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- So we just talked about
how urine is formed,

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dilute versus concentrate.

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We know that concentrated urine will help

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to maintain the water balance.

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Well, helping maintain water balance

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will help to increase or
decrease blood volume.

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By increasing or decreasing blood volume,

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that's one way to effect blood pressure.

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So you have two more hormones here.

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Aldosterone and renin.

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Both aldosterone and renin can help

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keep your salt, sodium
chloride, in proper balance.

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The proper amount of salt attracts

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the proper amount of water.

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Well, the kidneys also help
with acid based balance.

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Helps with the pH balancing
and the pH buffering.

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So it keeps the blood
pH in the normal range.

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The kidneys help control
red blood cell production.

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The kidneys can produce a
hormone, erythropoietin.

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That hormone will be
secreted by the kidneys

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when the kidneys realize there's

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not enough oxygen in the blood.

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So you can make more red blood cells.

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More red blood cells means
more oxygen transports.

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Activating vitamin D.

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Can take this inactive form and turn it

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to an active form, the kidneys.

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So really there's a lot of
things the kidneys can do.

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More than just this water
balance we've mentioned before.

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Now we start dealing with
water balance and blood volume.

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Blood volume and blood
pressure are completely linked.

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You can't really alter blood volume

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without altering blood pressure

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unless something else comes in the body.

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So let's start dealing
with how water balance

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works on blood volume.

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We look at the kidneys, the hypothalamus,

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and posterior pituitary.

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Well the hypothalamus is
just the bottom of the brain.

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Just part of your central nervous system.

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Posterior pituitary is part of the

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endocrine system, produces hormones.

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We have these negative feedback loops

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that help to regulate the hormone.

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We're looking at AHD, or
anti-diuretic hormone.

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So if you have too much
anti-diuretic hormone,

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you conserve too much water.

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Well if you conserve too much water,

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you're gonna end up with basically

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an overdose of water in your body.

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Well if you don't have enough ADH,

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anti-diuretic hormone, you can have

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too little water in your body.

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So we have this negative feedback loop

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where if there's a problem, which means

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too much or too little,
it'll help to regulate

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the amount of anti-diuretic hormone.

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Well this also helps to
deal with your thirst.

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If you have enough
fluids, you're hydrated,

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you're not as thirsty.

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But if you're dehydrated
you'd need more fluid,

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then you can increase your thirst.

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So you say this term anti-diuretic,

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well what really is a diuretic?

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A diuretic will increase the formation

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and excretion of urine.

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That means it causes fluid
to be lost in the body.

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Lasix, a medication.

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Caffeine, think coffee.

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Alcohol, all those are diuretics.

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They all cause an increase in fluid loss.

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Now the case of Lasix, the medication,

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a lot of times that's prescribed
for high blood pressure.

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If a person has high blood pressure,

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they take Lasix, the drug there,

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and it reduces the blood
volume, reduces blood pressure.

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Caffeine.

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Well that causes problems
with sodium reabsorption.

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If you can't keep the
proper levels of sodium

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or salt in your body, you
can't get enough water.

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Alcohol, alcohol is directly
works on anti-diuretic hormone.

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Alcohol, the more you have,
the more it inhibits ADH.

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The more ADH is inhibited,
the more fluid is lost

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in the body because you're not
trying to conserve any of it.

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So how about aldosterone and renin?

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Aldosterone and renin are both hormones.

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Now aldosterone at least
will be pretty much

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indirectly dealing with
a decreased blood volume

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or decrease in blood pressure.

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Because aldosterone itself will

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help with sodium reabsorption.

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So what ends up happening
is when blood volume

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or blood pressure goes down,

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the kidneys release renin.

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Renin goes this whole series of reactions,

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something called angiotensin II.

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And don't worry about what
the reactions are in between.

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The important part is
renin from the kidneys

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ends up being converted to angiotensin II.

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Angiotensin II will cause
the release of aldosterone.

