Final answer:
Gland secretion solely triggered by changes in nutrient concentration in the blood is regulated through humoral regulation, responding to fluctuations in blood ion or nutrient content.
Step-by-step explanation:
If a gland's secretion is regulated only by changes in nutrient concentration in the blood, the control of its hormone release is known as humoral regulation.
This is because humoral stimuli refer to control mechanisms that respond to changes in the extracellular fluid or blood ion and nutrient levels. Hormones may also be released in response to other controls, such as hormonal stimuli, prompted by other hormones, or neural stimuli, initiated by nerve signals.