Pathology Flashcards
(196 cards)
Apoptosis
Programmed cell death; ATP required. Intrinsic or extrinsic pathway; both pathways lead to activation of cytosolic caspases that mediate cellular breakdown. No significant inflammation (unlike necrosis). Characterized by deeply eosinophilic cytoplasm, cell shrinkage, nuclear shrinkage (pyknosis) and basophilia, membrane blebbing, nuclear fragmentation (Karyorrhexis), and formation of apoptotic bodies, which are than phagocytosed. DNA laddering is a sensitive indicator of apoptosis; during karyorrhexis, endonucleases cleave at internucleosomal regions, yielding fragments in multiples in 180 bp. Radiation therapy causes apoptosis of tumors and surrounding tissue via free radical formation and dsDNA breakage. Rapidly dividing cells (eg skin, GI mucosa) are very susceptible to radiation therapy-induced apoptosis.
Intrinsic apoptotic pathway
Involved in tissue remodeling in embryogenesis. Occurs when a regulating factor is withdrawn from a proliferating cell population (eg a decrease in IL-2 after a completed immunologic reaction leading to apoptosis of proliferating effector cells). Also occurs after exposure to injurious stimuli (eg radiation, toxins, hypoxia). Changes in proportions of anti- and pro-apoptotic factors leading to an increase in mitochondrial permeability and cytochrome c release. BAX and BAK are proapoptotic proteins; Bcl-2 is antiapoptotic. Bcl-2 prevents cytochrome c release by binding to and inhibiting Apaf-1. Apaf-1 normally induces the activation of caspases. If Bcl-2 is overexpressed (eg follicular lymphoma), then Apaf-1 is overly inhibited, leading to a decrease caspase activation and tumorigenesis.
Extrinsic pathway
There are two pathways: ligand receptor interactions (FasL binding to Fas [CD95]) and immune cell (cytotoxic T-cell release of perforin and granzyme B). Fas-FasL interaction is necessary in thymic medullary negative selection. Mutations in Fas increases the number of circulating self- reacting lymphocytes due to failure of clonal deletion. After Fas crosslinks with FasL, multiple Fas molecules coalesce, forming a binding site for a death domain-containing adapter protein, FADD. FADD binds inactive caspases, activating them. Devective Fas-FasL interactions contribute to autoimmune disorders.
Necrosis
Enzymatic degradation and protein denaturation of cell due to exogenous injury, leading to leak of intracellular components. Inflammatory process (unlike apoptosis).
Coagulative necrosis
Seen in ischemia/infarcts in most tissue (except brain). It is due to ischemia or infarction; proteins denature, then enzymatic degradation. On histology, cell outlines are preserved; there is also an increase in cytoplasmic binding of acidophilic dyes.
Liquefactive necrosis
Seen in bacterial abscesses, brain infarcts (due to an increase in fat content). It is due to neutrophils releasing lysosomal enzymes that digest the tissue; enzymatic degradation first, then proteins denature.
Caseous necrosis
Seen in TB, systemic fungi (eg Histoplasma capsulatum), Nocardia. It is due to macrophages walling off the infecting microorganism, leading to granular debris. On histology, there are fragmented cells and debris surrounded by lymphocytes and macrophages.
Fat necrosis
Seen in enzymatic acute pancreatitis (saponification) and nonezymatic breast trauma. It is due to damaged cells release lipase, which breaks down fatty acids in cell membranes. On histology, there is an outlines of dead fat cells without peripheral nuclei; saponification of fat (combined with Ca) appears dark blue of H&E stain.
Fibrinoid necrosis
Seen in immune reactions in vessels. It is due to immune complexes combined with fibrin, leading to vessel wall damage. On histology, there are vessel walls that are thick and pink.
Gangrenous necrosis
Seen in distal extremity, after chronic ischemia. In dry gangrenous necrosis, it is due to ischemia (on histology, coagulation is seen). In wet gangrenous necrosis, it is due to superinfection (on histology, liquefaction is seen).
Cell injury reversible with O2
There is ATP depletion, cellular/mitochondrial swelling (a decrease in ATP leads to a decrease activity of Na/K pumps), nuclear chromatin clumping, a decrease in glycogen, fatty change, ribosomal/ polychromal clumping detachment (a decrease in protein synthesis), and membrane blebbing.
Cell injury irreversible with O2
There is nuclear pyknosis, karyorrhexis (destructive fragmentation of the nucleus of a dying cell), karylolysis (the complete dissolution of the chromatin of a dying cell), plasma membrane damage (degradation of membrane phospholipid), lysosomal rupture, mitochondrial permeability/ vacuolization; phospholipid- containing amorphous densities within mitochondria (swelling alone is reversible).
Ischemia susceptible areas of the brain
They are located between the cortical territories of the anterior cerebral artery (ACA), middle cerebral artery (MCA), posterior cerebral artery (PCA) boundary areas. Watershed areas (border zones) receive dual blood supply from most distal branches of 2 arteries, which protects these areas from single-vessel focal blockage. However, these areas are susceptible to ischemia from systemic hypoperfusion. Hypoxic ischemic encephalopathy (HIE) affects pyramidal cells of hippocampus and Purkinje cells of the cerebellum.
Ischemia susceptible areas of the heart
Subendocardium (left ventricle)
Ischemia susceptible areas of the kidney
Straight segment of the proximal tubule (medulla) and the thick ascending limb (medulla)
Ischemia susceptible areas of the liver
Area around central vein (zone III)
Ischemia susceptible areas of the colon
Splenic flexure and rectum. Watershed areas (border zones) receive dual blood supply from most distal branches of 2 arteries, which protects these areas from single-vessel focal blockage. However, these areas are susceptible to ischemia from systemic hypoperfusion.
Red infarcts
Red (hemorrhagic) infarcts occur in venous occlusion and tissue with multiple blood supplies, such as liver, lung, and intestine; reperfusion (eg after angioplasty). Reperfusion injury is due to damage by free radicals. Red=Reperfusion.
Pale infarcts
Pale (anemic) infarcts occur in solid organs with a single (end-arterial) blood supply, such as heart, kidney, and spleen.
Atropy
There is a reduction in the size and/or number of cells. Causes include: a decrease in endogenous hormones (eg post menopausal ovaries); an increase in exogenous hormones (eg factitious thyrotoxicosis, steroid use); a decrease in innervation (eg motor neuron damage); a decrease in blood flow/nutrients; a decrease in metabolic demand (eg prolonged hospitalization, paralysis); an increase in pressure (eg nephrolithiasis); occlusion of secretory ducts (eg cystic fibrosis, calculus/stone).
Inflammation
Characterized by rubor (redness), dolor (pain), calor (heat), tumor (swelling), and fanctio laesa (loss of function).
Vascular components of inflammation
an increase in vascular permeability, vasodilation, and endothelial injury.
Cellular components of inflammation
Neutrophils extravasate from circulation to injured tissue to participate in inflammation through phagocytosis, degranulation and inflammatory mediated release.
Acute inflammation
It is neutrophil, eosinophil, and antibody mediated. Acute inflammation has a rapid onset (seconds to minutes) and of short duration (minutes to days). Outcomes include complete resolution, abscess formation, or progression to chronic inflammation.