Cell Injury, Adaptations, and Death I and II Flashcards
Name the cellular response to:
Altered physiological stimuli or nonlethal injurious stimuli ⇒
- Increased demand, increased stimulation (e.g., by growth factors, hormones) ⇒
- Decreased nutrients, decreased stimulation ⇒
- Chronic irritation (physical or chemical) ⇒
⇒ Cellular adaptations
- ⇒ Hyperplasia, hypertrophy
- ⇒ Atrophy
- ⇒ Metaplasia
Name the cellular response to:
Reduced oxygen supply, chemical injury, microbial infection ⇒
- Acute and transient ⇒
- Progressive and severe (including DNA damage) ⇒
⇒ Cell injury
- ⇒ Acute reversible injury (cellular swelling and fatty change)
- ⇒ Irreversible injury (cell death)
- Necrosis
- Apoptosis
Name the cellular response to:
**Metabolic alterations, genetic or acquired, chronic injury ⇒ **
⇒ Intracellular accumulations, calcification
Name the cellular response to:
Cumulative sub-lethal injury over long life span ⇒
⇒ Cellular aging
How are tissues grouped based on their proliferative properties?
-
Labile cells
- Continuously dividing cells
- Hematopoietic cells, surface epithelia (ex.: linings of upper airways, gastrointestinal tract, skin, etc.)
-
Stable tissues
- Quiescent; minimal replicative activity normally
- Proliferate in response to injury
- Parenchyma of most solid organs (liver, kidney, pancreas)
- Endothelial cells, fibroblasts, smooth muscle cells
-
Permanent tissues
- Non-proliferative
- Neurons, cardiac muscle cells
Cellular Adaptations: Hypertrophy
-
Increase in size of cells = increase of size of organ
- Increased amounts of proteins and organelles
- Mechanisms: trophic or mechanical triggers to cell
- Occurs in cells that have limited or no capacity to divide
- Physiological Hypertrophy
- Pathological Hypertrophy
-
Physiological Hypertrophy
- Increased functional demand or hormonal stimulation
- Examples: Skeletal muscle hypertrophy in weight lifting athlete and uterus in pregnancy
-
Pathological Hypertrophy
- Example: Cardiac muscle hypertrophy seen in hypertension
Generally describe left ventricular hypertrophy:
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- Thick left ventricle & increased mass
- Adaptation in response to increased work load in hypertension (chronic hemodynamic overload)
- Also occurs with aortic valve stenosis
- Myofibers enlarge: synthesis of more filaments
- Clinical manifestations:
- initially no clinical signs, but eventually, heart reaches a limit beyond which enlargement of muscle mass cannot compensate for increased work & heart failure occurs.
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Cellular Adaptations: Hyperplasia
Increase in cell number
- Occurs in cells capable of division
- labile and stable cells
- Physiologic Hyperplasia
- Pathologic Hyperplasia
-
Physiologic Hyperplasia
- Hormonal hyperplasia of female breast at puberty and in pregnancy
- Compensatory hyperplasia of liver after partial resection
- Connective tissue response with wound healing
-
Pathologic Hyperplasia
- Excessive stimulation by growth factors or hormones
- Example:
- Hormonal imbalance stimulates endometrial hyperplasia
- Skin warts and mucosal lesions associated with viral infections
- papilloma viruses
- Reversible
- Cells respond to normal regulatory mechanisms
- Clinical significance: Increases risk for cancer
Describe benign prostatic hyperplasia. What makes it different from other hyperplasias?
