Two separate questions

[AA|FCB|DOC]

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I had two different questions I wanted to clarify. One of them is about blood osmolarity. So I'm a bit confused as to what it means to have high or low blood osmolarity. Does a high blood osmolarity mean we have a high concentration of solutes in the blood?


My other questions is regarding capacitor dielectrics. On the micro level what does a dielectric exactly do? I read something about it affecting the field between the capacitor. Also, are polar molecules better dielectrics or nonpolar ones?

Thanks in advance

 

[AFLATPEG]

I had two different questions I wanted to clarify. One of them is about blood osmolarity. So I'm a bit confused as to what it means to have high or low blood osmolarity. Does a high blood osmolarity mean we have a high concentration of solutes in the blood?

osmolarity measures the solute concentration per liter.
Yes, so you're right:
high blood OsM = high solutes in the blood

 

[AFLATPEG]

My other questions is regarding capacitor dielectrics. On the micro level what does a dielectric exactly do? I read something about it affecting the field between the capacitor. Also, are polar molecules better dielectrics or nonpolar ones

from my understanding...

dielectrics increase the capacitor's surface charge.
the more polar, the more it increases.
so yes, i think the more polar, the better dielectric if you're trying to increase your capacitor.

because, you know C'=kC
if C' is your new capacitance, k=dielectric constant (always greater than or equal to 1), C is the original capacitance.
anytime you insert a dielectric, you increase your capacitance.


didn't really answer your question on a micro level.. haha but yeah.

 

[gwjib04]

My other questions is regarding capacitor dielectrics. On the micro level what does a dielectric exactly do? I read something about it affecting the field between the capacitor. Also, are polar molecules better dielectrics or nonpolar ones?

Simply put, dielectrics have high bond energies so the electrons are resistant to moving and therefore won't conduct electricity.

Water is a good insulator when it is in pure form. It is polar so it is a good dielectric

Explanation:
The 2 plates of a capacitor can't touch and are separated by air. They are oppositely charged + and - because they are connected to opposite sides of the battery. If the battery is very powerful (high voltage), the charges on the capacitor's plates have enough energy to simply jump the air gap because they have exceeded the dielectric constant of air. Even air can conduct electricity if the voltage is high enough. This is "arcing". But other materials are more resistant to conduction than air (dieletric of air = 1) so if we put them between the plates, the amount of charge that can be on each side of the capacitor increases. These materials are insulators. You can look them up in a table of dielectric constants.

 

[milski]

Resistance/conductivity is not a good explanation for increased capacitance of a capacitor with a dielectric core. It will explain the change in breakdown voltage but not the change in capacitance at lower potentials when there is no charge moving through the dielectric.

You can also compare the resistance and the dielectric constant for water to something like neon. You'll find that water is both better dialectic and better conductor.

The reason for the increased capacitance is the increased energy density that the dielectric allows. If you have some dielectric outside of electric field, the dipoles of its molecules are randomly oriented. When you move it inside an electric field, it will create a torque on them and orient them parallel to itself. That will increase the potential energy stored in the dielectric. The more polar the molecules are, the larger the torque is and the more potential energy can be stored.

 

[AA|FCB|DOC]

osmolarity measures the solute concentration per liter.
Yes, so you're right:
high blood OsM = high solutes in the blood

Ok that is what I thought, but just to make sure so why do people say if you have low blood osmolarity then the body will want to release aldosterone. I know aldosterone will reabsorb Na but it will also reabsorb water too, so would that not just cancel out?

Resistance/conductivity is not a good explanation for increased capacitance of a capacitor with a dielectric core. It will explain the change in breakdown voltage but not the change in capacitance at lower potentials when there is no charge moving through the dielectric.

You can also compare the resistance and the dielectric constant for water to something like neon. You'll find that water is both better dialectic and better conductor.

The reason for the increased capacitance is the increased energy density that the dielectric allows. If you have some dielectric outside of electric field, the dipoles of its molecules are randomly oriented. When you move it inside an electric field, it will create a torque on them and orient them parallel to itself. That will increase the potential energy stored in the dielectric. The more polar the molecules are, the larger the torque is and the more potential energy can be stored.

