Chapter 2: Cellular Responses to Stress and Toxic Insults: Adaptations, Injury, Death Flashcards
Study of the structural, biochemical, and functional changes in cells, tissues, and organs that underlie disease
Pathology
Common reactions of cells and tissues to injurious stimuli; not tissue specific (ex: acute inflammation in response to bacterial infections produces similar reaction in most tissues)
General pathology
alterations and underlying mechanisms in organ specific diseases such as ischemic heart disease
systemic pathology
- cause of disease=______
- sequence of cellular, biochemical, and molecular events that follow the exposure of cells or tissues to an inhurious agent= ______
- structural alterations induced in the cells and organs of the body that are either characteristic of a disease or diagnostic of an etiologic process= ______
- functional consequences of the changes=_____
- etiology
- pathogenesis
- morphologic changes
- clinical manifestations
Etiology can be grouped into what two classes?
Genetic: (inherited mutations and disease associated gene variants or poymorphisms)
Acquired: ex: infectious, nutritional, chemical or physical
The end results of genetic, biochemical and structural changes in cells and tissues are _____
Functional abnormalities which lead to clinical manifestations (symptoms and signs)
How do diseases start?
cell injury–>tissue injury–>organ injury
Increase in cell SIZE that results in an increase in the size of affected organ
hypertrophy
*Hypertrophy is the result of increased production of cellular proteins!
increase in cell NUMBER in organ or tissue in response to stimulus
hyperplasia
decrease in size and metabolic activity of cells; reduction in size of organ or tissue due to a decrease in cell size and number
atrophy
change in phenotype of cells
metaplasia
When 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, _____ results
cell injury
Is cell injury reversible?
Yes, but only upto certain point. If stimulus persists/is severe, cell suffers IRREVERSIBLE injury leading to cell death
Adaptation–>reversible injury–>cell death
Cell death is the end result of progressive cell injury. What are some of the causes of cell death?
ischemia (reduced blood flow), infection, toxin
May also be physiologic: embryogenesis, organ development and maintainence of homeostasis
Two pathways of cell death are?
Necrosis and apoptosis
*Nutrient deprovation triggers an adaptive cellular response called autophagy that also results in cell death
Metabolic derangement of cells and sublethal, chronic injury may be associated with ______ of lipids, proteins and carbs
intracellular accumulations
What is often deposited at sites of cell death?
Ca, leading to pathologic calcification
Reversible changes in size, number, phenotype, metabolic activity, or functions of cells in response to changes in their environment
Adaptations
What is the most common stimulus for hypertrophy of muscle?
increased work load
What causes hypertrophy of the heart?
chronic hemodynamic overload resulting from hypertension or faulty valves
Example of hormone induced enlargement of an organ from hypertrophy?
uterus during pregnancy–estrogen induced
First step in cardiac hypertrophy
integrated actions of mechanical sensors (triggered by increased workload), growth factors (TGF-B, IGF-1, FGF), and vasoactive agents (a-adrenergic, endothelin-1, and angiotensin II)
Second step in cardiac hypertrophy:
Signal transduction: PI3 kinase/AKT pathway (excercise induced hypertrophy), GPCR induced by growth factors and vasoactive agents (pathologic hypertrophy)
Third step in cardiac hypertrophy11
activation of transcription factors like GATA4, NFAT, MEF2 which all coordinate to increase the synthesis of proteins that are responsible for hypertrophy
Example of hypertrophy switching contractile proteins:
alpha isoform of myosin heavy chain is replaced by the B isoform which has slower, more energenetically economical contraction (from adult to fetal forms)
Some genes that are expressed only during early development are reexpressed in hypertrophic cells. Example?
gene for atrial natriuretic factor expressed in both the atrium and the ventricle in embryonic heart but is down-regulated after birth but in cardiac hypertrophy, ANF gene expression increases
When the heart is no longer capable of adaptation via hypertrophy, what happens?
Regressive changes occur in myocardial fibers–lysis and loss of myofibrillar contractile elements–can lead to myocyte death resulting in cardiac failure
Drugs used to inhibit the signaling pathways in the heart to prevent damage target which transcription factors?
NFAT, GATA 4, and MEF2 genes
_____ due to the action of hormones or growth factors occurs in several circumstances: when there is a need to increase functional capacity of hormone sensitive organs; when there is need for compensatory increase after damage or resection
Pathologic hyperplasia
proliferation of glandular epithelium of female breast at puberty and during pregnancy is example of ____
hormonal hyperplasia
*this process is usually accompanied by enlargement (hypertrophy)
cells of the liver can proliferate so that organ grows back to normal size after resection is example of ____
compensatory hyperplasia
Bone marrow undergoing hyperplasia after acute bleed or after hemolysis uses which growth factor to stimulate the growth of red cell progenitors?
Erythropoietin
Most forms of pathologic hyperplasia are caused by _____. Example?
excessive or inappropriate actions of hormones or growth factors acting on cells
Ex: endometrial hyperplasia resulting from disturbance of balance between estrogen and progestrone resulting in increase in estrogen–PATHOLOGIC
Benign prostatic hyperplasia is another example of pathologic hyperplasia induced in responses to hormonal stimulation by ____
androgens
Is hyperplasia the same as cancer?
