Cell necrosis and degeneration

• Aerobic energy production


  Most complex, occurs in the mitochondria with the presence of oxygen, supplies 90% of the body's energy needs, requires the heart, lungs and all circulatory system to work efficiently, obtained from food, synthesized into ATP, stored as glycogen in the body, can also be obtained through the breakdown of fats and proteins which require more oxygen and carbohydrates, by-products are carbon dioxide (CO2) and water (H2O)
• Anaerobic energy production


  Occurs in the cytoplasm through the glycolytic process in the absence of oxygen, obtained from glucose, by-product is lactic acid
• Cell membrane


  • Encloses the cell in a double layer of phospholipids, allows passage of molecules in and outside the cell
• Nucleus


  • Contains the genetic information of the cell, organised into chromosomes, control centre of the cell
• Mitochondria


  • Site of respiration, ATP is generated
• Rough ER


  • Processes proteins produced by the ribosomes
• Smooth ER


  • Synthesizes lipids, phospholipids, steroids
• Ribosomes


  Responsible for protein synthesis
• Peroxisomes


  Contains enzymes that get rid of the peroxide in the cell
• Golgi apparatus


  • Packs lipids and proteins produced by the cell
• Lysosomes


  Contains digestive enzymes that engulf aged cells, food and bacteria
• Homeostasis


  The maintenance of a constant environment inside the body
• Structures involved in homeostasis


  • Nervous System
  • Endocrine System
• Factors in homeostasis


  • Temperature
  • Pressure
• Hypertrophy


  Increase in cell size in response to an increase in workload or increased mechanical stress of growth factors
• Hypertrophy


  • Involves increase in functional components
  • Occurs in cells that are unable to divide (cardiac or muscle tissue)
  • Occurs due to normal physiologic or pathological changes
• Hyperplasia


  Increase in the number of cells in an organ or tissue
• Hyperplasia


  • Occurs in cells that are able to divide (epithelium of intestinal tract)
  • Occurs in response to appropriate stimulus
  • Involves the activation of genes controlling cell proliferation
• Compensatory hyperplasia


  Involves the healing of connective tissue
• Atrophy


  Decrease in cell and organ size
• Atrophy


  • Cells have decreased mitochondria or endoplasmic reticulum leading to decreased protein synthesis and metabolic activity
  • In response to decreased workload or adverse environment leading to decreased oxygen consumption and protein synthesis
• Causes of atrophy


  • Disuse
  • Denervation
  • Ischaemia (decreased blood flow)
  • Inadequate nutrition
• Metaplasia


  The change of one type of cell to another of the same differentiation
• Types of metaplasia


  • Squamous
  • Columnar
  • Mesenchymal
  • Osseous
  • Cartilaginous
• Causes of cell injury


  • Aging
  • Genetic defects
  • Immunological reactions
  • Ischaemia (lack of O2)
  • Thermal (radiation)
  • Mechanical (trauma, surgery)
  • Infectious
  • Physical
  • Toxic
• Free radicals


  Highly reactive chemicals with an unpaired electron
• Hypoxic cell injury


  Disrupts oxidative metabolism and generation of ATP, leading to a fall in pH and impaired calcium homeostasis
• Factors affecting cell injury


  • Type of injury
  • Severity of cell injury
  • Adaptation of the cell
  • Type of damaged cell
• Reversible cell injury


  Functional and morphological changes are reversible if the damaging stimulus is removed
• Irreversible cell injury


  Cell cannot adapt, leading to cell death
• Types of cell death


  • Necrosis
  • Apoptosis
• Apoptosis (cell suicide)


  1. Initial phase - caspases become catalytically active

  2. Execution phase - caspases degrade cellular components
• Apoptosis is a pre-planned regular process of cell death, where the cell takes an active role in its own death, needed for normal functioning
• Physiological examples of apoptosis


  • Embryo development
  • Hormone deprivation in menstrual cycle
• Pathological examples of apoptosis


  • Hypoxia
  • Neurodegenerative diseases (Alzheimer's, Parkinson's)
  • Viral infections (Hepatitis B and C)
• Necrosis (cell murder)


  Passive process that does not require energy, refers to the death of injured cells as a result of degradative action of enzymes
• Process of necrosis


  1. Loss of cellular integrity

  2. Leaking out of cellular contents

  3. Digestion of necrotic cell by lysosomes

  4. Damage to the nucleus (pyknosis, karyorrhexis, karyolysis)
• Necrosis always leads to inflammation in surrounding tissues and organs
• Infarction


  Necrosis as a result of cessation of blood flow
• Coagulative necrosis


  • Most common type
  • Cells become hard, dry and appear white
  • Characteristic of infarcts
  • Affects the heart and all solid organs except the brain, liver and spleen