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"Effects of" questions: direct effect vs neg feedback

Discussion in 'MCAT Study Question Q&A' started by futuredoctor10, Jan 3, 2009.

  1. futuredoctor10

    Classifieds Approved 10+ Year Member

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    I have some trouble on Biology questions involving "the effect of" a particular condition/pathology. Sometimes the answer (in EK) is the DIRECT effect. Other times, the answer is what the body would respond to help mitigate the pathology.

    For example:

    EK p.110, Q107.
    Insulin shock occurs when a patient self-administers too much insulin.
    The physiological effects of insulin shock most likely include:
    A) a pronounced increase in gluconeogenesis
    D) dangerously low blood glucose levels

    My Reasoning: Too much insulin, insulin causes low blood glucose. The blood glucose levels will be low, so the body physiologically responds to increase blood glucose - thus, I picked A: gluconeogenesis, which would increase the amount of glucose.

    EK Explanation: Recognize high insulin levels exist, go to the basics, insulin decreases blood glucose.

    EK p.103 ["Negative Feedback"]
    If ADH holds water in the body... increasing blood pressure, does a person with high blood pressure have a high ADH blood level or a low ADH blood level?

    Answer: Low ADH. The hormone level responds to the condition and to the body. If there is high blood pressure, ADH level drops.

    Based on the above question I thought if there is a low amount of blood glucose, the body responds to the condition by increasing blood glucose.

    Maybe I need to be careful and only do the "negative feedback" thinking when questions are involving HORMONES only.

    Since the glucose question is a pathology involving a sugar and not a hormone, it is different.

    EK p. 104, Q98.
    A patient develops an abdominal tumor resulting in secretion of large quantites of aldosterone into the bloodstream.
    Which will most likely occur?
    C: Levels of aldosterone secreted by the adrenal cortex will decrease.

    Too much aldosterone in the blood > so the answer of what will happen is that aldosterone secreted will decrease.

    Likewise in Q107, if there is too much insulin (too low blood glucose levels) > shouldn't the answer of what will happen
    be that more glucose will be synthesized/secreted into the blood: aka gluconeogenesis?

    Can't figure out what distinguishes how you answer 98 vs 107 unless:
    Does this mean you only answer questions about hormones with the whole "how will the body respond to mitigate the effect"?

    Please help!
     
    #1 futuredoctor10, Jan 3, 2009
    Last edited: Jan 3, 2009
  2. Charles_Carmichael

    Moderator Emeritus 7+ Year Member

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    For the insulin question, it asks what the effects of insulin shock (excess insulin) would be. Insulin does not cause gluconeogenesis; glucagon initiates gluconeogenesis. Insulin decreases glycogenolysis and gluconeogenesis while promoting glycogen formation. The way I see that question, it's asking what the effect of insulin is on the body and insulin would cause low blood glucose levels and it doesn't promote gluconeogenesis.

    For the ADH question, it seems like it's asking what the body's response (in terms of ADH secretion) is if too much water is retained. ADH is used to regulate serum osmolarity; if the osmolarity is low, it means there's an excess of water and ADH secretion is inhibited to water is lost and the normal osmolarity is reestablished and vice versa. So this question is asking what the ADH response would be when too much water is retained in the body; the answer is that the blood levels of ADH would drop to get rid of the excess water.

    For the aldosterone question, it's asking what the result would be if there was too much aldosterone in the blood that is secreted by a tumor but not the adrenal cortex. I'm not sure what the other answer choices are but I'm assuming the one you posted is supposed to be the correct one. Since aldosterone stimulates Na reabsorption and K secretion at the distal tubules, this would lead to a drop in plasma K concentration and an increase in plasma Na concentration. By reabsorbing Na, water is also reabsorbed and this increases blood volume. Stimuli for the secretion of aldosterone from the adrenal cortex include low blood volume and high plasma K concentration...by taking away these two stimuli due to oversecretion of aldosterone by a tumor, you inhibit the secretion of aldosterone by the adrenal cortex. So the answer choice you listed makes sense.

    I think the important thing to understand is what the question is asking for. The first one was asking what the effects of insulin are (insulin does not promote gluconeogenesis and causes low blood levels of glucose); the second was asking what the effect of increased blood volume was on the ADH system (the lowered serum osmolarity decreases the secretion of ADH and lowers its blood levels); and the third one was asking what the effects of large quantities of aldosterone in the blood was (by taking away the stimuli for for normal aldosterone secretion by the adrenal cortex, the tumor causes a decreased secretion by the adrenal cortex). I hope my answers made sense to you. If not, I'd be happy to reply to any other questions you have.

    PS. Insulin is a hormone. It looked like your post suggested you didn't think it was but I might've misread it.
     
  3. futuredoctor10

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    Yep they do!

    That is my big issue with these types of questions.

    The insulin one is the one I had a problem with, but your explanation makes sense. Insulin causes low blood glucose levels, while glucagon initiates gluconeogenesis: thus you know high insulin levels will cause only low blood glucose.

    I tend to over-analyze or over-extend my logic sometimes. For insulin I thought "insulin is high, blood gluc levels are low, so lets do gluconeogenesis to raise the blood glucose levels." I know insulin cannot directly do this but I figured that the body [which has glucagon] could.

    However I think to avoid this over-extension of logic I should read the question carefully. It says "physiological effects of insulin shock" - in other words, effects of the INSULIN. It did not say "physiological effects of the body"!
     

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