EK Bio #472

[Scarletblack]

Hey guys,

I having a little trouble understanding this question:

A male with serum auto antibodies that bind to the thyroid gland TSH receptors should be considered as:

A. healthy, because negative feedback will regulate the level of thyroid hormone.
B. having low levels of thyroid hormone because auto-antibodies block TSH from binding to its receptor
C. having high levels of thyroid hormone because autoantibodies are overstimulating the thyroid gland
D. having low levels of thyroid hormone because auto-antibodies are destroying the thyroid gland

So I was like well the antibodies are blocking the site now, so the hormone reduced should be lower, so it should be B.

But it says that it is C. Which really is confusing me now. >_<

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[Bacchus]

The antibodies are binding to the site. The variable regions of the antibody are similar to the portion of TSH that binds to the receptor. Since the antibodies are binding to the TSH-receptor, activation occurs.

This is a textbook example of Grave's Disease. The question book probably does not tell you that because the pathophysiology of Grave's is its overstimulation of the thyroid.

 

[schlieren]

I also answered B to this question. So is this a peculiar case about thyroid, or auto-antibodies overstimulate receptors in general?

 

[Bacchus]

I wouldn't say its thyroid specific.

 

[coffeebythelake]

This is a tricky question because antibodies to receptors can be stimulatory in some cases (e.g., TSH receptor in Graves disease), and inhibitory in other cases (e.g., nAch receptor in myasthenia gravis). I think this kind of question is beyond the scope of what you need to know for the actual MCAT, unless additional information is given to you in the passage.

 

[alexandertg6]

the key to this question is that it says the male has serum auto antibodies TO THYRIOD tsh receptors. The thyroid doesnt know how much its secreting so constantly thinks its low.. blind secretion

hope that helps

 

[MLT2MT2DO]

the key to this question is that it says the male has serum auto antibodies TO THYRIOD tsh receptors. The thyroid doesnt know how much its secreting so constantly thinks its low.. blind secretion

hope that helps

Hyperthyroidism is an increase of of thyroxine, the hormone that is produced by the thyroid once TSH binds to the thyroids receptors.

The thyroid having no idea about how much TSH is being secreted has no affect on the negative feedback system.

Unlike everyone else I went with Hashimoto's Disease and answered "D" to this question. Without further explanation in a passage I agree that this is a bad question.

 

[ElliottB]

I don't think this is a bad question. It is a demonstration of negative feedback. The with the TSH receptors blocked, the thyroid will not know to downregulate production of TSH resulting in higher levels.

Am I totally off base here?

 

[Geekchick921]

I don't think this is a bad question. It is a demonstration of negative feedback. The with the TSH receptors blocked, the thyroid will not know to downregulate production of TSH resulting in higher levels.

Am I totally off base here?

I think you're over-thinking it. The receptors aren't blocked. The antibodies are bound to it, like TSH would be (true, they're blocking TSH but the thyroid doesn't know what's stimulating its TSH receptors, just that something is). The thyroid is effectively stuck in the 'on' position.

And I don't think this is what you meant, but to be clear, the thyroid doesn't produce TSH, the anterior pituitary does. The thyroid produces T3 and T4, which works with negative feedback on the anterior pituitary to stop producing TSH, but fat lotta good that will do with serum antibodies hogging the receptors for it.

 

[DavidMD2B]

Hey guys,

I having a little trouble understanding this question:

A male with serum auto antibodies that bind to the thyroid gland TSH receptors should be considered as:

A. healthy, because negative feedback will regulate the level of thyroid hormone.
B. having low levels of thyroid hormone because auto-antibodies block TSH from binding to its receptor
C. having high levels of thyroid hormone because autoantibodies are overstimulating the thyroid gland
D. having low levels of thyroid hormone because auto-antibodies are destroying the thyroid gland

So I was like well the antibodies are blocking the site now, so the hormone reduced should be lower, so it should be B.

But it says that it is C. Which really is confusing me now. >_<

I hope this helps explain this phenomena:

What is Graves’ disease?

The thyroid gland’s production of thyroid hormones (T3 and T4) is triggered by thyroid-stimulating hormone (TSH), which is made by the pituitary gland.
Graves’ disease, also known as toxic diffuse goiter, is the most common cause of hyperthyroidism in the United States. Hyperthyroidism is a disorder that occurs when the thyroid gland makes more thyroid hormone than the body needs.
The thyroid is a small, butterfly-shaped gland in the front of the neck below the larynx, or voice box. The thyroid gland makes two thyroid hormones, triiodothyronine (T3) and thyroxine (T4). Thyroid hormones affect metabolism, brain development, breathing, heart and nervous system functions, body temperature, muscle strength, skin dryness, menstrual cycles, weight, and cholesterol levels.
Thyroid hormone production is regulated by another hormone called thyroid-stimulating hormone (TSH), which is made by the pituitary gland located in the brain.
Graves’ disease is an autoimmune disorder, meaning the body’s immune system acts against its own healthy cells and tissues. In Graves’ disease, the immune system makes antibodies called thyroid-stimulating immunoglobulin (TSI) that attach to thyroid cells. TSI mimics the action of TSH and stimulates the thyroid to make too much thyroid hormone. Sometimes the antibodies can instead block thyroid hormone production, leading to a confusing clinical picture. The diagnosis and treatment of Graves’ disease is often performed by an endocrinologist—a doctor who specializes in the body’s hormone-secreting glands.


