GENERAL PATHOLOGY LABORATORY : ISCHEMIC STROKE

Group 4

Bacon, Jereel HopeChan Baquero, Vic BensonClerino, Mark ChristianIbona, HanzelJowak, HalimaNoynay, RiddleOng, Mary MadelenePidor, MaricaRamos, Walidah U.Usman, Hadja Yasmin

MEDICINE 2-A

Presentation of Case: An 81-year-old man unable to move his right arm or leg and unable to speak. The patient had a stroke about a year before with profound weakness of his left arm and leg.Brain Autopsy results: Patchy parenchymal loss and severe cerebrovascular atherosclerosis Multifocal parenchymal lesions on coronal sections of the cerebral hemispheres and some of which were centred at the depths of sulci Some lesions were granular or crumbly and some were cystic A large lesion in the left lateral frontal lobe and nearly the entire pons were simply softened

DIFFERENTIAL DIAGNOSIS

FINAL DIAGNOSISIschemic stroke- occurs when a blood vessel that supplies blood to the brain is blocked by a blood clot-presence of severe atherosclerosis-may happen in two ways: thrombotic strokeembolic stroke-symptoms muscle weakness, hemiparesis, aphasia

PATHOPHYSIOLOGY

TREATMENT AND MANAGEMENT1. Fibrinolytic Therapy fibrinolytics restore cerebral blood flow in patient and may lead to improvement or resolution of neurologic deficits. Unfortunately, fibrinolytics may also cause symptomatic intracranial haemorrhage. (ex. tPA)2. Intra-arterial Reperfusion theoretically, intra-arterial delivery may produce higher local concentration of the fibrinolytic agent at lower doses (and thus lower risk of systemic blee) and allow a longer therapeutic window.3. Antiplatelet Agents Aspirin, 323mg orally within 24-48 hours of ischemic stroke onset. The benefit of aspirin is modest but statistically significant and appears principally to involve the reduction of recurrent stroke4. Blood pressure control Thresholds for antihypertensive treatment in acute ischemic stroke patients who are not fibrinolysis candidate, are systolic blood pressure higher than 220mm Hg or diastolic pressure of 120 mm Hg. In those patients, a reasonable goal is to lower blood pressure by 15% during the first 24 hours.5. Mechanical Thrombectomy Mechanical clot disruption is an alternative for patients in whom fibrinolysis is ineffective or contraindicated.6. Medications medications for the management of ischemic stroke can be distributed into following categories: Anticoagulation Reperfusion Antiplatelet NeuroprotectivePROGNOSISIn the Framingham and Rochester stroke studies, the overall mortality rate at 30 days after stroke was 28%, he mortality rate at 30 days after ischemic stroke was 19%, and the 1-year survival rate for patient with ischemic stroke was 77%. However, the prognosis after acute ischemic stroke varies greatly in individual patients, depending on the stroke severity and on the patients premorbid condition, age, and post stroke complications.

QUESTIONS AND GUIDE TO DISCUSSION1. REVIEW THE ANATOMY AND HISTOLOGY OF THE ORGAN INVOLVEDThe brain is made of three main parts:1. Forebrain- consists of the cerebrum, thalamus, and hypothalamus (part of the limbic system).2. Midbrain- consists of the tectum and tegmentum3. Hindbrain- is made of the cerebellum, pons and medulla. Often the midbrain, pons, and medulla are referred to together as the brainstem. Cerebrum: The cerebrum or cortex is the largest part of the human brain, associated with higher brain function such as thought and action. The cerebral cortex is divided into four sections, called "lobes": the frontal lobe, parietal lobe, occipital lobe, and temporal lobe. Frontal Lobe- associated with reasoning, planning, parts of speech, movement, emotions, and problem solving Parietal Lobe- associated with movement, orientation, recognition, perception of stimuli Occipital Lobe- associated with visual processing Temporal Lobe- associated with perception and recognition of auditory stimuli, memory, and speechA deep furrow divides the cerebrum into two halves, known as the left and right hemispheres. Cerebellum: The cerebellum, or "little brain", is similar to the cerebrum in that it has two hemispheres and has a highly folded surface or cortex. This structure is associated with regulation and coordination of movement, posture, and balance. Brain Stem: This structure is responsible for basic vital life functions such as breathing, heartbeat, and blood pressure.The brain stem is made of the midbrain, pons, and medulla. Midbrain/ Mesencephalon- the rostral part of the brain stem, which includes the tectum and tegmentum. It is involved in functions such as vision, hearing, eye movement, and body movement. Pons- It is involved in motor control and sensory analysis. Important for the level of consciousness and for sleep. Some structures within the pons are linked to the cerebellum, thus are involved in movement and posture. Medulla Oblongata- this structure is the caudal-most part of the brain stem, between the pons and spinal cord. It is responsible for maintaining vital body functions, such as breathing and heart rate.

Blood Vessels of the BrainBlood is supplied to the brain, face, and scalp via two major sets of vessels: the right and left common carotid arteries and the right and left vertebral arteries.

