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Biliary tree

The biliary tree (also known as the biliary tract or biliary system) is comprised of the gallbladder, liver and bile ducts. These structures produce, store, and release bile to the small intestines, where it aids in the digestion of lipids.​. Created by Raja Narayan.

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  • leafers tree style avatar for user amy.hummel
    When the bile comes from the liver through the common hepatic duct, what directs it down the cystic duct into the gallbladder (instead of into the common bile duct)? Is there some type of valve?
    (7 votes)
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    • old spice man green style avatar for user http://facebookid.khanacademy.org/604799357
      From the Saladin textbook, "Bile gets into the gallbladder by first filling the bile duct, then overflowing into the gallbladder." The bile duct travels through the pancreas, and converges with the primary portion of the pancreatic duct. Where this empties into the duodenum, there is the hepatopancreatic sphincter, which is your answer.

      Personally, I think leaving out the fact that it travels down first is a huge omission and makes his explanation of the first step incorrect. Bile has to travel up the cystic duct, and just looking at a picture before reading anything this was my first question as well.
      (12 votes)
  • sneak peak green style avatar for user rinoa
    If the person does not have gallbladder, what happens to the bile ?
    Does he/she has any problem with their everyday life?
    (6 votes)
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  • blobby green style avatar for user LGphonetimes
    In one video you said that the fatty acids will be converted into chylomicrons and then transported through lymphatic capillaries (lacteals) where they will be digested and then transported into the blood circulation. But in this video you also state that the emulsified fat will be absorbed in the ileum. Can you clarify this a little please. Are they related concept or?
    (4 votes)
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    • winston baby style avatar for user Regie Layog
      If I understand correctly, emulsified fat would be called MICELLE (smaller globules of fat with bile salts surrounding it) and it would diffuse in the intestinal mucousa. However, the bile salts cannot enter the cellular membrane of the muscousa and it would stay on the lumen. Inside the intestinal mucousa the fat combines with proteins (now we call it LIPOPROTEINS) AND it is exocytosed as CHYLOMICRON. From here it passes through the LACTEALS (LYMPH vessels) and enters the veinous system,
      (7 votes)
  • blobby green style avatar for user Ahmed Tarek
    Hello

    i have a few questions in my mind

    1- where colecystokinin secreted from as it is hormone ? liver or what organ ?

    2- what are the completions of cholecystectomy to the patient ?
    (3 votes)
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    • leaf blue style avatar for user dysmnemonic
      1: Cholecystokinin is secreted from the first part of the duodenum in response to fats and oils coming from the stomach.

      2: For any surgery, there are general and specific complications. The general complications of surgery are things like wound site infection. For abdominal surgery there are additional general complications like the formation of adhesions in the abdominal cavity. More specific complications of cholecystectomy are things like damage to the bile ducts or accidental damage to the liver when the gallbladder is dissected away from it.
      (3 votes)
  • leafers sapling style avatar for user Max Shine
    So cells all have a lipid bilayer membrane - the stomach has mucus to prevent it from digesting itself, what's there to stop the bile from emulsifying the inner surface of the gallbladder and bile duct?
    (4 votes)
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    • duskpin ultimate style avatar for user Betty :)
      Compared to the pH gastric acid (1.5-3.5), bile is much more alkaline (6.8-8.05). Remember that 7 is neutral (plain water), and thus bile is less reactive and less chemically corrosive. Thus, the gallbladder and bile ducts don't need to have as durable a protective membrane. It still has one of course, but it won't be emulsifying itself because the membrane would not be made up of fats and lipids.
      (1 vote)
  • aqualine ultimate style avatar for user ch.n.
    do we have certain amount of bile salts in our body?
    do we lose bile salts? (and create new ones?)
    I wonder if someone's liver does not work properly anymore and transplanted the other's then whether the transplanted liver can do all these jobs to catch up the normal condition quickly...
    (2 votes)
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    • leafers seed style avatar for user PCMSIII
      The liver makes a certain amount of bile salts in order to maintain normal function. I don't know if there is a "standard" numerical value, but it produces them as needed. The liver produces bile and secretes it into the gallbladder. The gallbladder releases the bile after a fatty meal. The bile digests/binds fat in the chyme and both the bile and the fat are absorbed. The bile is actually recycled by the liver, so new bile production is relatively low. Not all of the bile is reabsorbed, however, to some is lost in the stool. Bilirubin and bile acids/salts give stool its color.

