The Pathology necrosis and gangrene.pptx

This course is for medicine students and lecturers.

1. Necrosis and Gangrene Necrosis: is the local death of tissue within the living individual. Aetiology. (1) Poisons: are included by (a) Chemical poisons : These may be strong acids and alkalies , drugs, insecticides, fungicides, and other toxic chemicals. (b) Toxins of pathogenic organisms : The toxins (harmful products) produced by bacteria, viruses, fungi, rickettsiae , protozoa, and metazoan parasites may cause necrosis

2. (c) Plant poisons : Alkaloids produce necrosis. Forexample : Mushrooms contain a toxic glycoside, phallin , which causes renal tubular necrosis.

3. ( 2) Disturbances in circulation : (a) Ischemia or loss of blood supply results in necrosis and infarction. (b) Passive hyperaemia: causes necrosis when it persists. ( c) General anaemia : may result in necrosis (brain and liver) if the amount of oxygen and nutrient is not sufficient to maintain cellular metabolism.

4. Cont… (3) Mechanical injuries: cause necrosis when tissues are crushed or when blood supply is injured or destroyed. (4) Thermal changes: Both heat and cold can coagulate protein and cause necrosis. (5) Electric currents produced by lightning or generators may coagulate or char tissues. High voltage electric currents cause coagulation of protoplasm.

5. Cont… (6 ) X- ray and nuclear fission substances cause protoplasmic alterations that result in necrosis.

6. Types of necrosis Coagulative necrosis: This is the most common type of necrosis. preservation of the basic structural outline of the coagulated cells or tissue, for at least some days. It occurs all the body except the brain. Denutration of structural proteins and enzymatic digestion. The heart, kidney, adrenal glands or spleen are good examples. The affected tissue is firm.

7. Coagulative necrosis a

8. Causes of coagulative necrosis 1. Ischemia due to thrombosis/ embolism as in infarcts. 2. Bacterial toxins e.g. Fusobacterium necrophorum in livers in cattle. 3. Muscular dystrophy due to deficiency of selenium and vit . E in cattle and sheep. 4 . Necrosis of renal epithelium due to poisoning from mercuric salts. Gross appearance : •Necrotic area is firm, thick with cooked meat appearance.

9. Liquefactive This type of necrosis is characterized by transformation of the tissue into a liquid mass in which cellular and architectural detail is lost . degradation of tissue by the action of powerful lysosomal enzymes. This type of necrosis mostly affect nervous system because of softness and little support and their very high lipid and water content. The outolytic enzymes in cells easily convert it into liquid or semi liquid mass.

10. Cont… Macroscopically: the tissue in the area of necrosis is liquefied ; and may be watery or semisolid in consistency.

11. Liquefactive necrosis a

12. Cont…

13. (3) Caseous necrosis: Caseous necrosis is characterized by the conversion of dead tissue into a homogeneous granular mass resembling cheese , and by the absence of both architectural and cellular detail. The term ' caseous ' means cheesy (L. caseus = cheesy). Caseous necrosis is encountered mainlv with tuberculosis in animals, and caseous lymphadenitis in sheep.

14. Cont… Macroscopically , the area of necrosis is a granular amorphous material resembling cheese. The mass is dry but creamy in consistency. It is soft, friable, and white-grey in colour.

15. Caseous necrosis a

16. (4) Fat necrosis: Fat necrosis is the death of adipose tissue within the living individual. There are three types: pancreatic, traumatic, and nutritional.

17. Pancreatic fat necrosis Pancreatic fat necrosis: is the death of adipose tissue in the vicinity of the pancreas due to the action of lipases. It is caused by some injury to the pancreas or its duct. Primary or secondary tumours of the pancreas may also induce this necrosis.

18. Cont… Acute pancreatitis is the most common cause in the dog, pig, and sheep. Powerful lipases released from the pancreas destroy not only the pancreatic substance itself, but also the adipose tissue in and around throughout the peritoneal cavity.

19. 2 . Traumatic fat necrosis Traumatic fat necrosis is the death of adipose tissue in an area of mechanical injury. It commonly occurs in subcutaneous adipose tissue due to mechanical injuries during working, fighting, or exercising. Examples: in canine from dog bites.

20. 3.Nutritional fat necrosis Nutritional fat necrosis: is a necrobiotic alteration in fat that is associated with extreme emaciation and debility. This form of fat necrosis occurs in starving or debilitated animals, usually observed in cattle and sheep in tuberculosis and Johne's disease ( paratuberculosis ). The necrosis may occur throughout the body but is most common in the abdominal fat (mesenteric, omental , and perirenal ).

21. Fat necrosis a

22. Cont… a

23. Gangrene Gangrene : is the invasion and putrefaction of necrotic tissue by saprophytic bacteria. Aetiology : Gangrene is seen most often in the lungs, intestine, mammary gland, heavy muscles of the thigh and shoulder, and the extremities. (1) Lungs: Gangrene occurs most commonly from faulty drenching of medicines. The medicine is often quite irritating and injures the lung.

24. Cont… As a result of the lung injury and invasion of the necrotic tissue by saprophytic organisms, gangrene occurs. (2) Intestine: the infarction results from a verminous thrombus in the anterior mesenteric artery, or the acute local passive hyperaemia associated with a malabsorption of the viscera (torsion, volvulus , or intussusception ) may cause gangrene of the intestinal tract.