Circle of WillisIs a part of the cerebral circulation and is composed of the following arteries: Anterior cerebral artery (left and right) Anterior communicating artery Internal carotid artery (left and right) Posterior cerebral artery (left and right) Posterior communicating artery (left and right) Basilar arteryThe cranial nerves:Twelve large nerves exit the bottom of the brain to supply function to the senses such as hearing, vision, and taste1. The Olfactory Nerve2. The Optic Nerve3. The Oculomotor Nerve4. The Trochlear Nerve5. The Trigeminal Nerve6. The Abducens Nerve7. The Facial Nerve8. The Auditory Nerve9. The Glossopharyngeal Nerve10. The Vagus Nerve11. The Spinal Accessory Nerve12. The Hypoglossal Nerve

Histology of BrainCerebellum Cortex, 40x, Scanning Objective, Silver stain

Cerebellar cortex, 400z, high power objective, Silver Stain

The brain is enveloped by a connective tissue called meninges to protect the central nervous system. It has three layers: dura mater which is the outer layer and it is closed to the skull. The inbetween is the arachnoid meninges which forms a spider-web like appearance and the inner layer is the pia matter which adheres to the brain and descends down into lines sulci.The visible layers in the cortex are the molecular layer and the granular layer with the pyramidal cells. The pyramidal cells initiate conscious motor activity. The largest is called the BETZ CELL. The dendrites of pyramidal cells collect information leading to initiation of motor impulse. The astrocytes supply nutrients to neurons and aids to the formation of blood brain barrier. The dendritic collaterals collect impulse towards the cell body and the axon conducts electrical impulses away from the cell body. Towards the center of the cerebrum is the medulla which has the white matter.Cerebellum, 40x, scanning objective, silver stain

Cerebellar cortex, 100x, Low power objective, Silver stain

The structure of the cerebellum is more refined and the sulci is deeper and also the gyru is narrower. It is also called folia. There three layers visible in the cerebellar cortex: Molecular layer, Purkinje cell layer and the granular layer. The purkinje cell layer controls motor movement. It has a GABA neurotransmitter which has inhibitory actions which reduces transmission of nerve impulse.

2. Understand how these cells respond to injury Cellular AdaptationsNew and altered steady states may be achieved with excessive physiologic stress or some pathological stimuli. Adaptations are reversible changes in the size, number, phenotype, metabolic activity, or functions of cells in response to changes in their environment. Such adaptations may take several distinct forms:1. Hypertrophy- refers to an increase in the size of cells that result in an increase in the size of the affected organ.2. Hyperplasia- is defined as an increase in the number of cells in an organ or tissue in response to a stimulus.3. Atrophy- is defined as a reduction in the size of an organ or tissue due to a decrease in cell size and number.4. Metaplasia is a reversible change in which one differentiated cell type (epithelial or mesenchymal) is replaced by another cell type.

Cellular SwellingThis is usually an early and common manifestation of non-lethal hypoxic injury.This is caused by the failure of Na+, K+-ATPase; resulting in sodium entering the cell and potassium leaving, and an isosmotic gain of water.The endoplasmic reticulum balloons out as does the mitochondria.This increase in water volume is known as "hydropic change" or "vacuolar change" if there is a formation of vacuoles.These changes are reversible if oxygenation is restored. Intracellular AccumulationsVarious substances can accumulate in cells and sometimes result in cell injury.This sort of cell injury is usually reversible. However, depending on the intensity and duration of the accumulation, it may become irreversible.

Cell DeathWhen the injury to the cell is irreparable, it will eventually lead to cell death.There are two important patterns of cell death: Apoptosis- is a pathway of cell death that is induced by a tightly regulated suicide program in which cells destined to die activate intrinsic enzymes that degrade the cells own nuclear DNA and nuclear and cytoplasmic proteins. Necrosis- Necrosis has been considered an accidental and unregulated form of cell death resulting from damage to cell membranes and loss of ion homeostasis.

3. Given the gross finding of the organ, identify type of necrosis involved in this caseLiquefactive necrosis (or colliquative necrosis) A type of necrosis which results in a transformation of the tissue into a liquid viscous mass.[1] Often it is associated with focal bacterial or fungal infections. In liquefactive necrosis, the affected cell is completely digested by hydrolytic enzymes, resulting in a soft, circumscribed lesion consisting of pus and the fluid remains of necrotic tissue. Dead leukocytes will remain as a creamy yellow pus.[1] After the removal of cell debris by white blood cells, a fluid filled space is left. It is generally associated with abscess formation and is commonly found in the central nervous system. For unclear reason, hypoxic death of cells within the central nervous system can result in liquefactive necrosis. This is a process in which lysosomes turn tissues into pus as a result of lysosomal release of digestive enzymes. Loss of tissue architecture means that the tissue can be liquefied. This process is not associated with bacterial action or infection. Ultimately, in a living patient most necrotic cells and their contents disappear.Cystic parenchymal lesion

