cell injury and cell death I and II Flashcards
what are the three possible consequences of cell injury?
reversible injury - altered cell recovers and returns to being a normal cell
permanent cell injury - permanently altered after injury
lethal cell injury - injury leads to cell death - leads to necrosis (ischemia or apoptosis)
what are some characteristics of normal liver tissue (histology)?
hepatocytes arranged in trabecular architecture forming sinusoids
lots of pink cytoplasm
blue nuceli that are centrally placed
with electron microscope - mitochondria roundish and in rER
what is steatosis?
accumulation of fat (TG) in hepatocytes - often due to alcoholic liver injury
would have elevated white count and elevations of liver enzymes because enzymes leak out of damaged cells
describe an example of reversible cell injury.
damage to liver due to alcoholism - steatosis
abstinence from alcohol can result in reversal of cells back to normal hepatocytes
what happens to alcohol in the liver?
metabolized to acetate
drives microsomal system that manages toxic agents - role in underlying injury of liver
also drives liver cell into oxidative stress and drive increase in NADH - has effect on liver’s regulation of lipid metabolism
how does NADH (and alcohol) affect lipid metabolism?
alcohol increases NADH
NADH decreases FA oxidation
NADH increases TG synthesis
what are the 5 effects of EtOH on hepatic lipid metabolism?
1: Mobilization of fatty acids from body stores
2: Decreased fatty acid oxidation
3: Increased triglyceride synthesis
4: Decreased lipoprotein synthesis
5: Decreased transport, glycosylation and secretion of VLDL
all results in buildup of TG in cells cause of decreased export from cells
what would a liver damaged by alcohol (steatosis) look like histologically?
clear spaces (circles) due to lipid buildup - hepatocytes begin to resemble fat cells - eventually will look completely like fat cells except for portal triads in tissue nuceli no longer solid blue - have blue rim and dot in center presence of neutrophils in sinuses - bright red dots much smaller than hepatocyte cells
what is mallory’s hyaline?
abnormality in cytoskeleton => aggregation of cytokeratin filaments in liver cells
what happens to hepatocytes after heavy alcohol use in those with mallory’s hyaline?
get permanently altered hepatocytes even after abstinence
(note, i don’t think they have mallory’s hyaline until they damage their liver)
get alcoholic hepatitis
what would the liver biopsy of a patient with mallory’s hyaline look like histologically?
dense pink “ropes” inside the cells
these are buildup of cytokeratin filaments
hepatocytes die and are removed
neutrophils present
what would a liver biopsy of a patient with hemochromatosis look like histologically?
rusty brown/tan color in hepatocytes = buildup of iron
much less pink
check with prussian blue stain - will stain iron blue - so would see liver cells filled with blue
what is hemochromatosis?
genetic liver disease that results in abnormal accumulation of iron in tissues
eventually results in cirrhosis - identify by lots of blue with prussian stain
what does prussian blue stain for?
iron in tissue - shows up blue
used to diagnose hemosiderosis
what is hemosiderosis? how do you treat it?
buildup of iron in tissues due to any cause - can be due to local injury such as local hemorrhage
treat by removing red cell mass and can also restrict diet but iron’s in almost everything
what would a liver with Cirrhosis look like?
actual liver (gross) would have lots of green nodules - lots of fibrous tissue - bumpy surface
what are the dangers of having too much iron?
causes inflammation and free radical accumulation
what is burkitt lymphoma?
malignancy of B lymphocytes with apoptotic cell death of malignant cells and phagocytosis of apoptotic bodies by macrophages
example of apoptosis due to lethal cell injury
what is the process of apoptosis?
activation of cytochrome C - activates enzymatic cascade - cell fragments - macrophages take away debris
what are some examples of things that can induce apoptosis?
radiation, some hormones, damage
what does burkitt lymphoma look like histologically?
starry sky pattern - lightly stained macrophages with apoptotic bodies surrounded by dense infiltrate of malignant lymphocytes
lymphocytes large and abnormal
macrophages present and contain little blue dots - phagocytized fragments of dead cells
what is ischemia?
effect of O2 deprivation on cell function and morphology
can be due to arterial occlusion
what is the result of ischemia on cells?
initially injury that leads to altered cells followed by irreversible progression to cell death => necrosis
what are some of the reversible effects of ischemia?
