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If an organ was to start failing, not total failure, such as the thyroid gland, is it possible that the fault may not lie in the failure of the organ but in the nerve signals coming from the brain?

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I'm in an inquisitive mood today. Sorry. :) –  user6116 Mar 30 at 18:35

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In many hormonrs, the hypothalamus produces a hormone which acts on the pituitary gland which subsequently acts on an end organ. Taking your example of the thyroid gland let's take a look at it.

The hypothalamus produces TRH which acts on the anterior pituitary causing it to release TSH which in turn stimulates the thyroid gland to make thyroid hormones T3 and T4.

Abnormal levels of thyroid hormone may be caused by problems in any one of the three stages. Problems on the end organ are termed primary, in the pituitary gland are termed secondary and in the hypothalamus tertiary.

For simplicity let's look at abnormally high levels of thyroid hormones called hyperthyroidism. In a patient with a primary or thyroid gland problem we expect high levels of thyroid hormones but low levels of TSH. The pituitary gland is trying its best to tell the thyroid gland, "No more!" but it won't listen. In secondary or pituitary disease, the pituitary gland is the bully pushing the thyroid gland to make lots of thyroid hormone by over production of TSH. Usually there are other hormone disturbances too in this case as the pituitary gland has a range of hormones it secretes. Also the swollen pituitary gland puts pressure on the nerves carrying vision leading to visual loss (specifically in the temporal fields). In this case the hypothalamus will be secreting low levels of TRH (which isn't routinely measured) trying to get the pituitary gland to stop acting out. The rarest situation is when the hypothalamus has the problem where every hormone is increased. However again this will be causes by something or the other detectable usually on imaging.

So the short answer is yes, but there will be other features. Primary or end organ dysfunction is most common and will cause characteristic findings in blood tests and examination (e.g. swollen thyroid gland) but secondary and tertiary disease can be figured out when other features are found in association.

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Hypothalamic/pituitary control of glands is still endocrine. Do you know of a nervous control of an endocrine gland ? (I know examples nervous control of exocrine glands but not endocrine glands; perhaps because nervous control is fast and shortlived whereas endocrine control is longlasting but slow) –  WYSIWYG Mar 31 at 12:09
    
Yes. All the above is the actions of the anterior pituitary gland. The posterior pituitary comprises of axons projecting from the hypothalamus which release vesicles full of hormones from neurones themselves. Then the adrenaline release system could qualify. Apart from hormones being slow they also have more widespread effects then nervous control. Perhaps that's why oxytocin and ADH are controlled in this way? –  AndroidPenguin Mar 31 at 13:18
    
@WYSIWYG Adrenal Medulla? –  Rory M Mar 31 at 14:18
    
@AndroidPenguin.. yeah i forgot the pituitary.. –  WYSIWYG Mar 31 at 15:00
    
@RoryM.. yes i was thinking about adrenaline.. Confirms that nervous control is for quick responses –  WYSIWYG Mar 31 at 15:02

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