00:00
Now when we've talked about hormones, right, we talked about the structure and function
changes first in the kidney, then we came to hormones. The first two we discussed were
ADH and ANH. Now, I want to take a look at the RAAS. We briefly introduced it at the
beginning of this series but I want to kind of walk you through it. So, what I asked you
to do is either put your finger on the screen or use your pen, but I want you to kind of
follow it through this diagram because they did an amazing job on creating this diagram
for you. So start with the kidneys. When your body experiences a drop in blood pressure
or a drop in fluid volume, you end up with renin being excreted. Now, renin hooks up with
angiotensinogen. Thank you to our liver. You end up with angiotensin I. Still with me?
Okay. Now, after angiotensin I connects with ACE, angiotensin-converting enzyme, that
comes from the lungs, it was in the vasculature there, you end up with angiotensin II.
01:09
This is a killer one. Right? So, what I want you to do is put a big fatty box around
angiotensin II because it is a bad ____. It is a potent vasoconstrictor. So see,
angiotensin II follow that arrow up. Those vessels clamp down like your body makes a
vasoconstrictor better than we can create synthetically. It's pretty amazing. Now
the other thing, angiotensin II, is right a potent vasoconstrictor but you also end up
with the release of aldosterone. Now follow aldosterone around. So when the adrenal
gland pumps that out, what happens? Ohhh, that tells my body or my kidneys to hang
on to more sodium and wherever sodium goes, water follows. So how the RAAS works,
body picks up. I need a higher blood pressure for whatever reason. So, it kicks in
to this RAAS since starting with renin. End-product, angiotensin II gives me a tight
vasoconstriction and you have volume expansion because I have the potent
vasoconstriction from the angiotensin II. I also have the stimulation of aldosterone and
aldosterone tells my kidneys to hang on to sodium and wherever sodium goes, water
follows and that's why I have more volume on-board. When I have more volume in my
intravascular space, my blood pressure will raise. Now, as Jose ages, here's the deal.
02:53
There is less aldosterone. Okay, so this kind of slows down his ability to reabsorb sodium
in the Loop of Henle because that's where it works, in the kidney. So, as Jose ages
he's going to have less aldosterone available so that way he is not going to be able to
hang on to much sodium as he could when he was younger. So, less sodium reabsorb
leads to a lower serum sodium level. Because I want to let that set in for just a minute.
03:26
Remember in seniors, this isn't for you, this is for our earlier nursing students, be kind
to them. When you draw a lab work, when we say serum sodium, lab tech comes or
the nurse will do it and they will draw a lab sample from a vein and they will check the
sodium level of your blood. Right? It's really hard to get a kneel into a cell to check
out what the intracellular sodium level is. So when you're looking at lab work, that's
what you're looking at. You're looking at the sodium level of the blood in the
intravascular space. In older person when you look at their lab values could likely have,
and I'm talking about healthy normal changes, their serum sodium, their blood sodium
level or Na as you see it represented, will be lower than they would have been as a young
adult. So we've got Jose here right in the salt shaker because this is why elderly have
relatively, okay, relatively lower serum sodium levels because I hear you, I hear you
coming for me because what you tell me is "Well my grandpa has to be on a low sodium
diet." Ahh but I would ask you "Does your grandpa have hypertension, history of
cardiovascular disease? What else would your grandpa have going on? Because Jose,
he has been age healthy, normal experience, that's his journey has been that without
cardiovascular disease. That's why he is likely to have relatively lower serum sodium
levels. So, in the healthy elderly, we're pretty sure could be estimated around 7%
of them have a serum sodium concentration of 137 or less. Now see if you can
remember what is the normal serum sodium level? Good deal. So now you can see why
he is definitely on the lower end of that scale. Now keeping in mind in the healthy elderly
individual, these serum sodium levels we're talking about are independent of their
volume status.