25. Cont…. (3) Extremities : Gangrene of the leg, ear, tail, wattle, or comb is associated with freezing. Freezing temperatures cause coagulative necrosis of tissue that is later invaded with saprophytic bacteria.

26. Types of gangrene Gangrene is of two types: dry gangrene and moist gangrene . Whether dry occurs or moist, depends on the amount of moisture as well as the temperature of the tissue.

27. Dry gangrene 1.Dry gangrene: is usually observed in the extremities. When necrosis occurs, circulation is no longer maintained. The necrotic tissue then gets dehydrated by evaporation and becomes dry. Since bacteria require moisture for growth, invasion and spread of bacteria in the area are slow. Besides moisture, the second determining factor for dry gangrene is temperature of the extremity.

28. Cont… When the tissue is dead and circulation absent, the part becomes cool. The growth of bacteria is suppressed. Invasion and spread of bacteria through the necrotic tissue are therefore slow. Macroscopically, the area is dry, shrivelled and appears mummified as a result of dehydration. The gangrened area is black in colour with putrid odour .

29. 2.Moist gangrene Moist gangrene occurs in the internal organs where there is an abundance of moisture and the temperature is higher. higher. With optimum conditions of moisture and warmth, the growth and spread of saprophytic bacteria are very rapid. The spread is particularly important when moist gangrene involves the intestinal tract , because numerous bacteria capable of invading the intestinal wall are contained within the contents of the intestine.

30. Cont… When the intestinal wall gets necrotic, rupture occurs and the faecal contents are discharged into the peritoneal cavity, spreading microorganisms throughout the viscera. The course of events is extremely rapid, and death occurs from septicaemia, toxaemia, and shock. Macroscopicall y, the gangrenous tissue is moist; and red, green, grey or black in colour as a result of iron sulphide formation.

31. Gas Gangrene, Malignant Oedema and Blackquarter (Blackleg ) These are specific types of moist gangrene frequently observed in humans and animals, and are due to invasion of the tissue by various clostridial organisms (Clostridium perfringens C. chauvoei , C. septicum , and C. novyi ). These organisms are inhabitants of the soil and the digestive tract. They enter into the wounds of various types, e.g., shearing, castration, docking, and ear notching. The injury to tissue results in necrosis, and in this necrotic tissue these organisms grow and multiply.

32. Cont… They produce toxins that kill the surrounding tissue. They then invade the necrotic tissue, spread throughout the body and bring about the death.

33. Postmortem change As soon as animal dies certain tissue change occur which are known postmortem change. Following factors influence the rapidity of postmortem changes: Environments: elevated summer temperature increase rate of enzymatic and bacterial activity; animals decompose very rapidly in the summer. The size of the individual : the larger animal the more rapid postmortem changes occur. This is because the larger animals require longer period of time before the body heat is dissipated.

34. Cont… 3. External insulation : thick cutaneous fur, feather, hair or wool prevents heat dissipation. As such sheep very rapidly because of insulating wool. 4. Nutritional states of the animal: fat is the insulating substance. The fatter the animal the slower will be loss of heat and the more rapid will be the rate of decomposition. Rigor mortis occurs much more rapid in fat animals than in emaciated animals.

35. Cont…. 5. species of the animal : the species of the animal also determine the character of the flesh.

36. The post mortem changes: The postmortem change are as following: Autolysis: is the digestion of tissue by their own cellular enzymes. Putrefaction: is the decomposition of tissue by enzymes of saprophytic bacteria. Rigor mortis: is the shortening and contraction of muscles which occur after death and results in stiffness and immobilization of the body. It begans the anterior portion and progress in a posterior direction(head, neck, trunk, and limbs).

37. Cont… Hypostatic congestion: is the accumulation of blood n the ventral portion of the organs and entire carcass, due to influence gravity. Pseudomelanosis : is the appearance of black, green, grey pigment in the tissue after death. Imbibition of the bile : is the yellow pigmentation of the tissue occurring in the vicinity of the gall bladder when the bile pigment diffuses into the surrounding tissues.

38. Cont… Post mortem clotting of blood: Is the coagulation of blood in the vessels after death. In the dead animal the endothelial cells begin to degenerate and liberate thromboplastin which then clots the blood with in the heart, arteries and veins. Imbibitions with hemoglobin : is the staining t=of tissue with hemoglobin. After death the erythrocytes are hemolysed by cellular and bacterial enzymes, and hemoglobin is liberated. Being soluble in body fluid, it diffuses into surrounding tissue and stains them red.

39. Cont… Postmortem emphysema : is the yellow accumulation of gas in tissue as a result of bacterial fermentation. Displacement of organs : occurs when the dead animal is rolled or moved. The intestine is the most commonly displaced.

40. Gout Gou t: is a disorder of uric acid metabolism by deposition of urate crystals in tissues. And is due to an increase the concentration of uric acid in the blood and body fluids. Elevation of the level of uric acid can be due to its over production or reduced excretion or both. Crystals of urate accumulate in the joints and excite an inflammation reaction and then cause a typical caase of gout arthritis.

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