What defines ischemia in terms of blood supply?

Ischemia is defined as a deficiency of blood supply to a tissue or organ. This condition can lead to a lack of oxygen and nutrients required for cellular metabolism, ultimately resulting in tissue damage or dysfunction. When blood flow is inadequate, the affected tissues cannot receive the necessary components for proper function, which is critical in many bodily processes, especially in the brain and heart. Understanding this concept is vital in healthcare, as ischemia can have serious implications if not addressed promptly, such as in cases of heart attacks or strokes. The other options describe conditions that either indicate adequate blood supply or are related to other physiological responses but do not correctly define the state of ischemia.