Some types of cell damage can be reversed once the insult is removed, while other types of cell injury are permanent. In cases where the pathogen is stronger than the cell, the damage to the cell may result in cell death.
Reversible & Irreversible Cell Damage
Initially, hypoxic injury is reversible. There is a decrease in respiration and ATP production is reduced. In order to attempt to maintain basic cell function some ATP production is sustained through . This inefficient process leads to a buildup of pyruvic acid inside the cell. Pyruvic acid is turned into acid, which continues to build up in the cytosol, causing the cytosol to become acidic. The low pH damages the membrane of the rough endoplasmic reticulum (RER), causing a decrease in protein synthesis. In low grade, sustained cases of hypoxia, amino acids are made into lipids and stored in cells capable of fat storage. The shortage of ATP also causes the sodium-potassium-ATPase to decrease its activity leading to an increase in intracellular sodium and a decrease in intracellular potassium. This disrupts the osmotic balance between the ECF and the ICF, and causes an influx of water seen as cellular . These changes are reversible. The time it takes for irreversible damage to occur will mainly depend on the cell type involved. If hypoxic conditions persist, the pH decreases to a point where enzymes are released into the cytosol. These enzymes attack the membranes of organelles such as the mitochondria as well as the entire cell membrane. Membrane damage is characterised as decreased phospholipids, cytoskeleton disruptions as well as free radical production all leading to a loss of membrane integrity. With loss of membrane integrity, we see an influx of ions into the cell. Calcium acts to further damage the mitochondria and the structural proteins of the cell. At this point the cell may continue to auto digest or heterolysis by a leukocyte may occur. In either case digestive enzymes may be spilled out into the ECF causing injury to the membranes of neighbouring cells. Cell death is called . Nuclear Changes during Cell Injury Cell injury often causes changes to the membrane and the contents of the nucleus. There are three patterns in nuclear injury that are seen associated with cellular injury.
______ - indicated by nuclear shrinkage and an increase in basophilia _– indicates fragmentation of the pyknotic (shrunken) nuclei – digestion of the nucleus by lysosomal enzymes
Types of Cellular Injury Some major types of cellular injury include hypoxic injury, chemical injury, viral injury and age- related injury.
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