Granular parenchymal lesion

Severe Cerebrovascular Atheroscleros

5. Discuss the mechanism of cell injury and cell death with emphasis to ischemic cell injury?Upon brain autopsy, there were severe cerebrovascular atherosclerosis.Atherosclerosis happens when there is a damage to the endothelium caused by high blood pressure, smoking, or high cholesterol causing an entry of LDL into the walls of the artery. When this happens the white blood cells are originally sent by the body's immune system to clean up LDL cholesterol pockets. When they stick to an artery they secrete a molecule called netrin-1, this stops normal migration of the macrophages out of the arteries. As a result, what you have left is a mixture of clumped up cholesterol pockets and white blood cells, this is the plaque that can disrupt blood flow.LEADING TO: Hypoxia (= decrease of oxygen supply) -most common cause of cell injury-occurs usually as a result of ischemia (= loss of blood supply), which occurs for example when arterial flow suffers from atherosclerosis or thrombotic occlusion of arteries - most common cause of hypoxia -is due to inadequate oxygenation, for example in cardiorespiratory failure-is caused by loss of oxygen-carrying capacity of the blood, either due to anemia (decreased capacity of the blood for oxygen), or after poisoning with carbon monoxide (CO)= loss of the carrying capacity of the blooddepending on the severity of hypoxia- the cell may undergo -adaptation-injury-cell death

As the oxygen tension within the cell decreases, there is loss of oxidative phosphorylation and decreased generation of ATP. The depletion of ATP results in failure of the sodium pump, with loss of potassium, influx of sodium and water, and cell swelling. There is progressive loss of glycogen and decreased protein synthesis. There may be severe functional consequences at this stage. If hypoxia continues, worsening ATP depletion causes further morphologic deterioration. The cytoskeleton disperses, resulting in the loss of ultrastructural features such as microvilli and the formation of "blebs" at the cell surface. "Myelin figures," derived from plasma as well as organellar membranes, may be seen within the cytoplasm or extracellularly. They are thought to result from dissociation of lipoproteins with unmasking of phosphatide groups, promoting the uptake and intercalation of water between the lamellar stacks of membranes. At this time, the mitochondria are usually swollen, owing to loss of volume control by these organelles; the endoplasmic reticulum remains dilated; and the entire cell is markedly swollen, with increased concentrations of water, sodium, and chloride and a decreased concentration of potassium. If oxygen is restored, all of these disturbances are reversible.

6. Discuss the causes of cell injury with emphasis to this particular case. Is this reversible or irreversible?

If ischemia persists, irreversible injury and necrosis ensue. Irreversible injury is associated morphologically with severe swelling of mitochondria, extensive damage to plasma membranes, and swelling of lysosomes. Large, flocculent, amorphous densities develop in the mitochondrial matrix. Death is mainly by necrosis. After death, cell components are progressively degraded, and there is widespread leakage of cellular enzymes into the extracellular space and, conversely, entry of extracellular macromolecules from the interstitial space into the dying cells. Finally, the dead cell may become replaced by large masses composed of phospholipids in the form of myelin figures. These are then either phagocytosed by other cells or degraded further into fatty acids. Calcification of such fatty acid residues may occur with the formation of calcium soaps.

7. Describe the morphologic alterations in cell injury. What are the different patterns of tissue necrosis?Morphology of cell injury 1.- Ultrastructural changes include:cellular swelling - it is near-universal manifestation of cell injuryformation of cytoplasmic blebs and distortion of microvillideterioration of cell attachments

mitochondrial changes- occur very rapidly in ischemic injury, but are delayed in some types of chemical injury.early after ischemia- swelling of mitochondrias due to changes in ionssmall to large size amorphous densities in mitochondrias- these consist of lipids or lipid-protein complexes- dense granules rich in calcium (appear early after reperfusion)endoplasmic reticulum- changes of ER occur early after injury due to changes in ion and water regulation - detachment of ribosomes and disaggregation of polysomes -result in decrease of proteosynthesisprogressive fragmentation of ER - results in formation of myelin figures - derived from plasma and organelle membranes (lipoproteins)alterations of lysosomes in cell injury- generally appear laterlysosomes become swollen, and after the onset of lethal injury lysosomes rupture and this event causes leakage of the lysosomal enzymes at this stage= irreversible cell injuryheterophagy- is the uptake of materials from the external environment by phagocytosis.examples: phagocytosis and degradation of bacteria by leukocytes, removal of necrotic debris by macrophages, reabsorption of protein autophagy- is the phagocytosis by lysosomes of deteriorating intracellular orgtanelles, including mitochondria and endoplasmic reticulum. Autophagy is particularly pronounced in cells undergoing atrophy. Lysosomes with undigested debris- are called autophagic vacuoles and may persist within the cells as residual bodies or may be extruded from the cell