No. While hyperplasia is distinct from cancer, pathologic hyperplasia constitutes a basis for which cancerous proliferations may arise—example: endometrial hyperplasia can lead to endometrial cancer
Hyperplasia is a characteristic response to what kind of infections?
viral infections]
ex: paillomavirus which cause skin warts and several mucosal lesions composed of masses of hyperplastic epithelium (viruses make factors that interfere with host proteins that regulate cell proliferation)–can be precursor to cancer like other hyperplasias
Hyperplasia is the result of ?
growth factor-driven proliferation of mature cells and, in some cases, by increased output of new cells from tissue stem cells
Examples of physiological atrophy
notochord and thyroglossal duct; decrease in size of uterus after parturition
6 main causes of pathologic atrophy:
- Decreased workload (atrophy of disuse)
- Loss of innervation (denervation atrophy)
- Diminished blood supply
- Inadequate nutrition
- Loss of endocrine stimulation
- Pressure
Name the cause of atrophy: when fractured bone is immobilized in a plaster cast or when a patient is restricted to bed rest resulting in skeletal muscle atrophy
atrophy of disuse
Name the cause of atrophy: damage to nerve leads to atrophy of muscle fibers supplied by those nerves
Loss of innervation
Name cause of atrophy: brain undergoes progressive atrophy bc of reduced blood supply (ischemia) as a result of artherosclerosis (senile atrophy–also affect heart)
Diminished blood supply
Name cause of atrophy: Protein-calorie malnutrition (marasmus) associated with utilization of skeletal muscle proteins as a source of energy after other reserves like adipose tissue have been depleted
Inadequate nutrtion
–leads to muscle wasting=cachexia; also seen with chronic inflammatory diseases and cancer mediated by TNF
Name cause of atrophy: Loss of estrogen stimulation after menopause results in physiologic atrophy of the endometrium, vaginal epithelium and breast
Loss of endocrine stimulation
Name cause of atrophy: an enlarging benign tumor causing atrophy in surrounding uninvolved tissues
Pressure
- due to ischemic changes caused by compromise of blood supply by pressure exerted by expanding mass
What are the fundamental cellular changes associated with atrophy?
decrease in cell size and organelles, reduction of metabolic needs of cell sufficiently to permit its survival
What happens early in the process of atrophic cells/tissues?
they have diminished function but CELL DEATH IS MINIMAL! But atrophy caused by gradually reduced blood supply may progress to the point at which cells are irreversibly injured and die by apoptosis
What is the mechanism of atrophy?
Results from decreased protein synthesis and increased protein degradation in cells which occurs via the ubiquitin-proteasome pathway: Nutrient deficiency and disuse may activate ubiquitin ligases which attach the ubiquitin peptide to cellular proteins for degradation in proteasomes
The process in which the starved cell eats its own components in an attempt to reduce its nutrient demand to match the supply is called ______
autophagy
In autophagy, the cell debris in the autophagic vacuoles that resist digestion and persist in the cytoplasm as membrane bound is called ________
residual bodies
This is an example of a residual body and when it is present in sufficient amounts, they impart a brown discoloration to the tissue (brown atrophy)
Lifofuscin granules
This is a reversible change in which one differentiated cell type (epithelial or mesenchymal) is replaced by another cell type
Metaplasia
The most common epithelial metaplasia is _____
columnar to squamous
Ex: respiratory tract in response to chronic irritation
Examples of metaplasia:
- Smoking: ciliated columnar in trachea/bronchi–>stratified squamous
- Stones in excretory ducts of salivary glands, pancreas, or bile ducts: secretory columnar–>stratified squamous
- Vit. A deficiency: induces squamous metaplasia in respiratory epithelium
Metaplasia allows for better adaptation to enviornment, but what is the caveat?
The original cell served an important function that the new cell type cannot do. For example: in resp. tract, although the epithelial tract becomes tough, important mechanisms of protection against infectionn–mucous secretion and ciliary action of columnar epithelium–are lost
Example of squamous TO columnar metaplasia:
Barret esophagus in which the esophageal squamous epithelium is replaced by intestinal-like columnar cells due to gastric acid; cancers may arise in these areas (glandular adenocarcinomas)
Formation of cartilage, bone, or adipose tissues that normally do not contain these elements is called ____. Example?
connective tissue metaplasia
example: myositis ossificans after intramuscular hemmorage results in bone formation in muscle–result of cell/tissue injury
What is the mechanism of metaplasia? does it result from a change in phenotype of an already differentiated cell type?
No. It is the result of a reprogramming of stem cells that are known to exist in normal tissues, or of undifferentiated mesenchymal cells present in connective tissue
- alter the activity of transcription factors that regulate differentiation (example: retinoic acid)
Hallmarks of reversible cell injury?
- reduced oxidative phosphorylation leading to low ATP
- cellular swelling caused by changes in ion concentrations and water influx
- changes in intracellular organelles like mitochondria and cytoskeleton
cell death characterized as “accidental” and unregulated resulting from damage to cell membranes and loss of ion homeostasis; lysosomal enzymes enter cytoplasm and digest the cell, cellular contents leak through the damaged plasma membrane into extracellular space where they elicit host reaction (inflammation)
Necrosis
Cell death characterized by nuclear dissolution, fragmentation of the cell without complete loss of membrane integrity and rapid removal of cellular debris and NO leakage of cellular contents so NO INFLAMMATION!
Apoptosis
Is necrosis pathological or physiological? What about apoptosis??
Necrosis is ALWAYS pathologic; apoptosis serves many normal functions and is not necessarily associated with cell injury
What is necroptosis?
A form of necrosis that is also a form of programmed cell death regulated by a series of signaling pathways
What are the 7 main categories of injurious stimuli leading to cell injury?
- Oxygen deprivation (hypoxia)
- Physical agents
- Chemical agents and Drugs
- Infectious agents
- Immunologic reactions
- Genetic derangements
- Nutritional imbalances
Causes of hypoxia:
ischeia (reduced blood flow), inadequate oxygenation of blood due to cardiorespiratory failure, and decreased oxygen-carrying capacity of blood as seen in anemia orCO poisoning or after severe blood loss
What are physical agents capable of causing cell injury?
mechanical trauma, extremes of temperature (burns and deep cold), sudden changes in atmospheric pressure, radiation and electric shock
Chemicals that may produce cell injury
glucose or salt in hypertonic concentrations, O2 at high concetrations, poisons like arsenic, cyanide or mercuric salts, air pollutants, insecticides, herbicides, CO, asbestos, alcohol and even therapeutic drugs
Infectious agents that can cause cell injury
submicroscopic virus, tapeworms, rickettsiae, bacteria, fungi, and higher forms of parasites
Immunologic reactions that cause cell injury
injurious reactions to endogenous self antigens leading to autoimmune disease, immune rxn to external agents like viruses
How do genetic defects cause cell injury?
