Necrosis L3 Dentists_.pdf

PRACTICAL GENERAL PATHOLOGY 3 LEC. NECROSIS THIRD YEAR COLLEGE OF DENTISTRY ACADEMIC YEAR 2024-2025 A.T : TAMEEM SHAREEF NECROSIS Is death of cells and tissues in the living animal. General causes of necrosis: Poisons and toxins: Chemical:...

PRACTICAL GENERAL PATHOLOGY 3 LEC. NECROSIS THIRD YEAR COLLEGE OF DENTISTRY ACADEMIC YEAR 2024-2025 A.T : TAMEEM SHAREEF NECROSIS Is death of cells and tissues in the living animal. General causes of necrosis: Poisons and toxins: Chemical: Strong acids, alkalies, insecticides, mercury etc. Infectious agents: Bacteria (Salmonella, Staphylococcus), viruses, fungi, protozoa etc. Circulatory disturbance: Anemia, congestion and ischemia. Mechanical injuries: Cutting, crushing and rubbing types. Physical : Extreme temperature, electricity GROSS APPEARANCE Affected areas white, gray or yellow in colour. Have a cooked meat appearance. Sharply demarcated (by red zone) from healthy tissue. In case of gangrene the area is green, orange or black ( iron sulphide) MICROSCOPIC APPEARANCE: The microscopic changes of necrosis vary with the type of necrosis. Some general changes of necrosis in the cytoplasm are: Eosinophilia: The cytoplasm stains darker red in colour. Swelling and vacuolation: The cells are swollen and contain different types of vacuoles. Changes in the nucleus: The nucleus may show condensation (Pyknosis), fragmentation (karyorrhexis) and may disappear (karyolysis). TYPES OF NECROSIS: 1. Coagulative necrosis: Most common type of necrosis. Structural outlines persist but cellular details are lost. Type of tissue can be recognized. Denaturation (coagulation) of structural and enzymic proteins blocks proteolysis.  Gross appearance: Necrotic area is firm, cooked meat appearance. It is sharply demarcated from the healthy areas. Microscopic appearance: Structural outlines are present; cellular details are lacking. Result: Dead tissues remain in the body for a long period, ultimately removed by macrophages. 2- Liquefactive necrosis: There is digestion and liquefaction of necrotic tissue. 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. Microscopic appearance: No structural 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 LIQUEFACTIVE NECROSIS 3- Caseous necrosis: Dead tissue is converted into a homogenous, granular mass resembling cheese. Cause: Associated with lesions of Mycobacterium tuberculosis and Arcanobacterium ovis, the cause of caseous lymphadinitis. Gross appearance: The area of necrosis is amorphous, granular, white-gray resembling cheese. The caseous mass is enclosed within a connective tissue capsule. Microscopic appearance: The necrotic tissue is amorphous, granular mass enclosed inside a zone of granulomatous inflammation, containing macrophages. No structural or cellular details are seen. CASEOUS NECROSIS: 4- Fat necrosis: Death of adipose tissue in a living animal. There are three types of fat necrosis …. ?! 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 FAT NECROSIS: