Chapter 21: Regulation of the Cell Cycle

OVERVIEW Numerous checks and balances ensure that the cell cycle is highly regulated, establishing a state of balance or homeostasis between cell proliferation, cell differentiation, and cell death. Certain cell types retain the ability to divide throughout their life spans. Others permanently leave the active phases of the cell cycle (G1 ? S ? G2) […]

Chapter 22: Abnormal Cell Growth

OVERVIEW Cells are often lost through death (apoptosis and necrosis), sloughing (e.g., shedding of cells lining the gastrointestinal tract and skin), or injury (e.g., bleeding). New cells replace cells at the same rate they are lost, a highly regulated state of balance known as homeostasis. If normal cellular regulatory mechanisms malfunction, unregulated and unchecked cell […]

Chapter 23: Cell Death

OVERVIEW All cells eventually die either by necrosis or apoptosis. Necrosis is a passive, pathological process induced by cellular injury or accidental means and often involves the simultaneous death of cells in groups (Figure 23.1). Necrotic cells have ruptured cell membranes allowing the cytoplasm and organelles to spill into the surrounding tissue fluids, often inducing […]

Chapter 24: Aging and Senescence

OVERVIEW Most eukaryotic cells undergo a finite number of cell divisions. Cell division is restricted by a process of replicative or cellular senescence where cells reach an irreversible arrest of cell proliferation. Several genes are known to play a role in the control of replicative senescence. There are also several hypotheses to explain the aging […]