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 as 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 with
the liver is that there is two inputs to the liver there is what's called a
portal vein and a 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 is 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 an 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 that they do and their output gets dumped into the 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 of the nutrients that you get absorbed take a first pass and
they go to the liver and that's kind of the circulatory and the endocrine and
the exocrine functions of the liver of course the exocrine functions are it
produces bile bile is'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 it 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 CKD 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 keep out of
sight
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 whereas 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 are productive or if my liver is damaged and not
functioning well and the damage is not dose-dependent so if the ast and the alt
are coming down so if they're going down 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 albumin and Pt let's talk about albumin we've
talked about album before specifically when we're talking
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 they're 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 I n 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
it's 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 going to
confound it or if the patient has hemophilia that's obviously going to
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 of a two-to-one or three-to-one ratio of ast
to alt in alcoholic liver disease okay the albumin is rely
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 test for liver disease and as a result
you will 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
you