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So really renin and aldosterone
are pretty much interlinked.

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Renin from the kidneys eventually

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makes it into angiotensin II.

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Angiotensin II causes the
release of aldosterone

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from the adrenal glands.

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Aldosterone causes an increase
in sodium reabsorption

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therefore more sodium coming in,

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means it'll attract more water in.

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So it's helping to increase blood volume

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or increase blood pressure.

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So what we're going to do is we're going

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to start with this
blood volume decreasing,

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so we're at the top middle.

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If your blood volume decreases,

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what's gonna happen is it's
gonna trigger your kidneys.

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The kidneys will release renin.

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Renin will eventually go through

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and be converted to angiotensin II.

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That converts to aldosterone.

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So angiotensin II causes
aldosterone to be released.

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The release of aldosterone
will help conserve salt.

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The more salt you keep, the more water

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will therefore follow the salt,

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helping to increase blood volume.

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Pretty much water follows salt.

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So keep more salt, keep more water.

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But another way to do it
is look at the top left.

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Anti-diuretic hormone.

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Increased anti-diuretic hormone means

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increasing more water conservation.

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Blood volume goes up.

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We've already mentioned
that the kidneys help with

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an acid-base balance,
that's blood pH balance.

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Well this gives a little
more of how it works.

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Your blood pH has to stay between

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7.35 and 7.45.

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Now that's not really a
very large range there.

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A tenth is all you get to move around.

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So one way that pH is
regulated is the kidneys.

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There's a lot of buffers that interact.

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There's also lungs that play a part.

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So it's not just the kidneys.

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There's one of many parts
in the pH regulation.

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The way the kidneys help to maintain pH

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is they reabsorb filtered bicarbonates.

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The bicarbonate that's reabsorbed

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is a major buffer in the blood.

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So by keeping more of it in the system,

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it helps to keep more of a buffer going.

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The kidneys can also secrete acid.

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Get rid of acid, get rid of hydrogen ions.

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That way it helps to also reduce
the amount of fluctuation.

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The hormone erythropoietin.

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Well if you start with a
decrease in the amount of oxygen,

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this could be the fact that there's

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not as much oxygen in the environment,

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your red blood cells
aren't carrying the oxygen,

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whatever it is.

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Something has caused the amount of oxygen

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in your blood to go down.

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So therefore if you decrease
the amount of oxygen,

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the kidneys can pick it up.

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They can sense it.

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They can secrete
erythropoietin, a hormone.

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The erythropoietin is going to cause

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an increase in red blood cell production.

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By making more red blood cells,

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there's more cells that can carry oxygen

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which means you will have an increase,

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traditionally at least, an increase,

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in oxygen content of the blood.

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So erythropoietin, red
blood cell production.

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And this vitamin D.

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When your skin is exposed to sunlight,

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what ends up happening is it'll produce

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an inactive form of vitamin D.

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Now you can't go out
there and sit in the sun

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for three or four hours and
say I got tons of vitamin D.

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Doesn't work that way.

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Usually about 20 to 30 minutes of exposure

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will max out the production of
this inactive vitamin D form.

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So 20, 30 minutes of sun
exposure is pretty much

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walking back and forth to a vehicle,

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maybe you're outside doing
something for a few minutes.

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It adds up throughout the day.

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The trick is, you have
to have the sun out.

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So depending on the environment,

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you might have a string
of days of cloudy days.

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It helps, ends up with a
reduction of vitamin D then.

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But thankfully you get some vitamin D

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in your food anyways, so it's
not the end of the world.

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But this inactive form of vitamin
D is transported to liver.

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Once transported it's modified.

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The vitamin D, the inactive form,

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is then converted to an
active form by the kidneys.

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So follow this through.

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Sun exposure on the skin produces

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an inactive form of vitamin D.

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That inactive vitamin D
form goes to the liver,

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it's modified a little.

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From there, the inactive vitamin D

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is converted to an active vitamin D,

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the real vitamin D, by the kidneys.