The liver made easy by Dr. Seheult of Understand the anatomy, functions, diseases, and lab tests (liver function tests) of the liver with …
welcome to another MedCram lecture
we're going to talk about the liver
there's been some requests to go over
the liver and we're going to look over
this and in terms of an overview and I
first like to start with the anatomy so
if you can imagine the liver it's a
pretty large organ sits in the abdomen
and it has a number of functions which
we're going to go over the first thing
you've got to look at as with anything
is see what goes into it and sees what
comes out of it the first thing that
you'll notice what the liver is that
there is two inputs to the liver there
is what's called a portal vein and
hepatic artery so this is the hepatic
artery and there's two of them they
split and this is not drawn to
anatomical scale it's kind of schematic
and this is coming from the heart so
this is oxygenated blood the other input
is the portal vein and this is coming
from the intestines and this is
important because a lot of medications
that you ingest and like pills the first
place that they go is to the liver and
so the metabolism of these medications
first occur in the liver this is called
first pass metabolism and then they go
on to the heart and that's the next part
of the drawing here you get the hepatic
vein and so you've got two inputs and
one output and so it's got to go through
the liver if it's coming from the portal
vein from the intestines now in terms of
output or exocrine we know where happens
to endocrine it goes into the blood but
in terms of exocrine there's two major
outputs you've got a hepatic duct a
right hepatic duct and a left to paddock
duct and they combine into the common
hepatic duct and then they meet up with
the cystic duct which is from the
gallbladder which stores bile and that
forms the common bile duct which then
dumps into the intestines and that's how
the body gets rid of it so the liver
really has two functions it has it
endocrine functions and it has exocrine
functions the endocrine functions are
hormones that are produced in the cells
they regulate glucose they produce
albumin there's a whole bunch of things
they do and their output gets dumped
into thee to the hepatic vein and that
goes on to the heart or it gets pumped
for the whole body the heart also pumps
oxygen blood to the liver because the
liver just like any other organ needs
oxygenated blood to survive and that's
where it gets its supply but the major
source of blood supply to the liver is
actually from the portal vein and this
includes the stomach the duodenum the
jejunum the ileum the colon all the way
down to the rectum basically is blood
all of the fatty acids all the nutrients
that you get absorbed to take a first
pass and they go to the liver and that's
kind of the circulatory and the the
endocrine and the exocrine functions of
the liver
of course the exocrine functions are it
produces bile bile Issa's are these
things that break down fats it what's
makes your poo look brown and 50% of it
approximately is stored in the
gallbladder at each meal so can be
ejected into the cystic duct into the
common bile duct and then into the
duodenum so it can help in aiding in
digestion the next I want to talk about
are the blood tests that are associated
with the liver and and these are
sometimes confusing let's go over those
the first one or the first type of blood
test that I want to go over or what I
call the cytotoxic blood tests so what
are the cytotoxic blood tests well the
first one is the AST this is also known
as the SG ot this enzyme is actually
made in the liver in fact it's not
specific to the liver it's in a number
of cells but you can see it in a number
of cells but also in the liver the other
one is the alt albumin and the PT by the
way the alt is also known as the s GPT
okay so ast and alt are simply enzymes
that are in the hepatocyte
and when the hepatocyte dies these
enzymes get released
so in this essence these are like
cardiac enzymes like when you have a
heart attack you release ck ck-mb
and troponin when you have an injury of
liver cells that's when the ast and the
alt go up now just like you can have
congestive heart failure and a low
ejection fraction and your heart is not
contracting very well and you have heart
failure you might not have elevated CK
CK and B intra ponens the same way that
if you can be in liver failure in other
words your hepatocytes are not producing
the things that the liver should do you
could also have low ast and alt so what
do we use ast and alt for these are
basically markers for hepatic
inflammation so hepatic inflammation is
tracked by and seen as elevations in the
alt and the ast and we'll get into a
little bit about that in just a second
so the ast specifically has low
specificity for the liver okay it's seen
in the peri portal key pata sites okay
whereas the alt has a high specificity
for the liver okay so think of the L
here and the alt as being standing for
liver where as s is more for muscle but
they're both seen in the liver now in
terms of both of these the ast and the
alt they both go up in all forms of
liver injury it's only good for recent
