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 […]

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 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 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 20: The Cell Cycle

Unit V: Regulation of Cell Growth and Cell Death Life is pleasant. Death is peaceful. It’s the transition that’s troublesome. —Isaac Asimov (American science fiction writer and biochemist, 1920–1992) Arguably the most important occurrences within the life of a cell are its generation from a progenitor followed by its demise, either through a natural or […]

Chapter 19: Steroid Receptor Signaling

OVERVIEW The use of intracellular receptors distinguishes classical steroid hormone signaling from signaling by hydrophilic signaling factors including peptide hormones and growth factors that use membrane-bound receptors. Intracellular receptors for steroids are located in the cytoplasm or in the nucleus of target cells. Steroid hormone receptors act as ligand-activated transcription factors, since their ligand (hormone) […]

Chapter 18: Catalytic Receptor Signaling

OVERVIEW Growth factors, cytokines (growth factors of the immune system), and some hormones are signaling molecules that use catalytic or enzymatic receptors to stimulate their target cells (see also LIR Immunology, Chapter 6). Most catalytic receptors are single-chain transmembrane proteins that associate with other single-chain transmembrane proteins upon ligand binding and signal via phosphorylation of […]

Chapter 17: G Protein Signaling

Cell Signaling Good communication is as stimulating as black coffee and just as hard to sleep after. —Anne Morrow Lindbergh (American author and aviator, 1906–2001) In: Gift from the Sea (1955) Soluble chemical signals sent from one cell to another are a basic means by which cell communication takes place. Hormones, growth factors, and neurotransmitters […]

Chapter 16: Drug Transport

OVERVIEW Most drugs must be transferred from their site of administration to the bloodstream in order to reach their target tissues within the body. Drugs administered intravenously are completely absorbed and the total dose of intravenously administered drugs reaches the systemic circulation. But drugs administered other ways may be only partially absorbed. Oral administration is […]

Chapter 15: Glucose Transport

OVERVIEW Glucose is essential for life. It is the major energy source for mammalian cells and its transport into cells is crucial for survival of both the cell and the individual. Most cells use facilitated transport for uptake of glucose by uniport since a concentration gradient often exists for glucose between extracellular fluids and the […]