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REPAIR OF
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REPAIR OF INJURIES In the See also:process of inflammation we have a See also:series of reactions on the See also:part of the tissues, and fluids of the See also:body, to counteract the See also:ill effects of irritation or injury, to get rid of the cause, and to repair its results. Injury and loss of See also:tissue are usually followed by repair, and both the destructive and reparative changes are, as a See also:rule, classified under the See also:term inflammation. The irritants may be bacteria and their toxins, or they may be See also:mechanical, chemical or thermic. We do not now concur with the old view that inflammation was essentially an injurious process; rather do we look upon it as beneficial to the organism. In the various reactions of the tissues against the exciting cause of the injury we see a striking example of a beautifully organized See also:plan of attack and See also:defence on the part of the organism. In some of the infective conditions the conflict fortifies the organism against future attacks of the same nature, as for example in the See also:immunity following many of the acute infective diseases. This acquired immunity is brought about by the development of a protective body as a result of the struggle of the cells and fluids of the body with the invading bacteria and their toxins. This resistance may be more or less permanent. If the invasion is due to a pus-producing micro-organism which settles in some See also:local part of the body, the result is an See also:abscess (fig. 25, P1. II.). Abscesses.—One can easily demonstrate all the actions and reactions which take See also:place in this See also:form of acute inflammation. In such a conflict one can see the presence of these See also:minute but dangerous foes in the tissues. At once they proceed to make See also:good their hold on the position they have secured by secreting and throwing out toxins which cause more or less injury to the tissues in their immediate neighbourhood. These micro-organisms having found in the tissues everything favourable for their needs, rapidly multiply and very soon produce serious results. At this point one's See also:attention is focused on the wonderful reactions possessed by the healthy tissues tc ^ombat these evil influences. In a very See also:short See also:period—within three or four See also:hours after infection-there appears to have been a See also:message conveyed to the defenders of the body both as to the point of attack and the nature of the invasion. There is thus brought into See also:play a series of processes on the part of the tissues—the vascular inflammatory changes—which is really the first move to neutralize the malign effects. We find at this See also:early See also:stage oedema of the part. This is an increased exudation of fluid from the engorged See also:blood vessels which not only dilutes the toxins, but is supposed to contain substances which in some way See also:act on these living micro-organisms and render them a more easy See also:prey to the polymorpho-nuclear leucocytes (fig. 23, Pl. II.)—cells that are motile and extremely phagocytic to these bacteria. At this stage the rapidity of the blood circulation has become greatly diminished. The polymorpho-nuclear leucocytes are seen in See also:great See also:numbers in the blood vessels. In See also:health these cells, belonging to our first See also:army of defenders, are found continually circulating in the blood stream in fairly large numbers; they are ever ready to See also:rush to the point of attack, where they at once leave the blood stream by passing through the See also:vessel walls—See also:emigration—into the tissues of the danger See also:zone. There they show marked See also:phagocytosis, attacking and taking up into their interior and destroying the micro-organisms in large numbers. At the same See also:time large numbers of these cells perish in the struggle, but even the See also:death of these cells is of value to the body, as in the process of breaking down there are set See also:free ferments which not only act detrimentally to the bacteria, but also may stimulate the bringing forward of another form of See also:cell defenders—the mononuclear leucocyte. To replace this cellular destruction there has been a demand for reinforcements on the See also:home centres of the polymorpho-nuclear leucocytes—the See also:bone marrow. This See also:call is immediately answered by an active proliferation and steady maturing of the myclocytes in the narrow to form the polymorpho-nuclear leucocytes. These then pass into the blood stream in very large numbers, and appear to be specially attracted to the point of injury by a See also:positive chemiotactic See also:action. This phenomenon, called chemiotaxis, has been studied by several investigators. See also:Leber experimented with several chemical compounds to find what reaction they had on these cells; by using See also:fine See also:glass tubes sealed at the See also:outer end and containing a chemical substance, and by introducing the open end into the blood vessels he found that the leucocytes were attracted—positive chemiotaxis—by the various compounds of See also:mercury, See also:copper, turpentin, and other substances. That See also:quinine, See also:chloroform, See also:glycerin, See also:alcohol, with others, had no attractive See also:influence on them—negative chemiotaxis. It was also found that a weak See also:solution may have a marked positive attraction whilst a strong solution of the same substance will have the opposite effect. It has been proved that the pyo-genic bacterial toxins, if not too concentrated, will attract the polymorpho-nuclear leucocytes, but if concentrated, may have a repelling influence. Then we have the See also:property of See also:adaptation, in which the negative reaction may be changed into a positive; a given toxin may at first repel the cell, but by a See also:gradual process the cell becomes accustomed to such a toxin and will move towards it. On reaching the vicinity they leave the blood stream and join in the warfare—many performing their See also:function of phagocytosis (q.v.), others falling victims to the toxins. The tissues of the part become disorganized or destroyed, and their place is taken by the See also:mass of warring cellular elements now recognized as pus.
