How is the release of anterior pituitary hormones regulated?
The release of hormones from the anterior pituitary gland is generally controlled by hormones from the hypothalamus.
The hypophyeseal-anterior pituitary portal system includes two capillary beds, one located near the hypothalamus, and another in the anterior pituitary. "Releasing hormones" from the hypothalamus control the release of hormones from the anterior pituitary.
A good example of this can be seen in the control of cortisol from the zona fasiculata in the adrenal cortex. While there are many conditions that can trigger an increase in cortisol, the most commonly discussed is due to increased stress.
During stressful situations, cortisol-releasing hormone or CRH is released from the hypothalamus, and triggers the release of adrenocorticotropin hormone, or ACTH, from the anterior pituitary. In turn, ACTH acts on the adrenal cortex to trigger the release of cortisol.
This hormone scheme is referred to as the hypothalamic-anterior pituitary-adrenal axis. The release of hormones from the anterior pituitary is almost always involved in some HPA axis where the hormone from the anterior pituitary acts to increase the level of another hormone released by a distal gland.
Note: hormones that cause the release of other hormones are called trophic hormones