can you guys help me work this out (a&p II experiment re: NaCl intake & aldosterone)

mkatts19 · Nov 2, 2012

I don't know how much help I will be.. but first and foremost, your understanding should come from your textbooks. If you understand it from there you should be able to answer majority of the questions for your assignment. To (hopefully) jumpstart some more thinking, consider:

How does aldosterone differ from ADH?

1 of them holds onto 2 things, the other holds onto just 1.. which is which and what? what causes it in both situations?

"but I can't figure out how to not use ADH in my answer for the aldosterone, because aren't they related in a situation like this?"

What would taking in a concentrated solution vs an non-concentrated one do to your body and urine output? This would help you understand the outputs you get with the different solutions/amounts. When you understand the why's of that, you should be one step closer in answering your questions :).

.What organs would be AFFECTED by too much aldosterone or too little? What would happen to them? What secretes it in the first place? And what would happen if this part of the body were to malfunction? What is the purpose of aldosterone and ADH? And how does it help or not-help the body? Answering these and getting the idea behind it will help you answer the other questions in your assignment as well.

"I have to answer questions about which group(s) were affected by aldosterone secretion, the location of the target cells and how the aldosterone exerts it's effect."

Hope this was of some help in some way!

pre-nurseshan · Nov 2, 2012

I hope it helps too! Let me see...

Concentrated sol'n means less water per solute: less water to retain vs Na which needs to be excreted. So there is the high initial NaCl conc in the hypertonic group, correlating with high osmolarity (inhibiting aldosterone secretion and promoting adh secretion). Aldosterone affects na and h2o, whereas adh only affects h2o (and is first stimulated by na)

I'm sorry, I have to post this to go back and look at the thread because I'm on my phone

pre-nurseshan · Nov 2, 2012

An isotonic solution has the approriate ratio of h2o:na, so excretion can continue at a normal level. There would be no net impact on aldosterone secretion here. The volume of output in the isotonic group shows an initial increase, followed by a steep and then a slight decrease. This reflects the initial intake of sol'n (mainly the h2o) being excreted, and then returning to homeostasis. The osmolarity of the isotonic group shows an initial steep decline, followed by a somewhat steep increase and then a slight increase. Does this correspond to the increased initial volume of output? And the same with the subsequent increase in osmolarity and leveling off of both measures? The osmolarity goes back up because the kidneys have excreted the excess volume of water that was taken in?

Is that right? It feels incomplete wrt to the isotonic group.

The NaCl concentration in all three groups roughly mirrors the osmolarity of each group - this is basically two different ways of measuring the same thing right?

pre-nurseshan · Nov 2, 2012

The hypotonic group is the one that will ultimately be affected by aldosterone secretion, because the sol'n in take is going to depress the blood na concentration > activating aldosterone secretion. So although the hypotonic group had the highest initial volume of urine output, the volume continually goes down (at a variable rate) because water follows salt. Meanwhile , the shape of the osmolarity & NaCl concentration line is almost exactly the same as the isotonic group, but the actual numbers are lower (the line for the hypotonic group is below the line for the isotonic group) ... so the same thing is happening in both cases, adjusting for no na input in the hypotonic group?

Let me go back and read what I have so far.

pre-nurseshan · Nov 2, 2012

Aldosterone affects the kidneys and the arterioles, elevating blood pressure and blood volume. The elevated blood volume helps maintain normal osmolarity wrt increased na retention. The increased bp ... is just a result of increased blood volume? So aldosterone secretion is useful to increase bp if necessary, but increased bp is not necessarily relevant in this situation except that it is a consequence of the experiment?

Ugh! I just don't feel like I'm putting these pieces together right!

pre-nurseshan · Nov 2, 2012

Ok, does blood na deficiency cause decreased blood volume because more water is absorbed into cells?

Halcyonn · Nov 3, 2012

Think about hyponatremia--which is caused by administering too much hypotonic solution. (over-hydration)

How does hyponatremia affect the blood's osmolarity? Which direction will the water move?

