apoptosis & necrosis

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The difference between apoptosis and necrosis

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  • 1. Which to choose?Apoptosis or Necrosis

2. Apoptosis (Gr. apo, off + ptosis, a falling). highly regulated cellular activity occurs rapidly and produces small membrane-enclosedapoptotic bodies, undergo phagocytosis by neighbouring cells ormacrophages. BUT cells undergoing necrosis as a result ofaccidental injury. 3. Desire to have Apoptosis Apoptotic cells: do not rupture andrelease none of their contents. release of cellular components causes a rapidseries of local reactions & cause inflammatoryresponse. In DNA Damaged Cells; such response isundesirable. Apoptosis occurs rapidly and eliminate the cellwithout repercussions. 4. A few examples Inside the thymus, T lymphocytes that mayreact against self-antigens receive signals thatactivate the apoptotosis. In the mature ovary, apoptosis happen in boththe monthly loss of luteal cells and removal ofexcess occytes + follicles. Plays an important role in formation of thecentral nervous system. Eliminating cells because of: lack of nutrients,by damage by free radicals; radiation, or by theaction of tumor suppressor proteins Note: First discovered in embryos, whereapoptosis is an essential for morphogenesis.Quicker than Mitosis; no traces. 5. How it happens? Most cells of the body can activate theirapoptotic program when major changesoccur in their DNA Ex: mutations accumulate in the DNA.prevents the proliferation to form atumour. Malignant cells deactivate the genesthat control the apoptotic process, thusavoiding death and allowing cancerprogression. 6. The Process1. Loss of mitochondrial function2. Fragmentation of DNA3. Shrinkage of nuclear and cell volumes4. Cell membrane changes5. Formation and phagocytic removal of theseapoptotic bodies 7. 1- Loss of mitochondrial functionI. Mitochondrial membrane integrity is notmaintained,II. End of normal activityIII. release of cytochrome c into the cytoplasmIV. Activates proteolytic enzymes(caspases).V. Initial caspases activate a cascade of othercaspases, resulting in protein degradationthroughout the cell. 8. Step 2&32- Fragmentation of DNAI. Endonucleases are activatedII. They cleave DNA between nucleosomes intosmall fragments.3- Shrinkage of cell and volume:Small dark-stained (pyknotic) nucleican sometimes be identified withthe light microscope 9. 4-Cell membrane changesI. The integrity of the plasmalemma ismaintained,II. cell undergoes dramatic shape changes,such as "blebbingIII. Phospholipids normally found only in the innerlayer move to the outer layer, serving assignals to induce phagocytosis. 10. (A) in epithelium of a villus from the lining of the small intestine (a), ina corpus luteum beginning to undergo involution (b), and epithelium ofa uterine endometrial gland at the onset of menstruation (c). X400.H&E. 11. Necrosis Caused by microorganisms, viruses,chemicals, and other harmful agents. Necrotic cells swell; their organellesincrease in volume; and finally they burst,releasing their contents into theextracellular space. Macrophages engulf the debris of necroticcells by phagocytosis and then secretemolecules that activate otherimmunodefensive cells to promoteinflammation. 12. ReferenceJunqueira's Basic Histology 12th ed.

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