2- Light microscopic changes.Reversible changes-in classic pathology nonlethal injury to cells were termed degenerations, dystrophies, but today it is common to designate them reversible injuries or regressive changestwo patterns can be recognized by light microscopy: 1-cellular swelling- appears whenever the cell is not capable of maintaining ionic and water homeostasisit is near-universal change in cell injury-is the first manifestation of cell injury-it may be sometimes difficult to appreciate with the light microscopy alone, better evident at the level of organ-grossly: the organ becomes paler, it shows an increased turgor, increased weightmicroscopically: enlargment of cells- if water continues to accumulate-small clear vacuoles appear within the cytoplasm (=distended segment of ER) =hydropic change or vacuolar degeneration, for example: epithelial cells of renal tubuli

2-fatty change- is more often encountered in the cells involved in fat metabolism, such as hepatocytes - Not so universal reaction as cell swelling. - refers to any abnormal accumulation of fat within parenchymal cells-different mechanisms account for fatty change - later will be discussed-fatty change is most commonly seen in the liver, heart, muscle,etc.-although fatty change is an indicator of nonlethal injury, in many situations is encountered in cells adjacent to those that have died and undergone necrosis

Cell death is an irreversible change in the cell associated with its endWe can distinguish two different types of cell death, that differ one from another in many aspects, particularly-in morphologic changes-in pathogenesis they have different causes different meaning and significanceThese are-apoptosis -necrosis

TYPES OF CELL DEATH - necrosis and apoptosis

APOPTOSIS-Distinctive type of cell death- occurs in physiological and embryological processes and appears to be a phenomenon whereby tissues control cell population numbers-apoptosis also occurs in pathological processes, such as inflammation and cancer, in an attempt by the body to arrest cell proliferation and tissue damage-Apoptosis- recognized as special type of cell death only recentlyApoptosis- should be differentiated from common necrosis- differs both in its biochemistry and in its morphologyIts designation apoptosis- it is a word from Greek language, which originally refers to falling of leaves from trees in the autumnSequence of events in apoptosis1- elevation of cellular calcium and rapid reduction of volume of the cell2- activation of calcium-dependent enzyme endonuclease which cleaves DNA3- fragmentation of DNA and marked condensation of both nucleus and cytoplasm4- formation of apoptotic bodies- small apoptotic bodies are composed of fragments of nuclei with condensed chromatin, larger apoptotic bodies are composed of both fragments of nuclei and condesed cytoplasm with preserved organelles5- apoptotic bodies are rapidly phagocytosed by epithelial cells in neibourghood or by macrophages - cell dying by apoptosis are recognized and phagocytosed soon after initiation of apoptosis ( role of vitronectin receptor- belongs to the family of so called integrins= adhesive cell surface and extracellular matrix proteins with important functions in cell-cell and cell-matrix interactions)Morphologic changes in apoptosisrapid volume reduction and formation of cytoplasmic blebs -shrinkage necrosisloss of cell - cell contactsformation of apoptotic bodiesphagocytosis of apoptotic bodies by macrophages, within which they undergo hydrolytic phagocytic degradationSignificance of apoptosis= programmed cell death, cell suicide, since it appears as apparently active process- it requires energy and protein synthesis. Apoptosis is dependent on gene activation and new protein synthesis. It is thought that the process is regulated by a number of apoptosis-associated genes. These include bcl-2 protein, which inhibits apoptosis and therefore extends cell survival, p-53 protein which normally stimulates apoptosis but mutated or absent favors cell survival.-it requires activation of enzymeapoptosis seems to be responsible for cell destruction in numerous physiologic events -apoptosis leads to removing of unwanted cellsphysiological apoptosis:occurs in a number of situations-is involved in normal tissue turnover-in hormone-induced atrophy (endometrium in menstrual cycle, mammary gland in menopause)- in developing tissues,-programmed cell destruction in embryogenesis, for example formation of digitspathological apoptosis:apoptosis may be involved in response to pathologic stimuli, -such as viral infection (for example- Councilman bodies in liver cells in viral hepatitis)-tumor regression induced by chemotherapy-probably the most interesting aspect is spontaneous occurrence of apoptosis in solid tumors of various types which is now being studied very intensively - involvement of apoptosis in tumor growth

necrosis is the most common pattern of cell deathin contrast to apoptosis- necrosis may be defined as the morphologic changes that following the cell death in a living tissue or organ resulting from the progressive degradative activity of catalytic enzymes These enzymes are derived either from dying cells themselves= autolysisor from lysosomal enzymes of leukocytes, referrred to as= heterolysis-Apoptosis is a death of isolated cell/cells and typically is not associated with tissue reaction, in contrast morphologic changes of necrosis are typically caused by tissue reactivity, such as active increase in blood supply of the tissue surrounding necrosis,-infiltration of the vicinity of necrotic area by inflammatory cells, especially by leukocytes-circumscription of the necrotic focus and subsequent healing

