00:01
So obligatory water loss
explains
why we cannot live without
actually ingesting or bringing in
more water.
00:11
We are going to lose water
through insensible water loss
from the lungs,
the skin, and the feces,
as well as sensible water loss
from our urine,
where we need to excrete waste
from the body.
00:28
This accounts for about a
500 milliliters of water loss
minimum in a day.
00:35
The volume of urine
excreted,
and the solute concentration
are also going to depend
on fluid intake,
diet,
and as well as water loss
via other avenues.
00:49
Other factors that may trigger
antidiuretic hormone release,
which is going to decrease
water loss in our urine
include large changes in our
blood volume or blood pressure.
01:02
If we have a decreased
blood pressure,
this causes an increase
antidiuretic hormone release.
01:10
This is going to be due to things
like the blood vessel baroreceptors
and the renin angiotensin
aldosterone mechanism.
01:19
The increase in
antidiuretic hormone release
is going to lead to
more water reabsorption
to the extracellular fluid,
which will then increase
our blood volume,
which consequently will increase
the blood pressure.
01:36
And decrease in blood volume
or blood pressure
can be caused by many things.
01:42
This includes intense sweating
during exercise,
vomiting or diarrhea
when one is sick,
severe blood loss,
traumatic burns,
and also prolonged fever.
01:57
So if we look at this or
to summarize this,
a decreased plasma volume
is going to lead
to a decreased blood pressure.
02:07
Also, an increased
extracellular fluid osmolality,
or an increase in the
sodium concentration in our plasma
is also going to set off
the same type of mechanism
that's going to lead to the release
of antidiuretic hormone.
02:26
Starting with the
decrease blood pressure,
we find that the baroreceptors,
and the atria of the heart
and the large vessels
are going to stimulate
the posterior pituitary
to release antidiuretic hormone.
02:41
If we look at the osmolality of our
extracellular fluids,
we find that this also can stimulate
the posterior pituitary
to release antidiuretic hormone.
02:54
The release of antidiuretic hormone
is then going to trigger the
collecting ducts of the kidneys,
which are going to lead to more
water reabsorption in the kidneys.
03:06
If we are reabsorbing more water,
that means we are secreting
or excreting less water.
03:12
So this is going to lead to a
very low amount of urine.
03:16
But it's also going to lead to an
increase in our plasma volume,
which is directly related to an
increase in our blood pressure.
03:25
And it's also going to lead
to a decrease
in our extracellular fluid
osmolality
which is going to lead to
our bodies returning back to
the homeostasis.
03:37
Once this occurs,
negative feedback
will feed back to the hypothalamus,
which will then stop this process
and stop the release of more
antidiuretic hormone.