Cell Injury and Cell Death - 08-10-2021 PDF

08-10-2021 Angela Bolla Sofia Bignami MOD – Cell pathology – Bonecchi Cell injury and cell death. Objectives of the lesson. List 7 common causes of cell injury; explain the difference between reversible and irreversible cell injury; describe the mechanisms of cell injury; describe patterns of necr...

08-10-2021 Angela Bolla Sofia Bignami MOD – Cell pathology – Bonecchi Cell injury and cell death. Objectives of the lesson. List 7 common causes of cell injury; explain the difference between reversible and irreversible cell injury; describe the mechanisms of cell injury; describe patterns of necrosis in tissues or organs. Cellular Responses to Stress and Cell injury. Noxious Stimuli In the last lesson we have explained how our cells, when stressed, can adapt to the stressful condition by increasing in size, or duplicating, or changing their differentiation Homeostasis: steady state state. Adaptations:And reversiblethey functionalcan adapt to the stress reaching a new and structural.changes homeostatic condition. When adaptation is not enough to overcome the stressful condition, or the cell is not able to adapt, cell injury occurs. Cell injury can also happen directly, when there is a cause of injury. Cell injury can be reversible if the cells are able to recover: the cells can go back to homeostasis. Our tissues can repair after an injury, and the repair can be complete, returning to the exact same initial homeostatic condition. In other cases, if the injury is severe or if the tissue is not able to repair, we have an irreversible injury, and as a consequence we will have either necrosis or apoptosis. Cell injury happens either when cells are stressed so much that they are not able to adapt anymore, or when they are exposed to inherently damaging agents, or when they suffer from intrinsic abnormalities (such as genetic problems). Causes of cell injury We will now describe the main causes of cell injury. 1. Oxygen deprivation. When a tissue is in a low-oxygen condition, this situation is called hypoxia. Hypoxia is a deficiency of oxygen, and it is one of the main causes of disease. The main problem in case of hypoxia is at the level of mitochondria: a reduction in aerobic oxidative respiration causes cell injury. And the causes of hypoxia may be: - Ischemia (which means a reduced blood flow in a tissue) 08-10-2021 Angela Bolla Sofia Bignami - Problems in the cardiovascular system (leading to an inadequate oxygenation of the blood) - Decreased capability of erythrocytes in transporting oxygen: this can either be due to an intrinsic genetic predisposition (as in anemic individuals) or it may secondary to another situation (like carbon monoxide poisoning) - Severe blood loss If the oxygen deprivation is mild, our cells can try to survive through adaptation. For example, when there is reduced blood flow in one of the two kidneys, the other one enlarges via the mechanism of hyperplasia. Otherwise, the other two possible consequences of hypoxia are cell injury and cell death (and the damage also depends on the cell type). 2. Physical agents. Other major causes of cell injury are various physical agents, such as: mechanical trauma, extreme temperatures, changes in the atmospheric pressure, radiation, electric shock. 3. Chemical Agents and Drugs. Many chemicals induce damage in cells, such as - - - Glucose or salt in hypertonic concentrations (electrolyte unbalance is another major cause of cell injury) Oxygen present at very high concentrations may be very toxic Poisons (such as arsenic, cyanide, mercuric salts) Environmental pollutants, insecticides, herbicides Carbon monoxide and asbestos Alcohol, which is particularly toxic for the brain (alcohol causes loss of neurons, which cannot be replaced). Therapeutic drugs (which in many cases have some side effects that may represent a cause of injury for some cell types) 4. Infectious Agents (microbiology). Viruses, bacteria, fungi, parasites. 08-10-2021 Angela Bolla Sofia Bignami 5. Immunologic reactions (immunopathology). Our immune system can cause cell injury: when you have either excessive or reduced immunological response, this can lead to many pathologies. Moreover, many diseases are of autoimmune origin, because our own immune system may react against our own cells or tissues. Inflammation is a necessary process, but it also detrimental (has many side effects), especially in the case of a chronic inflammatory disease. 6. Genetic derangements (medical genetics). Genetic abnormalities or mutations may produce different clinical phenotypes. DNA sequence variants that are common in human populations (polymorphisms) can also influence the susceptibility of cells to injury by chemicals and other environmental insults. 