Necrosis is the sum of the morphologic changes that follow cell death in living tissue or organ.These changes result from progressive degradative activity of enzymes of lethally injured cells (autolysis and heterolysis) on one hand side- and denaturation of structural proteinstwo principal processes influence the changes of necrosis:1-enzymatic digestion of the cell2-denaturation of proteins

DEAD CELL MORPHOLOGY: cytoplasm- increased eosinophilia-attributable in part to the loss of normal cytoplasmic basophilia caused by the RNA and in part by increased binding of eosin to denatured intracytoplasmic proteinsmore glassy appearance of the cell cytoplasm-due mainly to the loss of glycogen particles nucleus- nuclear changes can be reversible -clumping of the chromatin with large aggregates attached to the nuclear membrane or irreversible-1.- pyknosis = nucleus progressively shrinks and becomes dense mass of tightly packed chromatin2.- karyolysis = progressive dissolution of nuclear chromatin due to action of DNAases of lysosomal origin3.- karyorrhexis = nucleus may break up to many clumpsCauses of necrosis:Identical as those of cell injury in general terms, such as mechanical, chemical, physical, infectious agents, and hypoxia/anoxia

MORPHOLOGICAL TYPES OF NECROSIS 1.- COAGULATIVE NECROSIS-most common pattern of necrosis, is characteristic of hypoxic cell deathmacroscopic appearance: firm consistency, yellowish colour, dry appearance of the cut section-this pattern of necrosis-most commonly results from sudden severe ischemia (is encountered mostly in solid organs, such as kidney, heart, spleen, adrenal gland)pathogenesis: Coagulative necrosis implies preservation of the basic outline of coagulated cells for several days- nucleus usually disappears, but the shape of cell is preserved-Presumably, the pattern of coagulative necrosis results from severe intracellular acidosis which denaturates not only of structural proteins, but also enzymes (this block rapid proteolysis of the cell)finally, the necrotic cell breaks into fragments that are removed by phagocytosis of the cellular debris (by proteolytic enzymes of leukocytes and macrophages, immigrating into the necrotic focus)The best example of coagulative necrosis- myocardial infarctiongross appearance of acute myocardial infarct changes with timefewer than 8-10 hours- ischemic area is slightly paler, hardly discernableeven early infarct can be visualized by various histochemic reactions that may show depletion of oxidative enzymes from infarcted area microscopic appearance - in early acute infarction- cell swellingpyknosis, eosinophilia of cytoplasmby 18-24 hours -the infarct becomes apparent grossly - pale, more sharply circumscribed, hyperemic border- microscopically: total necrosis with loss of nuclei, heavy infiltrate of leukocytes, macrophagesby 3-7 days -more apparent hyperemia at the border of infarct, yellow-brown color, soft consistencyend of 1st week - infarct becomes circumscribed by highly vascularized scar tissue microscopically: there is a prominent fibrovascular reaction in margins6th week - total replacement by scar = myofibrosis

2. LIQUEFACTIVE NECROSIS-results from the rapid action of hydrolytic enzymes and occurs always when autolysis and heterolysis prevail over denaturation of proteins-characteristic of ischemic necrosis of brain, pancreasalso common in bacterial lesions - due to activity of enzymes of bacterial and leukocytic origin good example of liquefactive necrosis is brain infarctiongross morphology- necrotic area becomes very soft and fluidy- these changes are first detectable at about 12 hourswithin 2-3 day softening and discoloration become more apparentin large infarcts- there is marked swelling, tissue liquefaction results in subsequent pseudocystic degenerationno fibrous scar is formed, necrotic area changes into postmalatic pseudocyst (postnecrotic pseudocyst) =cystic space filled with debris, fluid

3. FAT NECROSIS-this refers to necrosis in adipose tissue -due to action of activated lipasesmost common-in acute pancreatic necrosis, in which active pancreatic enzymes cause focal necrosis of the pancreas and the adipose tissue throughout the abdomen-lipases are activated and released and destroy not only pancreatic tissue itself but also fat cells in the pancreas and also fat cells throughout the peritoneal cavity - Balser necrosis= sharply circumscribed foci of enzymatic necroses of fat tissue with shadowy outlines surrounded by a zone of inflammationthe released fatty acids then complex with calcium to create calcium soapsto the naked eye the necrotic foci appear opaque and chalky white or yellowish

4. CASEOUS NECROSIS-another distinctive type of necrosis that is a combination of coagulative and liquefactive necrosis. It is encountered in tuberculousis.Gross morphology:caseous necrosis appears grossly as soft, friable, whitish-gray debris resembling cheesy materialhence the term caseous necrosis.This appearance has been attributed to the specific lipopolysaccharides of the capsule of the agent, tuberculous bacillus (Mycobacterium tuberculosis)- the exact interactions with dead cells are not completely understood.Microscopy:Histologically, caseous necrosis appears as amorphous eosinophilic material with cell debrisThe caseous necrosis is surrounded by specific granulomatous inflammatory reaction (epithelioid histiocytes, giant cells of Langhans type, lymfocytes, plasmacytes).

