Apoptosis and necrosis are two mechanisms for cell death in multicellular organisms. Apoptosis is programmed cell death that helps remove damaged or unnecessary cells through a tightly regulated suicide process. The cell shrinks and fragments in a controlled way. In contrast, necrosis is unregulated cell death caused by external factors like infection or injury, where the cell swells and bursts, releasing harmful contents. Both cell death mechanisms help eliminate cells no longer needed by the body.

1. Apoptosis, necrosis,
Chapter 18

2. Continuity of life
• Only from existing cells come new cells.
• We are all decedents of the first cells on the
planet.
• A cell reproduces by duplicating its contents
and then dividing into two
• This cycle of events is known as the cell cycle

3. Cell division timing
• Different cells have cell cycles of
different lengths;
– Nerve Cells = never
– Human Liver Cells = 1 year
– Intestinal epithelial cells = 12 hours
– Yeast cells = 1.5 to 3 hours
– Bacteria = 90 minutes

4. Cell Death
• The body is very good at maintaining a
constant number of cells. So there has to
exist mechanisms for ensuring other cells in
the body are removed, when appropriate.
• cell death in multicellular organism is
controlled by two mechanism
• Two forms
– Apoptosis - suicide - programmed cell death
– Necrosis - killing - decay and destruction

5. • Pathway of cell death induced by a tightly
regulated suicide program.
• Controlled by specific genes.
• Fragmentation of DNA.
• Fragmentation of nucleus.
• Blebs form (outgrowth) and apoptotic bodies
are released.
• Apoptotic bodies are phagocytized.
• No neutrophils.

7. • Removal of damaged or unnecessary cells
• Due to Embryogenesis and fetal development
• Elimination of self-reactive lymphocytes. •
Death of cells that have served their function
• DNA damage due to radiation, chemotherapy. •
Accumulation of misfolded proteins which ends
with apoptosis

8. APOPTOSIS VS NECROSIS
• Apoptosis = necrosis
• Small scale large scale
• Control is present lost
• Cell contract cell swell
• Apoptic body forms cell membrane rapture
• Chemotactic no chemicals released
• Beneficial process harmful process

9. • Massage can com from outside or inside
• Extrinsic or intrinsic pathway
• genes release massage
• Caspase are activated
• DNA is broken down
• Nucleus splits into fragments then
apoptic bodies are formed
• Which are engulfed by nutrophils

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Cell Death -occurs more often than one imagines!
a) Most embryo development involves programmed cell
death.

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• b) The tail of the tadpole is absorbed via apoptosis.
• Also, in adult multicellular organisms cell death is a regular
occurrence.
• In humans EACH HOUR we lose many BILLIONS of cells via
apoptosis.

12. NECROSIS
• From the Greek "nekros" (dead body).
• Cells die naturally after a period of time, but may
also die as a result of injuries, infections, or cancer.
• Necrosis is the death of body tissue.
• It occurs when too little blood flows to the tissue.
• This can be from injury, radiation, or chemicals
• it can affect many areas of the body, including bone,
skin, organs and other tissues

13. • It s harmful process in which cells burst and release
toxins thus killing neighboring cells