Chemical Dipsticks: Diseases and Steps in Metabolism

by Carlo Raj, MD

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    00:00 Alright let's talk about chemical dipsticks and continue here Now as far as the explanation's concerned, The way that this is going to be done is the following: We're gonna begin at the top and we'll begin with the bone marrow And in the bone marrow, you're producing tons of RBCs Okay, now these RBCs will then be taken at some point How long does an RBC last? About 120 days, right? So after 120 days of life of an RBC, where does it then go to get destroyed? It goes to the spleen.

    00:32 It goes to the spleen so that it gets destroyed.

    00:35 And when it does so, it is then going to release tons of bilirubin.

    00:39 So this is going to be our brief discussion at this point, strictly in terms of bilirubin, you will see a picture, this very image in our discussion, we'll talk about hepatobiliary pathology All that I'm trying to do here in this discussion or this lecture series of urinalysis is for our understanding of bilirubin because you may or may not be familiar at this point So these RBCs after they get old, you see that first structure there? That's the spleen.

    01:11 That spleen is going to do then what? It's going to destroy my RBC You see that structure next to the spleen? What is that? That's the splenic macropage. What is it doing? Munch. It's eating. What is it eating? It's eating that RBC.

    01:25 And from your spleen, what are you gonna release into circulation? Good, you're gonna release bilirubin. What kind? Unconjugated bilirubin, right? What does unconjugated bilirubin mean? It's also called "indirect".

    01:39 What does that mean in terms of its characteristics? It is lipid-soluble. How can you confirm that? Remember that patient that I just gave you, with sickle cell disease? I told you there was icterus.

    01:51 Isn't that confirmation of lipid-soluble bilirubin, unconjugated? Yes it is.

    01:56 Now, this unconjugated bilirubin which is now in your blood, it's lipid-soluble, you have to make sure that it doesn't escape.

    02:05 How can you prevent this from escaping? It has a chaperone. What's the name of that chaperone? It's called albumin.

    02:13 So albumin and unconjugated bilirubin, do you see where it says number 2 in the black circle? That black circle around number two is the combination of your unconjugated bilirubin and your albumin bringing these two where? Good, you're bringing it to the liver. So what's going on at the liver? Conjugation. What's that mean? It's taking the lipid-soluble bilirubin and making it into water-soluble What's this process called? Conjugation.

    02:41 What's the name of that enzyme? UGT.

    02:43 Now, all that I'm doing here is setting you up and reviewing the metabolism of bilirubin So that you're clear as to what's occuring here when you go back and have your discussion of your urobilinogen and such.

    02:56 So now that you have your conjugated bilirubin, where are you gonna get this? Do you see where it says biliary tree? Find it? Good.

    03:03 So now you get it into the bilary tree.

    03:05 Once you get into the biliary tree, then where are you gonna head up next? Blood, or intestine please? Good, intestine.

    03:14 So you go into the second part of the duodenum, I go into the intestine, Who does? What kind of bilirubin? Conjugated bilirubin only.

    03:22 The conjugated bilirubin will go through the intestine and then in your intestine, What happens? You have numerous, numerous steps biochemically, in which you then produce urobilinogen, don't you? Now this urobilinogen, this urobilinogen, depending as to what form Your stercobilin, or you see where the urobilinogen is going to the kidney? Normally speaking, you should have trace amounts of urobilinogen in the form of urobilin which gives you what color of urine? Good, the normal gold yellow type of color, not dark yellow but golden But this is urobilinogen.

    03:58 So at this point, we have discussed different forms, different forms of bilirubin Unconjugated bilirubin, conjugated bilirubin, urobilinogen The only thing that I wish to bring to your attention so you see this as being one big example You see where's this bilary tree, what if there was obstruction? What kind of obstruction? Maybe a stone - choledocholithiasis or something like primary sclerosing cholangitis.

    04:23 What'd I say? primary sclerosing cholangitis.

    04:27 This is going to cause obstruction So any conjugated bilirubin that you produce in the liver, can you get into the biliary tree? Nope.

    04:36 So what's the only method that you can leave the liver? It's with the blood.

    04:40 So now you end up getting different components in your kidney don't you? Meaning to say that you might get conjugated bilirubin, you might end up getting some of that bilirubin as well.

    04:51 So what you wanna do between this figure and the previous table is then add in these specific pathologies that we talked about and then go through what it means in terms of urobilinogen and bilirubin You do that every single time, it will all settle in, trust me.

    05:06 In part two, we'll continue discussing our urinalysis.

    About the Lecture

    The lecture Chemical Dipsticks: Diseases and Steps in Metabolism by Carlo Raj, MD is from the course Urinalysis.

    Included Quiz Questions

    1. It is pathological if detected in the urine.
    2. It is free from albumin conjugation.
    3. It is not water-soluble.
    4. It is responsible for icterus.
    5. It is lipid-soluble.
    1. Conjugated bilirubin
    2. Splenic macrophages
    3. Intravascular hemolysis
    4. Extravascular hemolysis
    5. Unconjugated bilirubin
    1. Intrahepatic cholestasis
    2. Extrahepatic cholestasis
    3. Intravascular hemolysis
    4. Extravascular hemolysis
    5. The spleen is the site of pathology.
    1. It is derived from indirect bilirubin.
    2. It is derived from direct bilirubin.
    3. It is excreted as urobilinogen via the kidneys.
    4. It is derived from conjugated bilirubin.
    5. It is derived from water soluble bilirubin.
    1. Destruction by splenic macrophages after 120 days.
    2. Destruction by splenic neutrophils after 120 days.
    3. Destruction by hepatic macrophages after 120 days.
    4. Destruction by splenic macrophages after 100 days.
    5. Destruction by splenic interleukins after 120 days.
    1. It is transported to the spleen after conjugation.
    2. It is transported to the liver for conjugation.
    3. Albumin is necessary to conjugate.
    4. It becomes water soluble after conjugation.
    5. UDP-glucuronosyltransferase is required for conjugation.
    1. Intestine
    2. Liver
    3. Kidney
    4. Macrophages
    5. Spleen

    Author of lecture Chemical Dipsticks: Diseases and Steps in Metabolism

     Carlo Raj, MD

    Carlo Raj, MD

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