5. FIBRINOID NECROSIS-is a type of connective tissue necrosis seen particularly in autoimmune disease collagen and smooth muscle are affected (for example- in polyarteriitis nodosa- fibrinoid necrosis affects blood vessel walls)-fibrinoid necrosis is characterized by loss of normal structure of collagen fibres-causing teh change of tinctorial features of collagen-bright eosinophilia which resembles fibrin- derived from plasmatic fibrinogen

GANGRENOUS NECROSIS-it is not a distinctive type of necrosis, it is a necrosis secondary modified usually by the attack of bacterial agents. The term gangrene is commonly used in clinical practise to describe a condition when extensive tissue necrosis is complicated by bacterial infection.There are three major types of gangrene:dry gangrenewet gangrenegas gangrene-dry gangrene- necrotic tissue appears black and dry and is sharply demarcated from viable tissuemost commonly it occurs in extremities as a result of ischemic coagulative necrosis doe to arterial obstructionWhen the coagulative pattern prevails - dry gangrene developswhen liquefaction is more pronounced- wet gangrene develops-wet gangrene- results from severe bacterial inection of necrotic areamost commonly it occurs in the extremities due to arterial obstruction, but also in the internal organs, such as intestine- most common example- in acute suppurative appendicitisgrossly- tissue is swollen, reddish-black with extensive liquefactionwet gangrene is severe complication associated with high mortality rate-gas ganrene- is a wound infection caused by Clostridium perfringens and other types of Clostridia-it is characterized by extensive necrosis and tissue destruction and production of gas by fermentative action of bacteriagrossly- appearance similar as in wet gangrene with additional presence of gas in tissuescrepitus- a sound that can be detected by palpation of necrotic tissuesgas gangrene is associated with a high mortality rate

NECROSIS and APOPTOSIS

NecrosisApoptosis

Stimulihypoxia, toxinsphysiologic and pathologic

Histologycellular swelling, coagulation necrosis, disruption of organellessingle cells,chromatin condensation, apoptotic bodies

DNA breakdownrandom, diffuseinternucleosomal

MechanismsATP depletion, membrane injury, free radical damagegene activation, endonuclease

Tissue reactioninflammationno inflammation, phagocytosis of apoptotic bodies

8. Discuss and differentiate each type as to its causes, mechanism, gross and microscopic finding and give examples.

Causes of cell injury range from gross mechanical external causes to mild endogenous causes as genetic lack of enzymes etc.Virtually all forms of tissue injuries start with molecular or structural alterations in cells.Under normal conditions, the cells are in: homeostastatic steady stateNormal cell is confined to relatively narrow range of functions and structure by its genetic programme to handle normal physiologic demands.Cells react to adverse influence by1- adapting2- sustaining reversible injury3- suffering irreversible cellular injury- cell death More excessive stimuli (either physiologic or pathologic) may cause cellular adaptation -in order to reach altered steady state- for example, excessive work stress causes an increase in muscle mass that reflects the increase in size of the individual muscle fiber, results in higher level of metabolic activity and new equilibrium is reached- hypertrophy- on the other hand- atrophy- is adaptative response in which there is a decrease in the size and function of the cells- and results from a slow long-lasting decrease of blood supply if the limits of adaptative mechanisms are exceeded or when no adaptative response is possible- cell injury Reversible cell injury denotes pathologic changes that can be reversed when the stimulus is removed and the cellular injury has been mild. Cell injury is reversible only up to certain point. Irreversible cell injury denotes pathologic changes that are permanent and cause cell death, they cannot be reversed to normal statefor example: if the blood suply to heart muscles is cut off for 10-15 minutes- the myocardial cell experiences injury but it can recover to normal function, if the blood flow is cut off for longer period- the myocardial fiber dies-necrosis

