Revision sheet: Cell Injury and Protein Metabolism

📋 Course Outline

1. Types and Mechanisms of Cell Injury
2. Reversible Parenchymal Changes
3. Intracellular Water and Protein Accumulation
4. Mesenchymal Mucoid Edema
5. Fibrinoid Swelling

📖 1. Types and Mechanisms of Cell Injury

★ Must-know

• Cell injury may be reversible, irreversible, programmed, or residual, and its consequences include degeneration, cell death by necrosis, apoptosis, subcellular injury, intracellular accumulation of proteins, fats and carbohydrates, gangrene, and pathological calcification.

• The principal mechanisms of cell injury are ischemia and hypoxia, free-radical injury, toxic injury, and immune-mediated injury.

Further detail

• The listed mesenchymal changes are mucoid or chromotropic edema, fibrinoid swelling, hyalinosis, amyloidosis, mucinous changes, fatty infiltration, and extracellular pigment accumulation.

📖 2. Reversible Parenchymal Changes

★ Must-know

• Reversible parenchymal changes include intracellular accumulation of water, proteins, fats, carbohydrates, and pigments.

• Intracellular water accumulation includes cell swelling, hydropic changes, and vacuolar changes.

Further detail

• Intracellular protein accumulation includes hyaline-droplet changes in proximal convoluted tubules and Russell bodies in plasma cells.

💡 Memory Hook

Water → proteins → fats → carbohydrates → pigments

📖 3. Intracellular Water and Protein Accumulation

🔑 Key Concepts & Definitions

• Cell swelling : A reversible injury in which small cytoplasmic vacuoles represent distended and detached fragments of the endoplasmic reticulum, accompanied by loss of fine structures and blurred cell borders.

★ Must-know

• Vacuolar changes consist of fluid-filled cytoplasmic vacuoles and occur in the skin in smallpox, the liver in acute viral hepatitis, and the kidneys in nephrotic syndrome.

• The clinical significance of reversible cell injury is reduced organ function, such as impaired myocardial contractility.

• Hyaline-droplet changes in proximal convoluted tubules are microscopic protein droplets that may merge and fill the cell, occur mainly when the glomerular filter becomes more permeable to protein, and are seen in nephrotic syndrome, glomerulonephritis, and mercury or lead poisoning.

Further detail

• Cell swelling is most prominent in the kidneys, liver, and heart.

• Russell bodies are accumulations of immunoglobulins in the endoplasmic reticulum of plasma cells in myeloma.

• Alcoholic hyaline, also called Mallory bodies, occurs in hepatocytes during alcoholic hepatitis.

📖 4. Mesenchymal Mucoid Edema

🔑 Key Concepts & Definitions

• Mucoid edema : A mesenchymal change caused by accumulation of hydrophilic glycosaminoglycans in the interstitial substance, with penetration by plasma proteins and glycoproteins.

★ Must-know

• Accumulation of chromotropic substances makes the connective-tissue ground substance metachromatic, so toluidine blue produces a reddish rather than blue color.

Further detail

• Glycosaminoglycan depolymerization releases chondroitin-sulfuric and hyaluronic acids, which bind plasma proteins entering the connective tissue.

• Mucoid edema occurs in atherosclerosis and rheumatic diseases.

💡 Memory Hook

GAG accumulation → plasma protein penetration → metachromasia

📖 5. Fibrinoid Swelling

🔑 Key Concepts & Definitions

• Fibrinoid swelling : A mesenchymal change associated with immune-complex injury to the microcirculatory bed and connective tissue.

📝 Essential Points

• Fibrinoid swelling causes marked destruction of collagen fibers and penetration of plasma proteins, mainly globulins and fibrinogen, into connective tissue.

💡 Memory Hook

Immune-complex injury → collagen destruction and plasma protein entry

📊 Synthesis Tables

Parenchymal and Mesenchymal Changes

Category	Main location	Examples
Parenchymal	Within functional cells	Water, proteins, fats, carbohydrates, pigments
Mesenchymal	Interstitial connective tissue	Mucoid edema, fibrinoid swelling, hyalinosis, amyloidosis, mucinous changes, fatty infiltration, extracellular pigments