美国医学院讲师清晰讲解肝脏工作机理、内分泌与外分泌系统；毒细胞检测方法（ACT, SGOT, ALT, SGPT, Albumin, PK, PK/INR)及各自的局限性；急、慢性肝病检测值区别；酒精肝检测值；服用血液稀释药物对PK/INR值的影响等。
通过高质量医学视频课程，了解肝病其治疗(treatment)，肝功测试(liver function tests)和胆汁淤积性(cholestatic)疾病。
Welcome to another MedCram lecture! We’re going to talk about the liver. There have been some requests to go over the liver, and we are going to look over this. In terms of an overview, 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 is what goes into the liver and what comes out of it. The first thing that you’ll notice with the liver is that there are two inputs to it, which are called portal vein and hepatic artery. So this is the hepatic artery, and there are 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.
This is important because a lot of medications that you ingest like pills, the first place that they go is to the liver. So the metabolism of these medications first occurs in the liver, which is called the first-pass metabolism. Then they go on to the heart, and that’s the next part of the drawing here. You get the hepatic vein.
So there are two inputs and one output, and so it’s gonna 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 are two major outputs, you’ve got a hepatic duct, a right hepatic duct, and a left hepatic duct, and they combine into the common hepatic duct. 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 endocrine functions and exocrine functions. The endocrine functions are that hormones produced in the cells regulate glucose, produce albumin., etc. There are a whole bunch of things that they do, and their output gets dumped into the hepatic vein, and that goes on to the heart, where it gets pumped for the whole body.
The heart also pumps oxygenated 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, it is blood, all of the fatty acids, all of the nutrients that you get absorbed take the 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; biles are these things that break down fats. It’s 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 into the duodenum, so it can help in aiding indigestion.
The next I want to talk about are the blood tests that are associated with the liver, 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 is what I call the cytotoxic blood tests. So what are the cytotoxic blood tests? Well, the first one is AST. This is also known as the SGOT. This enzyme is actually made in the liver. In fact, it’s not specific to the liver; it is in a number of cells. But you can see it in a number of cells but also in the liver.
The other ones are the ALT, albumin, and PT. By the way, ALT is also known as the SGPT. AST and ALT are simply enzymes that are in the hepatocyte, and when the hepatocyte dies, these enzymes get released. So in essence, these are like cardiac enzymes, like when you have a heart attack, you release CK, CKMB, and troponin. When you have an injury of liver cells, that’s when the AST and 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 CKCK and be in troponin, the same way that if you can be in liver failure. In other words, your hepatocyte is 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 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 periportal hepatocyte.
Okay, whereas the ALT has a high specificity for the liver. Okay. So think of the L here in 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 ALT, they both go up in all forms of liver injury. It’s only good for a recent injury. So if there’s an 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 it is productive, or if my liver is damaged and not functioning well. And the damage is not dose-dependent. So if the AST and ALT are coming 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 so damaged that there are no more cells to damage, or it could mean 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 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 albumin 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, their albumins usually stay up. The reason why that is the case is because it has 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 hepatocellular disease. So it’s acute and chronic. The other way of looking at the PT is also the INR. 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 because any enzyme that is not successfully made in the liver, it 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.
这很重要，因为任何无法在肝脏中成功制造的酶都将干扰PT / INR。因此非常敏感。实际上，PT / INR是可以完成的最敏感的肝功能检查。换句话说，这是由于肝脏开始衰竭而开始变坏的第一件事，因为它需要在肝脏中合成的大量蛋白质。
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 the liver disease that could cause it? Obviously, if the patient has low vitamin K, that’s going to be a confounder. if the patient obviously is on coumadin, which is a blood thinner, that’s going to confound it. So if they have low vitamin K, just given 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 is acute damage. It has a lower specificity for the liver than those Alt. It’s increased in all types of liver injury. It’s only good for a 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 ALT may be very similar, sometimes that you even hear of a 2 to 1 or 3 to 1 ratio of AST to ALT in alcoholic liver disease.
Albumin is reliable for chronic hepatocellular injury. It is 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 in 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!
白蛋白对显示慢性肝细胞损伤是可靠的。它在肝脏中合成。它是慢性肝病的标志，记住，它的半衰期约为20天。 PT可能是对肝脏疾病最敏感的血液检查。您将在慢性肝病中看到这些升高。请记住，如果您给患者服用warfarin 或 coumadin或具有这种性质的东西，显然会升高。好了，这样就可以得出结论。加入我们的下一个讲座，下次讲座将讨论胆汁淤积性肝功能检查。非常感谢！