During embryogenesis, apoptosis eliminates damaged or dysfunctional germ cells, superficial cells during tissue morphogenesis, and cells that fail to make the proper functional connections with neighboring cells (95). The key features of apoptosis, and its major regulatory and effector molecules, have been conserved throughout metazoan evolution. However, the number and complexity of proteins and reactions that regulate and execute apoptosis have increased greatly during vertebrate evolution (96). Further, in complex organisms, apoptosis is important for maintaining tissue homeostasis, and for eliminating dysfunctional, damaged, and/or potentially cancerous cells throughout life (93,97).

An important function of apoptosis is to provide a mechanism for eliminating unwanted cells without cell lysis. This is important because cell lysis frequently results in local tissue destruction, owing to the release of degradative enzymes from the lysed cells and the inflammation reactions that it frequently elicits. Thus, apoptosis allows organisms to remove damaged or dysfunctional cells with minimal collateral damage to the tissue. In postmitotic tissues, where cell proliferation cannot replace lost cells, apoptosis minimizes the cell loss. In renewable tissues, where cell proliferation can replace cells that are lost, apoptosis is an important mechanism for maintaining the size, integrity, and health of the tissue.

How to Stay Young

How to Stay Young

For centuries, ever since the legendary Ponce de Leon went searching for the elusive Fountain of Youth, people have been looking for ways to slow down the aging process. Medical science has made great strides in keeping people alive longer by preventing and curing disease, and helping people to live healthier lives. Average life expectancy keeps increasing, and most of us can look forward to the chance to live much longer lives than our ancestors.

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