injury so if there's old injury you
won't see these elevated okay these tell
you nothing about residual function okay
so if these are low it doesn't mean that
your liver function is low it just means
there's no current inflammation going on
in the liver it doesn't tell me if my
liver is good and they're productive or
if my liver is damaged and not
functioning well and the damage is not
so if the ast and the alt are coming
this doesn't necessarily mean as a good
thing or it's a bad thing in other words
a decrease could mean better or worse so
in other words if the ast and alt are
coming down it could be that the liver
is so damaged that there's no more cells
to damage or it could be that the ast
and alt are coming down therefore the
damaged has ceased okay it's kind of
like fire and smoke this is kind of like
your smoke now you could see smoke go
away for two reasons either because
there's no more stuff to be burned or
because the fire has been put out okay I
hope that makes sense okay so I cleared
the page so we can talk about albumen
and Pt let's talk about albumin we've
talked about album before specifically
when we're talking about anion gap
albumin is a very complicated protein
it's made in the liver and it's pretty
reliable for looking at chronic
hepatocellular injury so if the albumin
is low that usually equals chronic liver
injury so someone has an acute problem
with the liver there albumins usually
stay up and the reason why that is the
case is because it's got about a 20-day
half-lives which means it takes a long
time for the albumin levels to start to
go so I would say this is a good marker
for chronic liver disease finally in the
cytotoxic category let's talk about the
PT so what is the PT PT is the
prothrombin time and it's pretty
reliable for both acute and chronic
about a cellular disease so it's acute
and chronic the other way of looking at
the PT is also the eye and R so for
instance the PT might be 10 the INR is
1.0 usually the PT is about 10 times
that of the INR but not always and this
is pretty important and I'll tell you
why because the PT or the INR simply
measures the time of prothrombin to do
its work in other words to have clotting
it's a clotting time and clotting times
require many different enzymes that are
made in the liver this is important so
that because any enzyme that is not
successfully made in the liver is going
to interfere with the pt/inr
so it's very sensitive in fact the
pt/inr is the most sensitive liver
function tests that can be done in other
words this is the first thing that
starts to get bad as the liver starts to
fail because it requires so many
proteins that are synthesized in the
liver and so what are the things that
are associated with the PT well its
factors you may remember this from the
clotting cascade but factors related to
vitamin K which are 2 7 9 10 also 1 and
5 are related to the PT so what are some
causes that could do this well if the
liver is not synthesizing these factors
it's going to take longer for
coagulation to occur and therefore your
PT and your INR will go up so in liver
disease instead of it being a nice 1.0
you start to see it to go to 1.5 2.0 etc
this is usually a good sign of chronic
liver disease or acute liver disease and
it tells you just how bad their livers
are now what are some other things other
than liver disease that could cause it
obviously if the patient has low vitamin
K that's going to be confounder if the
patient obviously is on coumadin which
is a blood thinner that's gonna confound
it or if the patient has hemophilia
that's obviously gonna confound it so if
they have low vitamin K just give them
vitamin K if they have cumin and
obviously you're not going to use this
test to see if they have liver disease
because you're trying to get their INR
up anyway because that's why they're on
a blood thinner in the first place okay
so let's review the ast is a blood test
that will tell you if there's a cute
damage it has a lower specificity for
the liver than does alt it's increased
in all types of liver injury it's only
good for recent injury there's no
indication of residual liver functional
capacity the damage is not dose
dependent all of those go for the alt
except the alt is a little bit more
specific so I would expect the alt to be
higher if it's specific to liver disease
the one exception to this is if you have
alcoholic liver disease in which case
the ast and the alt may be very similar
sometimes that you even hear
two to one or three to one ratio of ast
to alt in alcoholic liver disease okay
the albumin is reliable for chronic
hepatocellular injury it's synthesized
in the liver it's a marker for chronic
liver disease and it's half-life
remember is about 20 days the PT is
probably the most sensitive blood tests
for liver disease and as a result you'll
see these elevations and chronic liver
disease remember it's obviously going to
be elevated if you're given the patient
warfarin or coumadin or things of that
nature great so that concludes this join
us for our next lecture which is going
to talk about cholestatic liver function
tests thanks very much

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