Because of deficiency of functional proteins like enzyme defects in inborn errors of metabolism or accumulation of damaged DNA or misfolded protein leading to cell death.
Examples of nutritional imbalances leading to cell injury:
protein-calorie deficiency leading to death, vitamin deficiencies, anorexia nervosa; nutritional excess can also cause cell injury: cholestrol leading to artherosclerosis, obesity associated with diabetes and cancer
Which method detects the changes associated with cell death/injury first–histochemical/ultrastructural technique or light microscopy?
histochemical/ultrastructural–minutes to hours
light microscopy–hours to days
*morphologic manifestation of necrosis takes more time to develop than reversible damage such as ischemia of myocardium–swelling–in minutes
Reversible cell injury characterized by:
genralized swelling of cell and its organelles, belbbing of plasma membrane, detachment of ribosomes from ER and climbing of nuclear chromatin; leads to decreased ATP,loss of cell membrane integrity, defect in protein synthesis, cytoskeletal damage and DNA damage
Severe mitochondrial damage with depletion of ATP and rupture of lysosomal and plasma membranes are associated with necrosis or apoptosis?
Necrosis
What two important features of reversible cell injury can be recognized under the light microscope?
Cellular swelling fatty change (lipid vacuoles in cytoplasm)--seen in hepatocytes and myocardial cells
cellular swelling affecting many cells in organ causing pallor, increased turgor, and increase in weight of organ; small clear vacuoles in cytoplasm; this pattern of non lethal injury is called ____
hydrophic change or vacuolar degeneration
- cells may also show increased eosinophilic staining which becomes more pronounced with progression to necrosis
Ultrastructural changes of reversible cell injury:
plasma membrnae blebbing/blunting/loss of microvilli
mitochondrial swelling and appearance of small amorphous densities
Dilation of ER with detachment of polysomes–intracytoplasmic myelin figures
nuclear alterations with disaggregation of granular and fibrillar elements
The morphologic appearance of ____ as well as ____ is the result of denaturation of intracellular proteins and enzymatic digestion of the lethally injured cell
necrosis, necroptosis
Where do the enzymes that digest the necrotic cell come from?
lysosomes of dying cells themselves and from lysosomes of leukocytes involved in inflammatory reaction
The EARLIEST histologic change from myocardial necrosis does not become apparent until ____ later
4-12 hours later
*BUT because of loss of plasma membrane integrity, cardiac specific enzymes and proteins are rapidly released from necrotic muscle and can be detected in blood 2 hrs after necrosis
Necrotic cells show increased _____ atrributable to loss of cytoplasmic RNA (which binds the blue dye, hematoxylin) and in part to denatured cytoplasmic proteins (which bind the red dye eiosin)
eosinophilia in H&E stains
*loss of glycogen particles makes necrotic cells have glassy homogenous appearance than normal cells
In necrotic cells, dead cells may be replaced by large whorled phospholipid masses called _____derived from damaged cell membranes
myelin figures; phospholipid percipitates and is then phagocytosed by other cells and further degraded into fatty acids–calcification of such fatty acids results in calcium soaps–dead cell becomes calcified
In electron microscopy, what are necrotic cells characterized by?
Discontinuities in plasma and organelle membranes, marked dilation of mitochondria with the appearance of large amorphous densities, intracytoplasmic myelin figures, amorphous debris, and aggregates of fluffy material probably representing denatured protein
What 3 nuclear change patterns do you see in necrosis due to non-specific breakdown of DNA?
- Karyolysis: basophilia of chromatin may fade, reflects loss of DNA bc of enzymatic degradation by endonucleases
- pyknosis: nuclear shrinkage and increased basophilia–chromatin condenses into solid, shrunken basophilic mass
- karyorrhexis: pyknotic nucleus undergoes fragmentation
* After a day or two, the nucleus in the necrotic cell disappears
Architecture of dead tissues is preserved for at least some days; firm texture; proteolysis of dead cells is blocked so eosinophilia, anucleate cells may persist for days or weeks
Coagulative necrosis
Ischemia caused by obstruction in a vessel may lead to coagulative necrosis in all organs except ____
The brain
A localized area of coagulative necrosis is called an ______
Infarct
_______ necrosis is characterized by digestion of the dead cells, resulting in transformation of the tissue into a liquid viscous mass; seen in focal bacterial or sometimes fungal infections; necrotic material is creamy yellow (pus)
Liquefactive
- hypoxic death of cells in CNS manifests as liquefactive necrosis as well
______ necrosis is usually applied to the limbs (lower leg) that has lost its blood supply and has undergone necrosis (coagulative) involving multiple tissue planes.
