Death and Necrosis LECTURE FIVE DR.ABDIAZIZ ABDI MOHAMED ABDI 4/10/2016

Contents Definition Death and Necrosis Macroscopic characteristic of death tissues Causes of Necrosis Necrosis and autolysis Types of necrosis Fate of necrotic tissues DR.ABDIAZIZ ABDI MOHAMED ABDI 4/10/2016

Necrosis and autolysis Autolysis is death of cells and tissues after the death of the animal (somatic death) and it should be distinguished from necrosis. DR.ABDIAZIZ ABDI MOHAMED ABDI 4/10/2016

AUTOLYSIS NECROSIS 1. No sharp line of demarcation between affected and healthy tissue 1. A line of demarcation is usually present 2. Circulatory changes like congestion and haemorrhage are not present. 2. Circulatory changes are present 3. Inflammatory changes are not present. 3. Inflammatory changes like infiltration of leukocytes are present. 4. Growth of saprophytic bacteria, bacillary rods in long chains are often present. 4. Saprophytic growth not seen, but pathogenic bacteria maybe present. DR.ABDIAZIZ ABDI MOHAMED ABDI 4/10/2016

Types of necrosis Coagulative Necrosis Liquefactive Necrosis Caseous Necrosis Fat Necrosis DR.ABDIAZIZ ABDI MOHAMED ABDI 4/10/2016

COAGULATIVE NECROSIS:- Local death of cells/ tissue in living body characterized by loss of cellular details, while tissue architecture remains intact. Most common type of necrosis. Architectural outlines persist but cellular details are lost. Type of tissue can be recognized. DR.ABDIAZIZ ABDI MOHAMED ABDI 4/10/2016

Ischemia due to thrombosis/ embolism as in infarcts. Causes: Ischemia due to thrombosis/ embolism as in infarcts. Bacterial toxins e.g. Fusobacterium necrophorum in livers in cattle. Muscular dystrophy due to deficiency of selenium and vit. E in cattle and sheep. Necrosis of renal epithelium due to poisoning from mercuric salts. DR.ABDIAZIZ ABDI MOHAMED ABDI 4/10/2016

Necrotic area is firm, opaque with cooked meat appearance. Gross appearance: Organ becomes gray/white in colour, firm, dense, depressedwith surrounding tissue. Necrotic area is firm, opaque with cooked meat appearance. It is sharply demarcated from the healthy areas. Microscopic appearance: Architectural outlines are present; cellular details are lacking. • Nucleus absent or pyknotic. • Cytoplasm becomes acidophilic. Result: Dead tissues remain in the body for a long period, ultimately removed by macrophages. DR.ABDIAZIZ ABDI MOHAMED ABDI 4/10/2016

LIQUEFACTIVE NECROSIS Local death of cells/ tissues in living body There is digestion and liquefaction of necrotic tissue. characterized by rapid enzymatic dissolution of cells. The intracellular hydrolases and proteolytic enzymes of leucocytes play role in dissolution of cells. Liquefactive necrosis: There is digestion and liquefaction of necrotic tissue. DR.ABDIAZIZ ABDI MOHAMED ABDI 4/10/2016

Causes: 1.Occurs due to toxins produced by pyogenic bacteria (staphylococci, streptococci, etc.). 2.Liquefaction also occur due the secretion of neutrophils which accumulate in the inflammatory areas as in abscesses. 3. Some chemicals like turpentine oil also attract neutrophils and cause pus formation and liquefactive necrosis. 4. The necrosis in the nervous tissue is mostly liquefactive due to high content of lipids and water. DR.ABDIAZIZ ABDI MOHAMED ABDI 4/10/2016

It is a localized collection of pus, surrounded by fibrous capsule. Gross appearance: The necrotic tissue is liquefied and filled with semisolid creamy liquid called pus. Pus: It is a thick, white or yellow, creamy liquid consisting of exudate of leukocytes, tissue debris and microorganisms. Proteolytic enzymes released from neutrophils cause liquefaction of dead cells. Abscess: It is a localized collection of pus, surrounded by fibrous capsule. Empyema: It is accumulation of pus in a body cavity. DR.ABDIAZIZ ABDI MOHAMED ABDI 4/10/2016