As soon as the fluids and the polymorpho-nuclear leucocytes have succeeded in diminishing the virulence of the micro-organism, the second See also:line of defenders—the large mononuclear leucocytes (fig. 23, Pl. II.) make their See also:appearance at the See also: They are seen pushing their way right into the field of conflict and greedily ingesting both See also:friends and foes. The first defenders, the polymorpho-nuclear leucocytes, having performed their functions, are of no more use to the organism and are therefore removed by the mono-nuclear phagocytes as useless material (fig. 3t, PI. III.). The tissues having now mobilized an army that completely surrounds the fighting zone, there is a gradual and See also:general advance made from all sides. The vanguard of this advancing army is composed of a more or less compact layer of the mono-nuclear phagocytes (polyblasts) accompanied by numerous new vessels. These phagocytic cells carry out the See also:complete removal of all the injured warring elements and the damaged tissues of the part. The vessels are only temporary channels by which is brought forward the See also:food See also:supply that is needed by the advancing army if it is successfully to carry on its function; they probably also drain off the deleterious fluid substances formed by the cellular disintegration that has taken place in the part. Closely on the advance of this army of phagocytes or See also:scavenger cells follows the third line of defenders, the connective tissue cells or fibroblasts. All these cells are probably of local origin and are now stimulated to make good the damage. The connective tissue cells or fibroblasts (fig. 32, Pl. III.) are seen in active proliferation around the phagocytic zone. First they are See also:round or See also:oval in shape; later they become spindle shaped, arranging themselves in layers. Then they develop definite fibrils which differentiate into fibrous laminae forming a919 zone which shuts off the abscess from the healthy tissue and so prevents the further invasion and injurious effects of the micro-organism. By the aid of the new fibroblasts this fibrous tissue zone gradually encroaches on the pus See also:area and replaces the phagocytic layer of cells as they proceed with the absorption of the pus mass (fig. 33, Pl. III.). When complete removal of the pus mass has been accomplished by the process of absorption, the damaged area is replaced by the new fibrous tissue, which later becomes condensed and forms the cicatricial or scar tissue (fig. 35, Pl. III.)—a healed abscess. Wounds.—The healing of wounds is brought about by similar processes to that seen in the See also:evolution of an abscess. If the injury be a small incised See also:wound through the skin and sub-cutaneous tissues without any septic contamination, there usually follows a minimum of reaction on the part of the tissues. As the edges of the wound are brought into accurate apposition there is little or no blood lodged between them, so that an extremely narrow See also:strip of See also:fibrin glues the cut edges together. This strip is rapidly replaced, mainly by the connective tissue cells of the adjOining tissue growing across the temporary filled See also:breach and firmly uniting the two cut surfaces. The vascular changes are practically absent in healing by first intention. Healing by second intention, or granulation, is usually seen where there has been loss of tissue, or extensive damage. The reactions of the tissues vary in degrees according to the nature and severity of the injury. In resenting such insults, a remarkable uniformity and regularity in the processes is brought about by the different cells and fluids of the healthy tissues of the body. Although we have not reached a stage of certainty regarding their origin, function and destiny, See also:recent investigations have brought forward See also:evidence to elucidate the importance of the part played by the different cells in the various types of the inflammatory process. If there be a loss of tissue brought about by severe injury to the skin and the deeper tissues, there is usually an extravasation, of blood from the severed vessels. Along with the exuded serum this fills up the breach in the tissues and the whole is rapidly formed into a fibrinous mass due to the disintegration of the polymorphonuclear leucocytes setting free their ferment. The ferment thus set free brings about the coagulation of the serum, which acts as a protective and temporary scaffolding to the injured tissues. See also:Ling between the fibrin mass and the healthy tissues is a zone ofy injured and degenerated tissue elements, the result of the trauma. As early as six hours after the injury the polymorpho-nuclear leucocytes are seen passing in large numbers from the