[SOUND].
[MUSIC]
Now Paracelsus didn't say the last word on
toxicology.
And there are some things that he didn't
say.
So, for instance, when a poison enters the
body, it doesn't just have to enter the
body.
It has to reach the target organ.
So it has to be absorbed into the body.
And then it has to build up into the, in
the target organ.
To a lethal level.
But at the same time the body will
be kindly excrete that chemical to get it
out.
So it's not a simple as Paracelsus was
saying.
So lets take an example from the element
mercury.
There are many ways you can conceive of
mercury getting into a human body.
Mercury is a liquid.
So one way you could swallow liquid
metallic mercury.
And it really won't do you much harm.
In the old days medical thermometers were
contained mercury in glass.
And of course if you went to the doctor
and you said you had a
fever the doctor would give you a
thermometer and say put this under your
tongue.
And, of course, every year there were
cases of people who bit
a little too hard on the thermometer,
broke it open, swallowed the mercury.
Didn't really do them any harm.
And the reason is that mercury really
doesn't
get absorbed when it's in its liquid metal
state.
It's a very strange liquid because it's
not a
wet liquid and it doesn't absorb into the
body.
You could also think that as mercury is a
liquid you could put
it in a syringe and you could inject it
into someones blood stream.
Now this is not good.
Okay it's not good for your health to do
this but even if you inject what should be
a
lethal amount of mercury it won't kill you
because
again the metallic mercury is not going to
be absorbed.
Well what about compounds of mercury?
Well mercurous chloride, HgCl, also known
as calomel, is poisonous.
You could eat it and this will cause
poisoning.
But even more poisonous is mercuric
chloride, HgCl2.
This is much more toxic.
Even for the same amount of mercury.
And the reason is that mercuric chloride
is
much more soluble in water than mercurous
chloride.
And therefore, it's absorbed by the body
much more rapidly.
And will therefore reach high
concentrations inside the body, much
faster.
Now, finally what about mercury vapour?
If you take mercury and you heat it, you
boil
it, there's going to be mercury vapor in
the atmosphere.
And this is going to be absorbed very
rapidly.
Because if you breathe in mercury vapour
into
your lungs, it will go straight into the
bloodstream.
And this is why there's a picture of King
Charles the II of England on the slide.
King Charles the II had many hobbies.
He was very fond of horse racing.
He was very fond of actresses.
But he was also interested in chemistry,
and apparently
he had his own chemistry laboratory in the
palace.
And one theory about his death, which
happened
quite suddenly, was that maybe he had an
accident
in the laboratory while distilling
mercury, and he breathed
in mercury vapor, and this is what
poisoned him.
So the root of administration of a
particular poison is very effective.
As we've said, to be effective the poison
must get into the target organ.
And there are various different routes of
administration that we can consider.
One is oral administration and this is
where
the poison goes in through the mouth, and
down into the stomach and then it will
be absorbed into the body from the
digestive tract.
Intravenous administration is possible and
this is where
the poison is directly injected into the
person's bloodstream.
Okay, this method of poisoning is
typically fast and efficient.
And this is the one that is used in
those U.S. states where they still have
the death penalty.
Poisoning can also occur by inhalation; if
the poison is in gas
or vapor form, is breathed in to lungs and
then into the bloodstream.
Poisons can also be absorbed through the
mucus membranes.
This for instance the lining of the nose.
Inside there is a mucus membrane and
poison can be
absorbed through those membranes again,
very fast and very efficient.
So here we have, the human body and
digestive system and the lungs.
So stuff, food, drink, air comes in
through the nose and mouth.
And then, the gases go down into the
lungs.
Where gases can be then absorbed into the
blood stream.
Food and drink then goes down into the
stomach and into the intestines.
For processing and absorption.
So all those things coming into the body,
things like fats, proteins, and
minerals will be absorbed by the body and
other materials may be absorbed with them.
And all the waste products will then be
expelled from the body.
Now you'll notice in the center of this
diagram is the liver.
And the liver is very important to
toxicology.
The liver is a huge chemical processing
plant in the center of the body.
And.
It is used by the body for detox, okay,
you don't need to go and pay
someone money to detox you because your
liver is doing it to you all the time.
And one of the things the liver will try
to do is any
substance that it doesn't want, think
should
be there, any substance it doesn't like.