Gangrenous
When bacterial infection is superimposed on gangrenous necrosis and there is more liquefactive necrosis because of the actions of degradative enzymes in bacteria and the attracted leukocyte so, it gives rise to ___ ______
Wet gangrene
________ necrosis is associated with tuberculosis; cheese like, white; on microscopy necrosis looks like a structureless collection of fragmented or lysed cells and amorphous granular debris enclosed within a distinctive inflammatory border known as _____
Caseous, granuloma
______ necrosis refers to focal areas of fat destruction from release of activated pancreatic lipase so into pancreas and peritoneal cavity
Fat
*Pancreatitis: pancreatic enzymes leak out of acinar cells and liquefy the membranes of fat cells in the peritoneum; the released lipases split the triglycerides esters contained within fat cells; the FAs combine with calcium to produce chalky white areas (fat saponification); basophilic calcium deposits
_______ necrosis is seen in immune reactions involving blood vessels; typically occurs when complexes of antigens and anti-bodies are deposited in the walls of the arteries; deposits of immune complexes with fibrin that has leaked result in bright pink and amorphous appearance in H&E stains
Fibrionoid
- Cellular swelling, fatty change, plasma membrane blabbing, loss of microvilli, mitochondrial swelling, dilation of ER, eosinophilia due to low cytoplasmic RNA
- Increased eosinophilia, nuclear shrinkage, fragmentation, dissolution; breakdown of plasma membrane and organellar membrane, abundant myelin figures, leakage and enzymatic digestion of cellular contents
- Reversible cell injury
2. Necrosis
The cellular response to injurious stimuli depends on what 3 factors? What are the consequences of cell injury dependent upon
Cell response depends on :Nature of injury, it’s duration, and its severity
Consequences dependent on type, state and adaptability of the injured cell
In electron microscopy, what are necrotic cells characterized by?
Discontinuities in plasma and organelle membranes, marked dilation of mitochondria with the appearance of large amorphous densities, intracytoplasmic myelin figures, amorphous debris, and aggregates of fluffy material probably representing denatured protein
What 3 nuclear change patterns do you see in necrosis due to non-specific breakdown of DNA?
- Karyolysis: basophilia of chromatin may fade, reflects loss of DNA bc of enzymatic degradation by endonucleases
- pyknosis: nuclear shrinkage and increased basophilia–chromatin condenses into solid, shrunken basophilic mass
- karyorrhexis: pyknotic nucleus undergoes fragmentation
* After a day or two, the nucleus in the necrotic cell disappears
Architecture of dead tissues is preserved for at least some days; firm texture; proteolysis of dead cells is blocked so eosinophilia, anucleate cells may persist for days or weeks
Coagulative necrosis
Ischemia caused by obstruction in a vessel may lead to coagulative necrosis in all organs except ____
The brain
A localized area of coagulative necrosis is called an ______
Infarct
_______ necrosis is characterized by digestion of the dead cells, resulting in transformation of the tissue into a liquid viscous mass; seen in focal bacterial or sometimes fungal infections; necrotic material is creamy yellow (pus)
Liquefactive
- hypoxic death of cells in CNS manifests as liquefactive necrosis as well
______ necrosis is usually applied to the limbs (lower leg) that has lost its blood supply and has undergone necrosis (coagulative) involving multiple tissue planes.
Gangrenous
When bacterial infection is superimposed on gangrenous necrosis and there is more liquefactive necrosis because of the actions of degradative enzymes in bacteria and the attracted leukocyte so, it gives rise to ___ ______
Wet gangrene
________ necrosis is associated with tuberculosis; cheese like, white; on microscopy necrosis looks like a structureless collection of fragmented or lysed cells and amorphous granular debris enclosed within a distinctive inflammatory border known as _____
Caseous, granuloma
______ necrosis refers to focal areas of fat destruction from release of activated pancreatic lipase so into pancreas and peritoneal cavity
Fat
*Pancreatitis: pancreatic enzymes leak out of acinar cells and liquefy the membranes of fat cells in the peritoneum; the released lipases split the triglycerides esters contained within fat cells; the FAs combine with calcium to produce chalky white areas (fat saponification); basophilic calcium deposits
_______ necrosis is seen in immune reactions involving blood vessels; typically occurs when complexes of antigens and anti-bodies are deposited in the walls of the arteries; deposits of immune complexes with fibrin that has leaked result in bright pink and amorphous appearance in H&E stains
Fibrionoid
- Cellular swelling, fatty change, plasma membrane blabbing, loss of microvilli, mitochondrial swelling, dilation of ER, eosinophilia due to low cytoplasmic RNA
- Increased eosinophilia, nuclear shrinkage, fragmentation, dissolution; breakdown of plasma membrane and organellar membrane, abundant myelin figures, leakage and enzymatic digestion of cellular contents
- Reversible cell injury
2. Necrosis
The cellular response to injurious stimuli depends on what 3 factors? What are the consequences of cell injury dependent upon
Cell response depends on :Nature of injury, it’s duration, and its severity
Consequences dependent on type, state and adaptability of the injured cell (skeletal muscle can withstand hypoxia much better than cardiac muscle)
______ _____ results from different biochemical mechanisms acting on several essential components
Cell injury
Reduction in ATP levels is fundamental cause of necrotic cell death associated with both hypoxic and chemical injury. What are the major causes of ATP depletion?
Reduced supply of oxygen and nutrients, mitochondrial damage, and the actions of toxins like cyanide
Membrane transport, protein synthesis, lipogenesis, and the deacylation-reacylation reaction all require what molecule?
ATP
Consequence of reduced ATP levels in cell:
- Cell swelling and ER dilation bc plasma membrane energy dependent sodium pump activity reduced
- Cell energy metabolism changed bc low O2–>low of. Phos–>low ATP->high AMP->anaerobic glycolysis->glycogen stores rapidly depleted->lactic acid buildup->low pH->decreased enzyme activity
- Ca pump doesn’t work so Ca influx into cell causing damage
- Reduction in protein synthesis bc ribosomes detach from ER
- Low O2/glucose->misfoled proteins->unfolded protein response->cell injury/death
- Necrosis
Mitochondria are critical players in cell injury and cell death by all pathways bc they produce ATP. How is mitochondria damaged?