How does hyponatremia affect blood pressure and blood volume?

Once you answer those questions, think about what hormones the body will release in response to those conditions. Think specifically about the GFR and ADH, Aldosterone and ANP.

pre-nurseshan · Nov 3, 2012

Mkatts19 and halcyonn - thank you so much for responding to this poor pre-nursing student! I really appreciate it!

I'm starting to think that I'm overcomplicating this in my mind, which is my tendency.

This is what I have so far:

Q: There are several stimuli for the release of aldosterone. Identify three of these stimuli and state which one of them was specifically involved in our wet lab. Identify the location/s of the target cells and explain how aldosterone exerts it's effect on it's target cells.

A: Aldosterone secretion by the adrenal cortex is stimulated by dehydration, Na+ deficiency, and blood loss. The operative stimulus in this experiment was Na+ deficiency. The sodium deficiency was caused by decreased blood osmolarity subsequent to the intake of a hypotonic solution. Decreased blood osmolarity, if uncorrected, would cause cell death by osmotic lysis.

Aldosterone secretion corrects Na+ deficiency by causing the kidneys to reabsorb Na+. Without suffiecient Na+ in the blood, water can be absorbed into the cells, which causes a decreased blood volume. Decreased blood volume means decreased blood pressure, and decreased blood pressure stimulates the renin-angiotensin pathway. [i describe the renin-angiotensin pathway which] stimulates the release of aldosterone.

Aldosterone targets cells in both the kidneys and the arterioles. It stimulates the arterioles to vasoconstrict, which increase in blood pressure helps to inhibit the kidneys from releasing renin, but it also acts directly on the kidneys to reabsorb Na+, preventing it from being excreted in the urine. Since water follows salt, the retention of Na+ means that water iis also retained, and blood volume increases.

So I feel like I answered that question okay, but question two ... I feel like I get what's happening, but I can't figure out how to explain it in clinical terms.

Q: Observe the trends in the data in each group for each variable. Identify the group/s that was/were affected by increases or decreases in aldosterone release. For the affected group/s, explain how the actions of aldosterone did or did not influence each variable over the enitre 120 minutes.

So with volume of output, the hypotonic group starts out the highest and has a steady, if variable rate, of decrease. I think this is because blood volume increased and the body hurried to eliminate excess water, but then too much Na+ was going out so the aldosterone kicked in and that's why both volume of output and osmolarity decline at 60 mins. Then homeostasis is getting closer but there's still too much water so osmolarity goes back up (not to the same as where it started though) and urine output continues but at a lesser rate.

The hypertonic group is going to be affected by ADH instead of aldosterone - only thing is aldosterone secretion is inhibited by high osmolarity. (My lab partner is answering the questions about ADH)

The isotonic group is the control basically, but I can't quite figure out why 1) the volume of output in the isotonic group starts out lower than the hypotonic group *but then* rises to the same level as the hypotonic group at 60 mins, and then has a first steep and then then slight decline, and 2). Why the osmolarity trends in the hypotonic and isotonic group are basically the same, just the actual numbers are different; I.e., they do the same thing but quantities are different because input was different.

Near as I can figure ... I'm going to post and go back and look at the questions halcyonn asked.

pre-nurseshan · Nov 3, 2012

So GFR drops when bp drops - bp drops when blood volume drops - when GFR drops less urine is produced...

That makes sense wrt the hypotonic group, but I just can't figure the initial rise for the isotonic group.

Halcyonn · Nov 4, 2012

I think I may have an idea of what is tripping you up. Mainly because we just covered this in my A&P class and the exact same thing was tripping me up, too! :)

When the body is reabsorbing something, it isn’t adding anything it is simply holding onto what it already has. If a patient is experiencing hyponatremia, they have low Na+ levels. Reabsorbing Na+ won’t increase Na+ levels.

Does that make sense?

So, if the body can’t increase Na+, what can it do to increase osmolarity?