Morphologic Diagnosis

3D ATP

• Degree, duration, distribution
• Adjective (usually for inflammation)
• Tissue*
• Process*

* MOST IMPORTANT

Process

• Inflammatory (-itis)
• Degenerative (-osis, -opathy)
• Disorders of growth (-trophy, -plasia, -oma)
• other: genetic, metabolic, etc...

Adjective

• Hemorrhagic, necro-hemorrhagic
  
• Suppurative or purulent (pus)
• Fibrinous (exudative change of fibrous tissue), Fibrinopurulent
• Sclerosing (scarring)
• Caseous (cottage cheese)
  
• granulomatous (granulomas)
• necrotizing, fibrinonecrotic
• Exudative (serous vs. catarrhal)
• Proliferative
• Emphysematous (gas bubbles in it
  

Other terms for exudate

• Mucopurulent
• Fibrinopurulent
• Non-suppurative
• pyo-, eosinophilic-, or lympho-granulomatous

Degree

• Minimal
  
• Mild: mild exudative changes, little discernable tissue destruction
  
• Moderate: prominent vascular & cellular exudative changes, moderate tissue destruction
  
• Marked
• Severe: substantial destruction
  

(very subjective)

Duration

• Peracute: very rapid onset, lasts hours, exudative, few cells
• Acute: onset in few hours, can last days, with cell infiltration, primarily neutrophils
• Subacute: onset in days, can last into weeks. Exudative changes diminished. Cell infiltrate changes from neutrophilic to lymphoid cells and macrophages
• Chronic: Onset days to weeks following injury, can last years. mononuclear intration, tissue regeneration, neovascularization and fibrosis
• Chronic-active: recurrent bouts of active inflammation superimposed on chronic inflammation
  

Etiologic Diagnosis

• A diagnosis denoting cause with two elements: cause and tissue process (e.g. bacterial pneumonia)

Histopathology

• Tissue fixation and sectioning with H&E stain

Histochemistry

• trichrome: collagen ("fibrosis")
• silver stains: GMS and other stain types of reticular connective tissue and some microorganisms
• PAS: carbohydrates (includes many microbes)
• Gram, Acid Fast, etc... (microbes)
• etc...

Immunohistochemistry

Use of an Ab to identify a specific epitope with colorimetric identification of bound Ab.

Cellular Response and Consequences of Injury

• Depends on type of cell and its physiologic state, and type, duration, and severity of injury
• Injury at one site leadds to injury at another
• Morphologic changes occur only after some critical system is damaged

Causes of Cell Injury

• Oxygen Deprivation:
  • Hypoxia/Ischemia/Infarction
• Physical:
  • Trauma, heat, cold, ionizing radiation
• Chemical:
  • Bacterial, plant & synthetic toxins. oxidative injury
• Infectious
• Immune Reactions
• Genetic
• Nutritional

General Mechanisms of Cell Injury

• ATP Depletion
• Calcium
• Membrane Permeability
• Mitochondrial Damage
• Oxygen & Reactive oxygen spp

ATP Depletion

Results in inhibition of:

• Membrane transport
• Protein Synthesis
• Lipogenesis
• Phospholipid turnover

Increased cytoplasmic [Ca++]

Results from cell injury, and activates:

• Phospholipases
• Proteases
• ATPases
• Endonucleases

Membrane Permeability

Caused by:

• Bacterial toxins, viral proteins
• Complement, perforins
• Chemical and physical agents

Results in:

• ATP depletion
• Ca++ activated phospholipases

Mitochondrial damage

Caused by:

• Increased calcium
• Oxidative stress
• Phospholipid breakdown and breakdown products

Results in:

• Mitochondrial permeability transition, cytochrome C leakage, loss of membrane potential

Oxygen and Reactive Oxygen Species (ROS)

Derived from:

• normal cellular metabolism
• inflammatory cells

Damages:

