Technical Discussion

The pituitary gland is often portrayed as the "master gland" of the body. Such praise is justified in the sense that the anterior and posterior pituitary secrete a battery of hormones that collectively influence all cells and affect virtually all physiologic processes.

Lay Interpretation

The pituitary gland is called the Master Gland as almost all significant functions within the body fall under the influence of the pituitary gland at some point.

The pituitary gland may be king, but the power behind the throne is clearly the hypothalamus. As alluded to in the last section, some of the neurons within the hypothalamus - neurosecretory neurons - secrete hormones that strictly control secretion of hormones from the anterior pituitary.

The hypothalamic hormones are referred to as releasing hormones and inhibiting hormones, reflecting their influence on anterior pituitary hormones.

Hypothalamic releasing and inhibiting hormones are carried directly to the anterior pituitary gland via hypothalamic-hypophyseal portal veins. Specific hypothalamic hormones bind to receptors on specific anterior pituitary cells, modulating the release of the hormone they produce.

The hypothalamus is responsible for stimulating and inhibiting pretty much all of the functions of the pituitary gland.

As an example, thyroid-releasing hormone from the hypothalamus binds to receptors on anterior pituitary cells called thyrotrophs, stimulating them to secrete thyroid-stimulating hormone or TSH. The anterior pituitary hormones enter the systemic circulation and bind to their receptors on other target organs. In the case of TSH, the target organ is the thyroid gland.

Clearly, robust control systems must be in place to prevent over or under-secretion of hypothalamic and anterior pituitary hormones.

A prominent mechanism for control of the releasing and inhibiting hormones is negative feedback. Details on the control of specific hypothalamic and anterior pituitary hormones is presented in the discussions of those hormones.

The following table summarizes the major hormones synthesized and secreted by the pituitary gland, along with summary statements about their major target organs and physiologic effects. Keep in mind that summaries are just that, and ongoing research continues to delineate additional, sometimes very important effects.

A final point to be made is that individual cells within the anterior pituitary secrete a single hormone (or possibly two in some cases). Thus, the anterior pituitary contains at least six distinctive endocrinocytes.

The table to the left shows the amazing array of functions ultimately dependant upon the function of the pituitary gland.

The pituitary gland is made up of many different types of cells, each producing a single hormone.  Thus, this gland contains at least six distinctive cell types, each with very different functions.

The cells that secrete thyroid-stimulating hormone do not also secrete growth hormone, and they have receptors for thyroid-releasing hormone, not growth hormone-releasing hormone. The image below is of a section of canine anterior pituitary that was immunologically stained for luteinising hormone (black stain) and prolactin (purple stain). The unstained cells in the image are those that secrete the other pituitary hormones.

The technical information on these pages is the work of Professor Bowen et al, Colorado State University and are reproduced without endorsement of any kind.  The "lay" interpretations are the work of this site and do not necessarily reflect Professor Bowen's opinions.