dilated and congested blood vessels of the tissues at the margin of the wound into the injured zone, where they carry on an active phagocytosis. It is believed also that they secrete bactericidal substances and ferments which bring about the liquefaction of the fibrin and the damaged tissues—histolysis—and thus assist the process of absorption. They appear to prepare the injured zone for the coming of the next series of cells. Their function being at an end they give way to these cells which carry on the process of absorption. In a period varying from twenty-four to See also:thirty hours there is marked evidence of the removal of the degenerated cellular elements in the damaged zone by the mono-nuclear phagocytes. Numerous fibroblasts, together with polyblasts, are visible in the fibrin mass, and the vessels at the periphery of the damaged zone are now seen to be sending out offshoots which assist in the process of absorption. These vascular buds grow out in various directions as little solid projections of cells; they then become channelled and form the new but temporary meshwork. After two to four days these processes are more clearly emphasized. By these processes we reach the stage where the fibrin mass and damaged tissues have been completely removed, and replaced by a temporary vascular and cellular tissue, known as granulation tissue (fig. 34, P1. III.), which in turn has to give way to the more See also:firm and differentiated fibrous tissue. By this time the skin epithelium may have grown over the wound. After five to seven days we find the connective tissue cells taking the principal part in the See also:building up of the new permanent tissue, for at this stage there is an active proliferation of the fibroblasts. These cells of various shapes are seen in large numbers, mainly lying in a direction parallel to the new vessels and capillaries, which all run at right angles to, the wound surface. The branching processes of these cells apparently anastomose with one another and form a delicate supporting network. It is from these cells that the fine fibrillar substance is formed, and from this stage onwards—eight to fifteen days—there is a steady increase in the new fibrils, giving more See also:density to the new tissue. At the same time there is brought about an alteration in the arrangement of the position of the fibroblasts. These become spindle shaped with their See also:long See also:axis more and more assuming a position at right angles to the vessels (fig. 34, Pl. III.) ; the two edges of the wound are thus more firmly See also:bound together. As their fibrils become more developed they gradually form fibrous laminae which are laid down first in the deeper part of the wound. When this process has reached a certain stage and all the absorption necessary has occurred the new blood vessels, from the increasing pressure of the successive fibrous layers, gradually dwindle and become obliterated, i.e. at a period corresponding to the condensation of the fibrous laminae and the disappearance of the cellular See also:character of the granulation tissue. Thus is formed in the damaged area a permanent tissue known as scar tissue (fig. 35, Pl. Ill.). Fibrosis.—Where a chronic inflammatory process has taken See also:possession of an See also:organ, or, let us say, has been located in periosteum or other fibrous part, there is a great tendency to the See also:production of cicatricial fibrous tissue in mass. Thus it is laid down in large quantity in cirrhosis of the See also:liver, See also:kidney or See also:lung, and reacts upon these See also:organs by contracting and inducing See also:atrophy. The term " cirrhosis " or " fibrosis " is usually applied to such a See also:condition of organs (See also:figs. 36 and 37, Pl. IV.), that of " sclerosis " is used when such a deposition of fibrous tissue occurs within the central See also:nervous See also:system. See also:Gull and See also:Sutton asserted that in particular states of body, and more especially i`n the condition associated with cirrhotic kidney, such a fibrosis becomes general, See also:running, as they alleged it does, along the adventitia of See also:arteries and spreading to their capillaries. They supposed that it was accompanied by a See also:peculiar hyaline thickening of the arterial See also:wall, usually of the tunica intima, and hence they termed the supposed diseased See also:state " arterio-capillary fibrosis," and gave the fibrous substance the name " hyaline-fibroid." They held that the cirrhotic kidney is simply a local manifestation of a general fibrous disease. Their theory, however, has fallen into disfavour of See also:late years. Additional information and CommentsThere are no comments yet for this article.
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