so when we're thinking about the
functions of the liver one way to think
of it is that the liver is just a huge
filter here we have the liver there and
your provide of the abdomen and here we
have the length of the gastrointestinal
tract so that's all of the
gastrointestinal tract from the
esophagus right through to the colon and
of course the gastrointestinal tract is
drained by numerous blood vessels we'll
just draw a couple there so numerous
blood vessels are draining the
gastrointestinal tract and these are
going to be venous vessels now instead
of these venous vessels draining
directly back into the systemic
circulation as is the case with
virtually all of the tissues that
doesn't happen they actually collect
together into a single vessel called the
hepatic portal vein and the hepatic
portal vein goes to the liver and breaks
up again into numerous smaller vessels
which eventually take blood into the
hepatic capillaries the sinusoids so
this is the hepatic portal vein and we
could say that a portal vein is one that
starts and ends in capillaries now
having said that there is some
oxygenated blood going into the liver
here small amount 20-25 percent of the
blood supply to the liver is going in
via the hepatic artery but most of the
blood go in to the liver is coming
through the hepatic portal vein so it's
actually venous blood coming in this
direction it'll still be partly
oxygenated so arterial blood going in
here in the Apothic artery and venous
blood entering via the apatit portal
vein and only when the blood has been
through the liver sinusoids are going to
drain into progressively larger venous
vessels which eventually leave as
hepatic veins
and that's the blood living in the
Apache veins is going to take blood back
into these inferior vena cava where it
does go back to thee to the right side
of the heart so what we see is the liver
is essentially filtering everything
that's coming from the gut so what is
coming from the gut well in the gut
there's going to be incredible amounts
of bacteria bacterial cells and these
bacterial cells as they metabolize are
going to release toxins and these toxins
some are going to be absorbed so that
means that the hepatic portal vein is
going to be carrying a lot of toxins now
we don't want these toxins to go
straight back into the venous blood
because that would make us feel ill we
don't want toxins so they go to the
liver first to the liver sinusoids into
the liver cells into the event
individual the pata sites where the
toxins can be broken down so it's an
important filter for toxins it's a
filter between the gastrointestinal
tract and the systemic circulation the
similar affect with drugs really if you
take drugs by the interval route via the
glass stones via the gastrointestinal
tract that is what enter will means via
the gastrointestinal tract then some of
the blood sort of the drug rather some
of the drug that's in the
gastrointestinal tract is going to be
absorbed of course that's the whole
point in taking the drug for systemic
administration and that drug is going to
go to the liver and the drug is going to
go through the liver first before it
gets to the systemic venous circulation
so this means when you a swallow a drug
or you give a drug PR any drug go via
the gas from Steindl tract that drug is
going to go through the liver before it
reaches the systemic circulation and a
proportion of that drug is going to be
broken down the first time it goes
through the liver and this is called the
first pass metabolism effect so first
pass metabolism is the proportion of a
drug
is broken down on his journey from the
gastrointestinal tract to the venous
circulation as it goes as it goes
through the liver so the liver cells are
capable of recognizing and chemically
breaking down a wide variety of toxins
bacterial activity in the gut generates
a large amount of toxins as we've said
and these waste products are transported
to the liver via the hepatic portal vein
and these are broken down to less toxic
substances and these are less toxic
substances often excreted by the kidneys
or they can be incorporated into bile
for excretion in the feces and most
drugs are really recognized as toxins by
the liver and are broken down to
metabolites so an active drug is broken
down to metabolites which may be active
or inactive pharmacologically speaking
so we see the livers in this important
filtering position now if this liver
failure in this failure of the liver
then drugs won't be broken down as
normal and can reach toxic levels even
although normal doses are being given so
that's why it's very important with
reduced liver function we really
consider carefully the amount of drugs
were giving especially we're giving them
enter early although all drugs are
broken down by the liver is just the
first pass effect delivers the drug to
the liver in concentrated form we always
have to think about that because the
doses in liver failure are probably
going to be less because there's going
to be less hepatic breakdown of the drug
less of the drug is going to be
converted into inactive metabolites
prior to excretion and most hormones
have broken down by the liver after a
period of time circulating in the blood
as well so liver failure again can
therefore result in increased plasma
concentrations of things like thyroid
hormone or Easter gene or or cortisol
and in the liver there's lots of
macrophages that the cook for cells so
called cook for cells which are
macrophages so if any bacteria do get
into
liber by the Apache portal vein again
they're going to be filtered out in
phagosome phagocytosed by the the
macrophages these active phagocytic
macrophages the the cook for cells in
the liver and actually the macrophages
in the liver are also going to break
down some old red blood cells as well
but that's most of the role of the
spleen breaking down the old the old red
blood cells so we see the livers
breaking down toxins because it's in
this ideal position to act as a filter