Microscopic appearance: No architectural or cellular details are visible in the area of necrosis. The necrotic area usually appears as a cavity containing a mass of necrotic neutrophils, bacteria and tissue debris. The entire necrotic mass is surrounded by a fibrous connective tissue capsule. DR.ABDIAZIZ ABDI MOHAMED ABDI 4/10/2016

CASEATIVE NECROSIS Local death of cells/ tissue in living body; the dead cells/ tissue is characterized by presence of firm, dry and cheesy consistency ,Dead tissue is converted into a granular mass resembling cottage cheese. . It occurs due to coagulation of proteins and lipids. DR.ABDIAZIZ ABDI MOHAMED ABDI 4/10/2016

Causes of caseous necrosis Caseous necrosis is associated with diseases in which granulomatous lesions occur such as: Tuberculosis Caseous lymphadenitis Mycotic infections, etc.). DR.ABDIAZIZ ABDI MOHAMED ABDI 4/10/2016

Gross appearance: The area of necrosis is a granular, friable, white-gray resembling cottage cheese. The caseous mass is enclosed within a connective tissue capsule. The term "caseous" is derived from the gross appearance of the necrotic tissue (white and cheesy). DR.ABDIAZIZ ABDI MOHAMED ABDI 4/10/2016

Microscopic appearance: The necrotic tissue is agranular mass enclosed inside a zone of granulomatous inflammation, containing macrophages. No architectural or cellular details are seen. Calcification commonly occurs in the necrotic areas. DR.ABDIAZIZ ABDI MOHAMED ABDI 4/10/2016

Fat necrosis: Death of adipose tissue in a living animal Fat necrosis is a distinctive type involving adipose tissue in which adipose tissue form glycerine and fatty acids combine with metallic ions (Na, K, Ca) to form soap (saponification). . There are three types of fat necrosis: Pancreatic Traumatic and Nutritional DR.ABDIAZIZ ABDI MOHAMED ABDI 4/10/2016

Pancreatic fat necrosis: Causes: Death of adipose tissue in and around pancreas. Causes: Pancreatitis and/or injury to pancreas and its ducts release lipases which attack adipose tissue in the peritoneum. Hydrolysis of triglycerides releases fatty acids which combine with calcium to produce chalky white areas (saponification). Gross appearance: Necrotic fat appears as white or yellowish chalky masses. A zone of inflammation appears around the necrotic areas. Microscopic appearance: The necrotic tissue is solid and homogenous and there are numerous small needle-shaped clefts occupied by fatty acid crystals. DR.ABDIAZIZ ABDI MOHAMED ABDI 4/10/2016

Nutritional fat necrosis: Traumatic fat necrosis: It occurs in subcutaneous adipose tissue caused by mechanical injury. Nutritional fat necrosis: This form of fat necrosis is seen in sheep and cattle with extreme debility and emaciation e.g. Tuberculosis and Paratuberculosis Large, solid, chalky white masses occur in the mesenteric adipose tissue. May interfere with passage of ingesta. DR.ABDIAZIZ ABDI MOHAMED ABDI 4/10/2016

Fate of necrotic tissues 1- Liquefaction and removal. 2- Liquefaction and cysts formation 3- Liquefaction and abscess formation. 4- Encapsulation without liquefaction DR.ABDIAZIZ ABDI MOHAMED ABDI 4/10/2016

6- Organization or replacement by scar tissue 6- Organization or replacement by scar tissue. 7- Calcification 8- Regeneration 9- Gangrene DR.ABDIAZIZ ABDI MOHAMED ABDI 4/10/2016

THANKS DR.ABDIAZIZ ABDI MOHAMED ABDI 4/10/2016