Necrosis Lecture Notes PDF

Definition Pathology is the study of disease by scientific methods. The word pathology came from the Latin words “patho” & “logy”. ‘Patho’ means disease and ‘logy’ means study, therefore pathology is a scientific study of disease Cell death Cells can die by one of the following two ways: 1. Necro...

Definition Pathology is the study of disease by scientific methods. The word pathology came from the Latin words “patho” & “logy”. ‘Patho’ means disease and ‘logy’ means study, therefore pathology is a scientific study of disease Cell death Cells can die by one of the following two ways: 1. Necrosis 2. Apoptosis In necrosis, excess fluid enters the cell, swells it, & ruptures its membrane which kills it. The enzymes responsible for digestion of the cell may be derived from the lysosome of dying cells themselves and from lysosomes of leukocytes cells Necrosis occurs by the following mechanisms: A. Hypoxia B. B. Free radical-induced cell injury C. C. Cell membrane damage D. D. Increased intracellular calcium level CAUSES. OF CELL INJURY AND NECROSIS 1-Ischemic and Hypoxic Injury Ischemia, or diminished blood flow to a tissue, is a common cause of acute cell injury underlying human disease ) 2-Chemical (Toxic) Injury mercuric chloride poisoning may occur from ingestion of contaminated seafood 3-Infectious agent : viral ,bacterial ,fungal infection 4-immunologic reaction : although the immune systems defends the body against pathogenic microbs ,immune reaction can result in cell injury and tissue injury 5- genetic defect : Types of necrosis The types of necrosis include: 1- Coagulative necrosis : Cogulative necrosis most often results from sudden interruption of blood supply to an organ, especially to the heart 2 Liquefactive necrosis :Liquefactive necrosis is characterized by digestion of tissue. It shows softening & liquefaction of tissue. It occurs in suppurative infections characterized by formation of pus.  3. Fat necrosis : Fat necrosis can be caused by trauma to tissue with high fat content, such as the breast 4. Caseous necrosis : Caseous necrosis has a cheese-like (caseous, white) appearance to the naked eye. Caseous necrosis is typical of tuberculosis.  5. Gangrenous necrosis : This is due to vascular occlusion & most often affects the lower extremities and bowel called wet gangrene if it is complicated by bacterial infection which leads to superimposed liquefactive necrosis. Whereas it is called dry gangrene if there is only coagulative necrosis without liquefactive necrosis Necrosis type of cell death that is associated with loss of membrane integrity and leakage of cellular content ,largely resulting from the degradative action of enzymes on lethally injured cells The enzymes responsible for digestion of the cell may be derived from the lysosome of dying cells themselves and from lysosomes of leukocytes cells Morphology of necrosis : 1-cytoplasmic changes ,increased eosinophilia (pink stain from the eosin dye, compared with viable cells the cells are more glassy 2-Nuclear changes. Nuclear changes assume one of three patterns, all due to breakdown of DNA and chromatin. The basophilia of the chromatin may fade (karyolysis), activity. A second pattern is pyknosis, characterized by nuclear shrinkage ; karyorrhexis, the pyknotic nucleus undergoes fragmentation. In 1 to 2 days, the nucleus in a dead cell may completely disappear..  Apoptosis Apoptosis is the death of single cells within clusters of other cells. (Note that necrosis causes the death of clusters of cells.) In apoptosis, the cell shows shrinkage & increased acidophilic staining of the cell. This is followed by fragmentation of the cells. These fragments are called apoptotic bodies. Apoptosis usually occurs as a physiologic process for removal of cells during embryogenesis, menstruation, etc… It can also be seen in pathological conditions caused by mild injurious agents. Apoptosis is not followed by inflammation or calcification. The above mentioned features distinguish apoptosis from necrosis Morphologic appearance of apoptotic cells. Apoptotic cells in a normal crypt in the colonic epithelium are shown. Note the fragmented nuclei with condensed chromatin and the shrunken cell bodies