- Very common in men > 50 years old
- Results in formation of nodules in prostate gland in the periurethral region ⇒ varying degrees of urinary obstruction
- Underlying cause is unknown
- Mechanism: androgen-induced release of growth factors increases proliferation of stromal cells ⇒ decreases death of epithelial cells
- Differs from endometrial hyperplasia in that it is not associated with increased risk of prostate cancer
Give a clinical example of both hyperplasia and hypertrophy:
Enlargement of uterus during pregnancy (gravid)
Cellular Adaptations: Atrophy
Decrease in size of a cell due to loss of cell substance
- If severe ⇒ decreased organ size
- Decreased protein synthesis & increased degradation
- Decreased function, but not death
- Physiologic Atrophy
- Pathologic Atrophy
-
Physiologic Atrophy
- Loss of hormonal stimulation
- ex: endometrium at menopause
-
Pathologic Atrophy
- Decreased functional demand
- ex: broken arm in cast
- Loss of innervation
- ex: trauma to peripheral nerve
- Inadequate nutrition
- calorie or protein deficit
- Decreased functional demand
Cellular Adaptations: Metaplasia
One adult cell type is replaced by another adult cell type (that is better able to handle the stress)
-
Adaptive process to chronic stress +/or persistent cell injury
- Examples: Chronic smokers, Chronic gastric acid reflux
- Cells are “reprogrammed”
- Stem cells differentiate along a new pathway
- Reversible
- May be associated with risk of cancer
Describe the two types of metaplasia:
-
Epithelial metaplasia
-
Ciliated columnar epithelium becomes squamous epithelium
- __ex. Trachea/bronchi of smokers
-
Squamous epithelium becomes gastric/intestinal type epithelium
- ex. Distal esophagus in those with reflux
-
Ciliated columnar epithelium becomes squamous epithelium
-
Mesenchymal metaplasia
- Bone formation in soft tissue (muscle/connective tissue) at sites of injury
Describe squamous metaplasia of trachea & bronchi in smokers:
-
Respiratory epithelium:
- ciliated columnar epithelium
⇒ squamous epithelium
- ciliated columnar epithelium
- Stimulus that causes metaplasia may predispose to development of malignant neoplasm (squamous cell carcinoma)
Describe the process of Barrett Esophagus:
Squamous epithelium (distal esophagus) ⇒ glandular epithelium (stomach)
-
protects against reflux of stomach acid
- predisposes to development of glandular carcinoma (adenocarcinoma)
What happens with squamous metaplasia in the endocervix?
- columnar becomes squamous
- increases risk of HPV infection
What are the 2 types of oxygen deprivation?
hypoxia and ischemia
What is the difference between hypoxia and ischemia?
-
Hypoxia
- Inadequate oxygenation of blood
- ex: lung disease, lack of oxygen in ambient air
- Reduced oxygen-carrying capacity of blood
- ex: anemia, cyanide
- Inadequate oxygenation of blood
-
Ischemia
- lack of blood supply to site
- ex: coronary artery disease/heart attack, stroke
- lack of blood supply to site
Besides oxygen deprivation, what are the other etiologies of cell injury?
- Physical agents
- Trauma, temperature extremes, radiation, etc.
- Chemical agents
- Chemicals (sodium, glucose), poisons, asbestos, etc.
- Infectious agents
- Viruses, fungi, bacteria, parasites, etc.
- Immunologic reactions
- Autoimmune diseases, hypersensitivity
- Genetic derangements
- Point mutations, polymorphisms, etc.
- Nutritional imbalances
- Protein / calorie imbalance, vitamin & mineral deficiencies, etc.
- Aging: decreased ability to repair damage
What is cell injury a result of?
Continued severe stress (intrinsic and extrinsic) to a point that the cell reaches its limit and can no longer adapt
Irreverisble Cell Injury (cell death):
Causes and Types (2)
-
Inability to reverse mitochondrial dysfunction
- lack of oxidative phosphorylation & ATP generation
- Disturbance of membrane function
Two Types:
- Necrosis
- Apoptosis
Cell Death: Necrosis vs. Apoptosis
- Cell size:
- Nucleus:
- Plasma Membrane:
- Cellular Contents:
- Adjacent Inflammation:
- Physiologic or Pathologic Role:
Necrosis
- Cell size: Enlarged
- Nucleus: Pyknosis, karyorrhexis, karyolysis
- Plasma Membrane: Disrupted
- Cellular Contents: Enzymatic digestion: may leak out of cell
- Adjacent Inflammation: Frequent
- Physiologic or Pathologic Role: Invariable pathologic
Apoptosis:
- Cell size: Reduced
- Nucleus: Fragmentation into nucleosome-size fragments
- Plasma Membrane: Intact: altered structure
- Cellular Contents: Intact: may be released in apoptotic bodies
- Adjacent Inflammation: No
- Physiologic or Pathologic Role: Often physiologic: elminating unwanted cells. May be pathologic
Morphology of Reversible Cell Injury
- Fatty change
- Cellular Swelling
-
Fatty change
- Lipid vacuoles in cytoplasm
- Occurs with toxic and hypoxic injury
- Primarily in cells dependent on fat metabolism
- Example: fatty liver secondary to toxins (alcohol)
-
Cellular Swelling
- Hydropic change or vacuolar degeneration
- Results from failure of membrane pumps to maintain homeostasis: membrane blebs
- Vacuoles appear in cells corresponding to distended endoplasmic reticulum
Describe the pathogenesis and clinical manifestations of fatty liver:
- Yellow color and “greasiness” indicates steatosis (fat accumulation)
- Hepatocytes are injured resulting in an intracellular accumulation of triglycerides, liver enlargement and elevated liver enzymes
- leak from injured hepatocytes
- Clinical manifestations: depend upon specific cause & how severe the injury
- It is reversible if cause is removed.
- Mild: no effect on cell function.
- Severe: impairs cell function, may lead to cell death, eventual cirrhosis if injury continues
What are some causes of fatty liver? What other organs accumulate fat?
-
Common causes:
- toxins (including alcohol)
- obesity
- malnutrition
- carbon tetrachloride
- anoxia
- diabetes
- viral infections
- Other organs accumulate fat also:
- heart, skeletal muscle, kidney
Why would the liver accumulate fat?
- impairment of microsomal & mitochondrial functions
- decreased fatty acid oxidation
- decreased apoprotein formation
- increased mobilization of fatty acids from periphery
Describe Vacuolar (hydropic) Change:
Hydropic change (cellular swelling) of kidney tubules:
- First manifestation of many types of cell injury
- Corresponds to distended endoplasmic reticulum
- Also seen:
- plasma membrane blebs
- swollen mitochondria
- clumped nuclear chromatin
- Also seen:
- When many cells in an organ are affected ⇒ organ weight is increased and appears swollen
Morphologic Features of Necrosis
- increased eosinophilia
- nuclear shrinkage
- fragmentation
- breakdown of plasma membrane & organelle membranes
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List the types of necrosis (6):
- Coagulative necrosis
- Liquefactive necrosis
- Caseous necrosis
- Gangrenous
- Fat necrosis
- Fibrinoid necrosis
Coagulative Necrosis:
- Etiology:
- Morphology:
- Areas affected:
-
Etiology:
- Results from hypoxic or anoxic injury due to ischemia (infarct)
-
Morphology:
- Persistence of dead cells with intact outlines but with loss of cellular details
- Injury denatures both cellular proteins and enzymes (no proteolysis takes place)
-
Areas affected:
- Occurs in all solid organs (except for the brain)
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Liquefactive Necrosis
- Etiology:
- Pathogenesis:
- Morphology:
-
Etiology:
- Complete digestion of the dead cells
-
Pathogenesis:
- Commonly seen with bacterial and fungal infections
- Microbes stimulate accumulation of WBC
- WBCs release digestive enzymes
- Necrotic cells together with acute inflammatory cells = pus
- EXCEPTION: brain infarcts results in liquefactive necrosis (reasons not understood)
-
Morphology:
- Tissue is semi-liquid as it has been dissolved by hydrolytic enzymes
- from lysosomes in WBCs attracted to the area
- Tissue is semi-liquid as it has been dissolved by hydrolytic enzymes
Caseous Necrosis:
- Etiology:
- Morphology:
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-
Etiology:
- Characteristic of tuberculous infection
-
Morphology:
- Gross appearance resembles cheese
- Crumbly (friable) appearance of necrosis
- Fragmented and coagulated cells with loss of tissue architecture (no cell outlines)
- Usually surrounded by a border of inflammatory cells forming a distinctive pattern (granuloma)
- Gross appearance resembles cheese
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Gangrenous Necrosis
- Dry gangrene vs. wet gangrene
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- Not a specific type of necrosis but a term used for ischemic coagulative necrosis of lower or upper extremity
-
Dry gangrene vs. wet gangrene:
- When a bacterial infection is also present, the necrosis has liquefactive characteristics (wet gangrene)
- Also used for severe necrosis of other organs:
- Ex: gangrenous bowel, gangrenous appendix, gangrenous gallbladder
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Fat Necrosis:
- Areas affected:
- Pathogenesis:
-
Areas affected:
- Typically seen in the pancreas in acute pancreatitis
-
Pathogenesis:
- Injury to pancreas releases lipase which liquefies fat and splits triglycerides
- Fatty acids combine with calcium to form chalky white material (saponification)
- Can also occur as a result of trauma to fatty tissue with release of lipases and triglycerides
- Example: Fat necrosis of breast
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Fibrinoid Necrosis:
- Deposition of immune complexes (antigens & antibodies) in vascular wall
- Fibrin-like (suffix “-oid” means “like”)
- Bright pink amorphous appearance
-
Occurs in vasculitis syndromes
- Polyarteritis nodosa, giant cell arteritis, etc.
