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Positive & Negative Feedback

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Positive & Negative Feedback

Postby sariko » Thu Aug 11, 2005 10:03 pm

Hello all, I'm new here!

I need help with finding some examples of positive and negative feedback. If you could list any you know of and explain why it would be very helpful.

Thank you!

Edit: I managed to find some from a different website. Thank you anyway!
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Postby Miko » Fri Aug 12, 2005 2:21 am

What do you mean positive and negative feedback? Feedback of what? :?:

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Postby chemistry_freako » Fri Aug 12, 2005 3:32 am

do u mean of homeostasis? Negative feedback is mainly how homeostasis is maintained, and positive feedback includes processes like blood clotting

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Postby Dr.Stein » Fri Aug 12, 2005 4:32 am

Negative and positive feedback is a common mechanism in Endocrinology, to regulate the production (including synthesis and secretion) of such hormone(s). Since I am into that field, so what I explain is about hormone. I have no idea if there is another feedback things in other fiels, but I think the principal is somewhat similar.

In general this mechanism is used to maintain the constant level of hormone within our body, or homeostasis, to anticipate excessive or lack of hormone level, in which will lead to adverse effect(s) to target tissues.

Here I give you an explanation using example, cos I think this will help you better rather than using a definition:

Negative feedback:
When the level of blood testosteron is increasing, this hormone will give a signal to hypothalamus and hypophyse to stop the production of GnRH and LH, respectively, to prevent the excessive level of hormone in blood. In contrast, when the level of blood testosteron is decreasing, this hormone will give a signal to hypothalamus and hypophyse to stimulate the production of GnRH and LH, respectively, so the hormone level will increasing to the normal level, then it will be maintain in that level.

Positive feedback:
~ Before ovulation, ovarium secretes estrogen to stimulate the maturation of the ovum. The current level of estrogen will give a signal to hypothalamus and hypophyse to stimulate the production of GnRH and FSH, respectively, so the estrogen level will be increasing til reaches the peak. This is when ovulation occurs.

~ After ovulation, ovarium secretes progesteron to stimulate the growth of endometrium. The current level of progesteron will give a signal to hypothalamus and hypophyse to stimulate the production of GnRH and LH, respectively, so the progesteron level will be increasing til reaches the peak.

When progesteron reached the peak, it will give a negative feedback to the production of FSH, so that the production of estrogen. This estrogen will stimulate the contraction of uterine muscles, so this is when the menstrual cycle begins.

I hope I am not confusing you. Please draw your conclusion to define the negative and positive feedback, so I know you got my point. Thank you and good luck with your study :wink:
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Allosteric Feedback

Postby ashwinvirus » Wed Jul 02, 2008 12:04 pm

hi,, these negative and positive feedbacks are preety easy once you get the idea but this allosteric feedback is confusing me,, can anyone please help me out n soon.
i have to appear a exam by next month,, i would be very grateful.
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Postby MrMistery » Wed Jul 02, 2008 5:47 pm

allosteric feedback? I think that just means that the feedback - either positive or negative - is exerted through allosteric regulation of an enzyme.
"As a biologist, I firmly believe that when you're dead, you're dead. Except for what you live behind in history. That's the only afterlife" - J. Craig Venter
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positive and negative feedback loops

Postby biodawgg » Fri Jul 18, 2008 2:52 am

simple example of a negative feedback loop is the hypothalumous control of body temperature.

when the body is to cold receptors, ie: nerves, send messages to the control centre, ie: the hypothalumous, this stimulant causes the control centre to inform the effector(s) to counter the stimulant. ie: the muscles begin to perform minute contrations to create metabolic heat, blood vessals constrict. the result of this is that the body may begin to over heat. this new stimulant causes the control centre (hypoth.) to instruct the effector(s) to kick in. for example sweating , vaso-dialation, etc...

in each case the result of the effectors action becomes the new stimulant and an opposite reaction occurs in a controlled manner and therefore homeostasis in body heat is maintained- this only occurs in endothermic organisms.

example of positive feedback is were stimulant causes the effector to increase the effect of the stimulant. for example, pressure on the uterus muscles during child birth increases the dialation and pressure.. thus it is a positive feedback loop.
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