Source: http://endocrine.niddk.nih.gov/pubs/graves/

 

[badmintondr]

Just saying, from my MCAT perspective, this has nothing to do with Grave's disease (no offense to you guys). But I also concur with what ElliotB said, I believe this is a question regarding negative feedback. If you go over (forgot which EK chapter) it states that most of the times, you should think of hormones in terms of ...how and why the body will respond to XX condition instead of what you think will result from the situation. In this case, you shouldn't think "Hmm blocked TSH glands means less thyroid hormones. Darn." It should be like more "Hmm the body blocked TSH because it's probably over-secreting thyroid hormones so the body is reacting by blocking the TSH receptors."

Ya...this is what I got from EK at least.

 

[Bacchus]

Just saying, from my MCAT perspective, this has nothing to do with Grave's disease (no offense to you guys). But I also concur with what ElliotB said, I believe this is a question regarding negative feedback. If you go over (forgot which EK chapter) it states that most of the times, you should think of hormones in terms of ...how and why the body will respond to XX condition instead of what you think will result from the situation. In this case, you shouldn't think "Hmm blocked TSH glands means less thyroid hormones. Darn." It should be like more "Hmm the body blocked TSH because it's probably over-secreting thyroid hormones so the body is reacting by blocking the TSH receptors."

Ya...this is what I got from EK at least.

This is classic Grave's disease. I'm not trying to be superior, but undergraduate immunology and medical school immunology have described it as such.

 

[MegaSpectacular]

Just saying, from my MCAT perspective, this has nothing to do with Grave's disease (no offense to you guys). But I also concur with what ElliotB said, I believe this is a question regarding negative feedback. If you go over (forgot which EK chapter) it states that most of the times, you should think of hormones in terms of ...how and why the body will respond to XX condition instead of what you think will result from the situation. In this case, you shouldn't think "Hmm blocked TSH glands means less thyroid hormones. Darn." It should be like more "Hmm the body blocked TSH because it's probably over-secreting thyroid hormones so the body is reacting by blocking the TSH receptors."

Ya...this is what I got from EK at least.

What Bacchus said...

And dude, the body doesn't make antibodies to stop a hormone from working BY DESIGN. It just stops making the hormone or down regulates the receptor.

I don't know if there is a biological instance where your body actually creates an antibody to stop its own receptors from working (on purpose, not a disorder/disease). Biologically that would be inefficient and wouldn't make much sense.

 

[dingyibvs]

Hey guys,

I having a little trouble understanding this question:

A male with serum auto antibodies that bind to the thyroid gland TSH receptors should be considered as:

A. healthy, because negative feedback will regulate the level of thyroid hormone.
B. having low levels of thyroid hormone because auto-antibodies block TSH from binding to its receptor
C. having high levels of thyroid hormone because autoantibodies are overstimulating the thyroid gland
D. having low levels of thyroid hormone because auto-antibodies are destroying the thyroid gland

So I was like well the antibodies are blocking the site now, so the hormone reduced should be lower, so it should be B.

But it says that it is C. Which really is confusing me now. >_<

Let's go over this step by step:

1)TSH usually binds to TSH receptors, which stimulates the release of thyroid hormones.
2)Now the auto antibodies bind to TSH receptors, which should also stimulate the release of thyroid hormones, thus giving the person a high level of thyroid hormones(answer C)
3)Negative feed back SHOULD reduce the amount of TSH produced in order to reduce the thyroid hormone levels, but none of the answers describe the amount of TSH produced, only the amount of thyroid hormones produced.

 

[Bacchus]

What Bacchus said...

And dude, the body doesn't make antibodies to stop a hormone from working BY DESIGN. It just stops making the hormone or down regulates the receptor.

I don't know if there is a biological instance where your body actually creates an antibody to stop its own receptors from working (on purpose, not a disorder/disease). Biologically that would be inefficient and wouldn't make much sense.

Not that I'm aware of. Your immune system can make Abs against Abs to lessen the secondary response (by theory...I don't think proven yet).

 

[MLT2MT2DO]

Let's go over this step by step:

1)TSH usually binds to TSH receptors, which stimulates the release of thyroid hormones.
2)Now the auto antibodies bind to TSH receptors, which should also stimulate the release of thyroid hormones, thus giving the person a high level of thyroid hormones(answer C)
3)Negative feed back SHOULD reduce the amount of TSH produced in order to reduce the thyroid hormone levels, but none of the answers describe the amount of TSH produced, only the amount of thyroid hormones produced.

In hyperthyroidism, TSH is often reduced.

 

[MegaSpectacular]

In hyperthyroidism, TSH is often reduced.

lol. Yeah, I would think so.

That is irrelevant in this question. Antibodies are creating the high hormone levels.