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Anatomy and Physiology Hootan Zandifar M.D. Anatomy and Physiology of the Skin Skin More than a simple barrier Functions: immune response, regulates temperature, fluids and electrolyte balance. Heaviest human organ 3.79kg 2nd Largest surface area 1.7m2 Variations in color, thickness, connective tissue content, and number of adnexal structures. Important clinically for wound healing and esthetics Anatomy and Physiology of the Skin • Preoperative evaluation of the skin is important. – – – – – Fair skin, light hair, and blue eyes- are at risk for prolonged redness of postoperative scars Dark skin, hair, and eyes- are at risk for hyperpigmented scars that may persist postoperatively History of keloids and hypertrophic scars are important Hyperextensibility of joints, lax skin, and Gorlin’s sign, are increased risk for widen scars. Common skin conditions: Atopic dermatitis, psoriasis, and eczema are at increase risk for wound infections. Anatomy and Physiology of the Skin • Epidermis– – – • keratinizing stratified squamous epithelium Turnover 30 days 0.075-0.15mm thick, thin at birth and increases during puberty and thins again during the 5th and 6th decades of life Four Layers – – – – Stratum basale (basal cell) Stratum spinosum (prickle cell) Stratum granulosum (granular cell) Stratum corneum (Keratin) Anatomy and Physiology of the Skin • Four Cell Types – Keratinocytes- 80% • • • – Found throughout the epidermis Produces Keratin Source of squamous cell carcinoma Melanocytes• • • Neural crest origin located in the basal cell layer equal number in all races– – • – produces melanin which protects nuclei in prickle cell layer Langerhans’ Cells• • • – absent in Vitiligo Tyrosinekinase absent in Albinism Contain Birbeck’s granules antigen presentation Decrease with UV light exposure Merkel’s Cells• • • Neural crest origin function unknown Merkel’s cell tumors Anatomy and Physiology of the Skin • Rete pegs – – – – Irregular projections of the epidermis which interdigitate with corresponding upward elevations of the dermis called dermal papillae. Important in preventing shearing of the epidermis Absent in scars Decreases with aging Anatomy and Physiology of the Skin • Epidermal appendages – Pilosebaceous Unit • • • • • – – – – Sebaceous gland Hair shaft Hair follicle Arrector pili muscle Sensory organ The unit has a motor and sensory component and is responsible for producing sebum and hair. Different components dominate depending on the location. The complete pilosebacous unit is absent on mucous membranes. The Pilosebaceous unit aids in reepithelialization of partial thickness wounds. Anatomy and Physiology of the Skin Dermis • Thickness varies – – • < 1mm eye lids, 1.5mm temple, 2.5mm scalp, >4mm on the back Increases in thickness from birth to 4th or 5th decades and is thicker in males Two layers – Papillary dermis• • • – thin superficial layer adnexal structures Type III collagen Reticular dermis• • • thicker deep layer Type I collagen most abundant Scar formation Anatomy and Physiology of the Skin • Dermis – Collagen • • • Synthesized by fibroblast Provides mechanical strength and extensibility Configuration changes throughout life. – – – • • Small parallel to skin surface in infancy Young adult- randomly arranged in papillary dermis and large bundles of loosely interwoven collagen that are tightly packed Elderly collagen is more compact due to decrease in ground substance Continuous state of synthesis and degradation Decreases by 1% per year during adult life – – Increase in collagenase synthesis from sun exposure Decrease in collagen production Anatomy and Physiology of the Skin • Dermis – Elastic Tissue • • • • • • Synthesized by fibroblast and is made of elastin and a microfibrillar matrix Responsible for recoil and elastic properties of skin Continuous state of synthesis and degradation. Thin and run perpendicular to the skin surface in the papillary dermis. Thicker and run parallel to the skin surface in the reticular dermis. Sun-damaged causes thickening and clumping of elastic fibers in the papillary dermis Anatomy and Physiology of the Skin • Dermis – Ground Substance • • • • • • Connective tissue and cellular components are embedded in ground substance. Synthesized by fibroblasts, mast cells, and smooth-muscle cells Composed primarily of fibronectin, glycosaminoglycans, hyaluronic acid, chondroitin-sulfate, and dermatan sulfate. Important in maintaining skin hydration and tensile elasticity of compressed skin. Decreases with age. Dehydration of skin due to the displacement of ground substance is responsible for biological creep of skin. Creep plays a role in immediate intraoperatie tissue expansion Hypertrophic scars and keloids