Hypothalamus/Pituitary, Insulin feedback loops?

VirginiaEMT

VirginiaEMT

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I really need some advice locating a place that explains the functions of these negative feedback loops. I have been at this for 5 hours today and feel like I have gotten nowhere. Any advice?
 
That's a really complicated question to ask...

If Vene refers you to a book it usually means the answer is long and better answered by a fuller understanding of anatomy and physiology.
 
let's just say I hope your test isn't tomorrow, because negative feedback is the key to all of endocrinology.
 
Veneficus said:
let's just say I hope your test isn't tomorrow, because negative feedback is the key to all of endocrinology.
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No test tomorrow, I'm actually just sitting here reading and studying some and thought this would be good to study so I will have a better understanding. I'm actually on break.
 
VirginiaEMT said:
No test tomorrow, I'm actually just sitting here reading and studying some and thought this would be good to study so I will have a better understanding. I'm actually on break.
Click to expand...

The endocrine section of an A&P book is your best bet. Probably 100-300 pages of "light" reading for the simple answer to your original question.

I just finished reading "Martini fundamentals of A&P" and really enjoyed it.

Vene loves Guytons. Odds are he knows a good book... (guytons is all physiology I believe, around 1000 pages of easy to understand wording)
 
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The book Vene suggested would be your best friend. Must have.
 
PoeticInjustice said:
The book Vene suggested would be your best friend. Must have.
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I have it and I'm too lazy to read it after finishing the above mentioned book for my class. I got an A though :)
 
I'm doing this off the top of my head so there may be a mistake or two.

Negative feedback helps to control the release and presence of chemicals (such as hormones) in the body. There are a variety of axes that have been proposed or determined, such as the HPA, HPG, HPT.

Receptors in the hypothalamus will detect low levels of a certain hormone and will consequently expel a releasing hormone which travels to the pituitary, which will then subsequently release a tropic hormone to act on the organ in control of that particular hormone that is deficient in the body.

Or, receptors in the hypothalamus will detect high levels of a certain hormone and consequently decrease the releasing hormone expelled which induces the pituitary to decrease its release of tropic hormone which will induce the endocrine gland to decrease its release of the respective hormone.

So in the HPA axis (hypothalamic-pituitary-adrenal axis), after a stressful event occurs, there will be an increased amount of cortisol circulating in the blood. The hypothalamus will detect high levels of cortisol and will decrease its release of corticotropin releasing hormone (CRH) which will induce the pituitary to decrease or cease its release of adrenocorticotropic hormone (ACTH) which will then induce the cortex of the adrenal glands to decrease its release of gluccocorticoids such as cortisol.

There's a lot of big funny words there but it's pretty simple. The hypothalamus, pituitary, and whatever respective endocrine gland all work together to control levels of a hormone.

There are some positive feedback loops, the most popular being the estrogen-leutinizing hormone loop towards the end of the follicular phase during the ovarian cycle in females.


Now here's the relatively tricky part. If a healthy individual is given an agonist for a particular hormone such as cortisol, you would expect to see a huge increase in cortisol in the blood. This however is not true! After administering the agonist, such as dexamethasone, there is a marked decrease in cortisol. This is because the negative feedback loop works to cease the release of CRH, ACTH, and cortisol. In individuals with a dysregulated HPA axis, you would still see relatively high levels of circulating cortisol.

When you have a thyroid test done, they check your thyroid stimulating hormone or TSH. If your TSH is relatively high, then it suggests your thyroid is not making enough T3 and T4. If it was, there would be a negative feedback on the hypothalamus from the circulating levels of T3 and T4, and thus a negative feedback on the pituitary to cause a healthy level of TSH. This could be a form of hypothyroidism (low levels of thyroid).

If your TSH levels are LOW, this would suggest you have high circulating levels of T3 and T4 and are thus having a negative feedback affect on the hypothalamus and thus the pituitary. This may indicate hyperthyroidism.


I'm not sure if the pancreas is part of a hypothalamus-pituitary axis...
 
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eprex said:
I'm doing this off the top of my head so there may be a mistake or two.

