Therefore, with a high-dose suppression test, the production of ACTH will decrease leading to a decrease in cortisol. A pituitary adenoma will still respond to the hypothalamic-pituitary axis however, it needs more feedback to do so. A high-dose, typically 8 mg, dexamethasone-suppression test is done. If the secondary hypercortisolism is suspected, testing must be done to differentiate between a pituitary cause or an ectopic cause. Cushing syndrome is associated with ectopic ACTH production. Normal feedback loop mechanisms do not control the production of the hormone. Benign or malignant tumors secrete hormones. Diseases associated with the adrenals include Addison and Cushing.Įctopic secretion refers to the production of a hormone outside of its normal physiology mechanism.
The adrenal can also be hypofunctioning or hyperfunctioning. It is a pituitary infarct after massive blood loss during childbirth.
Sheehan syndrome is a less common cause of pituitary insufficiency. It can also be caused by pituitary apoplexy, a sudden hemorrhage into a pituitary tumor causing sudden loss of ACTH. Pituitary insufficiency is usually the result of an adenoma that destroys the gland. The pituitary can be hypofunctioning or hyperfunctioning, leading to either a decrease or increase, respectively, in ACTH. Issues can be with the pituitary, adrenals, or ectopic secretion. They could have been named something else, like "primary tropic" and "secondary tropic" but this terminology keeps them separate as "tropic hormones that cause release of other tropic hormones.Pathophysiology associated with ACTH can stem from 3 different mechanisms. Therefore, the sequence is releasing -> tropic -> non-tropic. In terms of overall neuroendocrine function, the "releasing" hormones all cause release of tropic hormones, which in turn cause release of hormones that affect other tissues. They are easily identified in a list of hormone because they all share a naming convention where they are called "_-releasing hormone" and their primary function is to cause the pituitary to release whatever is in the "_". Therefore, they aren't really released into the broader circulation (they can get there, but they'd be in too low a concentration). The special thing about the ones your textbook is specifically highlighting as releasing hormones is that they communicate from the hypothalamus to the pituitary through the hypophyseal portal system, vessels that travel directly from the hypothalamus to the anterior pituitary. The releasing hormones could also be considered tropic hormones, and indeed they fit the definition as you noticed, but aren't usually named as such. So are they identical? And if not, what distinguishes between them? And yet my textbook appears to use the terms separately later on as if they're related rather than identical (e.g.: "the pituitary gland is controlled by the hypothalamus via releasing hormones and it secretes tropic hormones" (pg. 394)įrom the work I've done, it all seems to indicate that releasing hormones regulate the secretion of other hormones, and that tropic hormones target and stimulate other endocrine glands (to release hormones). Other hormones are called tropic hormones. Hormones that stimulate endocrine glands to release Stimulate the pituitary gland to secrete hormones that act on otherĮndocrine glands. Which often travel to the pituitary gland. Hypothalamus secretes what are referred to as releasing hormones, Here's what the textbook says (McGraw Hill Bio 12, 2011):Īfter receiving signals from various sensors in the body, the I've been reading my textbook and two terms have appeared that, after a bit of looking, I still can't seem to be able to distinguish.
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