• Membranes
• Proteins
• Nucleic acids

Reversible injury due to hypoxia

• ATP depletion: increase in inorganic phosphate within cell signals increase in anaerobic glycolysis, glycogen stores are depleted and pH drops
• Lack of ATP shuts down Na-K ATPase in cell membrane: Concentration gradients diminished, so nothing compensates for protein concentration gradient, and cell begins to accumulate water via osmotic mechanisms
• Ca-ATPases also begin shutting down; increased intracellular Ca++ slightly. Incrased osmolarity brings water in, + now enters organelles. Dilation of ER, and ribosomes detach
• Water moves into mitochondria --> minor swelling and minimal loss of granularity
• Cytoskeleton disperses, surface blebs and myelin figures (injured membrane) appear
  

Cell Swelling

Names:

• Hydropic change, Hydropic degeneration
• Cloudy Swelling
• Vacuolar degeneration
  

Microscopic Appearance: Enlarged, pale staining "glassy" or "cloudy" cytoplasm

Ultrastructure: Dilated organelles and cytocavitary network, esp ER

Transition to Irreversible Injury

Same changes continue which result in 2 main morphologic events:

• Degranulation of RER (loss of ribosomes)
• Moderate to severe mitochondrial swelling "high amplitude swelling"

Irreversible Ischemic Injury

• Severe mitochondrial swelling
• Massive calcium influx
• Increased membrane permeability
• Lysosomes leak (activation of acid hydrolases)
• Cellular enzymes leak into extracellular space (useful for diagnosis)
• Pyknosis (shrunken nucleus due to acid)
• Ca++ deposits begin to form in mitochondria as the cells can't deal with all the Ca++ from ER and extracellular space

Final Morphology due to Ischemic injury

• Pyknosis or karyorrhexis (clumped nuclear debris throughout nucleus) or karyolysis (nucleus fades away as endonucleases activated by Ca++)
• Mitochondrial mineralization and dissolution
• Dissolution of ER
• Dissolution of plasma membrane
• Hyperacidophilia: proteins coagulate/denature, and open up binding site for eosin

Ischemia/Reperfusion Injury

• Continued cell death following reperfusion
• reperfusion in low Ca++ environ or in the presence of Ca++ channel blockers results in ultrastructural changes indicative of "irreversible" cell death, but these cells can recover
• Immediately following increase in intracellular Ca++, numerous ATPases, proteases, and phospholipases activated
• ROS from parenchymal and infiltrating inflammatory cells
• ROS exacerbate mitochondrial permeability transition
• Expression of cytokines and adhesins promote inflammatory cell influx
  

Fatty Change

• Second most common type of cell injury
• Occurs in cells which handle large amts of lipids
• Detected as excess accumulation of intracellular lipid; "deposition injury"
• Degree of accumulation determines whether or not cell injury occurs
• Gross appearance: organ enlarged, friable, greasy with rounded margins with yellow orange in color. floats in formaldehyde
• Microscopic appearance: vacuoles few and large or many and small. well demarcated, round, appear empty because lipids removed in processing. visualized with oil red-O and sudan black in frozen sections
  

Cell Death

• Necrosis: passive, degradative, from fatal cell injury
• Apoptosis, pyroptosis, pyronecrosis, necroptosis, autophagy & oncosis: programmed cell death.

Cell death & Inflammation

• Necrosis, oncosis, pyroptosis, and pyronecrosis all produce inflammation
• Apoptosis, autophagy don't

Morphology of Apoptosis

• pyknosis and karyorrhexis without karyolysis
• increased cytoplasmic eosinophilia
• formation of apoptotic bodies: cell fragments bounded by plasma membrane containing normal organelles and condensed nuclear fragments

Biochemical features of apoptosis

• Enzyme cascade resulting in protein cleavage by activated caspases
• Protein crosslinking
• DNA cleavage by endonucleases
• Phagocytic recognition; phosphatidylserine and thrombospondin