Liver | Gastrointestinal system physiology | NCLEX-RN | Khan Academy
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Liver | Gastrointestinal system physiology | NCLEX-RN | Khan Academy

Voiceover: The next accessory organ we’re going to talk about in
the GI tract is the liver. The liver, and that’s this
big fatty guy right here. Now, the liver has to be one of the coolest organs in the body. It’s the only one that
you can take a piece of, this small chunk right here, and transplant into a
recipient that has cirrhosis or liver failure, and
it can grow to become a much larger organ that
can sustain the patient. How wild is that? And so to better understand
the liver, we’ll start by discussing the main functions
it’s responsible for. The first thing we need to think about is that it’s responsible for metabolism, metabolism, and that involves
the breakdown of nutrients or catabolism, and I’ll just
write cat right here, catabolism, as well as the buildup
of larger macromolecules, and that’s through anabolism. So, catabolism and anabolism
are achieved in the liver. The other function the
liver is responsible for is storage of these nutrients. When we’re not breaking them
down or building them up, we need to have a place
for them to hang out, and so, they’re
responsible for the storage of our carbohydrates, so I’ll
just write carbs right here, and also mainly our
fats, so these two guys, and they’re stored in
three different ways. First, carbs or fats can
be stored as glycogen. Glycogen is just a
polysaccharide, so a linkage of a whole bunch of
monosaccharides or simple sugars. The other thing that we can
store our carbs or our fats as are lipoproteins, lipo meaning fatty and proteins meaning, well,
protein, and then lastly, we can also store these
guys as triglycerides, triglycerides, which is
one of the forms of fat that we ingest in our food. Now, these are two of
the major macromolecules we use for energy. The other major macromolecule
class that the liver sees are proteins, but these aren’t
really stored in the liver. Instead, they’re processed
into molecules like albumin and then cast off into the bloodstream, where they’ll float around
and carry out other functions, until they need to be
retrieved by the liver to be broken down or
used for other molecules. The other major process the
liver is responsible for is called detoxification, detoxification, and this is one of those
awesome scientific terms where the function is in the name. This is where we take
toxins and modify them so they can’t harm our body. This is achieved mainly by
cytochrome P450 enzymes, cytochrome P450, and these
are kind of funky enzymes, because unlike the other
ones you’ve probably heard about before, these
don’t bind a specific single substrate or molecule. If you remember an enzyme like phenylalanine hydroxylase,
that’s something that will add a hydroxyl group to phenylalanine and only phenylalanine,
but cytochrome P450’s will take a whole bunch
of different substrates and react with them. That’s something that’s pretty unique to this class of enzymes. Now, because of these
cytochrome P450 enzymes, we have a problem when
we take medications. In fact, we have a
decrease in drug efficacy because of this detoxification process, and what we mean by drug efficacy is the amount of an effect
a drug is able to have, and so, if the liver or these enzymes perceive medications that we ingest to be foreign or like toxins,
they’re going to try and break them down so they don’t
cause an effect to our body. So, doctors knows this,
and because of that, a specific dose must be given to account for the amount of a drug that’s going to be
detoxified by the liver. And finally, as we’ll talk
about in a separate video in better detail, the last thing that the liver is responsible
for is bile production, bile production, and as you might recall from our discussion on small bowel, bile is needed for the
absorption of fats from our food. Okay, so now that we
understand what are the main functions of the liver, how does it get all the
nutrients that we ingest and absorb from our intestinal
tract to be metabolized or stored or detoxified in the liver? Well, let’s take a look at
the blood supply to the liver. So, one of the things that
makes the liver so unique is that it has two
separate blood supplies. The first, that comes in
from the intestinal tract, is from the portal vein. The portal venous system
is another term for it, and the portal vein
supplies the liver with nutrient-rich blood, nutrient-rich. So, where do these nutrients come from? Well, food that’s absorbed
in the intestinal tract will then go through the
circulation and end up in the portal vein, to
be delivered to the liver for metabolism, and so we
consider this blood to be nutrient-rich, but where does
the liver get its oxygen from? Well, that’s a separate blood source, and that’s actually through what’s called the proper hepatic artery,
the proper hepatic artery, and as the name suggests,
this is arterial blood that will be supplying
oxygen-rich red blood cells. So great, these are the two different sources of blood that go to the liver. Well, what about blood
that leaves the liver? There’s one main vessel that carries blood out of the liver, and that’s
called the hepatic vein. The hepatic vein is the exact
opposite as the two other types of vessels we just talked about. It’s nutrient- and oxygen-poor. Blood that leaves through the hepatic vein from the liver will
circulate back to the heart to receive oxygen, flow
past the intestines to receive nutrients, and
then return to the liver, either through the portal vein or through the proper hepatic artery. The other output of the liver, that I guess I should mention right now, we’ll talk about in more
detail in a separate video, is bile, and bile mainly leaves the liver through what’s called
the common hepatic duct, the common hepatic duct, common hepatic duct that will take bile.

About James Carlton

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23 thoughts on “Liver | Gastrointestinal system physiology | NCLEX-RN | Khan Academy

  1. Fats cannot be stored as glycogen as they cannot be converted into glucose which is the substrate for glycogenesis… and lipoproteins are not a means for storage of fats in the liver, it is a means for transport around the body. If your liver is storing fats you should seek medical attention because you have fatty liver disease.

  2. Why I'm resistant/immune to any medications/drugs? Painkillers, Anti-depressants other stimulants never worked for me for my entire life, however, for my sister it works always and almost instantly with the same dosage. Drugs have no effect on me and also no side effects at all. I would rather prefer to get some side effect to be sure that my body is reacting to the medication. Otherwise it feels like it's washed out from my body in the first minute after I take it.

  3. Thank you for this video. Super helpful. Also, I find nothing wrong with your writing. Super easy to read and understand.

  4. not all substances cause an increase in the p450 cytocrom system activity (which means less drug efectiveness). proton bomb inhibittors, for example, have a contrary effect.

  5. Thank you for making our lives easier. Thank you all who teach and convey knowledge over the internet. You are a bless.

    A medical student.
    Thanks again for well explained video! I appreciate it. 2/6/2018 😀

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