Which physiological response is a potential effect of oligaemia?

Reduced oxygen delivery to tissues is the correct physiological response associated with oligemia, which refers to a deficiency in the volume of blood in the body. When blood volume is decreased, particularly in relation to the body's needs, the delivery of oxygen to tissues suffers. This occurs because the blood, which carries oxygen via hemoglobin, is limited; hence, less oxygen is transported to various cells and organs, leading to potential hypoxia.

Oligemia can occur due to various reasons, such as dehydration, blood loss, or vascular conditions that compromise blood flow. As tissues receive inadequate oxygen, they can struggle to maintain cellular functions effectively, which can lead to organ dysfunction if prolonged.

In the context of the other choices, while increased heart rate may be a compensatory mechanism in response to decreased blood volume to maintain perfusion, it is not a direct effect of oligemia. Heightened alertness generally corresponds to a response mediated by increased blood flow and oxygenation, which is contrary to the effects of oligemia. Expanded blood vessel diameter, or vasodilation, is typically associated with increased blood volume or certain physiological responses like inflammatory reactions, not with oligemia.