Cell Death (Apoptosis, Necrosis)
Apoptosis
Programmed/ genetically controlled cell death
Steps of Cell & Tissue Death (Necrosis)
Necrosis
Process of cell death, manifests as specific tissue appearances, depending on the type of tissue & cause of death
2) Liquefactive
Usually occurs in brain due to fatal injury of neurons & glial cells causing release of lysosomal enzymes (Which digest & liquify tissue). Tissue has pockets of liquid, bacteria & debris in cyst-like sacs
3) Gangrenous
A type of necrosis in which bacteria & leukocytes have liquified tissue
1) Coagulative
Most common type of necrosis; seen in ischemic heart & kidney. Tissue is firm, gelatinous & opaque due to lack of blood supply & protein denaturation. Cells lack a nucleus & tissue may be retained.
Dry Gangrene
Usually the result of cutting of arterial blood flow to extremities; characterized by slow spread, absence of infection & presence of demarcation line around affected area. A form of coagulative necrosis.
Gas Gangrene
Caused by clostridia infection, usually in large traumatic wounds - the organisms digest underlying connective tissue & progressively move through healthy & damaged tissue. Gas bubbles are caused by tissue fermentation
Wet Gangrene
Has no demarcation line & characterized by a cold, swollen, pulseless area in which liquifaction is occurring; foul odour = bacterial action is spreading rapidly. A form of liquefactive necrosis.
Developmental Elimination of fetal structures
Compensatory/"Self-sacrifice"
Programmed elimination of cells w/ genetic lesions
Step 3) Lysosomal release of enzymes & Ca++ infiltration of mitochondria cause death of cells
Step 4) Digestion of cell organelles
Step 2) Mitochondrial integrity is lost from Ca++ in mitochondria; causes loss of oxidative ATP
Step 5) Alteration of the nucleus, such a pyknosis (condensed nucleus) & karyolysis (loss of nucleus)
Step 1) Membrane distortions lead to rapid Na+ Ca++ & H2O influx; causes leakage of cell parts
Possible Outcomes
3) Replacement by Hyaline (Becomes glassy; made of non-cellular tissue); mostly occurs in proteinaceous tissue, but can also occur in non-proteinaceous tissue
2) Repaired by Formation of Scar Tissue
4) Calcification
1) Replaced by Functional Tissue
Caseous Necrosis
Tissue becomes, crumbly & cheese-like in appearance; surrounded by inflammatory cells & features complete destruction of tissue. Seen in lungs & kidneys; caused by TB, syphilis & certain fungi
Dystrophic
Calcium salts accumulating on dying/dead tissue or in unhealed, chronically damaged tissue (Can occur in lungs, joints, cardiovascular system). Can occur physiologically or pathologically. Happens in everyone, at some point…
Metastatic
Calcification due to calcium imbalance (can be hormonal) in the system w/ calcium precipitating in kidney, blood vessels & connective tissue.