Endocrine Secretion Pathways

The pituitary gland controls the activity of many, but not all, the endocrine glands. In some cases control occurs through a chain of related hormones. You can inspect several types of hormone control chains below by sequentially clicking the shadowed text in the chains. In some cases, peripheral endocrine gland activity is ultimately controlled by the hypothalamus (brain), which secretes releasing peptides that stimulate the pituitary to secrete intermediate peptide hormones that directly control the activity of the peripheral glands. The peripheral gland hormones feed back on the hypothalamus and pituitary to decrease the output of the intermediate control hormones, maintaining a balance of hormone production. Note that the parathyroid glands are not centrally controlled (they respond directly to the concentration of ionized calcium in the plasma).

General considerations in endocrine evaluation:

  1. Laboratory testing plays a prominent role, but a good physical exam and history are just as important

  2. Analysis of hormone pairs is an important diagnostic technique that allows physicians to determine whether problems result from dysfunction in the pituitary or the peripheral endocrine glands. Click the shadowed text in the new window to display the relationships between pituitary and peripheral endocrine hormones in pituitary or peripheral gland disorders.

  3. Challenge testing usually involves treating a patient with a peripheral or pituitary hormone and observing the effect on the other hormone. Some types of challenge testing involve giving the patient a physiological stimulus (e.g., water loading or water restriction) and observing the response of the body. In either case, the response helps define a disorder and determine its location.

  4. Circadian and ultradian rhythms occur in both pituitary and peripheral hormones. Circadian rhythms are variations in secretory patterns that extend over a day (24 hr). Cortisol shows a circadian rhythm (high in the morning, low in the evening) that requires the use of separate reference ranges for morning and evening. Ultradian rhythms are shorter than a day, extending over minutes to hours. Pulsatile secretion of prolactin is an example of an ultradian rhythm.

  5. High sensitivity immunoassays for hormones have become widely available over the last several years and make the analysis of low levels of pituitary hormones practical.

Endocrine Overview Pituitary Gland
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Last modified: 1/16/97; Author: J. Harrison