Final answer:
When biologists speak of one hormone directly controlling the secretion of another hormone, they are describing a situation where the secretion of a hormone is regulated by the presence or activity of another hormone.
Step-by-step explanation:
When biologists speak of one hormone directly controlling the secretion of another hormone, they are describing a situation where the secretion of a hormone is regulated by the presence or activity of another hormone. This is known as hormonal control or hormonal regulation. An example of this is the hypothalamus and pituitary gland controlling the secretion of hormones from the adrenal glands in response to changes in glucocorticoid hormone levels in the blood.