Ok thanks I think this makes sense. So could you also say polar molecules tend to be better dielectrics because their electric dipoles can be aligned better and this can result in a bigger electric field that will fight the electric field of the capacitor and thus let more charge be stored?

 

[milski]

Ok thanks I think this makes sense. So could you also say polar molecules tend to be better dielectrics because their electric dipoles can be aligned better and this can result in a bigger electric field that will fight the electric field of the capacitor and thus let more charge be stored?

That's very close to what happens, with some minor corrections, none of which is likely to matter for the MCAT. All dielectrics can align equally well, but polar molecules have larger dipoles, so it takes more work to align them completely. They do end up having a stronger electric field when finally lined up. That field does "fight" the electric created between the plates and is called polarization field.

 

[BerkReviewTeach]

On the micro level what does a dielectric exactly do? I read something about it affecting the field between the capacitor. Also, are polar molecules better dielectrics or nonpolar ones?

Look at the picture in Figure 8-8 of your physics book II. Before the dielectric it shows a maximum of 10 (+) charges on the left plate and a maximum of 10 (-) charges on the right plate. After the dielectric (in this case a polar material) is added, it aligns in a way to offest some of the charges on the plates. So instead of +10 and -10, it feels like the plates are +8 and -8, which will allow for a little more current flow over to make the plates feel +10 and -10 again. But in actuality, there are 12 (+) charges on the left plate and 12 (-) charges on the right plate, so it has exceeded the previous maximum. In essense, the capacitor is holding 20% more charge, so we can say that the dielectric material has increased the capacitance by a factor of 1.2. This would result in that material being asign a dielectric constant of 1.2.

As mentioned before, the dielectric cannot be a conducting material, otherwise the charge would flow across the electric field between the two plates and cancel itself out, disspating any stored charge.

 

[AFLATPEG]

Ok that is what I thought, but just to make sure so why do people say if you have low blood osmolarity then the body will want to release aldosterone. I know aldosterone will reabsorb Na but it will also reabsorb water too, so would that not just cancel out?

hm, i think the Na+ will get pumped back out. because you know your intracell Na concentration is lower than the extracell. the whole purpose of aldosterone is to increase your blood volume (lower blood OsM), and increase your blood pressure.

 

[Leonardo Noto]

Ok that is what I thought, but just to make sure so why do people say if you have low blood osmolarity then the body will want to release aldosterone. I know aldosterone will reabsorb Na but it will also reabsorb water too, so would that not just cancel out?

Aldosterone causes a retention of sodium and secondarily causes retention of free water, but only because of the osmotic gradient that is created by the sodium. So if you have hypoosmolar blood the net intravascular ("in the blood vessels") increase in sodium will be greater than the net intravascular increase in free water because the free water in the bloodstream is also equilibrating with the intracellular compartment (when you're hyponatremic--"low sodium"--the osmotic pull is relatively greater in the intracellular compartment than when you have a normal concentration of sodium in the blood).

As an aside:

Conn's Syndrome is caused by an aldosterone-producing tumor and it results in hypernatremia (too high of a [Na] in the blood) and hypokalemia (too low of a [K] in the blood).

Addison's Disease results when the body can't produce enough aldosterone. President JFK had this disease, which results in hyponatremia (too low [Na]) and hyperkalemia (too high [K]). Low blood pressure is a common symptom due to low sodium-->low oncotic pressure of the blood-->low plasma volume and low blood pressure.

Remember that aldosterone primarily functions by activating a Na/K pump in the distal tubules of the nephron (in the kidneys) which retains 3 Na for every 2 K that it pumps out. This is not an electrically neutral proposition which means that it requires energy in the form of ATP (active transport!).

Aldosterone is produced in the adrenal cortex. The adrenal glands sit on top of the kidneys like a hat and the cortex has three layers. The zona glomerulosa produces aldosterone, the zona fasiculata produces glucocorticoids, and the zona reticularis produces sex hormones. You can remember this by the acronym "GFR" (which is also the acronym for glomerular filtration rate, a measure of the functioning of the kidneys) and "the deeper you go the sweeter it gets" (the zona glomerulosa/salty aldosterone, zona fasciculata/GLUCOcorticoids, zona reticulata/SEX hormones).

Dr. Leonardo Noto
www.leonardonoto.com