decreased oxidative phosphorylation in mitochondria => decreased ATP => decreased Na pump activity; increased glycolysis; detachment of ribosomes so decreased protein synthesis
Na and Ca2+ will come into cell cause of problem with Na/K ATPase (cause of low ATP)
cell swells
what are the irreversible effects of ischemia?
at certain point cell can no longer recover - likely due to damage to mitochondria - now no longer reversible
mitochondria releases cytochromes so that apoptosis is triggered
what would heart tissue look like histologically after ischemia?
enlarged cells
cells paler because of increased cell volume (cell swelling)
can see space in cells = edema fluid in cell
describe the role of Ca in cell death.
affects mitochondria, rER, cell membrane, nucleus adversely
if don’t correct mitochondrial abnormality cells won’t be able to do oxidative phosphorylation
what would mitochondria look like on EM after ischemia? (said he wasn’t going to ask us about this?)
mitochondria swell up
inner membranes begin to break down first
what happens to mitochondria after ischemia?
become porous, enter low energy state, lose enzymatic systems and cannot recover after a while
what is necrosis?
morphologic changes from cell death in living tissue cumulative effect of: - enzymatic degradation of dead cells - primarily mediated by lysosmal enzymes - denaturation of proteins
what determines the appearance of necrosis?
cause of injury
type of tissue
host response to the injury (inflammation)
what are the two types of necrosis (list)?
coagulative necrosis
liquefactive necrosis
what is coagulative necrosis?
most common form
denaturation of cell proteins dominates
eg when you fry an egg
infarction (ischemic cell death) is a common example
what is liquefactive necrosis?
usually necrosis with extensive acute inflammation (eg bacterial or fungal infections) resulting in fairly complete digestion of tissue (liquification)
abscess and cerebral infarction are common examples
pus
what are examples of coagulative necrosis?
1: myocardial infarction
2: renal infarction
3: pulmonary infarction
what would myocardial infarction look like (gross images)?
in gross images, thin regions due to long term necrosis and scarring so there’s no muscle there - don’t grow myocardial cells back
what would myocardial infarction look like histologically?
dead myocardial fibers - know they’re dead because they’re shrunken and thin and have lost their nuceli - coagulative necrosis - contractile proteins have coagulated
plus tiny dark blue/purple dots = neutrophils
what would renal infarct look like histologically?
large spaces with no nuclei - will be paler than surrounding regions - narrow at medulla and wider toward cortex
what would a lung with hemorrhagic pulmonary infarct look like?
appears dark red to black - red because there’s a hemmorhage from the bronchial artery even though the pulmonary artery is blocked
what is a reperfusion infarction?
red infarct caused when perfusion is immediately restored to the dead tissue
what are examples of liquefactive necrosis?
1: cerebral infarction (stroke)
2: necrotizing fungal pneumonia
why does the brain undergo liquefactive necrosis? what would it look like (gross)?
structure and circulation
get hemmorhage and that makes the area appear black, but the area itself is gone
what would a lung with fungal pneumonia look like?
on xray, opaque white
in autopsy, grey regions, developing abscess, eventually get hole in lung
in histology - lots of actue inflammation and abundance of neutrophils
what type of necrosis is gangrenous necrosis?
both coagulative (typically ischemic but can also be due to frostbite) mixed with superimposed bacterial infection that causes liqueficative necrosis
what does gangrenous necrosis look like?
tissue turns black
what is enzymatic fat necrosis?
necrosis of fat by pancreatic lipases
FA released from fat cells combine with Ca2+ resulting in saponification
results in chalky yellow deposits
what does enzymatic fat necrosis look like?
chalky yellow deposits on pancreas (can be in other areas of body sometimes too)
when becomes really bad gets black due to hemorrhage
what is caseous necrosis? (type of necrosis and what disease it’s associated with)
type of necrosis classically associated with TB - combination of coagulative and liquifactive necrosus
what does caseous necrosis look like?
looks like cheese (or mold)
amorphous eosinophilic acellular material in center of granulomas
in histology - liquefied tissue that leaves a cavity
can see cavity in gross disection
what are the two major classes of etiologic factors?
genetic - eg inherited mutations, disease-associated variants, polymorphisms
acquired - infectious, nutritional, chemical, physical
what is pathogenesis?
sequence of events in the response of cells or tissues to the etiologic agent, from the initial stimulus to the ultimate expression of the disease
what are examples of adaptive responses in cells to altered physiological stimuli and some nonlethal injurious stimuli (reversible)?
