all tissues heal by similar mechanisms wound healing is a complex process of overlapping phases that is initiated by an injury or wound normal wound healing is divided into phases defined by characteristic cellular populations and biochemical activities these phases include hemostasis inflammation proliferation and remodeling let us focus on the first phase of wound healing which is hemostasis immediately after injury disruption of blood vessels leads to hemostasis the key players in this stage are platelets and clotting factors which normally circulate in the blood hemostasis involves vasospasm vessel constriction platelet plug formation and activation of the coagulation system the final product of all of this is a fibrin mesh in addition to achieving hemostasis the fibrin mesh serves as scaffolding for the migration into the wound of inflammatory cells such as polymorphic Lucy which are your neutrophils and monos sites or macrofagos platelets release a number of substances which help initiate wound repair such as platelet derived growth factor transforming growth factor beta platelet activating factor and fibronectin platelets also releases serotonin facilitating cell Migration by increasing vascular permeability in addition injured endothelial and tissue immune cells release prostaglandins and cyto kindes which promote the inflammatory response the inflammatory response being an increase in adhesion molecules to allow infiltration of inflammatory cells cyto kindes to to attract the inflammatory cells and also it causes vasod dilation and increases vascular permeability to facilitate the transport of the inflammatory cells and this all will lead to our second phase of wound healing which is inflammation in inflammation the key players are the neutrophils and the macrofagos neutrophils are the first inflammatory cells that infiltrate the wound C peing at 24 to 48 hours the primary role of neutrophils is phagocytosis which is eating of things such as the bacteria and tissue debris macrofagos is the most important regulatory cell in the wound healing inflammatory phase typically they appear in the wound sight 72 hours after the injury macrophages are very important in wound healing as they play many roles including fagy yosis of bacteria and tissue debris Recruitment and activation of fiber blasts endothelial cells and more inflammatory cells angiogenesis which is the formation of new blood vessels and lastly as we will soon find out promoting The extracellular Matrix synthesis which is important to create new tissue basically this leads to our third phase of healing which is proliferation during the proliferative phase a new vascular bed is formed to provide oxygenated blood to the wound and the wound fills then with granular tissue the key players here are the cells that have been recruited and have proliferated thanks to the cyto kindes released by The macrofagos during the inflammatory phase these cells include fibroblasts endothelial cells and in skin injury keratinocytes the proliferative phase can be subdivided into three major processes angiogenesis granulation and reepithelialization in angiogenesis the endothelial cells proliferate extensively forming new blood vessels and this process is promoted by cyto kindes and growth factors such as tumor neosis Factor Alpha transforming growth factor beta and Vascular endothelial growth factor angiogenesis is essential to successful wound healing in granulation which is the second step growth factors such as platelet drop growth factor and transforming growth factor beta attract fiber blasts to the wound and fiber blasts are the cells which produce the granulation tissue fiber blasts proliferate and form this Matrix consisting of adhesive proteins proteoglycans and glycosaminoglycan gel as well as fibrous proteins such as collagen and elastin and these components are essential for new Matrix formation and tissue repair granulation tissue the third is reepithelialization after the provisional Matrix has been formed the surrounding keratinocytes will facilitate reepithelization by proliferating and migrating across the damaged area to reestablish barrier function the Final Phase of wound healing is the maturation or remodeling the primary purpose of the remodeling phase is the formation of new epithelium and scar tissue and this process can take up to a year to complete the main players here are the fibroblasts and their evolution called the myofibroblasts firstly remodeling involves a balance of Matrix accumulation as well as later dampening The Matrix formation and actually causing Matrix to break down essentially during the remodeling process fiberblast will alter the extra cellular matrix that is produced they will transform to myofiber blasts and then they will undergo apoptosis or cell death myofiber blasts are quite amazing they are capable of Contracting as they contain actin filaments the contraction of the myofiber blasts and the alteration in The Matrix material produces the scar tissue scar remodeling will continue for many months 6 to 12 months after the injury gradually the cells in the scar will undergo apoptosis resulting in a mature avascular and a cellular Scar and so that completes wound healing and the four phases but it's important to know that there are so many factors that can lead to impaired healing and these factors can be divided into local factors or systemic factors local factors include the wound type the wound size and location if there's a pressure on the wound if there's edema or dehydration the blood supply to the wound if there's an underlying infection or foreign material systemic factors include increasing age certain medications such as the use of steroids or antibiotics comorbidities including diabetes hot failure and obesity as well as nutritional deficiency specifically vitamin C now focusing on skin wounds or cutaneous wounds specifically there are two main types of healing there's primary intention or secondary intention primary intention is where the edges are sutured or stapled close and the wound heals quickly with minimal tissue loss this typically occurs during surgery healing by secondary intention occurs when the sides of the wound are not opposed therefore healing must occur from the bottom of the wound upwards in healing by secondary intention the wound heals through a process that includes granulation tissue formation and reepithelialization specifically secondary intention wound healing is commonly done after an excessive loss of soft tissue such as major trauma or severe burns myofiber blasts play a major role in this type of wound healing so in summary wound healing involves four phases hemostasis inflammation proliferation and remodeling we discussed factors that could impair wound healing local factors and systemic factors