contain an excessive amount of ground substance and why pressure helps to reduces their size. Anatomy and Physiology of the Skin • Dermis – Cellular components • Fibroblast– – – – • most abundant cell located mainly in the papillary dermis. Produces collagen, elastin, and ground substance Behaves as a contractile cell during wound contraction Number decrease with age Mast cells – – – Are found perivascularly and in the papillary dermis May produce ground substance Abundant in scars and histamine production and release is responsible for puritus in hypertrophic scars and keloids Anatomy and Physiology of the Skin Skin – Nerve supply • • • • • • Allows the skin to accurately interpret and adapt to continuous sensory input from the environment. Sensory nerves relay pain, temperature, pressure, and proprioception Merkel cell complexes located in the epidermis respond to touch. Meissner’s corpuscles located in the papillary dermis mediate fine touch sensation. Pacinian corpuscles located in the deep subcutaneous tissue mediate deep pressure and vibration. Efferent nerves in the dermis innervate blood vessels and adnexal structures. Anatomy and Physiology of the Skin • Skin – Vascular supply • Rich source of blood to the head and neck via the internal and external carotid arteries. – • Two vascular plexuses – – • Low infection rate. Superficial plexus- located in the superficial papillary dermis. Provides nutrition to the epidermis via diffusion. Deep plexus- located in the superior aspect of the reticular dermis. It is supplied from subcutaneous perforators and provide nutrition to the skin appendages and supply the superficial plexus Venous and lymphatic drainage follow the vascular plexuses Relaxed Skin Tension Lines (RSTLs) RSTLs perpendicular to the underlying facial musculature Exception: central eyelids In the neck perpendicular to areas of flexion Place incisions along RSTLs Relaxed Skin Tension Lines Lines of Maximum Extensibility Lines of Maximum Extensibility (LMEs) are perpendicular to RSTLs Facial Subunits Physiology of Wound Healing 3 overlapping phases: Inflammatory (reactive) phase Proliferative (regeneration) phase Remodeling Inflammatory Phase (Injury-Day 4) Hemostasis Brief initial vasoconstriction Platelet activation and aggregation Coagulation and complement pathways Platelet degranulation Fibrin clot initiates inflammatory phase Vessel dilation and inc. permeability Release of chemoattractants for inflammatory cells Influx of WBC’s Initially PMN’s Shift to macrophages (day 2) Inflammatory Phase Macrophages Phagocytosis Clears wound of bacteria and debris Secrete growth factors Attract endothelial cells, fibroblasts, and keratinocytes for repair Mediators Involved in Wound Healing Eicosanoids Prostaglandins Prostacyclins Thromboxanes Leukotrienes Lipoxins Cytokines Chemokines Lymphokines Monokines Interleukins Interferons TNF GM-CSF Nitric Oxide (NO) Growth Factors PDGF EGF FGF TGF Proliferative Phase (Day 4-14) Principle Steps Epithelialization Angiogenesis Granulation tissue formation Collagen deposition Epithelialization EGF, TGF-α, KGF Morphologic changes in keratinocytes at wound edge seen within hours of injury Marginal basal cells migrate Angiogenesis TNF-α Migration of capillaries into wound bed Granulation PDGF and EGF Fibroblasts migration Collagen and ECM replaces initial fibrinplatelet matrix Dense population of blood vessels, macrophages, and fibroblasts within an ECM “Beefy red” appearance Secondary to new capillary network Contraction Surrounding skin pulled in toward open wound Degree varies Greatest in trunk Least in extremities Intermediate in head and neck Mechanism Myofibroblasts – contain smooth muscle Remodeling Phase (Day 8 – 1 Year) Collagen deposition & organization Maximum collagen deposition by 21 days Never as organized as uninjured skin Thicker fibers and more x-linking Fibroblasts become myofibroblasts Matrix metalloproteinases (MMPs) Modulate deposition and organization of ECM Scar remodeling and contraction Wound Strength 1 week: 3% 3 weeks: 30% >3 months: 80% Scar remodeling continues for up to 12 months Wound healing Hypertrophic Scars vs. Keloids Hypertrophic Scars Within wound margins Onset early after injury Regress with time More responsive to excision Keloids Extend beyond wound margins Delayed onset Grow and recur Gross Appearance Raised Rubbery Firm Histology of Keloids Excessive collagen Irregular bundles Basics of wound closure Hootan Zandifar M.D. Prior to Closure A,B,Cs, ATLS Hemostasis Thorough irrigation of the wound Removal of foreign bodies to avoid future infection or tattooing. Injection of local anesthetic usually with epinepherine for vasoconstriction. Local Anesthetics Esters (deactivated locally in tissues) Cocaine (only for topical not for injection) Procaine (Novocaine) Amides (deactivated in the liver) Xylocaine (Lidocaine) Bupivicaine (Marcaine) Prilocaine Local Anesthetics Cocaine (max dose 4 mg/kg) Procaine (max dose 7 mg/kg not to exceed 350600 mg) Local Anesthetics Lidocaine (max dose 4.5 mg/kg without epinepherine and 7 mg/kg with epinepherine) 3 formulations 0.5 % has 5 mg/cc 1.0 % has 10 mg/cc 2.0 % has 20 mg/cc Bupivicaine (max dose 3 mg/kg) Prilocaine (max dose 7 mg/kg) Local Anesthetics Toxicity First level CNS excitation (agitation, muscle twitching, hypertension, emesis, sweating) Benzodiazepine to prevent seizures, Oxygen, possible need for intubation Second level CNS depression (somnulence, coma, bradycardia, hypotension, cardiovascular depression leading to shock and cardiorespiratory arrest) ABCs, ACLS, Pressors Prilocain can cause meth-hemoglobinemia like poisoning that is treated with methylene blue Local Anesthetics Epinepherine (max dose of 10 mcg/kg) Formulations 1:100,000 has 10 mcg/cc 1:200,000 has 5 mcg/cc 1:1,000 has 1,000 mcg/cc Toxicity – Sympathetic activation (tachycardia, hypertension, diaphoresis…) Treat with beta blockers Tissue handling Be gentle—hooks, non-crushing forceps DEBRIDEMENT: don’t be afraid to debride Re-cutting the wound: bevel the edges Allows for skin eversion Closures Eversion of wound edges Make incisions perpendicular to the skin (unless in hair bearing areas) Good technique: twist your wrist, insert needle at correct angles (90 Degrees to the skin) Cleaning the wound: dilute H2O2, dilute betadyne solutions, saline Techniques Techniques Wrong method Correct method Needle point Geometry Taper-Point •Suited to soft tissue •Dilates rather than cuts Reverse cutting •Very sharp •Ideal for skin •Cuts rather than dilates Conventional Cutting •Very sharp •Cuts rather than dilates •Creates weakness allowing suture tearout Taper-cutting •Ideal in tough or calcified tissues •Mainly used in Cardiac & Vascular procedures. Wound Closure Basic suturing techniques: Simple sutures Mattress sutures Subcuticular sutures Goal: “approximate, not strangulate” Simple Sutures Simple interrupted stitch Single stitches, individually knotted (keep all knots on one side of wound) Used for uncomplicated laceration repair and wound closure Mattress Sutures Horizontal mattress stitch Provides added strength in fascial closure; also used in calloused skin (e.g. palms and soles) Two-step stitch: Simple stitch made Needle reversed and 2nd simple stitch made adjacent to first (same size bite as first stitch) Mattress Sutures Vertical mattress stitch Affords precise approximation of skin edges with eversion Two-step stitch: Simple stitch made – “far, far” relative to wound edge (large bite) Needle reversed and 2nd simple stitch made inside first – “near, near” (small bite) Subcuticular Sutures Usually a running stitch, but can be interrupted Intradermal horizontal bites Allow suture to remain for a longer period of time without development of crosshatch scarring Suturing Rule of halves Suturing Rule of halves Closures Absorbable Fast Absorbing gut Chromic Gut Vicryl PDS Non-absorbable Nylon Prolene Silk Absorbable vs. Non-Absorbable Closures Smaller sutures on face: 5-0 or 6-0 Prolene vs. Nylon COLOR MATTERS (hairline, ear crevices, eyebrows) Neck: 5-0 sutures Scalp: staples Leave tails to remove non-absorbable “If you had to take them out” Deeper stitches Deeper stitches: are used for support to remove tension and close dead space With tension removal less scarring Last longer: ABSORBABLE Vicryl PDS Chromic “Burying the knot”: buried interupted “Difficult” closures Lips: align the vermillion: key stitch Eyelid: if thru and thur: Ears: exposed cartilage / auricular hematomas Align the grey line Repair perichondrium, Close cutaneous layers Avulsion injuries: reattach if little pedicle versus pocket principle Nose: Exposed cartilage Through and Through lacerations. Close the inside first. Secondary Intention Concave surfaces Lateral forehead Glabella Medial Canthal Subunit Depressed area of ear Supraalar hollow of nose Soft tissue triangles Philtrum Perinasal melolabial Fair healing Nasal sidewall subunit Lateral canthal subunit Animal Bites Most infections are mixed bacteria of aerobic and anerobic. Need wide spectrum antibiotics Many organisms produce beta-lactamase Augmentin oral drug of choice. Unasyn or Zosyn for IV treatment. Copious irrigation of the wound is a must. Human Bites Mixed aerobic and anerobic Can treat with Augmentin or Clindamycin Debate to close or not to close human bites because of risk of infection. Irrigate 48 hours of IV antibiotics delayed closure vs. secondary intention vs. primary closure after irrigation with oral antibiotic use. Tetanus Thank You.