Reversible Cell Injury

Objective

At the end of this lecture, student will be able to

•         Explain the sequence of changes occurring during reversible cell injury

•         Explain the morphology of cell injury

•         Describe the pathogenesis of cell injury due to hypoxia and ischemia

Reversible cell injury

Reversible cell injury is the initial response of a cell to a stressor. It is a critical stage as the cell has the potential to recover. Common stressors include toxins, infections, and nutritional imbalances. We will explore the sequence of changes during this stage, understanding the intricate mechanisms involved.

Causes of Injury

In this section, we will discuss the various causes of cell injury. These can range from physical trauma to chemical damage. It’s essential to recognize these causes to better understand how cell injury occurs.

Pathogenesis of reversible cell injury due to hypoxia and ischemia

•       If hypoxia and ischemia is for short duration, the effects are reversible

Sequence of changes occurring during reversible cell injury

• ↓ cellular ATP
• ↓ intracellular pH
• Damage to plasma membrane Na⁺ pump
• ↓ protein synthesis
• Functional consequences
• Ultra structural changes

Decreased cellular ATP

•       ATP required for – Membrane transport

                                     – Protein synthesis

– Lipid synthesis

– Phospholipids metabolism

•       Source of ATP – Aerobic and anaerobic respiration

•       Hypoxia and ischemia limits the supply of oxygen to cells, decreases ATP production

Decreased intracellular pH

•       Low oxygen supply

•       Aerobic respiration by mitochondria fails

•       ATP generation by anaerobic glycolytic pathway

•       Depletion of glycogen

•       Accumulation of lactic acid

•       Low pH of cell

•       Acidosis and clumping of chromatin

Damage to plasma membrane sodium pump

•       Na⁺/K⁺ ATP ase –  operates at plasma membrane

•       Allows active transport of Na⁺  out of a cell

•       Diffusion of K⁺ into cell after depolarization

•       Low ATP affects Na⁺ pump functioning

•       Outward diffusion of K⁺ ions

•       Intracellular accumulation of Na⁺  

•       Increased intracellular  water –  swelling of affected cell

Decreased protein synthesis

•       Continuation of hypoxia

•       Detachment of ribosome from granular ER

•       Polysomes degraded to monosomes

•       Decreased protein synthesis

Functional consequences

•       Myocardial contractility ceases in 60 sec of coronary occlusion

•       Reversed if circulation restored

Ultrastructural changes

•       Normal structure of ER is affected

•       Membrane bound polyribosome detach from rough ER

•       Swelling of mitochondria

•       Myelin figures appear in cytoplasm

•       Loss of microvilli

•       Reduced synthesis of ribosomal RNA in nucleolus

Morphology of reversible cell injury

Reversible cell injury causes cell degeneration

Cellular swelling

•       Due to influx of Na⁺ ions & H₂O , escape of K⁺

•       Common causes  – Bacterial toxins

                                     – Chemicals

– Poisons

– Burns

•       Most affected organs – Kidney, Liver and Heart

•       More vacoules appear

•       ER dilates, ribosomes detach

•       Mitochondrial swelling

Fatty changes

•       Steatosis – Accumulation of fat within parenchymal cells

•       Occurs common in liver

•       In non – fatty tissues – heart skeletal muscles and kidney

Other changes

•       Cytoskeletal changes

•       Lysosomal changes

•       Hypertrophy of smooth ER

•       Intracellular accumulation of protein and glycogen

•       Mitochondrial changes

Summary

•       Hypoxia and ischemia causes cell injury

•       If hypoxia and ischemia is for short duration, cell injury can be reversed

•       Reversible cell injury brings about decreased cellular ATP, intracellular pH, damage to plasma membrane, decreased protein synthesis and ultra-structural changes

•       Reversible cell injury causes cell degeneration

FAQs

Q1: Can all cell injuries be reversed?

Yes, in the early stages, most cell injuries are reversible. However, if the damage is severe and prolonged, it can become irreversible.

Q2: What are the common causes of cell injury?

Common causes include infections, toxins, physical trauma, and nutritional imbalances.

Q3: How can one prevent cell injury due to hypoxia?

Preventing cell injury due to hypoxia involves ensuring an adequate supply of oxygen. This can be achieved through various medical interventions.

Q4: What is the significance of organelle alterations in cell injury?

Organelle alterations provide insights into the extent of cell damage and can help diagnose specific conditions.

Q5: Are there treatments available for cell injury due to ischemia?

Yes, there are various treatments available, including medications and medical procedures. The choice of treatment depends on the specific case and severity.