Final answer:
A typical mammalian cell in fast-dividing conditions completes the cell cycle in about 24 hours, with specific phases like the S phase lasting around 10 hours. Hormones and environmental factors can affect the cell cycle timing that varies among different cell types, with some never dividing after reaching the phase.
Step-by-step explanation:
The time it takes for a mammalian cell to complete the cell cycle is variable, but for rapidly dividing cells in culture, it's typically about 24 hours. The cell cycle consists of several phases: the G₁ phase, which lasts approximately nine hours, the S phase, which lasts about 10 hours, the G₂ phase, about 4.5 hours, and the M phase, approximately 0.5 hours. Specialized cells, such as those found in the cortex or heart, may spend their entire lifespan in a phase called G₀ and never divide, whereas cells in early embryonic stages can have much shorter cycles.
The control of the cell cycle involves a complex interplay of internal and external regulatory mechanisms. For example, the release of hormones like human growth hormone (HGH) can influence the initiation of cell division, whereas environmental factors such as cell crowding can inhibit it. As a cell grows, its efficiency decreases due to the reduced surface-to-volume ratio, prompting cell division to maintain optimal function.