CAUSES OF CELL INJURY Hypoxia (= decrease of oxygen supply) -most common cause of cell injury-occurs usually as a result of ischemia (= loss of blood supply), which occurs for example when arterial flow suffers from atherosclerosis or thrombotic occlusion of arteries - most common cause of hypoxia -is due to inadequate oxygenation, for example in cardiorespiratory failure-is caused by loss of oxygen-carrying capacity of the blood, either due to anemia (decreased capacity of the blood for oxygen), or after poisoning with carbon monoxide (CO)= loss of the carrying capacity of the blooddepending on the severity of hypoxia- the cell may undergo -adaptation-injury-cell deathfor example: -if femoral artery is narrowed (due to atherosclerotic or atherothrombotic reduction of the lumen of the affected vessel)- skeletal muscles of the leg decrease in size= atrophy. This reduction in size of cell mass may achieve a new balance on the lower level, but severe and prolonged hypoxia will induce severe injury and cell death. physical agents - many forms of physical energy may give rise to cell and tissue injury, such as mechanical trauma, extremes of temperature, sudden changes in atmosphere pressure, electromagnetic energy, radiation and electric shockThe most important and frequent in clinical practice are consequences of mechanical forces (traffic accidents).Changes in atmosphere pressure and hypotermia are relatively uncommon causes of injury, but hypertermia (burns) are encountered more often. Radiation injury- have also assumed importance as potential causes of widespread destruction chemical agents -the list of chemicals that may cause cell and tissue injury includes -poisons-arsenic, cyanide, mercuric salts,etc-air pollutants-insecticides and herbicides-alcohol, narcotic drugs-variety of therapeutic drugs and even oxygen in high concentrations infectious agents- these agents range from the submicroscopic viruses, rickettsiae to bacteria, fungi and higher forms of parasites. immunologic reactions -immune system works in a defense against biologic agents. Immune reactions may, however cause cell injury-first- so called anaphylactic reaction - to a foreign protein or drug-second- reactions to endogenous self-antigens are responsible for a number of so called autoimmune diseasesgenetic derangements-genetic defects cause a number of diseasesGenetic injury may result in severe defects and congenital malformations (Downs syndrome) or in mild derangements and errors of metabolism (lack of a distinctive enzyme ), etc.nutritional disbalances- even now nutritional errors continue to be major cause of cell injury.-protein-calorie deficiencies- chiefly among underprivileged population-deficiencies of specific vitamins-nutritional excesses have become important in cell injury among overprivileged population (excess in lipids-predispose to atherosclerosis, cause obesity, influence diabetes mellitus).

GENERAL MECHANISMS OF CELL INJURY.Four intracellular systems are particularly vulnerable to cell injury:1. maintenance of the integrity of cell membrane (upon which the osmotic homeostasis of the cell is dependent)2. aerobic respiration involving oxidative phosphorylation and production of ATP (mitochondria)3. synthesis of functional and structural proteins (Golgi)4. preservation of the genetic apparatus of the cell (nucleus)

Important aspects of cell injury:-the following factors influence severity of injury, consequences of cell injury depend both on cell and the injurious agent, and other factors 1- wide-spread effect of changes-whatever the first point of injury in the cell is - wide-range secondary effects. Above mentioned four vulnerable systems are closely related, thus injury at one of them leads to widespread secondary effectsfor example-impairment of aerobic respiration disrupts the energy-dependent sodium pump- results in loss of ionic and fluid balance- causes alterations in the intracellular content of water and ions- cell swelling 2- time factor- morphologic changes of cell injury become apparent only after some critical time.for example- light microscopic changes characteristic of cell death do not occur in the myocardium until 10-12 hours after total injury- but irreversible injury actually occurs within 20-60 minutes!! 3- cell susceptibility to injury- reactions of the cells to pathologic stimuli depend on the type of the cell. The consequences of cell injury depend on the type, state and adaptability of the cell. Important factors in the cell are:-nutritional state, hormonal status, metabolic activity and demands of the cell. How vulnerable is the cell when exposed to hypoxia?- high susceptibility-neurons (3-5 minutes)- intermediate- myocardium, hepatocytes, renal epithelial cell (20-120 minutes)- low susceptibility- fibroblasts, epidermis, skeletal muscles ( many hours) 4- reactions of the cell to pathologic stimuli depend on the type of injury, its duration, its severity, thus short ischemia may induce reversible injury, while more prolonged ischemia might lead either to cell death or to slow irreversible injury.

MECHANISMS OF CELL INJURY IN HYPOXIC INJURY. reversible cell injuryHypoxia first causes loss of phosphorylation in mitochondria- results in decrease of production of energy rich-ATP - loss of ATP (which is a energy source) has widespread effects on many systems in the cell-for example-heart muscle stops to contract within 60 seconds after coronary occlusion (noncontractility does not mean the cell death)the decrease in cellular ATP stimulates increase of anaerobic glycolysis= the other source how to generate energy for the cellglycogen is rapidly depleted, glycolysis results in accumulation of lactic acids - it reduces pH intracellularly - at this point, there is also early clumping of nuclear chromatinenergy-dependent sodium pump slows down the activity - sodium pump keeps normally the concentration of potassium (K+) significantly higher intracellularly.Failure of active transport through the cell membrane causes that sodium (Na+) accumulates within the cell and potassium diffuses out of the cell - it leads to important movement of water intracellularly=morphologic changes in reversible cell injury-cellular swelling -due to accumulation of catabolites of metabolism and water intracellularly-loss of microvilli-blebsswelling of cisternae of endoplasmic reticulum -detachment of ribosomes from the granular ER due to disruptions of energy-dependent interactions between membranesmyelin figures- derived from plasma or from membranes of organelles. They are thought to results from dissociation of lipoproteins.All the above mentioned changes are reversible if oxygenation is restored. irreversible cell injury-if ischemia persists, irreversible injury develops. Irreversible injury is marked by severe mitochondrial vacuolization, extensive damage to plasma membranes, swelling of ribosomes, swelling of ribosomes. Injury to lysosomal membranes leads to leakage of lysosomal enzymes into the cytoplasm,there is no universal biochemical point of no return, transitions from reversible injury to cell death. critical events for irreversible cell injury:-1- ATP depletion inability to reverse mitochondrial dysfunction (lack of oxidative phosphorylation and production of energy )-2- Cell membrane demage-the earliest phase of irreversible injury is associated with functional and structural defects in cell membranes-great deal of evidence indicates that cell membrane damage is a central factor in the pathogenesis of irreversible injury-intact cell membranes are essencial to the maintenance of normal cell permeability and volume- loss of membrane integrity causes massive influx of calcium from the extracellular space- resulting in mitochondrial dysfunction, inhibition of intracellular enzymes, denaturation of proteins

