<25% results in cellular death.

<25% results in cellular death.

• A. 25-30%
• B. 30-50%
• C. <25%
• D. 50-70%

Answer: (C)

The idea being tested is that there is a critical minimal level of blood flow below which cells cannot stay viable. Cells rely on oxygen and nutrients delivered by the blood to make ATP and to power ion pumps that maintain cell integrity. When perfusion drops, ATP falls, ion pumps fail, and with time the cell can no longer maintain its membranes and intracellular balance. There is a threshold below which the energy deficit becomes irreversible, leading to cellular death. In many tissues, this tipping point is reached when perfusion falls to less than about a quarter of normal flow, so saying that less than 25% of normal blood flow results in cellular death reflects that critical limit. Above that level, cells may still survive for a period or recover once flow is restored, depending on tissue type and duration of ischemia.

The idea being tested is that there is a critical minimal level of blood flow below which cells cannot stay viable. Cells rely on oxygen and nutrients delivered by the blood to make ATP and to power ion pumps that maintain cell integrity. When perfusion drops, ATP falls, ion pumps fail, and with time the cell can no longer maintain its membranes and intracellular balance. There is a threshold below which the energy deficit becomes irreversible, leading to cellular death. In many tissues, this tipping point is reached when perfusion falls to less than about a quarter of normal flow, so saying that less than 25% of normal blood flow results in cellular death reflects that critical limit. Above that level, cells may still survive for a period or recover once flow is restored, depending on tissue type and duration of ischemia.