Negative feedback helps to control the release and presence of chemicals (such as hormones) in the body. There are a variety of axes that have been proposed or determined, such as the HPA, HPG, HPT.

Receptors in the hypothalamus will detect low levels of a certain hormone and will consequently expel a releasing hormone which travels to the pituitary, which will then subsequently release a tropic hormone to act on the organ in control of that particular hormone that is deficient in the body.

Or, receptors in the hypothalamus will detect high levels of a certain hormone and consequently decrease the releasing hormone expelled which induces the pituitary to decrease its release of tropic hormone which will induce the endocrine gland to decrease its release of the respective hormone.

So in the HPA axis (hypothalamic-pituitary-adrenal axis), after a stressful event occurs, there will be an increased amount of cortisol circulating in the blood. The hypothalamus will detect high levels of cortisol and will decrease its release of corticotropin releasing hormone (CRH) which will induce the pituitary to decrease or cease its release of adrenocorticotropic hormone (ACTH) which will then induce the cortex of the adrenal glands to decrease its release of gluccocorticoids such as cortisol.

There's a lot of big funny words there but it's pretty simple. The hypothalamus, pituitary, and whatever respective endocrine gland all work together to control levels of a hormone.

There are some positive feedback loops, the most popular being the estrogen-leutinizing hormone loop towards the end of the follicular phase during the ovarian cycle in females.


Now here's the relatively tricky part. If a healthy individual is given an agonist for a particular hormone such as cortisol, you would expect to see a huge increase in cortisol in the blood. This however is not true! After administering the agonist, such as dexamethasone, there is a marked decrease in cortisol. This is because the negative feedback loop works to cease the release of CRH, ACTH, and cortisol. In individuals with a dysregulated HPA axis, you would still see relatively high levels of circulating cortisol.

When you have a thyroid test done, they check your thyroid stimulating hormone or TSH. If your TSH is relatively high, then it suggests your thyroid is not making enough T3 and T4. If it was, there would be a negative feedback on the hypothalamus from the circulating levels of T3 and T4, and thus a negative feedback on the pituitary to cause a healthy level of TSH. This could be a form of hypothyroidism (low levels of thyroid).

If your TSH levels are LOW, this would suggest you have high circulating levels of T3 and T4 and are thus having a negative feedback affect on the hypothalamus and thus the pituitary. This may indicate hyperthyroidism.


I'm not sure if the pancreas is part of a hypothalamus-pituitary axis...
Click to expand...

This is exactly what I can't figure out. I can comprehend the hypothalamus- pituitary- thyroid loop, but does the feedback loop that control blood glucose levels also start at the hypothalamus-pituitary area of the brain? If so, what regulatory hormones are secreted?
 
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VirginiaEMT said:
This is exactly what I can't figure out. I can comprehend the hypothalamus- pituitary- thyroid loop, but does the feedback loops that control blood glucose levels also start at the hypothalamus-pituitary area of the brain?
Click to expand...

I believe hypothalamus has involvement to some degree in every visceral function. The hypothalamus essentially acts as the filter of the CNS and relays that information into an endocrine response.
 
VirginiaEMT said:
I really need some advice locating a place that explains the functions of these negative feedback loops. I have been at this for 5 hours today and feel like I have gotten nowhere. Any advice?
Click to expand...

The internet, they can't post anything on the internet that isn't true....... It is the law
 
Textbook of Medical Physiology (Guyton and Hall) 11th ed.

