Compensation of energy deficit
When cellular structures are damaged, mitochondria suffer first, which leads to a drop in ATP resynthesis during tissue respiration. To survive, the cell triggers a cascade of compensatory reactions:
- Activation of alternative pathways: glycolysis becomes the main source of energy. If the damage is mild or moderate, the activity of oxidation and phosphorylation enzymes may increase.
- Optimization of transport and utilization: the delivery of ATP to effector structures is accelerated using key enzymes—adenine nucleotide translocase and creatine phosphokinase. The efficiency of energy utilization enzymes (ATPases) is also increased.
- Energy conservation: the cell reduces the intensity of plastic processes (synthesis of structural elements) and limits its functional activity.
Protection of membranes and enzyme systems
The antioxidant defense system (AOD) plays a key role in protecting cellular structures. Superoxide dismutase (SOD) inactivates superoxide oxygen radicals, while catalase and glutathione peroxidase cleave peroxide compounds. Polyenzyme systems neutralize lipid peroxides, significantly reducing the pathogenic effects of free-radical reactions.
Damage is always accompanied by intracellular acidosis. Protein, phosphate, and carbonate buffers are activated to combat it. Simultaneously, endoplasmic reticulum microsomal enzymes accelerate the physicochemical transformation of pathogenic agents (oxidation, reduction, demethylation) and trigger gene derepression to synthesize new membrane components to replace lost ones.
Restoration of ion and water balance
Disruption of ion pumps due to ATP deficiency and membrane damage leads to water and electrolyte imbalance. The cell compensates for this in several ways:
- Metabolic adjustment: glycolysis activation is accompanied by the release of potassium ions, which compensates for their loss through damaged membranes.
- Buffer action: a decrease in hydrogen ion concentration helps restore the optimal ratio of potassium, sodium, and calcium in the cytosol.
- Transport activation: restoration of ATP synthesis provides energy for ion pumps, enhancing transmembrane transport.
The result is the normalization of intracellular fluid volume, which prevents cell and organelle swelling.
Genome repair and heat shock proteins
The DNA repair system operates to restore the genetic code. Chain breaks caused by free radicals or radiation are stitched together by ligase enzymes. Damaged segments are replaced with normal ones (excision repair), and foreign fragments are eliminated.
Epigenetic regulation mechanisms are used to fix minor genome defects. For example, demethylases remove methyl groups, which helps restore normal gene expression. This normalizes transcription, translation, nuclear division (nucleotomy), and cell division (cytotomy).
Heat shock proteins (HSP), such as HSP 70 and HSP 90, play a special role. They are synthesized in response to hypoxia, viruses, chemical agents, or temperature changes, preventing cell death and ensuring proper folding (conformation) of other proteins.
Regulatory and structural adaptation
Cellular adaptation is complex in nature and implemented at three levels: metabolic, functional, and structural.
- Regulatory reactions: the cell changes the number of receptors, their sensitivity to biologically active substances, and the activity of intracellular mediators (second messengers).
- Functional rest: a temporary decrease in activity makes it possible to redistribute resources, significantly reduce the scale of alteration (damage) at the moment the pathogenic factor acts, and ensure rapid recovery after its elimination.
- Structural changes: with prolonged or repeated exposure to a pathogenic factor, standard adaptive processes develop, such as hypertrophy, hyperplasia, atrophy, metaplasia, and dysplasia.
Briefly: answers to topical questions
How does intracellular acidosis affect the activity of lysosomal enzymes during alteration?
Intracellular acidosis during cell damage activates lysosomal hydrolases and promotes the release of enzymes from lysosomes. During damage, glycolysis activation leads to lactate accumulation and a decrease in pH.
Acidification of the environment leads to the following consequences:
- Activation of lysosomal hydrolases — causes autodigestion of the cell.
- Increased activity of lipases, phospholipases, and proteases — is accompanied by intensive hydrolysis of phospholipids, glycoproteins, cytoskeleton proteins, and enzymes.
As a result, membrane permeability increases, the activity of cellular enzymes decreases, and membrane lysis develops.
What is the pathogenetic role of calcium ion accumulation in the cytosol during membrane damage?
The accumulation of Ca^{2+} ions inside the cell triggers a cascade of enzymatic reactions involved in the damage of cellular structures.
Main effects of Ca^{2+} excess:
- Activation of ATPases — accelerates ATP breakdown and worsens the energy deficit.
- Activation of phospholipases — leads to the destruction of membrane phospholipids and membrane lysis.
- Activation of proteases — causes the destruction of cytoskeleton and membrane proteins, which also contributes to membrane lysis.
- Activation of endonucleases — leads to DNA and RNA hydrolysis.
In addition, excess Ca^{2+} has an uncoupling effect in mitochondria and suppresses ADP rephosphorylation. Mitochondrial destruction may be associated with membrane overstretching in the presence of excess Ca^{2+} and fluid.
What are the pathways of cell death when defense and repair mechanisms are depleted?
The sources describe necrosis and regulated types of cell death.
The main pathways include:
- Necrosis — the result of a combination of membrane lysis and the destruction of genetic material.
- Apoptosis — regulated death involving caspases, the formation of apoptotic bodies, without the release of cell contents outward and without inflammation.
- Necroptosis — a genetically controlled process morphologically resembling necrosis; accompanied by cell rupture and the release of DAMPs, cytokines, and chemokines.
- Ferroptosis — regulated death dependent on iron and glutathione, associated with impaired function of glutathione peroxidase 4, accumulation of reactive oxygen species, and lipid peroxidation of membranes.
- Pyroptosis — regulated death involving caspases, accompanied by pronounced inflammation and the release of DAMPs and proinflammatory cytokines IL-1β and IL-18.
To memorize the main directions of cell defense, use the rule: Energy (glycolysis), Membranes (antioxidants), Ions (pumps and buffers), Genome (DNA repair), Regulation (receptors).
Class and exam questions
How does the cell compensate for potassium loss during membrane damage?
In a damaged cell, potassium content usually decreases due to increased membrane permeability. Glycolysis activation is accompanied by the release of potassium ions from intracellular structures, which helps compensate for these losses and maintain ion homeostasis.
What is cellular "functional rest"?
This is a protective reaction in which the cell temporarily reduces its specific function and the intensity of plastic processes. This allows for the redistribution of energy resources, an increase in adaptive capabilities, and a reduction in the scale of damage.
What is the role of heat shock proteins (HSPs)?
Stress proteins (e.g., HSP 70 and HSP 90) protect the cell from death when exposed to hypoxia, infections, or chemical agents. Their main function is to ensure the correct assembly (folding) and conformation of other intracellular proteins.
What else to study on this topic
- Mechanisms of DNA excision repair
- The role of demethylases in epigenetic regulation
- Standard structural changes: hypertrophy, hyperplasia, metaplasia
- Function of endoplasmic reticulum microsomal enzymes
- The relationship between intracellular acidosis and buffer systems
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