apoptosis

Programmed cell death — a controlled self-destruction sequence encoded in every cell. The organism sacrificing parts to preserve the whole.

mechanism

1. intrinsic pathway: mitochondrial stress releases cytochrome c, activating caspase-9
2. extrinsic pathway: death ligands (FasL, TNF) bind surface receptors, activating caspase-8
3. execution: caspase-3 cleaves structural proteins, DNA fragmented, cell shrinks into apoptotic bodies
4. cleanup: phagocytes engulf debris without triggering inflammation

biological role

Essential for embryonic development (sculpting fingers, pruning neural networks in the brain), immune system homeostasis (eliminating self-reactive lymphocytes), and tissue turnover. A human body destroys ~50 billion cells per day through apoptosis.

dysfunction

Insufficient apoptosis: cancer, autoimmune disease. Excessive apoptosis: neurodegeneration, ischemic damage.

connections

The cellular expression of fear — the readiness to dissolve for the sake of the system. Linked to violet as the color of transformation and death-rebirth cycles. Complements mitosis (growth) with removal.