macrophages: Macrophages are large white blood cells that play a critical role in the immune system, acting as key players in both innate and adaptive immunity. They are responsible for engulfing and digesting cellular debris, foreign substances, and pathogens, thus facilitating the body's defense against infections. Additionally, macrophages release signaling molecules that help coordinate the immune response and promote tissue healing.
Nutrition: Nutrition is the process by which living organisms obtain and utilize food substances to support growth, maintenance, and overall health. It plays a crucial role in various physiological processes, including metabolism, immune function, and tissue repair, making it essential for wound healing and the management of skin disorders.
Oxygenation: Oxygenation is the process of adding oxygen to the blood, primarily through the respiratory system where oxygen is inhaled into the lungs and transferred to the bloodstream. This vital function supports cellular metabolism and is crucial for healing processes, especially in wounds and skin disorders where adequate oxygen supply promotes tissue repair and reduces the risk of infection.
Peripheral artery disease: Peripheral artery disease (PAD) is a common circulatory condition characterized by narrowed arteries reducing blood flow to the limbs, most commonly the legs. This condition often leads to symptoms like leg pain during physical activity and can have serious implications for wound healing and skin health due to insufficient blood supply.
Pressure ulcer: A pressure ulcer, also known as a bedsore or decubitus ulcer, is a localized injury to the skin and/or underlying tissue that typically occurs over bony prominences due to prolonged pressure, often in individuals with limited mobility. These ulcers are associated with skin breakdown and can lead to serious complications if not properly managed, highlighting the importance of effective wound healing and skin care strategies.
Proliferation: Proliferation refers to the rapid increase or multiplication of cells, particularly in response to injury or inflammation. This process is essential during wound healing, as it leads to the formation of new tissues and the repair of damaged areas, ultimately restoring skin integrity and function. Understanding proliferation is crucial for grasping how the body responds to skin disorders and injuries.
Psoriasis: Psoriasis is a chronic autoimmune skin condition characterized by the rapid growth of skin cells, leading to thick, red, scaly patches on the skin's surface. This condition results from an overactive immune response that speeds up skin cell turnover, disrupting the normal structure and function of the skin. Psoriasis can significantly impact a person's quality of life and is often associated with other health conditions.
Re-epithelialization: Re-epithelialization is the process by which epithelial cells migrate and proliferate to cover a wound or injury site, restoring the integrity of the skin or mucosal surfaces. This critical mechanism is essential in wound healing, as it helps to re-establish the barrier function of the epithelium, preventing fluid loss and infection while promoting tissue repair.
Remodeling: Remodeling refers to the biological process of reshaping and reorganizing tissue, particularly in response to injury or changes in mechanical stress. This process is crucial in wound healing, as it helps restore the integrity and function of damaged skin by replacing old or damaged cells with new ones, ensuring that the skin can regain its strength and resilience over time.