It will chemically transform and then try
to get it removed.
Now let's consider food, what happens to
your food?
In particular, the proteins in your food.
Well, once the food gets into the stomach.
Chemical action in the stomach will start
to
break the proteins down into smaller
molecules called peptides.
That further down in the intestines those
peptides will be broken
down into the constituent amino acids
which will then be absorbed.
And will then be used by your body to
build.
Similarly sugars, saccharides, they will
be broken down to simpler
sugars which will then be absorbed and
your body will use them as fuel.
Now we mentioned earlier snake venom.
Snake venom is typically complex peptides.
Now, snakes, through their fangs, directly
inject their venom into the bloodstream,
but what if you were to drink snake venom?
[SOUND] Well, I have on good authority.
This is from one of the scientists of the
Red Cross snake farm in Bangkok.
That it is relatively safe to drink snake
venom.
And that is because it is a peptide.
So when it goes down into the digestive
system, those same enzymes that will break
up the peptides in your food to amino
acids will also act on the snake venom.
So it will simply be converted into its
harmless amino-acid constituents.
But, the man said, don't try this.
Because if you have any cuts or
lacerations,
for instance inside your throat, then the
snake venom
can be absorbed directly into the body,
avoiding the
digestive system, and then you're going to
be in trouble.
So please, don't try that at home.
Now after digestion all these molecules
will go into the blood stream.
So they will enter the blood stream, and
where do they go next?
Well if we look at the way the cir the
blood circulates in the body.
The blood that goes past the intestines
where
the absorption takes place, then flows to
the liver.
And, as I said, the liver is your detox
factory.
So, the liver will try and deal with any
toxic molecules
before they go to the rest of the body.
So it's only things that get past the
liver
which then go to the rest of the body
so the blood will flow back to the heart
and then through the arteries to all parts
of the
body.
Now we can see why inhalation of poisons
through the lungs is so effective because
blood that flows past the lungs does not
then go directly to the liver.
Blood that flows past the lungs can then
go to the whole body.
There's one more defense mechanism that
the body has.
And that is the blood-brain barrier.
The blood-brain barrier is a membrane
around the brain, and this
will exclude a lot of molecules that may
be in the blood from going into the brain.
So if you refer back to the case of
[UNKNOWN].
That molecule, that complex, toxic
molecule from
the curry was paralyzing his whole body.
But it wasn't paralyzing his brain.
And that's because the blood brain barrier
was
physically keeping that molecule out of
his brain.
Now, xenobiotics, literally these are
molecules that are strange.
And we use this term to refer to
molecules which are not naturally present
in the body.
And these molecules may be ones that we
are deliberately adding to our body.
Such as pharmaceuticals.
They may be illegal drugs.
They may be
natural substances such as nicotine or
caffeine which we're
deliberately imbibing but do not naturally
exist in the body.
Or they may be other substances such as
Ethanol.
And when your body detects that these
substances are coming in,
it will seek to deal with them in one way
or another.
For instance, it may accumulate them in
particular parts of the body.
For instance, elements such as lead or
strontium tend to accumulate in the bone
structure.
Elements such as Arsenic or thallium, the
body will try and excrete.
And one way it gets them out of the body
itself, for instance, is by depositing
them in the hair, and also in the
fingernails, where they can't do any harm.
Now for organic molecules, what your body
will typically do, and this
is done by the liver, is to transform them
in other compounds.
In particular, it will try and transform
them into compounds which
are more soluble in water, which are,
therefore, more easily excretable.
For instance, via the kidneys.
So let's take one of these molecules;
let's
take caffeine, which most people take
every day.
When you ingest some caffeine through
coffee or
tea or through some soft drink, some
energy drink.
It goes into your bloodstream, it
stimulates your brain, which is why you
take it, but your liver is trying to get
rid of the stuff.
And it transforms it.
So the caffeine molecule has these three
[UNKNOWN] groups.
Three of the nitrogen atoms.
It chops those off, one by one, to
make this more soluble compound, and that
is excreted.
And this is why, if you have a cup of
coffee, after a few hours, you start to
feel sleepy again.
Is because your liver has got rid of
all the caffeine, and it's time for
another dose.
[BLANK_AUDIO]