Increase in cytosolic Ca, reactive oxygen species, oxygen deprivation so they are sensitive to all injurious stimuli like hypoxia and toxins and mutations in mitochondrial genes leads to inherited diseases
3 major consequences of mitochondrial damage
- Formation of high conductance channel in mit membrane called mitochondrial permeability transition pore; opening of pore leads to failure of of phos and depletion of ATP–>necrosis
- Formation of reactive oxygen species
- Leakage of cytochrome c in cytosol due to increased permeability of outer mit membrane leading to apoptosis
What is the structural protein associated with the mitochondrial permeability transition pore? Clinical relevance?
Cyclophilin D
The immunosuppressive drug cyclosporine used to prevent graft rejection targets cyclophilin D to reduce cell injury by preventing opening of the mitochondrial permeability transition pore
What are the 3 mechanisms by which intracellular Ca causes cell injury?
- Accumulation of Ca in mitochondria results in opening of mitochondrial permeability transition pore and failure of ATP production
- Activates phospholipases (causes membrane damage), pro teases (break cytoskeletal proteins and membrane), endonucleases (fragments DNA), ATPases (rapidly depletes ATP)
- Causes apoptosis by activation of caspaces and increasing mitochondrial permeability
What pathologies are associated with cell injury caused by reactive oxygen species?
Chemical and radiation injury, ischemia-reperfusion injury, cellular aging and microbial killing by phagocytes
Free radicals may be present transiently at low concentrations without causing damage, but increased production of ROS leads to excess of ROS leading to a condition called _____ ______
Oxidative stress
- associated with cell injury, cancer, aging, Alzheimers’
- ROS also produced by macrophages during inflammation to clear dead cells and waste
What are the 6 ways of generating free radicals?
- Reduction-oxidation rxn that occurs during normal metabolic processes: O2->O2. (1e-)->H2O2 (2 e-)->OH.(3e-)
- Absorption of radiant energy (uv light, X-rays): H2O->OH. & H.
- ROS produced in leukocytes during inflammation–uses NADPH oxidase, xanthine oxidase to make O2.
- Enzymatic metabolism of exogenous chemicals or drugs (CCl4->CCl3.)
- Transition metals like iron and copper accept/donate free electrons-Fenton Rxn (H2O2+Fe2+->Fe3+ + OH. + OH-)
- Nitric Oxide from endothelial cells, macrophages, neurons can be converted to highly reactive proxynitrate (ONOO-) and NO2 and NO3-.
Free radicals are unstable and generally decay spontaneously. What are some other mechanisms by which free radicals are removed?
- Antioxidants block free radical formation; ex: Vit. E, A, ascorbic acid and glutathione in cytosol
- Free iron and copper forms ROS but minimizes ROS when bound to storage and transport proteins (transferrin, ferritin, lactose rain, ceruloplasmin)
- Enzymes like catalase, SOD, and Glutathione peroxidase act as free radical scavenging systems and breaks down H2O2 and O2.
Name the enzyme: present in peroxisomes, decomposes H2O2
2H2O2–>O2 + 2H2O
Catalase
Name the enzyme: converts O2.->H2O2
2O2. + 2H–>H2O2 + O2
Superoxide dismutases
*Manganese SOD localized in mitochondria while copper-zinc SOD found in cytosol!
Name the enzyme: protects against injury by catalyze get free radical breakdown: (H2O2 + 2GSH–>GSSG+ 2H2O or 2OH. + 2 GSH –>GSSG + 2H2O)
Glutathione peroxidase
*The intracellular ratio of oxidized glutathione (GSSG) to reduced glutathione (GSH) reflects oxidative state of cell and is important indicator of cells ability to detoxify ROS
What are the 3 main pathologic effects of free radicals?
- Lipid peroxidation in membranes: when double bonds in unsat FAs of membrane lipids are attacked by O2 derived radicals, esp OH.causing membrane damage
- Oxidative modification of proteins: damage active sites of enzymes, disrupt conformation of structural proteins and enhance proteasomal degradation of unfolded/misfolded proteins=cell damage
- Lesions in DNA: Free radicals cause single and double strand breaks in DNA, cross linking of DNA strands and formation of adducts–causes cell aging and malignant cells
Does ROS cause necrosis or apoptosis?
Both; can also produce degradative enzymes rather than direct damage of macromolecules.
Early loss of selective membrane permeability leading to overt membrane damage is a consistent feature of most forms of cell injury except _____
Apoptosis
What are the 4 main mechanisms of MEMBRANE damage?
- Reactive oxygen species–lipid peroxidation
- Decreased phospolipid synthesis–decreased ATP bc of damaged mitochondria and hypoxia
- Increased phospholipid breakdown–increased cytosolic and mit Ca; lipid breakdown products (free FA, acts carnitine and lysophospolipids) have detergent effect on membrane and cause change in permeability of substances
- Cytoskeletal abnormalities: protease activation due to high Ca damages cytoskeleton–in myocardial cells, cell swelling causes detachment of cell membrane from cytoskeleton leading to rupture
Major consequences of membrane damage (mitochondrial membrane, plasma membrane, and lysosomal membrane)
- Mitochondrial: membrane damage results in opening of mitochondrial permeability transition pore, leading to decreased ATP and release of proteins causing apoptosis
- Plasma membrane damage results in loss of osmotic balance and influx of ions/fluids/metabolites preventing ATP production and depletion
- Lysosomal membrane damage results in leakage of enzymes into cytoplasm and activation of acid hydrolases in acidic intracellular pH; lysosomes contain RNAses, DNAses and proteases, phosphatase said, glusidases leading to digestion of proteins, RNA, DNA and glycogen leading to necrosis
If damage to DNA is so severe that it cannot be repaired, what happens?
Apoptosis
Two phenomena that characterize irreversible cell injury:
- Inability to reverse mitochondrial dysfunction (lack ox phos and ATP production)
- Profound disturbances in membrane function
How can you detect tissue-specific cell injury and necrosis clinically?
