Question 52

[Guest]

Doesn't aldosterone increase Na+ reabsorption? So shouldn't B also be correct?

[admin]

Yes and no! Aldosterone acts on the distal convoluted tubule (which is part of the nephron) and the collecting duct to remove Na+ from the tubular system to bring it into the blood stream. The act of reabsorption (= to absorb again) will lead to increased Na+ in the blood stream which usually leads to increased blood pressure.

[briandgoudy]

So aldosterone triggered reabsorbtion of sodium in the nephron would lead to increased levels of sodium in the nephron, choice B. It seems like both answers are correct.

[admin]

No, reabsorption refers to the process which includes removing Na+ FROM the nephron TO blood vessels. Thus in response to aldosterone, Na+ concentration increases in blood vessels, not in the nephron.

[srraghav1542]

I have a qualms with both the answers and the explanation to this problem. First, lets deal with the answers: if the question says increased levels of hormones in the adrenal cortex will have which of the following effects, then it is non-specifically referring to glucocorticoids (cortisol), mineralocorticoids (aldosterone) and sex steroids (E.g. testosterone). Since it does not specify the type of hormone, A. Increased levels of protein synthesis is a viable answer. Sex steroids are in fact released from the adrenal cortex, and as we know, they bind to receptors in the nucleus to increase levels of transcription and translation of proteins.

Second, lets deal with the explanation. It says: Adrenal hormones such as glucocorticoids and catecholamines function to convert glycogen to glucose for energy use. This is true, but the question refers to the adrenal cortex, not the adrenal medulla. Thus, catecholamines (E.g. Epinephrine) which are released from the adrenal medulla, doesn't do any justice in explaining the right answer. If someone could explain this that would be great. Thanks

[admin]

Let's deal with your first concern first: your reasoning is very good regarding acknowledging the different hormones secreted by the adrenal cortex. And, you do not even have to specify sex hormones since many, many hormones may increase protein synthesis to one degree or another. So what we are really looking for is the best answer.

The primary purpose of sex hormones goes beyond protein synthesis. In fact, there is a whole category of hormones, the glucocorticoids, that operate throughout the organism to breakdown glycogen to an impressive degree (it is possible, in a relatively short period of time, to deplete the entire body's glycogen stores; incidently, exogenous steroids used illegally by some athletes in significant doses can significantly increase protein synthesis but that is beyond the MCAT).

The hormone, from the MCAT's point of view, most related to massive protein synthesis would be Growth Hormone (to a much lesser degree insulin).

Regarding your final point, yes indeed glucocorticoids are from the adrenal cortex and adrenaline (epinephrine) is from the medulla which is not being referred to in this question. We only mentioned adrenaline in context of glucocorticoids because they come from a similar part of the body and they share the effect of glycogen metabolism. We mention them together to make it easier to memorize but it is not meant to imply, nor do we say, that they both originate from the cortex.

[kauroon3107]

I am perplexed. My biology book says: cortisol reduces metabolism of glucose. It also says that cortisol increases the synthesis of glycogen. Then, how cortisol increases metabolism and synthesis of glycogen at the same time? The book says that cortisol increases metabolism of fats and proteins. Based on my other readings, cortisol reduces metabolism of glucose so that it is available for use by brain.

Could you please explain where is my error?
thanks

[admin]

I will not comment about your book but rather about the MCAT. The following is quoted from Wikipedia and is the extent of knowledge that you require for the MCAT:

Cortisol counteracts insulin by increasing gluconeogenesis . . . This leads to increased circulating glucose concentrations (in the blood) by increasing gluconeogenesis. There is an increased glycogen breakdown in the liver. Prolonged cortisol secretion causes hyperglycemia.

http://en.wikipedia.org/wiki/Cortisol

[stoneprod7112]

so would it be correct to assume that cortisol and other glucocorticoids reduce the metabolism of glucose, encourage the metabolism of proteins and fats. While at the same time increasing the metabolism of glycogen. Thereby still allowing more glucose for the brain but not the rest of the cells? this would seem to be consistent with everything I am gathering from this post and prior knowledge of teh glucocorticoids secreted from the adrenal cortex.

[emilie.maz5603]

Glucocorticoids function to increase blood glucose. They do this by stimulation of gluconeogenesis (forming new glucose from amino acids/lipids) and decreasing glucose storage, by preventing it from going into the muscle and fat cells. They do not cause glycogen metabolism.

[adrianaard2607]

I'm thinking about this question really peculiarly..

adrenal glands (medulla) makes NE and E, right? They are proteins, so couldn't A be true? in addition, how do we know that the question is talking about the cortex, and not the medulla?