1: hypertrophy - increase in size of cells
2: hyperplasia - increase in number of cells
3: atrophy - decrease in size and number of cells
4: metaplasia - change in phenotype of cells
what are some examples of altered physiological stimuli and nonlethal injurious stimuli?
increased demand, increased stimulation (eg by growth factors, hormones)
decreased nutrients, decreased stimulation
chronic irritation (physical or chemical)
what are adaptations?
reversible functional and structural responses to more severe physiologic stresses and some pathological stimuli, during which a new but altered steady state is achieved, allowing the cells to continue to survive and function
what results in cell injury?
when the limits of adaptive responses are exceeded or if cells are exposed to injurious agents or stress, deprived of essential nutrients, or become compromised by mutations that affect essential cellular constituents
what are the two pathways of cell death?
necrosis and apoptosis
autophagy can also occur in response to nutrient deprivation
what is pathologic calcification?
when cell death results in the deposition of Ca
what are the hallmarks of reversible cell injury?
reduced oxidative phosphorlyation with resultant depletion of energy stores (ATP)
cellular swelling due to changes in ion concentrations and water influx
intercellular organelles may should alterations
when does necrosis versus apoptosis occur?
necrosis = when damage to membranes is severe, lysosomal enzymes enter the cytoplasm and digest the cell, cellular contents leak out
apoptosis = when when DNA or proteins are damaged beyond repair and cell kills itself
necrosis is always pathologic, whereas apop has many normal physiological functions
what is hypoxia? what is its effect on cells?
deficiency of O2
reduces oxidative respiration - cells will adapt, undergo injury, or die
what are some causes of hypoxia?
reduced blood flow (ischemia)
inadequate oxygenation of blood due to cardiorespiratory failure
decreased O2 carrying capacity of blood (anemia and CO poisoning)
severe blood loss
what are the two features of reversible cell injury that can be recognized under a light microscope?
cellular swelling and fatty change
when does cellular swelling occur?
when cell are incapable of maintaining ionic and fluid homeostasis
result of failure of energy-dependent ion pumps in the plasma membrane
when does fatty change occur? how does it appear under microscope? what cells does it occur in?
in hypoxic injury and various forms of toxic or metabolic injury
see lipid vacuoles in cytoplasm
seen mainly in cells dependent on fat metabolism (ie hepatocytes, myocardial cells)
what are the histological ultrastructural changes of reversible cell injury?
1: plasma membrane alterations (blebbing, blunting, loss of microvilli)
2: mitochondrial changes (swelling, appearance of small amorphous densities
3: dilation of the ER (with detachment of polysomes, intracytoplamic myelin figures may occur)
4: nuclear alterations (disaggregation of granular and fibrillar elements)
what is the morphology of necrotic cells?
increased eosinophilia in H&E stains (due to loss of cytoplasmic RNA and denatured cytoplasmic proteins)
may have more glassy, homogenous appearance (due to loss of glycogen particles)
cytoplasm vacuolated (appears moth-eaten)
dead cells replaced by myelin figures
nuclear changes
what are myelin figures?
large, whorled phospholipid masses derived from damaged cell membranes that replace necrotic cells
these are then phagocytised or calcified
what are the nuclear changes that can occur in necrotic cells?
three possible patterns:
1: karyolysis - bacsopilia of the chromatin fades (loss of DNA because of enzymatic degradation by endonucleases)
2: pyknosis - nuclear shrinkage and increased basophilia (chromatin condenses into solid mass)
3: karyorrhexis - pyknotic nucleus undergoes fragmentation
nucleus will disappear eventually
what is an infarct?
localized area of coagulative necrosis
what is fibrinoid necrosis?
seen in immune reactions involving blood vessels
when complexes of antigens and antibodies are deposited in the walls of arteries
these deposits and fibrin that’s leaked out of vessels make bright pink and amorphous appearance in H&E
what is dystrophic calcification?
if necrotic cells and debris are not removed promptly - attract Ca salts and other minerals => calcification
how is ATP produced?
oxidative phosphorylation of adenosine diphosphate => reduction of O2 by the ETC
glycolytic pathway - makes ATP in absence of O2
what are the major causes of ATP depletion?