Hypothalamus Controls Pituitary Secretion
Almost all secretion by the pituitary is controlled by either hormonal or nervous signals from the hypothalamus. Indeed, when the pituitary gland is removed from its normal position beneath the hypothalamus and transplanted to some other part of the body, its rates of secretion of the different hormones (except for prolactin) fall to very low levels. Secretion from the posterior pituitary is controlled by nerve signals that originate in the hypothalamus and terminate in the posterior pituitary. In contrast, secretion by the anterior pituitary is controlled by hormones called hypothalamic releasing and hypothalamic inhibitory hormones (or factors) secreted within the hypothalamus itself and then conducted, as shown in Figure 75–4, to the anterior pituitary through minute blood vessels called hypothalamic-hypophysial portal vessels. In the anterior pituitary, these releasing and inhibitory hormones act on the glandular cells to control their secretion. This system of control is discussed in the next section of this chapter. The hypothalamus receives signals from many sources in the nervous system. Thus, when a person is exposed to pain, a portion of the pain signal is transmitted into the hypothalamus. Likewise, when a person experiences some powerful depressing or exciting thought, a portion of the signal is transmitted into the hypothalamus. Olfactory stimuli denoting pleasant or unpleasant smells transmit strong signal components directly and through the amygdaloid nuclei into the hypothalamus. Even the concentrations of nutrients, electrolytes, water, and various hormones in the blood excite or inhibit various portions of the hypothalamus. Thus, the hypothalamus is a collecting center for information concerning the internal well-being of the body, and much of this information is used to control secretions of the many globally important pituitary hormones.
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Without posting the entire chapter, the hypothalmus receives and filters information and controls the pituitary which further goes on to have a role in almost all major bodily functions to some degree be it directly or indirectly.
 
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The major control of blood glucose, especially insulin release, has nothing to do with the HPA axis. For insulin release, the beta cells continually take up glucose, which gets converted to ATP. Increased ATP shuts down a potassium channel, leading to depolarization of the beta cells and activation of calcium channels. Increased calcium concentration results in insulin release.

Now where the HPA axis affects glucose levels is by controlling the release of glucocorticoids during stress situations (including diseased states). Hypothalamus->corticotropin releasing hormone->pituitary->adrenocorticotropic hormone->adrenal->cortisol.
 
JPINFV said:
The major control of blood glucose, especially insulin release, has nothing to do with the HPA axis. For insulin release, the beta cells continually take up glucose, which gets converted to ATP. Increased ATP shuts down a potassium channel, leading to depolarization of the beta cells and activation of calcium channels. Increased calcium concentration results in insulin release.

Now where the HPA axis affects glucose levels is by controlling the release of glucocorticoids during stress situations (including diseased states). Hypothalamus->corticotropin releasing hormone->pituitary->adrenocorticotropic hormone->adrenal->cortisol.
Click to expand...

Do you actually remember that at all times or do you refer to the book?
 
NYMedic828 said:
Do you actually remember that at all times or do you refer to the book?
Click to expand...


I couldn't recall the names of the hormones, but the concept that glucose->ATP->depolarization->insulin release wasn't something I had to look up, as well as stress responses/cortisone release. A lot of the mechanical specifics is common among other cells. Nerve conduction works in a similar way of depolarization->opening of Ca++ channels->neurotransmitter vesicles attaching to snare proteins->fusion with membrane->neurotransmitters entering the synaptic cleft.

In regards to the stress response, patients with adrenal insufficiency who are on glucocorticoid supplementation are taught to take extra doses when they get sick and are given extra doses when they undergo procedures (stress dose).

I'll also generally look things up quickly just to confirm what I'm posting just to make sure it's correct.
 
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VirginiaEMT said:
This is exactly what I can't figure out. I can comprehend the hypothalamus- pituitary- thyroid loop, but does the feedback loop that control blood glucose levels also start at the hypothalamus-pituitary area of the brain? If so, what regulatory hormones are secreted?
Click to expand...

I've never heard of an HPP axis, although I only studied basic endocrinology. A quick google search shows nothing of the sort.

It's possible some pathways have evolved to be more complex than others. The release of pancreatic enzymes and hormones are controlled by the small intestine and the autonomic nervous system. High levels of blood glucose trigger the release of insulin, while low levels or insufficient levels of blood glucose can be elevated by epinephrine, cortisol (which does have an HP axis), and glucagon.
 
NYMedic828 said:
Do you actually remember that at all times or do you refer to the book?
Click to expand...

Isn't he in medical school? I know most of my stuff from ta'ing for endocrinology. Hope I get into med school this year!
 
JPINFV said:
The major control of blood glucose, especially insulin release, has nothing to do with the HPA axis.
Click to expand...

I hope you and the OP understand that was not the point I was making, but giving an example of my favorite negative feedback loop.
 
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