What are the principal targets for cellular injury? By what mechanism are the targets affected?
-
Mitochondria
- depletion of ATP & ↑ reactive oxygen species-ROS
-
Calcium homeostasis
- intracellular entry of calcium
-
Cellular membranes
- increase permeability
-
DNA & cellular proteins
- damage to DNA, protein misfolding
Mitochondrial damage results in ___ ________.
- Major Causes:
ATP depletion
-
Major Causes:
- Decreased oxygen
- Decreased nutrients (glycogen)
- Specific toxins (cyanide)
- ATP: required for synthetic & degradative cell processes
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What happens as a result of ATP depletion in the mitochondria?
Production of reactive oxygen species (ROS)
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Effects of increased intracellular calcium:
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Accumulation of Oxygen-derived Free Radicals
(Oxidative damage)
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What are the mechanisms of membrane damage? What are the etiologies of membrane damage?
-
Causes:
- ischemia
- microbial toxins
- complement
- other physical/chemical agents
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Ischemic vs. Hypoxic Injury
-
Ischemia (decreased blood flow) injures tissues faster than hypoxia (decreased oxygen level)
- No delivery of substrates for glycolysis
- Both aerobic & anaerobic glycolysis cease
- No removal of metabolites by blood flow
- Most common cause of cell injury
- No delivery of substrates for glycolysis
- Hypoxia: anaerobic glycolysis continues
-
In each: reduced supply of oxygen
- Results in reduced production of intracellular ATP
- Leads to failure of other energy dependent systems
- *Factors affecting cell injury and death**
- *Cell response depends upon:**
-
Type of injury
- Ischemia vs. hypoxia; toxins, infection, etc.
-
Duration & severity of insult
- Example:
- IF complete ischemia: death in 15 to 20 minutes
- IF blood flow reduced by half: it takes 3-4 hours for cell death
- Example:
Factors affecting cell injury and death
Outcome depends upon:
-
Cell type:
- Example: Neurons are particularly sensitive to lack of oxygen
- In other tissues: skeletal muscle dies in 2-3 hours; cardiac muscle in 20-30 minutes, etc.
-
Extent of collateral flow:
- from vessels around the area affected
What are other factors that affect cell injury and death (besides injury and cell type)?
Additional factors:
- genetics
- hormones
- nutritional status of cell/organ
Reperfusion Injury
- Definition:
- Mechanisms:
-
Definition: Restoration of blood flow to ischemic tissue may increase cell injury
- Occurs most frequently in brain and heart
-
Mechanisms:
- Increased free radical generation
-
Incomplete reduction of oxygen occurs with ischemia
- Restoration of oxygen allows production of free radicals which increase tissue damage
-
Increased leukocytes, plasma proteins, & complement (inflammation)
- Production of adhesion molecules and cytokines by damaged tissue attract inflammatory cells that increase extent of injury
Chemical (toxic) injury:
Mechanims (2)
Many drugs/toxins are metabolized in liver; it is often site of drug toxicity
-
Direct toxins:
- Bind to cellular organelle or molecular component
-
Toxic metabolites:
- Toxin is “activated”
- Often by P-450 oxidases in liver smooth ER
Give an example of a direct toxin that causes cell injury:
Example:
- Mercuric chloride binds to cell membrane proteins
- Results in decreased membrane transport and increased membrane permeability
Give an example of a toxic metabolite that causes cell injury:
Examples:
- Acetominophen (tylenol)
- Carbon tetrachloride converted to toxic free radical which breaks down ER membranes
Apoptosis characteristics:
- The plasma membrane is intact
- No leakage of cell contents
- No inflammation
Causes of apoptosis:
Physiologic Conditions
- during embryogenesis
- involution of hormone dependent tissues after hormone deprivation (ex. pregnancy)
- cell loss in proliferating cells maintains constant number (ex. GI epithelium)
- death of inflammatory cells (neutrophils, lymphocytes) after completion of immune response
- elimination of self-reactive lymphocytes
- death induced by cytotoxic-T lymphocytes
Causes of apoptosis:
Pathologic condtions
-
Eliminates cells with DNA damage (ex. radiation, chemo, etc.)