7. Nutritional imbalances. This is said to be the major cause of cell injury. Nutritional imbalances comprise not only deficiencies in nutrition (protein/calories deficiencies, deficiencies of specific vitamins), but also hyper nutrition. In our society a major role is played by anorexia nervosa, nutritional excesses (obesity results in the metabolic syndrome), composition of the diet (an excess intake of cholesterol and lipids can cause atherosclerosis). Cell injury principles When it comes to cell injury, we can describe three main principles: - - - The consequences of cell injury depend on the type, state, and adaptability of the injured cell. We have described many different cell types in our body that are differently able to adapt and respond to the injury. Cell injury results from different biochemical mechanisms acting on several essential cellular components. At the level of single cells there are biochemical modifications that will induce this cell injury. The cellular response to injurious stimuli depends on the type of injury, its duration and its severity. The cell starts to try to overcome the stress by adaptation, and then if the injurious stimulus persists this will lead to an irreversible injury. 08-10-2021 Angela Bolla Sofia Bignami You can think about a ‘point of no return’: when a normal cell is subjected to injury, it starts to undergo reversible changes, but after the point of no return it will undergo irreversible changes. Therefore, if the duration of the exposure to the cause of injury is short you may arrive up to the point of no return, and then go back to the normal homeostatic situation through adaptation. In this graph we have on the X axis the duration of the injury, whereas the effect of the injury on the Y axis. Before the ‘point of no return’ (dashed line in the graph) you have reversible cell injury: the cell loses progressively its function. After you have passed that point, you start to have the signs of irreversible cell injury: irreversible injury starts with the accumulation of biochemical alterations, which then lead to some ultrastructural changes (visible only with the electron microscope), and later on to changes that you are able to see on a light microscope, and then finally you can see some gross morphologic changes with naked eye. One example of irreversible injury is myocardial infarction. When you have a myocardial infarction, you have a hypoxic state in the heart which leads to irreversible cell injury and therefore cell death by necrosis. At the beginning of the infarction, you cannot see morphological changes in the patient: you can only detect biochemical alterations, measuring cardiac specific enzymes and proteins (for example, 08-10-2021 Angela Bolla Sofia Bignami inflammatory proteins) that appear in the serum of the patient within 2 hours after the oxygen deprivation. Instead, the morphological changes (visible under light microscope) take longer to appear: from 4 to 12 hours. General morphologic alterations in cell injury. When there is a reversible injury, the cell becomes bigger: there is a generalized swelling of the cell and its organelles (the ER, the mitochondria). The ribosomes detach from the ER. There is still integrity of the membrane (the cell is not ruptured and there are no pores), but there is also the extrusion of structures from the plasma membrane, called ‘membrane blebs’. Also the membrane of the nucleus is intact, but you start to see clumping of the chromatin. All these changes are mainly caused by a decreased generation of ATP due to problems in mitochondria. Instead, when the injury progresses in time and becomes irreversible you will have loss of cell membrane integrity, problems in protein synthesis, damage of the cytoskeleton and DNA damage. Tissue-specific morphology of reversible cell injury. There are two changes that are very common which are responses to a reversible injury: 1) Hydropic change (typical of the kidney) There is an accumulation of water inside the vacuoles of the cells. This occurs because when you have cell injury, you normally have problems in ATP production, so you also start to have problems in the pumps that maintain 08-10-2021 Angela Bolla Sofia Bignami the correct concentration gradient of ions through ATP hydrolysis, which leads to an accumulation of water. It still a reversible change. 2) Fatty changes (typical of the liver and myocardial cells) This is another common response of cells to a reversible injury: instead of accumulating water, these cells accumulate lipids in their vacuoles. The picture on the right depicts the gross uniform change of the liver, called ‘fatty metamorphosis’: this liver is slightly enlarged and has a pale yellow appearance, seen both on the capsule and cut surface. The picture on the left shows the histologic appearance of hepatic fatty change (reversible injury of the liver). The lipids accumulate in the hepatocytes as vacuoles. • These vacuoles have a clear appearance with H&E staining (because in the sample preparation lipids are washed away). • The most common cause of fatty change in developed nations is alcoholism. The lipids accumulate when lipoprotein transport is disrupted and/or when fatty acids accumulate. Alcohol, the most common cause, is a hepatotoxin that interferes with mitochondrial and microsomal function in hepatocytes, leading to an accumulation of lipid. Both these reversible changes are better appreciated by EM that may show blebbing