reduced O2 supply
reduced nutrient supply
mitochondrial damage
actions of some toxins (eg cyanide)
what are the consequences of depletion of ATP?
reduced Na/K ATPase
cellular energy metabolism altered - oxidative phos ceases ==> increased rate of anaerobic glycolysis => glycogen stores rapidly depleted
failure of Ca pump => influx of Ca
if prolonged, structural disruption of protein synthetic apparatus => reduction in protein synthesis
proteins may be misfolded => misfolded protein response
eventually irreversible damage to mitochondrial and lysosomal membranes => necrosis
what can cause mitochondrial damage?
increases of cytosolic Ca reactive O2 species O2 deprivation (hypoxia and toxins) mutations due to inherited diseases
what are the consequences of mitochondrial damage?
formation fo high-conductance channel in membrane = mitochondrial permeability pore => loss of mitochondrial membrane potential => failure of oxidative phos => depletion of ATP => necrosis
proteins sequestered between inner and outer membranes released - these can trigger apoptotic pathways
what is the role of cyclophilin D?
structural component of mitochondrial permeability transition pore
target of immunosuppressive drug cyclosporine
what causes an increase in cytosolic Ca concentration?
ischemia
certain toxins
initially due to release from intracellular stores
later due to increased influx across plasma membrane
how does influx of Ca cause cell injury?
accumulation of Ca in mitochondria => opening of mitochondrial permeability transition pore ==> failure of ATP generation
increased cytosolic Ca activates some enzymes
increased cellular Ca => apoptosis via direct activation of caspases and increasing mitochondrial permeability
how are free radicals generated?
reduction-oxidation reactions that occur during normal metabolic processes
absorption of radiant energy
produced in activated lymphocytes during inflammation
enzymatic metabolism of exogenous chemicals or drugs
transition metals donate or accept
NO can act as free radical
what does glutathione peroxidase do?
protects against injury by catalyzing free radical breakdown
what are the pathologic effects of free radicals?
lipid peroxidation in membranes => peroxides, membrane damage
oxidative modification of proteins
lesions in DNA (single and double strand breaks, crosslinking, adducts)
what are the mechanisms that create membrane damage?
reactive O2 species
decreased phospholipid synthesis
increased phospholipid breakdown
cytoskeletal abnormalities
what are the consequences of membrane damage?
- mitochondrial membrane damage => opening of mitochondrial permeability pore and decreased ATP production and release of apoptotic proteins
plasma membrane damage => loss of osmotic balance and influx of fluids and ions and loss of cellular contents
injury to lysosomal membranes => leakage of enzymes into cytoplasm and activation of acid hydrolases
what could create DNA damage that can’t be corrected?
exposure to DNA damaging drugs
radiation
oxidative stress
what are the two phenomena that characterize irreversible damage?
inability to reverse mitochondrial dysfunction
profound disturbances in membrane function
which is worse: hypoxia or ischemia? why?
ischemia is worse because the cells are deprived of glycolytic substrates as well as O2, so can’t make up for the O2 lack with anaerobic glycolysis, whereas hypoxic tissue still has access to arterial glycogen supplies
what is the mechanism behind cell swelling due to hypoxia or ischemia?
depletion of ATP => failure of Na pump => loss of K => influx of Na and H2O => cell swelling
what are the morphological steps of ischemia?
associated with severe swelling of the mitochondria, extensive damage to plasma membranes, swelling of lysosomes
large, flocculent, amorphous densities develop in mitochondrial matrix
influx of Ca occurs
death by necrosis but apoptosis also contributes
what does hypoxia-inducible factor-1 do?
promotes new blood vessel formation
stimulates cell survival pathways
enhances anaerobic glycolysis
protective response to hypoxic stress
what is ischemia-reperfusion injury?
reperfused tissues may sustain loss of cells in addition to cells that are irreversibly damaged at the end of ischemia
how does reperfusion injury occur?
new damaging processess are set in motion during reperfusion => death of cells that might have recovered otherwise
what pathologic states can induce apoptosis?
- DNA damage (radiation, chemo, hypoxia)
- accumulation of misfolded proteins - in ER => ER stress
- cell death in certain infections
- pathologic atrophy in parencymal organs after duct obstruction
what are the morphologic changes seen in apoptosis?
