Alongside most cells there is either a basement membrane or a collagenous network made by fibroblasts that will guide the cells growth. Since ischaemia and most toxins do not destroy collagen, it will continue to exist even when the cells around it are dead. Example
Acute tubular necrosis (ATN) in the kidney is a case in which cells heal completely by regeneration. ATN occurs when the epithelial cells that line the kidney are destroyed by either a lack of oxygen (such as in hypovolemic shock, when blood supply to the kidneys is dramatically reduced), or by toxins (such as some antibiotics, heavy metals or carbon tetrachloride).Although many of these epithelial cells are dead, there is typically patchy necrosis, meaning that there are patches of epithelial cells still alive. In addition, the collagen framework of the tubules remains completely intact.The existing epithelial cells can replicate, and, using the basement membrane as a guide, eventually bring the kidney back to normal. After regeneration is complete, the damage is undetectable, even microscopically.Healing must happen by repair in the case of injury to cells that are unable to regenerate (e.g. neurons). Also, damage to the collagen network (e.g. by enzymes or physical destruction), or its total collapse (as can happen in an infarct) cause healing to take place by repair. Genetics
Many genes play a role in healing. For instance, in wound healing, P21 has been found to allow mammals to heal spontaneously. It even allows some mammals (like mice) to heal wounds without scars.
Spastic quadriplegia can be caused by a condition known as periventricular leukomalacia which results in the formation of lesions and holes in the white matter of the brain.Prior to the 26th week of maturation, the fetal brain is particularly susceptible to various toxins whose effects can ultimately hinder normal development. Exposure of the brain to infectious agents is especially dangerous because they can trigger immune responses that activate cytokines and lead to inflammation of the brain. Some infections that have been linked to the development of spastic quadriplegia include meningitis, herpes, rubella, and encephalitis. A difference in blood types between the mother and the fetus can also initiate a problematic immune response and cause brain damage. Severe jaundice, can also lead to brain damage and spastic quadriplegia due to a buildup of bilirubin in the blood.Bleeding in the brain caused by fetal strokes, blood clots, weak and malformed blood vessels, or high maternal blood pressure may also lead to brain damage causing spastic quadriplegia. Maternal infection, most specifically pelvic inflammatory disease, has been shown to increase the risk of fetal stroke.Hypoxia, lack of oxygen to the brain, can also cause damage in the cerebral motor cortex and other brain regions. This lack of oxygen can be the result of placenta malfunction, womb rupture, umbilical cord damage, low maternal blood pressure or asphyxia during labor and delivery.Children who experienced many complications during birth, such as, prematurity, insufficient oxygen, low birthweight, aspiration, head injury, or bleeding in the brain have a greater risk of developing spastic quadriplegia.