of the plasma membrane, swelling of mitochondria and dilatation of ER. Necrosis. When we move from a reversible cell injury to an irreversible cell injury, this leads to a type of cell death that is called necrosis. Necrosis is an “accidental” and unregulated form of cell death, which requires damage to the cell membrane and loss of ion homeostasis. Lysosomal enzymes are released from the lysosome (its membrane is damaged), they enter in the cytoplasm and digest the cell, giving rise to a set of morphologic changes that are described as “necrosis”. When you have damage of the cell membrane, the intracellular contents is released into the extracellular space, where they elicit a host reaction: this type of cell death always happens together with 08-10-2021 Angela Bolla Sofia Bignami inflammation: because you have release of radical oxygen species that are highly inflammatory, but also of many enzymes which degrade the extracellular matrix eliciting an inflammatory response. The first cell type arriving in the site of inflammation are neutrophils (have polymorphonuclear appearance and many granules in the cytoplasm). Necrosis is the pathway of cell death in many commonly encountered injuries, such as those resulting from ischemia, exposure to toxins, various infections, and trauma. Morphologic alterations in irreversible cell injury (necrosis). The changes are produced by enzymatic digestion of dead cellular elements, denaturation of proteins and autolysis (by lysosomal enzymes). Cytoplasm - increased eosinophilia. The membrane is broken and there is formation of myelin figures: they are probably accumulations of large, phospholipid masses derived from damaged cell membranes. In the nucleus you have a nonspecific breakdown (fragmentation) of DNA leading to three different possible situations, also depending on the types of enzymes that are released: – Karyolysis (complete dissolution of the chromatin due to the release of endonucleases from lysosomes) – Karyorrhexis (destructive fragmentation of the nucleus) – Pyknosis (condensation of chromatin) It takes hours to be morphologically evident. Example: in myocardial infarction, the earliest histologic evidence becomes apparent 4 to 12 hours later. Instead, released cardiac-specific enzymes are detected in the blood as early as 2 hours after myocardial cell necrosis. Patterns of necrosis. In different cells you can have different necrotic patterns. - Coagulative necrosis This coagulative pattern of necrosis is a very common consequence of an hypoxic injury, in all tissues with the exception of the brain. The reason is that many mechanisms happening in other tissues are not happening in the brain: in other tissues after necrosis we have the repair of the tissue, so macrophages arrive in the injured tissue, start to produce molecules and attract fibroblasts that will start to create a scar with the deposition of collagen, while in the brain there is no formation of scar tissue. In coagulative necrosis you do not have the complete loss of the tissue, you have a sort of maintenance of its structure. The outline of the dead cells is maintained, and the tissue is somewhat firm (not liquid). 08-10-2021 Angela Bolla Sofia Bignami The picture above on the left depicts the typical microscopic appearance of an injured myocardium (ischemic situation): the tissue is not recognizable (the cytoplasm and cell borders are not recognizable) but its structure is somehow maintained. You can find in coagulative necrosis all the three possible modifications of DNA: pyknosis (nuclei are shrunken and dark), karyorrhexis (fragmentation of nucleus), karyolisis (dissolution of nucleus). The picture on the right shows an infarction of the kidney. It is again a coagulative pattern of necrosis. - Liquefactive necrosis This pattern is opposite to coagulative necrosis. The dead cells undergo disintegration and affected tissue is liquified (liquefaction is due to the strong action of enzymes that are released). We have this type of necrosis usually when we have bacterial infections, or also consequently to an hypoxic injury in the brain tissue (infarction). The picture on the left depicts a liquefactive necrosis in the brain in a patient who suffered a "stroke" with focal loss of blood supply to a portion of cerebrum. This type of infarction is marked by loss of neurons and neuroglial cells and the formation of a clear space at the center left. You can appreciate a ‘hole’ in the brain: the tissue is not repaired. Liquefactive necrosis of the brain may be consequent to brain abscess, caused by bacterial infection: bacteria also produce other enzymes and when you have an infection, there is the increase in production of ROSs and defense molecule, which can induce this kind of necrosis in the brain. 