ch7_scar

ch7_scar - Scar formation and contraction around implants...

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Scar formation and contraction around implants A. Scar formation following trauma B. Scar formation around “inert” implant C. Chronic scar formation D. Mechanism of scar formation. Scar forms secondary to contraction E. Templates prevent scar formation around implants by blocking contraction
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A. Scar formation following trauma 1. Sources of trauma: energy sources . mechanical: deep cut, laceration, surgery thermal: fire, hot water. electromagnetic: UV, electrical discharge nuclear: radiation therapy.
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Skin: reversible injury Spontaneous regeneration of excised epidermis Figure by MIT OCW. Left: a controlled injury (e.g. stripping or blistering) which leaves the dermis intact. Right: the epidermis recovers completely at the defect site. Hair follicles are lined with epidermal tissue and also regenerate.
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Skin: irreversible injury Spontaneous healing of skin excised to full thickness by contraction and scar formation. The dermis does not regenerate. Figure by MIT OCW. Left: Excision of the epidermis and dermis to its full thickness. Right: Wound edges contract and close, while scar tissue forms simultaneously in place of a physiological dermis. The epidermis that forms over the scar is thinner and lacks undulations (rete ridge).
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Peripheral nerve: reversible injury Mildly crushed nerve heals spontaneously by regeneration Figure by MIT OCW. Within the nerve fiber, axons and their myelin sheath are regenerative. Top: Following mild crushing injury, the axoplasm separates and the myelin sheath degenerates at the point of injury. However, the basement membrane stays intact. Bottom: The nerve fiber regenerates after a few weeks.
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Peripheral nerve: irreversible injury Transected nerve heals spontaneously by contraction and neuroma (neural scar) formation. No reconnection of stumps. Figure by MIT OCW. Most supporting tissues (stroma) that surround nerve fibers are not regenerative. Thus, while nerve fibers can regenerate following a transection, the other tissues in the nerve trunk cannot regenerate. After transection, the nerve trunk stumps become neuromas - clumps of scarred tissue that close largely by contraction.
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Severity of injury determines its reversibility Figure by MIT OCW.
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Scar formation following trauma (cont.) 2. Morbidity of trauma, scar formation and contraction on finger joint it prevents movement (“contracture”) in peripheral nerves (neuroma) it prevents conduction of electric signals (paralysis) in neck or face it creates serious problems of social acceptance around suture points (e.g., following caesarian section) surgical adhesions prevent normal function of intestines or lungs (e.g.,following heart surgery)
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Images removed due to copyright restrictions. Poster warning NFL football players not to tackle with the crown of their helmet ("Play Heads-Up!) Diagram describing angioplasty.
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B. Scar formation around “inert” implant 1. Scarring following implantation of any nondegradable prosthesis (e.g., silicone, polyethylene) 2. Constrictive scar tissue (fibrous capsule) around implant
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This note was uploaded on 11/11/2011 for the course BIO 2.797j taught by Professor Matthewlang during the Fall '06 term at MIT.

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ch7_scar - Scar formation and contraction around implants...

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