Using serum samples–leakage of intracellular proteins through damaged cell membrane and into circulation
- examples: creating kinase and Troponin for heart; alkaline phosphatase for liver and bile duct epithelium; transaminase said for hepatocytes
______ is the most common type of cell injury in clinical medicine and it results from hypoxia induced by reduced blood flow, most commonly due to mechanical arterial obstruction; can also be caused by reduced venous drainage
Ischemia
Difference between hypoxia and ischemia in terms of anaerobic glycolysis? which is more severe?
Hypoxia: energy production via glycolysis can continue
Ischemia: compromises the delivery of substrates for glycolysis due to accumulation of metabolites/exhaustion of glycolytic substrates
Ischemia causes more rapid and severe cell and tissue injury than hypoxia
Mechanism of ischemic cell injury
O2 falls->loss of ox phos->low ATP->sodium pump failure->efflux of K->influx of Na/water-> cell swelling; also influx of Ca causes damage; loss of glycogen and decreased protein synthesis; more ATP depletion due to prolonged hypoxia->cytoskeleton disperses->loss of microvilli and blebs form; myelin figures from degenerating cell membranes within cytoplasm or EC; ER dilation; mit swollen
**IF O2 IS RESTORED, ALL OF THESE REVERSIBLE! If ischemia persists, irreversible injury and necrosis ensue
Cell death caused by persistent ischemia and reperfusion injury is mainly by necrosis or apoptosis?
Necrosis but apoptosis also contributes
After myocardial infarction, which can be detected first—morphological changes or elevated enzymes (Troponin, creatine kinase MB) in blood?
Enzymes in blood due to leakage across abnormally permeable plasma membrane!
The transcription factor called ____ protects against hypoxic stress by promoting new blood vessel formation, stimulating cell survival pathways and enhancing anaerobic glycolysis
Hypoxia-inducible-factor 1
What is a therapeutic intervention used to treat ischemic and traumatic brain and spinal cord injury?
Inducing hypothermia (reducing body temp to 92 degrees) which reduces metabolic demands of the stressed cells, decreases cell swelling, suppresses formation of free radicals and inhibits the host inflammatory response
What does restoring blood flow to ischemic tissues do to the tissue?
If cells are reversibly injured, restoration of blood flow promotes recovery but can also paradoxically exacerbate the injury and cause cell death
Why is ischemia-reperfusion clinically important?
Because it contributes to tissue damage during myocardial and cerebral infarction
Reperfusion injury occurs because the new damaging processes are set in motion during reperfusion causing the death of cells that could otherwise recover. What are the mechanisms of reperfusion injury?
- Oxidative stress-incomplete reduction of O2 by damaged mit or bc of oxidases in leukocytes, endothelial cells, parynchymal cells; antioxidant defense compromised
- Intracellular calcium overload: begins during acute ischemia but exacerbated in reperfusion due to influx of Ca from membrane damage and ROS mediated SR->causes MPTP to open leading to further ATP depletion
- Inflammation: signals from dead cells, recruit neutrophils (anti-neutrophil therapeutic treatment)
- Activation of complement: IgM deposits in ischemic tissues and during reperfusion, complement activated
Which organ is a frequent target for drug/chemical toxicity? Why?
The liver because many drugs are metabolized in liver
Two pathways by which chemicals induce cell injury:
Direct toxicity and indirect toxicity
Direct toxicity is when chemicals injure cells directly by combining with critical molecular components. What are two classical examples?
- In mercuric chloride poisoning, Mercury binds to sulfhydryl groups of membrane proteins causing increased permeability and inhibiting ion transport; affect organs that concentrate, use, absorb, excrete–aka GI tract and kidney
- Cyanide poisons Mit cytochrome oxidase inhibiting ox phos
- Other antineoplastic agents and antibiotics
Aside from direct toxicity, chemicals can induce cell injury by converting chemicals into toxic reactive metabolites which then act on target molecules. Which enzymes mediate this conversion? Where is it located? How do they cause cell injury? Example?
Cytochrome P-450 in smooth ER of liver and other organs; causes injury by forming free radicals leading to lipid peroxidation
Ex: CCl4 converted to CCl3. by cyt p450 which causes lipid peroxidation and damages cell structures; acetaminophen also converted to toxic product in liver leading to cell injury
____ is a pathway of cell death 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
Apoptosis
Apoptotic cells break up into fragments called ____ ____
Apoptotic bodies
Does apoptosis elicit the inflammatory pathway?
NO!! Because dead cell and its fragments are rapidly devoured before the contents leak out
5 PHYSIOLOGIC situations where apoptosis is needed:
- Destruction of cells during embryogenesis–implantation, organogenesis, metamorphosis
- Involution of hormone-dependent tissues upon hormone withdrawal–endometrial breakdown during menstrual cycle, follicular atresia in menopause, prostatic atrophy after castration, regression of lactating breast after weaning
- Cell loss in proliferating cell populations–immature lymphocytes in BM and thymus, B lymphocytes in germinal centers that don’t express Ag receptor, epithelial cells in intestinal crypts
- Elimination of potentially harmful self-reactive lymphocytes–prevent autoimmunity
- Death of host cells that have served their useful purpose such as neutrophils in acute inflammatory response and lymphocytes at the end of immune response–deprived of survival signals (GF)
Causes of apoptosis:
DNA damage, accumulation of misfolded proteins, cell death in certain infections (viral–adenovirus and HIV; T cell mediated cell death in tumors and transplant rejection), pathologic atrophy in parynchymal organs after duct obstruction (pancreas, partotid gland, kidney)
Morphological changes associated with apoptosis:
- Cell shrinkage
- Chromatin condensation (peripherally)
- cytoplasmic blebs and apoptotic bodies
- Phagocytosis of apoptotic cells or cell bodies by macrophages
- NO inflammation, plasma membrane intact until last stage
___ pathway is the major mechanism of apoptosis in all mamilla an cells
Mitochondrial–results from increased permeability of the outer mit membrane with release of pro-apoptotic molecules from mitochondrial inter membrane space into cytoplasm
The release of mitochondrial pro-apoptotic proteins is tightly controlled by ___ family of proteins
BCl2
Anti-apoptotic proteins are ____, ____ and ____
BCl2, BCl-XL, MCL1–located in outer mit membrane and cytosol and ER membrane–prevent leakage of cytochrome c by making outer mit membrane impermeable
*possess 4 BH domains
Pro-apoptotic BCl family proteins
BAX, BAK–have four BH domains
*oligomerize within outer mit protein and promote mit outer membrane permeability
Sensor proteins of BCl family:
BAD, BIM, BID, Puma, Noxa–only 1 BH domain (BH3 only proteins)–senses cellular stress and damage, regulate balance bw pro and anti apoptotic proteins
Once in cytosol, cytochrome c binds to protein called _____ which forms a wheel like hexameter called the apoptosome
APAF-1
*apoptosome binds caspase 9 leading to execution cascade
What is the function of IAPs (inhibitors of apoptosis)? Example?
