Endocrine glands or ductless glands produce hormones and directly pour their secretion in the blood. These glands do not go on producing hormones.
Their secretion is controlled by feedback information system. Thus their over production of hormones is controlled.
For example, a hormone called TSH is secreted by pituitary gland. TSH stimulates the production of thyroxin from the thyroid gland.
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But if there is over production of thyroxin hormone, this hormone acts on pituitary gland and controls the production of TSH.
As a result, the production of thyroxin by the thyroid gland is controlled. Thus, TSH and thyroxin control the level of each other. This mechanism of opposing effect is called feedback mechanism.