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of this work would inspire further research in this important area. One possible future research direction would be to use thermal-infrared imagery and compute the thermal differences between pre and post surgery images. However, such an approach first requires creating a large face database that contains pre and post operative thermal infrared images. VI. ACKNOWLEDGMENT Shorter version of this manuscript was published in the proceedings of IEEE CVPR Workshop on Biometrics 2009. The authors thank the American Society for Aesthetic Plastic Surgery for providing sample images and the Apollo Hospitals Educational and Research Foundation (India) for approving/facilitating pre-surgery and postsurgery face data collection. The authors would also like to thank the reviewers for providing useful comments. REFERENCES [1] American Society for Aesthetic Plastic Surge Principles of Plastic Surgery, Wound Healing, Skin Grafts and Flaps George Adigbli, Feras Alshomer, Jekaterina Maksimcuka, Shadi Ghali 1. INTRODUCTION Plastic and reconstructive surgery is a branch of surgery that specialises in restoring form and function to damaged or missing tissues and skin. The causes of such defects are usually related to surgery, injury, illness or congenital abnormality. This rapidly evolving specialty is based upon the exploitation of key principles of anatomy, physiology, pathology and surgery. Mastery of these principles as well as the acquisition of sound surgical technique enables plastic surgeons to constantly adapt to the wide variety of individual cases they face and provide functional and aesthetic solutions. Comprehensively describing and explaining all of the principles of plastic and reconstructive surgery would require far more space and time than can be afforded in a single chapter. This chapter will therefore focus on key principles that will allow non-specialists to understand the fundamentals of this specialty. The first section concentrates on the basic sciences of skin anatomy and the pathology of wound healing relevant to plastic surgery. The second section will evaluate practical plastic surgery principles used every day in clinical and operative practice. Once completed, the reader should be well equipped to understand more sophisticated concepts conveyed in the literature. 2. THE SKIN A detailed knowledge of the structure and function of the skin is essential in plastic and reconstructive surgery because every surgical procedure involves traversing the skin in some fashion. 2.1. Structure and function of the skin The skin is the largest organ in the body. Some of the many functions carried out by this vast organ include (Richards, 2008): 4 Textbook of Plastic and Reconstructive Surgery Physical protection Protection against ultraviolet light Protection against microbial invasion Prevention of fluid loss Regulation of body temperature Sensation Immunological surveillance Aesthetics and communication. The skin is composed of three major tissue layers, the epidermis, dermis and hypodermis, and also of various structures known as appendages. The epidermis is the outermost, protective layer of the skin. The thick dermis lies beneath this layer and contains most of the skin appendages. The hypodermis lies beneath the dermis and is predominantly composed of adipose tissue. 2.1.1. Epidermis The superficial epidermis is composed of keratinised stratified squamous epithelium. The predominant cell type is the keratinocyte, which produces fibrous keratin to provide protective and waterproof functions to this layer. Three other cell types make up this layer: Melanocytes – produce melanin which dissipates ultraviolet radiation and aids the production of vitamin D from sunlight; Merkel cells – sensory cells associated with light touch discrimination; and Langerhans cells – immune surveillance dendritic cells (antigen-presenting cells). Structurally, the epidermis is composed of five distinct layers, each of which has its own cellular make up and function. From deep to superficial they are: Stratum germinativum – the actively proliferating basal cell layer, containing melanocytes; Stratum spinosum – contains keratinocytes; Stratum granulosum – the site of protein synthesis – contains mature keratinocytes; Stratum lucidum – clear layer present only on the palms and feet; and Stratum corneum – contains thick, non-viable keratinised cells, which protect against trauma and sebaceous glands, which produce bactericidal sebum. This layer also insulates against fluid loss. 2.1.2. Dermis The dermis is the middle layer of the skin. It is predominantly composed of connective tissue comprising collagen, elastin, ground substance and vascular plexus in a bundled and woven arrangement. Structurally it consists of two layers: Principles of Reconstructive Surgery 5 The superficial papillary dermis, which consists of areolar (loose) connective tissue; and The deep reticular layer, which consists of dense irregular connective tissue. The dermis confers elasticity and flexibility to the skin and at the same time helps it to resist distortion, wrinkling and sagging. It is also the part of the skin where blood vessels and nerves end. The dermis consists predominantly of fibroblasts, collagen and extracellular matrix. 2.1.3. Hypodermis This is the deepest and thickest layer of the skin. It is often considered part of the dermis because it
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