2. CHEMICAL INJURYchemicals induce cell injury by one of two major mechanisms:1-some chemicals act directly by chemical bindings with some critical molecules or cellular organellesfor example: mercuric chloride poisoning (mercury binds directly to sulphydryl groups of cell membranes)--GIT and kidneyor anticancer drugs and some antibiotic drugs also induce cell damage by direct cytotoxic effects-2-other chemicals are not biologically active but convert into reactive toxic metabolits (role of free radicals for example)

3. INJURY INDUCED BY VIRUSESviruses induce cellular changes by two general mechanisms:1-cytolytic and cytopathic viruses cause various degrees of cellular injury and cell death2-oncogenic viruses stimulate host cell to proliferate and may induce tumorsCytopathic effects of viruses cause injury by two major mechanisms:-first is direct cytopathic effect, in which rapidly replicating virus particles interfere with some aspects of cell metabolism and cause cellular damage.Most directly cytopathic viruses have a high degree of cell specificity= viral tropism, caused by presence of membrane receptors on host cells, which interact with viral strucutresallow to attack to the host cellto enter the host cell and cause the injury by active reduplication of virus particles-second mechanism involves the induction of an immunological response-destruction of the cell by either antibody or cell-mediated reactions, for example the damage and death of hepatocytes caused by hepatitis B viruses are mediated by cytolysis induced by T-lymfocytesThe nature of cell response to viral replication depends on the host cell and type of virus and can have several forms:1-cell lysis-apparently due to rapid viral replication2-some viruses can cause cytoskeletal damage (for example disruption of vimentin) 3-cell may response by formation of giant multinucleate cells, due to cell-cell fusion, for example in measles or herpes virus infection 4-some viruses infected cells develop inclusion bodies, which contain virions or viral proteins in nuclei or cytoplasm

9. Discuss the features of necrosis and apoptosis

TWO PRICIPAL TYPES OF CELL DEATH

NecrosisApoptosis

DefinitionIs a pathway of cell death that is induced by a tightly regulated suicide program in which cells destined to die activate enzymes that degrade the cells own nuclear DNA and nuclear and cytoplasmic proteins.

Cell SizeEnlarged (Swelling)Reduced (shrinkage)

Plasma membraneLoss of membrane integrity; Damage is severe; DisruptedIntact; altered structure, especially orientation of lipids

NucleusPyknosis -> Karyorrhexis -> KaryolysisFragmentation into nucleosome-size fragments

Effect on inflammationElicit inflammation in the surrounding tissueNo inflammmmatory reaction

Cellular contentsLeakage of cellular contentsIntact; may be released in apoptotic bodies

Cause of AppearanceDenaturation of intracellular proteinsEnzymatic digestion (from the lysosomes of the dying cell)Activation of caspacesDNA & Protein breakdownMembrane Alterations and Recognition by Phagocytes

MechanismLysosomal enzymes enter the cytoplasm and digest the cellCells DNA or proteins are damaged beyond repair, the cell kills itself; Rapid removal of the cellular debris.

DiseaseALWAYS pathological process; Invariably pathologic (culmination of irreversible cell injury)May serve many normal functionCan progress to necrosis -> May be pathologic after some forms of cell injury, esp DNA damageNot necessarily associated with cell injury

Morphologyeosinophilia in H&E stainsLoss of cytoplasmic RNAGlassy homogenous appearanceLoss of glycogen particlesVacuolated and appears moth-eatenKaryolysis basophilia of the chromatinPyknosis nuclear shrinkage and basophiliaKaryorrhexis pyknotic nucles undergoes fragmentationCell ShrinkageChromatin condensationFormation of cytoplasmic bleps and apoptotic bodiesPhagocytosis of apoptotic cells or cell bodies, usually by macrphages

10. Discuss the clinic-pathologic correlation of ischemic cell injury in this particular caseIschemia Nutrient & O2 supply often due to blood flow & also by a venous drainage; both aerobic & anaerobic energy generation affected

Mechanisms of Ischemic Cell injury:O2 tension

Loss of oxid phosphorylation

Depletion of ATP

Na+ pump failure(loss of K+, influx of H2O, Na+ & Ca++)

swelling, progressive glycogen loss &protein synthesis

irreversible injury & necrosis