08-10-2021 - Angela Bolla Sofia Bignami Caseous necrosis Caseous necrosis (caseous in Latin means cheese) is a specific form of coagulative necrosis, that is typical of infections by mycobacteria, like the mycobacterium tuberculosis. The mycobacterium tuberculosis causes the formation of granuloma in tissues, normally in the lungs, and in the central part of the granuloma normally the tissue undergoes caseous necrosis (you cannot recognize the nuclei of the cells in the center, the tissue acquires a cheese-like structure). In the granuloma the predominant cells are inflammatory cells: there are many macrophages, and also Langhans cells, which are the giant multinucleated cells you can see on the bottom left part of the image; these are the typical cells of the granuloma, therefore they are very useful for diagnosis. This type of necrosis is happening not only in the lungs but also for example in lymph nodes of the lungs. - Fat necrosis This pattern is characterized by an enzymatic or traumatic damage to fatty tissue. Example: necrosis of fat by pancreatic enzymes (caused by pancreatitis). Cellular injury (which may be caused by pancreatitis) to the pancreatic acini leads to release of powerful enzymes which damage fat through the production of soaps, and these appear grossly as the soft, white areas seen here on the cut surfaces. This pattern of necrosis happens mainly in the pancreas: when there is necrosis in the pancreas, there is the release of the pancreatic enzymes. which will digest the fat and produce the typical appearance of the pancreatic tissue that you can appreciate in the left picture (whereas the one on the right depicts a normal pancreas). - Gangrenous necrosis It can be a coagulative necrosis or a liquefactive necrosis. It is normally secondary to an ischemia, usually with a superimposed infection. 08-10-2021 Angela Bolla Sofia Bignami It usually involves the lower extremities and often is a type of coagulative necrosis. For example, in this case shown in the picture on the left, the toes were involved in a frostbite injury (exposure to extremely low temperatures). This is an example of "dry" gangrene in which there is mainly coagulative necrosis from the anoxic injury (lack of oxygen causes a complete death of the tissue, even if you maintain the structure of the organ). On the other hand, you can also have liquefactive gangrenous necrosis (picture on the right), for example secondary to a lack of oxygen with a superimposed bacterial infection. It is typical of diabetic patients, because you have problems in blood supply and you may have infections superimposed with the lack of oxygen. - Fibrinoid necrosis There is the deposition of a lot of fibrin, which is the product of the coagulation cascade. So we have the formation of these fibrin fibers which are very important for coagulation. Fibrinoid necrosis is typical of vessels. This pattern of necrosis is caused by immune-mediated vascular damage (much of the immune-pathology events give rise to problems in vessels). It is marked by deposition of this fibrin-like proteinaceous material in arterial walls and this causes necrosis of the vessels. Arterial walls typically appear smudgy and eosinophilic on light microscopy. Morphologic changes secondary to injury. We have analyzed the most important morphological alterations which are typical of cell injury, both reversible and irreversible, which are well summarized in the following picture and table. 08-10-2021 Angela Bolla Sofia Bignami Remember that karyolysis, karyorrhexis and pyknosis are typical of irreversible cell injury and remember the difference between the three. Key points: ▪ Reversible cell injury: Cellular swelling, fatty change, plasma membrane blebbing and loss of microvilli, mitochondrial swelling, dilation of the ER, eosinophilia (due to decreased cytoplasmic RNA) ▪ Necrosis: Increased eosinophilia; nuclear shrinkage, fragmentation, and dissolution; breakdown of plasma membrane and organellar membranes; abundant myelin figures; leakage and enzymatic digestion of cellular contents ▪ Patterns of tissue necrosis: Under different conditions, necrosis in tissues may assume specific patterns: coagulative, liquefactive, gangrenous, caseous, fat, and fibrinoid. It is also important to remember that the consequences of cell injury depend on the type, state, and adaptability of the injured cell. For example, in different tissues of the organism there is different susceptibility to Ischemic Necrosis: - High susceptibility: for neurons (in only 3-4 minutes after an ischemic situation they die) - Intermediate susceptibility: myocardium, hepatocytes, renal epithelium (these cells take 30 min – 2hr) - Low susceptibility: fibroblasts, epidermis, skeletal muscle (many hours). Depending on the cell type you can have different effects of the injury. Biochemical mechanisms. The third important concept is that cell injury results from different biochemical mechanisms acting on several essential cellular components: all these morphological modifications we have analyzed depend on biochemical mechanisms. 1) Depletion of ATP If you have ischemic situation (lack of oxygen supply) you will have damage to mitochondria, so you will have a decreased oxidative phosphorylation and therefore decreased ATP concentration. The depletion of ATP results in many problems in cells: - Decrease in activity of ATP-dependent pumps on the cell membrane: For example, if the Na/K pump is not working well, then you have less sodium ions going out. You will therefore have influx of Na+ and efflux of K+. 