1. Describe the process of tissue repair, making sure you indicate factors that influence this process.
The process of tissue repair, known as wound healing, is comprised of a continuous sequence of inflammation and repair, in which epithelial, endothelial, inflammatory cells, platelets, and fibroblasts participate (Wound). The process differs little from tissue to tissue, and with regard to the cause of the injury. The first five days are the inflammatory phase, which is initiated at the moment of injury. Traumatic wounds or surgery disrupt the tissue and cause hemorrhage, so exposure of blood to collagen initiates platelet degranulation and activation of clotting factors. Biological amplification systems are set in motion, and lead to clot formation and the accumulation of mitogens and chemoattractants at the wound site.
The production of prostaglandins and kinins leads to vasodilation and increased vascular permeability in the wound area, resulting in edema at the wound site (Wound). Circulating immune cells appear in the wound within six hours, and polymorphonuclear leucocytes (PMNs) enter the wound site to phagocytose any bacteria. The PMNs appear in the wound shortly after the injury occurs, and peak within 24 to 48 hours, after which the phagocytic activity is taken over by macrophages. The appearance of PMNs is not essential for wound healing to occur. Macrophages, which are also phagocytic, appear at the wound site within 48 to 96 hours, and remain until the wound heals, clearing bacteria and wound debris. They have a much longer lifespan than PMNs. Macrophages also release a number of chemical factors which attract other cells to the site, decontaminate and debride the wound, and release growth factors which promote granulation tissue formation to close the wound. All these transmitters are known as cytokines. T-lymphocytes appear around the fifth day.
The proliferative phase follows, and is chara...