EK Bio - hormonal reactions

SephirothXR said:

How are the blood levels of vasopressin and aldosterone in a dehydrated individual likely to compare with those of a healthy individual?
A. Vasopressin and aldosterone levels are likely to be lower in a dehydrated individual.
B. Vasopressin and aldosterone levels are likely to be higher in a dehydrated individual.
C. Vasopressin levels are likely to be higher while al- dosterone levels are likely to be lower in a dehy- drated individual.
D. Vasopressin levels are likely to be lower while al- dosterone levels are likely to be higher in a dehy- drated individual.

I thought of someone who has just drunk a lot of alcohol - vasopressin release is inhibited and therefore you get dehydrated. Of course it also makes sense that more ADH and Aldosterone would react to a person with low blood pressure. The answer is C, and I chose A thinking that b/c the person was lacking them, that's why the dehydration was caused, versus the hormones reacting to dehydration. Typically which will the actual MCAT focus on, reacting to existing conditions or something happening to the hormones, thus causing a condition like dehydration?

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Naturally, you don't look at the hormones as the cause of what happened. You look at them as the cure for the problem. Even EK stated this. So keep your focus on that the dehydrated person was not dehydrated due to lacking them but to some other factor and these choices of ADH (vasopressin) and Aldestrone are the solutions to such factors. The person is lacking water so water should be reabsorbed more in the tubules to keep the person from being more dehydrated and so ADH would be higher than normal because its job is to reabsorb water. Now, since there is more Na+ levels inside the body and outside the cells of the body, the body would get rid of those extra Na+ to keep the balance between water and Na+ and stop the release of water from the cells to maintain isotonic solution (Since there is more Na+ ions outside cells and less water, water from inside the cell will tend to go out to make a balance and thus the person feel more hydrated so decreasing Na+ will decrease the flow of water out of the cells). Since aldosterone function is to absorb Na+ and Cl- while excreting K+ and H+, the aldosterone levels would be decreased to stop absorbing Na+ and actually getting rid of it.

Thus, C is the correct choice.

Remember for the questions that ask for the hormonal level, in a way they are asking- given this condition, how will the hormone/s act?

- That is on page 103 Ek bio you will see that an example is given explaining how the body will respond in order to bring back to homeostasis.

As the person is dehydrated, he needs water so the ADH will be increased. Aldosterone increases the Na+ concentration and decreases the K+ concentration. when the Na+ concentration are increased, water follows it, therefore the aldosterone will increase as well.

Wiki: "Aldosterone is a hormone that increases the reabsorption of sodium ions and water and the release (secretion) of potassium ions in the collecting ducts and distal convoluted tubule of the kidneys' functional unit, the nephron. This increases blood volume and, therefore, increases blood pressure. ."

-http://www.youtube.com/watch?v=bg0kuu46KCM - explains this phenomenon

Would you please let me know the page number and which EK book (1001?) I am really puzzled and also you might want to refer to q 538( in 1001 EK that also explains this phenomenon the same way as I have mentioned here. Please check as I am confused with the answer choice. Is it a typo?

englishtablet said:

Remember for the questions that ask for the hormonal level, in a way they are asking- given this condition, how will the hormone/s act?

- That is on page 103 Ek bio you will see that an example is given explaining how the body will respond in order to bring back to homeostasis.

As the person is dehydrated, he needs water so the ADH will be increased. Aldosterone increases the Na+ concentration and decreases the K+ concentration. when the Na+ concentration are increased, water follows it, therefore the aldosterone will increase as well.

Wiki: "Aldosterone is a hormone that increases the reabsorption of sodium ions and water and the release (secretion) of potassium ions in the collecting ducts and distal convoluted tubule of the kidneys' functional unit, the nephron. This increases blood volume and, therefore, increases blood pressure. ."

-http://www.youtube.com/watch?v=bg0kuu46KCM - explains this phenomenon

Would you please let me know the page number and which EK book (1001?) I am really puzzled and also you might want to refer to q 538( in 1001 EK that also explains this phenomenon the same way as I have mentioned here. Please check as I am confused with the answer choice. Is it a typo?

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Why would it be a typo? Your explanation matches well with the answer choice. Are you confused by the fact that since aldosterone reabsorbs water as well, it will help the person become hydrated once again and therefore aldosterone levels should be higher than lower? If yes, then this concept would be true but the water wouldn't enter the cells in order to make a balance with the Na+ ions outside the cell so the person would still be dehydrated as I explained above. If no then what is your concern?

MShopes said:

(Since there is more Na+ ions outside cells and less water, water from inside the cell will tend to go out to make a balance and thus the person feel more hydrated so decreasing Na+ will decrease the flow of water out of the cells).

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Don't you mean that decreasing the Na+ uptake into cells will INCREASE the flow of water out of the cells, thereby making the person more hydrated?

If less Na+ is in the cell, then there is an even greater gradient between the inside (low Na+) and outside (high Na+), and thus more water will rush out of the cell.

I am actually interested in knowing why the aldosterone level will be low?

What hormones are released during dehydration?

ADH and aldosterone to be secreted. They stimulate the kidney to conserve body fluid by increasing reabsorption of water and sodium ions from the filtrate

water always moves to dilute. if you are reabsorbing sodium in the kidney (due to aldosterone) water will be reabsorbed as well to maintain proper blood osmolarity. A person who is dehydrated will have increased levels of aldosterone and ADH. Aldosterone and ADH work as a team. Water will be reabsorbed in the collecting duct due to increased reabsorbance of sodium in the DCT to help the individual stay hydrated.

Yes, it is also true that a side effect of this is increased BP, since blood volume would be greater. also, as MShopes stated, you should always think of the hormone as the solution to the problem, not the cause of it. This is the way to go about it in MCAT problems.

My bad guys. I forgot the part that Aldosterone absorbs Na+ and water to be taken inside the cell. I just thought Na+ gets reabsorbed but not taken to the inside of the cell. Since Na+ gets inside the cell, the water will follow it to the inside of the cell to keep the person hydrated so increasing aldosterone will help make the person more hydrated and thus the answer is B. My apologies once again but as a rule of thump, you always look at hormones as the solution to the problem not the cause of it.

thanks again SephirothXR for clarifying the mistake and the TYPO