08-10-2021 Angela Bolla Sofia Bignami Failure of the calcium pump leads to influx of Ca++ into the cell, activate various enzymes to the detriment of the cell. There is also influx of water inside the cell because of the generated ion imbalance. Therefore, as a consequence of the unbalanced ionic concentration, you will have cellular swelling (as a consequence of water influx due to problems in Na/K pump activity), and also swelling of organelles such as the ER, loss of microvilli, formation of blebs in the membrane. Increase in anaerobic glycolysis The depletion of ATP will also produce a change in the metabolic activity of the cells, increasing anaerobic glycolysis with loss of glycogen, accumulation of lactic acid and decrease of the pH. And the decrease of the pH interferes with enzymes activity and is the main cause of the clumping of the nuclear chromatin (that is a sign of reversible injury). Detachment of the ribosomes from the reticulum. This leads to a decrease in protein synthesis and increase in lipid deposition. If you only have a depletion of ATP, you have as a consequence these listed biochemical mechanisms, which are signs of REVERSIBLE injury. 2) Mitochondrial damage. If you have mitochondrial damage or dysfunction instead, you will have a decreased ATP generation and an increased production of reactive oxygen species (ROS, very damaging species), which will lead to multiple cellular abnormalities and eventually necrosis. The major consequences of mitochondrial damage are: - Formation of a high-conductance mitochondrial permeability transition pore (MTP). This pore forms on the membrane of mitochondria and therefore induces loss of mitochondrial membrane potential, resulting in the failure of oxidative phosphorylation. This is interesting because there is a drug, Cyclosporine, which targets the protein cyclophilin D, that is one of the structural components of the mitochondrial permeability transition pore. This drug blocks the opening of the pore on the surface of mitochondria and therefore prevents necrosis. It is mainly used as an immunosuppressive drug used, for example, to prevent graft rejection (avoid necrosis of grafted tissue). 08-10-2021 Angela Bolla Sofia Bignami But now there are also other ongoing clinical trials for using cyclosporine to reduce necrosis in other tissues, for example for ischemic myocardial injury in humans. - Production of reactive oxygen species - Leakage of pro-apoptotic proteins (mitochondria are also the starting point for the apoptotic cascade) 3) Influx of Calcium. Cytochrome C Extracellular Ca++ is normally 15X higher than cytosolic Ca++. Influx of calcium to the cytosol comes from the extracellular fluid and from Calcium stores inside the mitochondria and the endoplasmic reticulum of our cells. If the concentration of Ca++ increases, you will have the activation of many enzymes: Phospholipases: which damage cell membranes (degrading phospholipids) ATPases: which will degrade ATP (which is already depleted because of the stressful condition) Proteases: damage membrane proteins and cytoskeleton Endonucleases: damage DNA Therefore, with the increase of the Ca++ concentration inside the cell, you will have the activation of all the main mechanisms of cell death, either through severe damage to membranes of lysosomes and leakage of lysosomal enzymes or through apoptosis. This occurs particularly in hypoxia and ischemia and with certain toxins. Preventing the rise in Ca++ or restoring its concentration to normal levels prevents cell death. 4) Accumulation of Oxygen-Derived Free Radicals (Oxidative Stress). Normally their concentration is kept very low because they are very dangerous species, because they can damage all the structures we have in a cell: they can induce lipid peroxidation, protein modifications, DNA mutations. These species are released by mitochondria if they are damaged. 08-10-2021 Angela Bolla Sofia Bignami The cells of our immune system (mainly macrophages and neutrophils) are able to normally synthesize ROS to kill the pathogen, because they have a specific enzyme (NADPH oxidase). This demonstrates the danger that these species represent for a cell. Free radicals have a single unpaired electron in the outer orbit. They are highly reactive with adjacent molecules. They are usually derived from oxygen to produce reactive oxygen species, superoxide, hydroxyl radicals, H2O2, etc. ROS damage proteins, lipids, carbohydrates, nucleic acids. ROS are normally produced during cellular respiration. Protective molecules include superoxide dismutase, glutathione peroxidase, vitamin E, vitamin C, catalase. These damaged molecules may themselves be reactive species with a chain reaction being set up with widespread damage. Free radicals may be a common pathway for most types of cell damage, particularly oxygen-derived free radicals (oxidative stress). • Some examples are: – oxygen toxicity, ischemia/reperfusion injury, radiation injury (hydrolyses H2O to OH & H), metabolism of