Liver Explained Clearly – Pathophysiology, LFTs, Hepatic Diseases
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Liver Explained Clearly – Pathophysiology, LFTs, Hepatic Diseases

September 16, 2019


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

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  1. See the whole series at www.medcram.com along with other top quality videos including reviews in pulmonary, cardiology, infectious disease, and hematology!

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