Blocks the activation of caspases including executioner caspases like caspace 3 and keep cells alive
- ex: Smac/Diablo enters cytoplasm, bind to and neutralize cytoplasmic proteins in mit pathway of apoptosis
This pathway of apoptosis is initiated by engagement of plasma membrane death receptors on a variety of cells
Extrinsic Patway
Death receptors are members of the ____ receptor family
TNF
Two best known death receptors:
Type 1 TNF receptor (TNFR1) and FAs (CD95)
Where is Fas expressed? where is FasL expressed?
Fas expressed on many cell types; FasL expressed on T cells that recognize self antigens and cytotoxic T cells
What happens after Fas binds FasL?
3 or more molecules of Fas are brought together and their cytoplasmic death domains form a binding site for an adaptor protein, FADD, which binds multiple procaspase 8 (and 10 in humans) via death domain, cleavage of pro caspase 8->active caspase 8–>execution pathway
What protein inhibits the extrinsic pathway of apoptosis? Clinical relevance of this protein?
FLIP–binds pro-caspase 8 but cannot cleave and activate it because it lacks protease domain
Some viruses (and normal cells) produce FLIP and use this inhibitor to protect themselves from Fas-mediated apoptosis
Interconnections bw extrinsic apoptotic pathway and mitochondrial pathway
In hepatocytes and pancreatic Beta cells, caspase 8 from Fas signaling cleaves/activates BH3 only protein BID which then feeds into mitochondrial pathway=fatal blow to cells
The mitochondrial pathway leads to activation of the initiator caspase __ and the death receptor pathway to the initiator caspases __ and ___
9
8 & 10
–activate DNase to cleave DNA
phosphatidylserine in healthy cells vs. apoptotic cells
normally on inner leaflet of PM; flips out and expressed on outer membrane layer where it is recognized by several macrophage receptors
some apoptotic bodies are coated with _____ that is recognized by phagocytes and macrophages themselves may produce proteins that bind to apoptotic cells and target dead cells for engulfment
thrombospondin
Growth factor deprivation (hormones, antigens, cytokines) die by ____ pathway of apoptosis
mitochondrial–decreased synthesis of BCL2 BCLXL and activation of BIM and other pro-apoptotic members of the BCL2 family
Apoptosis caused by DNA damage is induced by the ___ gene
tumor suppressor–tp53–arrests cell cycle at G1 phase but if too damaged p53 induces apoptosis
*p53 stimulates production of BAX, BAK (pro-apoptotic) and some BH3 only proteins; absence of p53 can lead to neoplastic transformation
unfolded or misfolded polypeptides accumulate in the ER because of inherited mutations or stresses and activates signaling pathways that increase the production of chaperones, enhance proteasomal degradation of abnormal proteins and slow protein translation to reduce the load of misfolded proteins in the cell
unfolded protein response
If cytoprotective response is unable to cope with the accumulation of misfolded proteins, the cell activates caspases and induces apoptosis. THis process is called ______
ER stress
Granzymes cleave proteins at __ residues
aspartate
mutation of_____ is the most common genetic abnormality found in cancers
TP53
- defective apoptosis and increased cell survival=?
2. Increased apoptosis and excessive cell death=?
- cancers, autoimmune disorders
2. neurodegenerative diseases, ischemic injury (MI), stroke, death of virus infected cells in viral infection
characterized by loss of ATP, sweling of cell and organelles, generation of ROS, release of lysosomal enzymes and rupture of PM BUT ALSO genetically programmed signal transduction leading to cell death
Necroptosis
*CASPACE INDEPENDENT!
2 unique kinases associated with necroptosis
receptor associated kinase 1 and 3 (RIP1, RIP3) produced by ligation of TNFR1 (complex aslo includes caspase 8)
Diseases/physiologic processes where necroptosis is seen
formation of mammalian bone growth plate; cell death in steatohpatitis, acute pancreatitis, reperfusion injury, Parkinsons, cytomegalovirus (caspase inhibitor process)
cell death accompanied by release of fever inducing IL-1; inflammasome activates caspase 1 (IL1B converting enzyme) leading to activation of IL1; caspase 11 also induces cell death in this pathway
pyropoptis
Autophagy in which there is direct translocation across the lysosomal membrane by chaperone proteins
chaperone mediated autophagy
Autophagy in which there is inward invagination of lysosomal membrane for delivery
microautophagy
autophagy that involves the sequestration and transportation of portions of cytosol in a double membrane bound autophagic vacuole (autophagosome)
Macroautophagy
Steps of autophagy
formation of isolation membrane called phagophore and its nucleation; the isolation membrane is beleved to be derived from the ER–>elongation of vesicle–>maturation of autophagosome, its fusion with lysosomes and degradation of contents
microtubule associated protein light chain 3 (LC3)
What diseases is autophagy associated with?
