Final answer:
Ischemic injury to the kidneys occurs when mean arterial blood pressure falls below approximately 60 mm Hg, leading to insufficient blood flow and oxygenation, which can cause significant renal damage.
Step-by-step explanation:
Ischemic injury to the kidneys, which can result in conditions such as hypoxia and hypoxemia, usually commences when mean arterial blood pressure (MAP) falls below specific values. According to the provided information, the MAP normally ranges between 70-110 mm Hg. For the kidneys to maintain proper function and ensure sufficient glomerular filtration, the MAP should remain above approximately 60 mm Hg. If MAP falls below 60 mm Hg for an extended period, the blood pressure will not be high enough to maintain circulation to the kidneys, leading to ischemia. This reduction in blood and oxygen flow can significantly damage renal tissues and if not promptly corrected, can result in acute kidney injury or chronic kidney disease.