Cell Death

Cell death pathways help the body remove old or damaged cells. Cell growth and cell death must stay balanced. If this balance is disrupted, it may contribute to cancer or autoimmune diseases. Cell death was first noticed in the early 19th century, but experimental proof came later.

In 1842, Carl Vogt described cell death in a metamorphic toad. At that time, the process was not yet called cell death. Scientists identified separate cell death pathways in the 20th century after advances in...

Apoptosis is a controlled form of cell death that helps keep tissues healthy. The term comes from two Greek words, apo and ptosis, which mean separation and falling off. Hippocrates used the word to describe gangrene caused by bandaging fractured bones.

Apoptosis was separated from necrosis in 1970 after John Kerr described its distinct shape changes. In one experiment, loss of blood supply to liver tissue caused the tissue to shrink. Under an electron microscope, Kerr saw that hepatocytes had...

Caspases are cysteine proteases that help control cell death and immune defense. They act as effectors in apoptosis, which is the process of programmed cell death. The ced-3 gene in C. elegans was first linked to apoptosis, and it encodes a caspase similar to the interleukin-1-beta converting enzyme, or ICE, in mammals.

Caspases also have a role in inflammation. Inflammatory caspases activate pro-inflammatory cytokines, which help recruit immune cells and stop pathogens from replicating inside...

The extrinsic apoptotic pathway is a cell death process started by signals from outside the cell. In this pathway, extracellular death signals such as specific cytokines activate death receptors on the cell surface. Natural killer cells, or NK cells, and cytotoxic T-lymphocytes help carry out this response.

NK cells are part of the innate immune response, while cytotoxic T-lymphocytes belong to the adaptive immune response. These cells recognize receptors on altered cells and activate...

Intrinsic apoptosis is the cell’s built-in death response to internal stress. Cell injury, hypoxia, and DNA damage can start this process. The B-cell lymphoma 2, or Bcl-2, family of proteins is the main regulator of this pathway.

When DNA is damaged, checkpoint proteins such as Ataxia Telangiectasia Mutated, or ATM, and Checkpoints Factor-2, or Chk2, become active. They phosphorylate p53, a protein that helps control cell survival. p53 then turns on pro-apoptotic proteins such as Bax, Bak,...

Apoptotic cells must be cleared quickly so they do not cause inflammation, autoimmune disease, or necrosis. During apoptosis, cells break into apoptotic bodies that are then removed by phagocytosis, the process in which other cells engulf and digest them.

Professional phagocytes, such as macrophages and immature dendritic cells, handle this job most effectively. Some non-professional phagocytes, including epithelial cells and fibroblasts, can also take part, but they are less efficient. Normal...

Autophagy is a cell cleanup process that can also lead to cell death. Christian de Duve discovered autophagy, in which cell parts are enclosed in membrane-bound sacs called autophagosomes. These autophagosomes then fuse with lysosomes, which digest the material inside.

In many cells, autophagy helps prevent cell death. When damage becomes too severe to repair, however, the process can shift toward cell death. Autophagy can connect to apoptosis, necroptosis, and autosis, so it sits at an...

Necrosis is an accidental form of cell death that ends in cell lysis, or cell bursting. Rudolf Virchow first used the term in 1859 in his book Cell Pathology to describe advanced tissue breakdown. In high school biology, necrosis is often used to compare damaged cells with other ways cells can die.

Necrotic cells can look different depending on the tissue and the cause of injury. In coagulative necrosis, cells lose their nuclei but keep their basic shape because the enzymes that digest cell...