Cell Death

• Necrosis

  • unplanned cell death - cell dies prematurely
  • messy, cell 'explodes'
  • no ATP required, causes tissue inflammation
  • occurs when a cell suffers trauma
  • mechanical damage
  • chemical trauma
  • thermal burns
  • frostbite
  • oxygen deprivation
• Mitochondrial Pathway


  cell stress/internal DNA damage → mitochondria detects → releases cytochrome c and binds with protein → activates caspases → breakdown of organelles / digestion of cell contents (caspases cleave intracellular proteins, organelles breakdown) → cell shrinks → membrane blebbing and breakage (cytoskeleton gets digested, no structural integrity) → forms apoptotic bodies → apoptosis has occurred → phagocytes engulf apoptotic bodies
• Death Receptor Pathway


  the cell receives a death signal (from immune cells releasing death signalling molecule)→ caspase 3 gets activated straight away → digestion of cell contents → cell shrinks → membrane blebbing → apoptotic bodies → phagocytosis
• Apoptosis

  • programmed cell death - it is a natural and controlled process
  • clean, cell contents gets neatly packaged and cleaned up
  • ATP required, no inflammation
  • brings about cell death for
  • cells at the end of their natural life
  • dysfunctional, damaged or diseased cells
  • excessive cells
  • happens either through
  • the mitochondrial pathway (intrinsic pathway)
  • initiated if serious damage occurs inside the cell such as DNA damage
  • Death receptor pathway (extrinsic pathway)
  • initiated when cells haven't fully developed, or, excess cells due to immune response are produced or cells are not long useful
• Tumours

  When the rate of apoptosis decreases too much, cell growth can increase exponentially, resulting in the formation of tumours

  Benign

  • Slow-growing masses of cells that are generally enclosed, within a capsule, preventing the abnormal cells from separating and invading other parts of the body.

  Malignant

  • the cells of some benign tumours can mutate further and become malignant when they can invade nearby tissues and/or enter the bloodstream or lymphatic system. They can travel to other parts of the body and grow. metastasis
  • cancerous
• Cancer

  • Cancer cells are those that have become undifferentiated (unspecialised, like it reverts) and divide uncontrollably
  • spends less time in interphase, different physical strucures
  • self-sufficiency
  • can engineer own growth chemical signals
  • Increase survival
  • capable of reproductive immortality in theory
  • antigrowth deactivation
  • tumour cells can deactivate mechanisms put in place that prevent unnecessary cell division
  • blood supply formation
  • can form new blood vessels when growing to maintain adequate nutrient and oxygen supply. takes it away from other, healthy cells.
• Apoptosis and Cancer


  • low rates of apoptosis are good during embryonic development and childhood. mitosis should exceed the rate of apoptosis
  • this is to ensure growth
  • mitosis and apoptosis should be equal after.
  • apoptosis should occur when there's a damaged cell
  • mitosis should occur to replace the cell

  most of the time, when a cell becomes cancerous, other cells release a death ligand that instructs the cell to die. some cells have a mutated receptor. if it becomes cancerous, it begins to divide, each cell having that defective gene - !cancer proliferation!
• Carcinogens


  environmental factors

  • chemicals (tobacco), radiation (UV), viruses (HPV), x-rays
  • lung cancer

  genetic

  • some people are just born with genes that are more likely to mutate
  • breast cancer

  these increase the likelihood of mutations in a cell. Mutated cells may not be normal and develop an incorrect cycle of mitosis. They will then keep reproducing at a high rate, causing the body to put lots of energy into their production and upkeep. All of this energy being devoted to these cancer cells causes other normal cells to suffer and can ultimately lead to death.
• Apoptosis (detail)

  • caspases cleave intracellular proteins, leading to the breakdown of organelles
  • the cell and nucleus shrinks as intracellular material is broken down
  • as the cytoskeleton is digested, the structural integrity of the cell is weakened.
  • the membrane warps in a process called 'blebbing'
  • membrane detaches from the cell in membrane-enclosed vesicles known as apoptotic bodies
  • these contain the broken-down intracellular material
  • after apoptosis has occurred, phagocytes engulf and destroy the apoptotic bodies using their lysosomes to digest.