- cell shrinkage
- chromatin condensation
- formation of cytoplasmic blebs and apoptotic bodies
- phagocytosis of apoptotic cells or cell bodies, usually by macrophages
plasma membranes remain intact until last stages - become permeable
what are the phases of apoptosis and what occurs during them?
initiation phase: some caspases become catalytically active
execution phase: other caspases trigger degradation of critical cellular components
where do the signals for initiation of apoptosis come from?
intrinsic (mitochondrial)
extrinsic (death receptor-initiated)
how do mitochondria regulate apoptosis?
some proteins in mitochondria initiate suicide program - eg cytochrome c
controlled by Bcl family of proteins esp. Bcl-2, Bcl-x, Mcl-1
all normally regulate mitochondrial permeability and prevent leakage of mitochondrial proteins
if DNA damaged or ER stress occurs, other members of the Bcl family (Bim, Bid, Bad) activate Bax and Bak => oligodimers => insert into mitochondrial membrane => channels that allow proteins from inner mitochondrial membrane to leak out into the cytoplasm
cytochrome c released into cytosol and binds to Apaf-1 => apoptosome
binds caspase 9
how can apoptosis be activated extrinsically?
death receptors (TNF family) activated
eg Fas
FasL = fas ligand - expressed on T cells that recognize self antigens
Fas trimerizes - form binding site for FADD - binds inactive form of caspase-8 and multipule caspase-8 accumulate - cleave one another - triggers chain of caspase activation
can be inhibited by FLIP
what is autophagy? when does it occur?
when cell eats its own contents
survival mechanism in times of nutrient deprivation
intracellular organelles and portions of cytosol are sequestered in autophagic vacuole - fuses with lysosomes => autophagosome
what are the two types of substances that can accumulate in cells?
1: normal cellular constituents (water, lipids, proteins, carbs)
2: abnormal substances (exogenous like mineral or products of infectious agents, endogenous like products of abnormal synthesis or metabolism)
what are the four types of abnormalities that can result in abnormal intracellular accumulations?
1: normal endogenous substance produced at normal or increased rate but rate of metabolism is inadequate
2: abnormal endogenous substance due to defects in protein folding and transport and inability to degrade abnormal protein
3: normal endogenous substance accumulates because of defects in enzymes required for metabolism of the substance
4: abnormal exogenous substance is deposited and accumulates because the cell has neither the enzymatic machinery to degrade the substance nor the ability to transport it to other sites
what is steatosis?
abnormal accumulation of TG in parenchymal cells
what are the causes of steatosis?
toxins protein malnutrition diabetes mellitus obesity anoxia
what is MI? what are the consequences?
death of cardiac muscle due to prolonged severe ischemia
initially, cessation of aerobic metabolism => inadequate production of ATP and accumulation of potentially noxious metabolites (lactic acid)
loss of contractility
if fixed within 20-30 minutes, reversible
what are the events leading up to MI?
1: sudden change in atheromatous plaque
2: platelets adhere to exposed subendothelial collagen and necrotic plaque contents
3: platelets become activated and release granule contents
4: aggregate to form microthromi
5: vasospasm stimulated by mediators released from platelets
6: tissue factor activates the coagulation pathway - adds to bulk of thrombus
7: thrombus evolves to occlude lumen
what does triphenyltetrazolium chloride stain for?
highlights area of necrosis after infarct
imparts brick-red color to intact, non-infarcted myocardium where dehydrogenase activity is preserved
what is myocytolysis?
vacuolar degeneration
on margins of infarcts
large vacuolar space within cells that probably contain water
what is the extension of an infarct? why does it occur?
when infarcts expand beyond their original borders over a period of days to weeks via a process of repetitive necrosis of adjacent regions
central zone where healing is more advanced than in the periphery
can be due to retrograde propagation of thrombus, proximal vasospasm, progressively impaired cardiac contractility, deposition of platelet-fibrin microemboli or arrythmia
what are the clinical symptoms of MI?
myocardial proteins in plasma (myoglobin, cardiac troponins T and I, MB fraction of creatine kinase, lactate dehydrogenase)
ECG changes
rapid, weak pulse, profuse sweating
dyspnea
but can be entirely asymptomatic
what is hemochromatosis? how do you get it? what tissues does it affect?
excessive accumulation of body iron - most deposited in parenchymal organs (liver, pancreas) - heart, joints, endocrine organs
primary = homozygous-recessive inherited disorder due to excessive iron absorption