Cancer: both growth and defense
Neurodegenerative disorders: Alzheimers (increased autophagy), Huntington’s (impaired autophagy)
Infectious disease: mycobacteria Shigella spp and HSV1; macrophage deletion of Atg 5=TB
Inflammatory bowel disease: SNPs in autophagy related genes cause Chron’s and ulcerative colitis
____ is an adaptive response that is enhanced during nutrient deprivation allowing cells cell to cannibalize itself to survive
autophagy
Example of inadequate removal of normal substance secondary to defects in mechanisms of packagng and transport
fatty change (steaosis) in liver
accumulation of an abnormal endogenous substance as a result of genetic or acquired defects in folding, packaging, transport or secretion
mutated forms of a1-anti trypsin
Failure to degrade a metabilite due to inherited enzyme deficiencies
storage diseases
Deposition and accumulation of abnormal exogenous substance when the cell has neither the enzymatic machinery to degrade substance nor ability to transport it to other sites
carbon or silica particles
abnormal accumulations of triglycerides within parenchymal cells
steatosis–often in liver but can happen in heart, muscle, and kidney
causes include toxins, protein malnutrition, diabetes mellitus, obesity, and anoxia (in developed nations, caused mostly by alcohol and diabetes and obesity)
artherosclerosis appearance
foamy (foam cells)
cluster of foamy cells found in subepithelial connective tissue of the skin and in tendons producing tumorous masses known as xanthomas
acquired hyperlipidemia
Focal acculumations of cholestrol-laden macrophages occur in lamina propria of gallbladders
Cholestrolosis
type of lysosomal storage disease due to mutation of enzyme involved in cholestrol catabolism
Niemann Pick disease, type C
Defects in ___, ___ and___ can result in lipid overload
uptake, catabolism, secretion
Intracellular protein accumulation looks how morphologically?
rounded, eiosinophilic cytoplasmic droplets; disorders like amyloidosis, proteins deposit in extracellular space
______ of proteins can accumulate in porximal renal tubules in setting of chronic proteinuria. Reversible; droplets metabolized and clear if proteinurea resolves
reabsorption droplets
_____ proteins can accumulate if produced in excessive amounts (ex: Ig within plasma cells); then ER becomes grossly distended with eosinophilic inclusions called Russel bodies
Normally secreted proteins
Example of defective intracellular transport and secretion
a1-antitrypsin deficiency–partially folded intermediates of mutated proteins accumulate in hepatocyte ER–>emphysema
Intermediate filament excess (keratin, neurofilament) are hallmarks of cell injury. Keratin IF coalesce into cytoplasmic eiosinophilic inclusions called alcoholic hyaline. Examples of associated diseases?
neurofibrillary tangle in Alzheimers
example of aggregates of abnormal proteins (genetic mutations, aging, etc)
extracellular amyloid
deposit that imparts a homogenous glassy pink appearance in H&E stained histologic sections is called ____.
Hyaline change
intracellular hyaline change: proximal tubule epithelial protein droplets, Russell bodies, viral inclusions and alcoholic hyaline
extracellular hyaline change: damaged arterioles due to extravasated proteins
abnormal glycogen storage=?
abnormal glucose metabolism=?
glycogenoses
diabetes mellitus
Melanin or hemosiderin are examples of ___
pigements
Exogenous pigments:
carbon, coal dust-
-if visibly accumulated with macrophages and lymph nodes, called anthracosis
Endogenous pigments include:
Lipofuscin, melanin and homogentisic acid
wear and tear pigment associated with cellular tissue atrophy (brown atrophy); fine yellow brown intracytoplasmic granules; made of complex lipids, phospholipids and protein derived from cell membrane peroxidation
Lipofuscin
normal endogenous brown black pigment formed by enzymatic oxidation of tyrosine to dihydroxyphenylalanine in melanocytes
Melanin
black pigment formed in patients with alkaptonuria that deposits in skin and connective tissue; pigmentation called ochronosis
Homogentisic acid
hemoglobin derived, golden yellow brown granular intracellular pigment made of aggregated ferritin; associated with primary hemochromatosis bc of increased dietary absorption, thalassemia due to impaired utilization, hemolysis or chronic transfusions
hemosiderin
difference between dystrophic calcification and metastatic calcification
dystrophic arises in nonviable tissues in the presence of NORMAL calcium serum levels and metastatic calcification happens in VIABLE tissues in the setting of HYPERcalcemia
dystrophic calcification seen in?
damaged heart valves, artherosclerosis, and areas of necrosis (coagulative, liquefactive and caseous)
causes of hypercalcemia leading to metastatic calcification
high PTH, bone destruction (multiple myeloma), skeletal metastasis (breast cancer), high bond turnover (Pagets disease) or immobilization, vitamin D related disorders (vit D intoxication, systemic sarcoidosis), renal failure due to phospate retention and resulting hypocalcemia
____ _____ refers to the concept that cells have limited capacity for replication
cellular sensecence
Werner’s syndrome
due to DNA helicase mutation, accelerated aging occurs
RNA protein enzynme complex that maintains telomere length by using its own RNA as a template to add nucleotides to end of chromosomes
Telomerase
______ disiease is due to defective repair of DNA double strand breaks leading to genetic instability and premature aging
ataxia telangiectasia
Most effective way to prolong life span=
caloric restriction–promotes activity of sirtuins that has histone deacytelase activity; sirtuins reduce apoptosis and stimulate protein folding, increase metabolism and insulin sensitivity and reduce ROS; signaling through insulin like GF 1 receptors can also influence life span
