Anatomy and Physiology of Tissue Repair

Each structural element of tissue contributes to the healing process; adjunctive surgical closure and securement products can be used to enhance, support and strengthen these natural processes.

Skin closure is a factor in all the procedures discussed in this report (report #S175), since optimizing closure of skin incisions is an important aspect of all internal procedures. Surgical procedures often involve additional internal adhesive repair of internal tissues.

The Skin

The skin is our protection from the environment. It is a complex organ, protecting the body from chemical, biological and physical insult, retaining organs and tissues, regulating secretion of products such as pheromones, and controlling body temperature and other parameters. It is constantly renewed and maintained.

Each component of the skin contributes to the healing process and in recent years advanced wound management products have been developed to encourage repair of these individual tissues. The approach taken to wound care is defined by an understanding of how the skin repairs itself.

The skin is made up of an epidermal layer on the surface, and an inner layer called the dermis. Below the dermis is the subcutaneous tissue. Its complex structure enables skin to prevent bacterial and microbial infections and regulate temperature, among other functions. A number of organelles exist within the skin to control temperature and to provide blood and secretions to maintain tissue homeostasis.

The epidermis does not have blood vessels as it is only a few cells thick. It comprises a series of layered cells called strata with Latin names: basale, spinosum, granulosum, corneum, and, lucidum. The stratum corneum consists of keratinized cells that are sloughed off in response to wear-and-tear; the major function of this layer is to provide physical protection. Lower layers of the skin are responsible for prevention of dehydration, while the stratum granulosum provides immunological cells that mount a defense against microbial infection.

The basal layer contains keratinocytes and melanocytes that are responsible for major proliferative activity during skin regeneration and damage repair.

The cells of the epidermis have a relatively rapid turnover rate of approximately five weeks. This is why the proliferative layer has been used to generate tissue-engineered products for situations such as burn repair. It is this layer of cells that proliferates at the fastest rate to repair wounds. Proliferative cells migrate from healthy areas of skin into the damaged area and eventually coat the area with new skin. Mesh grafts are used to help this process to accelerate healing of badly burned patients.

The dermis is made up of two main layers. The comparatively thick reticular layer attaches to the epidermis; this layer has an advanced matrix structure associated with blood vessels and glycosaminoglycans and collagen. This layer is responsible for the variable thickness and elasticity of skin. The lower layer of the dermis contains more matrix materials, blood vessels and dermal organelles associated with homeostasis.

Also important for skin repair is the subcutaneous layer, which stores fat and serves to protect lower layers of tissue and support the layers above with nutrients, blood flow, immunological factors, and homeostatic control.

Internal Tissues and Organs

Internal tissues that are cut during surgery are components of specific organs and their surrounding connective tissues and vasculature. Surgery entails cutting through connective tissues that normally serves the purpose of binding, supporting, protecting, and separating tissues of different types. Connective tissues also supply nutrients and gaseous exchange to cells. Connective cells are separated from one another by a non-cellular matrix that may be solid (as in bone), soft (as in loose connective tissue), or liquid (as in blood). Two major types of connective tissue are loose connective tissue (LCT) and fibrous connective tissue (FCT). Collagen fibers often provide elasticity and flexibility in connective tissues.

Connective tissue occurs beneath epithelium in skin and many internal organs, such as lungs, arteries and the urinary bladder. This type of tissue also forms a protective layer over muscle, nerves, and blood vessels.  


From Report #S175, "Worldwide Surgical Sealants, Glues, Wound Closure and Anti-Adhesion, 2009-2013."

 

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