drugs, toxins, pollutants (e.g., paracetamol to reactive metabolite, cigarette smoke); – leukocyte killing of bacteria or in non-bacterial inflammations, release of iron in hemorrhages enhances oxidative stress (important in CNS), – lipid peroxidation of low-density lipoproteins in atherosclerosis, cancer production (damage to DNA), ageing. • Therapies for combating oxidative stress are available for prevention or treatment with antioxidants and/or free-radical scavengers. ROS may also cause DNA damage and therefore oxidative stress increases the predisposition to the onset of cancer. Another example which can demonstrate the detrimental effect that the excess of oxygen can have in a cell is called: ISCHAEMIA/REPERFUSION INJURY. When you have ischemic injury you have reduced ATP production, increased Ca++ concentration, … 08-10-2021 Angela Bolla Sofia Bignami But then when you have reperfusion of the tissue (you remove for example the clot/thrombus that has caused the ischemia) you may even have more damage than the ischemic initial situation. Because you will have a lot of oxygen in the cells and this induces the production of these ROS. 5) Mechanisms of membrane damage. The membrane may be damaged as we have seen because you have depletion of ATP and decreased phospholipid synthesis. The Ca++ may activate phospholipases. You can have the ROS that induce lipid peroxidation. Also the proteases can induce membrane damage by acting on membrane proteins or on proteins of the cytoskeleton (which are essential for membrane integrity). In summary, you have many mechanisms by which you can induce membrane damage. The consequences of membrane damage (not only the plasma membrane, but also the membranes of the internal organelles) are the following: • Mitochondrial membrane damage. Opening of the mitochondrial permeability transition pore, leading to decreased ATP generation and release of proteins that trigger apoptotic death. • Plasma membrane damage. Loss of osmotic balance and influx of fluids and ions, as well as loss of cellular contents. The cells may also leak metabolites that are vital for the reconstitution of ATP, thus further depleting energy stores. •Injury to lysosomal membranes Leakage of their enzymes into the cytoplasm and activation of the acid hydrolases in the acidic intracellular pH of the injured cell. Lysosomes contain RNases, DNases, proteases, phosphatases, and glucosidases. Activation of these enzymes leads to enzymatic digestion of proteins, RNA, DNA, and glycogen, and the cells die by necrosis. 08-10-2021 Angela Bolla Sofia Bignami 6) Damage to DNA and proteins. Normally DNA damage is characteristic of the apoptotic cell death. This is because DNA damage is too severe to be corrected (e.g., after exposure to DNA damaging drugs, radiation, or oxidative stress), therefore there is activation of a suicide program that results in death by apoptosis. Similar reaction is triggered by improperly folded proteins, which may be the result of inherited mutations or acquired triggers such as free radicals. Key points: Mechanisms of Cell Injury. • Mitochondrial damage: ATP depletion → failure of energy-dependent cellular functions → ultimately, necrosis; under some conditions, leakage of mitochondrial proteins that cause apoptosis • Accumulation of reactive oxygen species: covalent modification of cellular proteins, lipids, nucleic acids • Influx of calcium: activation of enzymes that damage cellular components and may also trigger apoptosis • Increased permeability of cellular membranes: may affect plasma membrane, lysosomal membranes, mitochondrial membranes; typically culminates in necrosis • Accumulation of damaged DNA and misfolded proteins: triggers apoptosis Questions. Which of the following is a morphologic alteration characteristic of irreversible cell injury? 1. Hydropic changes 2. Fatty changes 3. Blebbing of the plasma membrane 4. Swelling of mitochondria and dilatation of ER 5. Nuclear fragmentation 08-10-2021 Angela Bolla Sofia Bignami A 71-year-old woman had the loss of consciousness that persisted for over an hour. On awakening, she cannot speak nor move her right arm. Months later, a computed tomographic (CT) scan shows a large 5 cm cystic area in her left parietal lobe cortex. This CT finding is most likely the consequence of resolution from which of the following cellular events? 1. Liquefactive necrosis 2. Atrophy 3. Coagulative necrosis 4. Caseous necrosis 5. Apoptosis A 48-year-old woman has a malignant lymphoma involving lymph nodes in the para-aortic region. She is treated with a chemotherapeutic agent which results in the loss of individual neoplastic cells through fragmentation of individual cell nuclei and cytoplasm. Over the next 2 months, the lymphoma decreases in size, as documented on abdominal CT scans. By which of the following mechanisms has her neoplasm primarily responded to therapy? A Coagulative necrosis B Mitochondrial poisoning C Phagocytosis D Acute inflammation E Apoptosis Explanation: in apoptosis you have fragmentation of nuclei, but also of apoptotic bodies (so the fragmentation also of the CYTOPLASM).