Manual of Surgery | Page 7

of muscle transplanted from animals to fill up gaps in human muscle are similarly replaced by fibrous tissue. When a muscle is paralysed from loss of its nerve supply and undergoes complete degeneration, it is not capable of being regenerated, even should the integrity of the nerve be restored, and so its function is permanently lost.
Secretory Glands.--The regeneration of secretory glands is usually incomplete, cicatricial tissue taking the place of the glandular substance which has been destroyed. In wounds of the liver, for example, the gap is filled by fibrous tissue, but towards the periphery of the wound the liver cells proliferate and a certain amount of regeneration takes place. In the kidney also, repair mainly takes place by cicatricial tissue, and although a few collecting tubules may be reformed, no regeneration of secreting tissue takes place. After the operation of decapsulation of the kidney a new capsule is formed, and during the process young blood vessels permeate the superficial parts of the kidney and temporarily increase its blood supply, but in the consolidation of the new fibrous tissue these vessels are ultimately obliterated. This does not prove that the operation is useless, as the temporary improvement of the circulation in the kidney may serve to tide the patient over a critical period of renal insufficiency.
Stomach and Intestine.--Provided the peritoneal surfaces are accurately apposed, wounds of the stomach and intestine heal with great rapidity. Within a few hours the peritoneal surfaces are glued together by a thin layer of fibrin and leucocytes, which is speedily organised and replaced by fibrous tissue. Fibrous tissue takes the place of the muscular elements, which are not regenerated. The mucous lining is restored by ingrowth from the margins, and there is evidence that some of the secreting glands may be reproduced.
Hollow viscera, like the oesophagus and urinary bladder, in so far as they are not covered by peritoneum, heal less rapidly.
Nerve Tissues.--There is no trustworthy evidence that regeneration of the tissues of the brain or spinal cord in man ever takes place. Any loss of substance is replaced by cicatricial tissue.
The repair of Bone, Blood Vessels, and Peripheral Nerves is more conveniently considered in the chapters dealing with these structures.
#Rate of Healing.#--While the rate at which wounds heal is remarkably constant there are certain factors that influence it in one direction or the other. Healing is more rapid when the edges are in contact, when there is a minimum amount of blood-clot between them, when the patient is in normal health and the vitality of the tissues has not been impaired. Wounds heal slightly more quickly in the young than in the old, although the difference is so small that it can only be demonstrated by the most careful observations.
Certain tissues take longer to heal than others: for example, a fracture of one of the larger long bones takes about six weeks to unite, and divided nerve trunks take much longer--about a year.
Wounds of certain parts of the body heal more quickly than others: those of the scalp, face, and neck, for example, heal more quickly than those over the buttock or sacrum, probably because of their greater vascularity.
The extent of the wound influences the rate of healing; it is only natural that a long and deep wound should take longer to heal than a short and superficial one, because there is so much more work to be done in the conversion of blood-clot into granulation tissue, and this again into scar tissue that will be strong enough to stand the strain on the edges of the wound.
THE TRANSPLANTATION OR GRAFTING OF TISSUES
Conditions are not infrequently met with in which healing is promoted and restoration of function made possible by the transference of a portion of tissue from one part of the body to another; the tissue transferred is known as the graft or the transplant. The simplest example of grafting is the transplantation of skin.
In order that the graft may survive and have a favourable chance of "taking," as it is called, the transplanted tissue must retain its vitality until it has formed an organic connection with the tissue in which it is placed, so that it may derive the necessary nourishment from its new bed. When these conditions are fulfilled the tissues of the graft continue to proliferate, producing new tissue elements to replace those that are lost and making it possible for the graft to become incorporated with the tissue with which it is in contact.
Dead tissue, on the other hand, can do neither of these things; it is only capable of acting as a model, or, at the most, as a scaffolding for such mobile tissue elements as may be derived from, the parent tissue with which the graft is in contact: a portion of sterilised marine sponge, for example,