Necrosis | Cell Injury | General Pathology 🩺

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Necrosis | Cell Injury | General Pathology 🩺

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(0:00-2:40)
Necrosis is a PATHWAY to cell death; a result of IRREVERSIBLE injury. Cell Death due to an irreversible injury can follow one of two pathways; either Necrosis or Apoptosis.
Appreciate that; a dead tissue cut off from the body is not a necrotic tissue; a necrotic tissue would still be attached to the body; and it’s the body which would be initiating necrosis against it.

(2:41-4:00)
DIFFERENTIATE B/W NECROSIS & APOPTOSIS:
Necrosis is ALWAYS a pathological cell injury; which may be due to trauma, severe ischemia, toxins or radiations etc. In other words, it is always an "Unwanted" injury.
Apoptosis; may be physiological or pathological; when the body wants to remove some cells or even a tissue; it utilizes the process of Apoptosis. It is always "Wanted" or a "Needed" injury.

(4:01-6:54)
DEFINITION OF NECROSIS: A series of morphological changes, occurring in a lethally injured cell that cannot recover & reverse from nor adapt & adjust to the stress of injury.
These morphological changes take anywhere between 4-12 hours to appear histologically; at which point they can be observed with a light microscope. These changes may occur in the cell membrane, cytoplasm, nucleus or any other organelle of the cell.
Note that; just the Cell Injury itself is NOT necrosis; it’s the SERIES OF CHANGES that occur to a lethally injured cell that is referred to as Necrosis, and these changes will invariably lead to DEATH of the cell.

(6:55-14:34)
MECHANISM OF INJURY;
Necrotic cell cannot create its own ATP and ends up hogging the body's energy reserves; also due to Anaerobic Respiration, Lactic Acid accumulates and makes the intracellular environment acidic. Hence, there is a need to eliminate these injured cells.
Necrotic changes occurring in a cell take place through the following mechanism:
1-INTRACELLULAR PROTEIN DENATURATION; This includes Structural & Functional Proteins (e.g., enzymes, pumps, etc.); loss of structural proteins will destroy the cell's integrity & will result in a spillover of its contents.
2-ENZYMATIC DIGESTION of the severely injured cells; Lysosomes are organelles carrying a cell’s proteolytic enzymes. They may burst in an injured cell; which leads to proteolysis of all cellular components. Since, it’s the cells’ own enzymes doing the lysis, we call this Autolysis. When foreign enzymes released by either Neutrophils or a microbe present; it is Heterolysis.
All these processes further contribute to the morphological changes we define as Necrosis.

(14:36-20:17)
3-LOSS OF INTEGRITY of plasma membrane of a necrotic cell; Plasma Membrane of the cell is disrupted; Intracellular constituents come out into the extracellular environment; cell starts "bleeding" in a way; unable to maintain the integrity of its’ plasma membranes.
Injurious enzymes leak out and irritate surrounding tissues. An inflammatory response is elicited; vasodilation, increased permeability, leukocytes infiltration; trying to eat or remove necrotic cell and repairing tissues. [Necrosis does not occur in one cell alone; Apoptosis may].
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