- If repair processes fail, apoptosis is activated and the cell dies
- Radiation & many chemo drugs work via apoptosis
- Accumulation of misfolded proteins (ex. Alzheimer disease)
- Cell injury induced by viral infections (ex. HIV), induced by the virus or the host
- Organ atrophy with duct obstruction (example: Pancreas)
Morphology of Apoptosis
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- Cytoplasmic eosinophilia
-
Chromatin condensation & aggregation
- eventually karyorrhexis
- Cell shrinkage with cytoplasmic blebs & apoptotic bodies
- Phagocytosis without inflammation
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Describe the intrisnic mitchonidrial pathway for apoptosis:
Intrinsic pathway:
Bcl-2 proteins increase permeability of the mitochondria ⇒ allow cytochrome C to enter cyotplasm ⇒ resulting in caspase activation
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Cystic fibrosis, familial hypercholesterolemia, Tay-Sachs disease, Creutzfeldt-Jakob disease, Alzheimer disease, Huntington disease, Parkinson disease are all caused by what process?
Unfolded protein response & diseases caused by mis-folding of proteins ⇒ leads to apoptosis
Subcellular responses due to cell injury:
- Alterations of the cell resulting in distinctive morphology involving specific organelles
- Occur in acute (lethal) & chronic (on-going) injury as an adaptive response to injury
-
Results may be accumulation of abnormal substances
- Lipid accumulation already discussed
- May be seen in lysosomes, endoplasmic reticulum, mitochondria, etc.
- Examples: lipofuscin, carbon, iron, etc.
Lipofuscin in heart muscle:
- Indigestible material resulting from lipid peroxidation
- “Wear & tear” pigment, occurs predominantly with aging
- Particularly in heart, liver, & brain
What type of disease of Tay-Sachs Disease?
Lysosomal Storage Disease
-
Abnormal metabolism
- increased production of normal substance (gangliosides) because of lack of enzyme to degrade it
Anthracosis in lung:
Inhaled in air ⇒ **phagocytosed by alveolar macrophages **⇒ transported to regional lymph nodes
Give an example of hypertrophy of smooth ER in liver:
adaptative response to barbiturates & alcohol in hepatocytes (to maximize toxin removal)
What could cause mitochondrial change?
- mitochondria response to starvation (atrophy)
- alcohol (enlarge)
- myopathy due to respiratory chain enzyme abnormality (increase in number & show abnormal structure)
Cytoskeleton Abnormalities
- Consists of actin, myosin, microtubules & intermediate filaments
-
Accumulations occur with:
- Toxins: Alcohol - Mallory hyaline in liver
- Unknown causes: Alzheimer’s disease - Neurofibrillary tangle
-
Abnormal organization of microtubules
- Kartagener Syndrome: immotile cilia: sterility & lung infections
Describe the morphology and pathogenesis of hemosiderin in the liver:
-
Hemoglobin-derived pigment containing iron:
- yellow to golden-brown
- Occurs locally where there has been hemorrhage
-
Systemic deposition occurs:
- with increased absorption of iron, in anemias, with many transfusions, and in hereditary conditions
- Hemosiderin is found in many organs
- liver, bone marrow, spleen, lymph nodes
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Pathologic Calcification:
Dystrophic
- Non-viable, damaged or dying tissues
- Normal serum calcium
-
Examples:
- Atheromas
- Aortic valves in elderly
- Lymph nodes with old TB
- Gross: white gritty deposits
- Microscopically: basophilic
Pathologic Calcification:
Metastatic
- Normal tissues
-
Hypercalcemia
- Increased parathyroid hormone
- Destruction of bone
- Vitamin D intoxication
- Renal failure (most common cause)
-
Most common locations:
- Interstitial tissues (lung, kidney, gastric mucosa)
Cellular Aging
-
DNA damage increases with age
- Possible role of free radicals
-
Decreased cellular replication (“progressive replicative senescence”)
- Progressive shortening of telomeres (short DNA sequences at ends of chromosomes) over time in each cell division
- Lack of telomerase (maintains telomere lengths) in somatic cells
-
Defective protein homeostasis
- Decreases cell survival, replication, & function
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