      Rapid weight loss, high cholesterol, and some medications cause the liver to produce too much bile acid/cholesterol, which leads to the formation of gallstones.

      Transplanted livers begin to work immediately in most cases, and often begin to provide normalization of values within a few days.
      (3 votes)
  • starky sapling style avatar for user ForgottenUser
    How do bile salts make their way back to the liver?
    (1 vote)
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    • leaf blue style avatar for user dysmnemonic
      Bile salts are reabsorbed by the ileum, the last part of the small intestine. They enter the venous drainage from the ileum, returning through the superior mesenteric vein and then the hepatic portal vein. The portal vein then branches out into smaller veins in the liver, from which the hepatocytes can recover the bile salts.
      (3 votes)
  • blobby green style avatar for user Julie Kurz
    What happens to a person who has had his gallbladder removed, because I believe the gallbladder stores some of the bile like the liver.
    (1 vote)
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    • leaf blue style avatar for user dysmnemonic
      In the short term, someone who has had their gallbladder taken out needs to avoid eating large amounts of lipids (fats and oils), because they do lose that bile storage and there isn't enough to help absorb the lipids. Over time, the common bile duct grows in diameter and takes over some of the storage function of the gallbladder, and the patient can eat normal amounts of lipids again.
      (2 votes)
  • orange juice squid orange style avatar for user Ryan Yuan
    Can someone please answer that how does the fat absorbed by the illeum go back to the liver to be stored?
    (1 vote)
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  • leaf blue style avatar for user Steve Lira
    In a previous video I thought it was said the Jejunum is the main area of the small intestine that is the main area of absorption? In his video it is saying the Ilium is where the absorption is happening? I thought the Ilium is the main absorption for B vitamins and Bile salts only not fat?
    (1 vote)
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    • leafers seed style avatar for user DarcieMoe
      The Jejunum is the main area for absorption of carbs, nucleosides and protein but fat is primarily (completely?) absorbed in the Ilium. Lymphatic capillaries called lacteals are in the Ilium and these are the vessels that can take up chylomicrons.
      (2 votes)

Video transcript

- [Voiceover] I think we have a pretty good idea of how the liver works. One of the things I kinda touched on when we talking about our hepatic lobule is that we have bile that's produced in the liver and flows out through the common hepatic duct. Now bile is composed of two things. One are just bile pigments. Bile pigments are just sort of things that make the color or are not necessarily important for the function of bile. And the other thing that we have are bile salts. Now this is the most important part. This is what actually helps us emulsify, remember that term, emulsify which just means to organize to eventually absorb our fat. So bile salts help us emulsify fat. They allow us to turn fat into micelles, which can then be absorbed in the ileum. So let's take a step back and get a better idea of how our biliary tree really works. Remember the liver synthesizes bile but it doesn't necessarily store it. The bile that's made here actually goes through what's called the common hepatic duct. So this is the common hepatic duct that comes out of the liver. So bile that leaves from the liver after it's produced has to go somewhere to be stored. Where is it stored? One of the first places that it's going to go is this duct right here. And this guy is called the cystic duct. This is the cystic duct. And this is the next place that we see bile flow after the common hepatic duct. The cystic duct will then lead our bile to be stored momentarily in an organ that sorta sits as a blind pouch. This guy is our gallbladder. The gallbladder has one and one purpose only. This is the dude that stores our bile. This is where our bile hangs out until it's time to be released. So when bile just comes into our gallbladder and is just sitting there, what causes it to suddenly decide to leave and go somewhere else? As I'll mention in detail in a separate video the hormone that causes bile to be released from the gallbladder is called sort of a mouthful cholecystokinin. Cholecystokinin. Which is often abbreviated just CCK. Now this term might be a little crazy but if you ever heard of the surgical procedure called a cholecystectomy. Cholecystectomy, that's just the removal of the gallbladder. So cholecystokinin will cause our gallbladder to contract. And when the gallbladder contracts, remember it's a blind pouch, so this is just going to squeeze all the bile that's just sitting here right back out to flow through the cystic duct and now go somewhere else. The next place you're gonna have bile flow through is going to be another duct altogether. Now this guy is called the common bile duct. The common bile duct. And this is sorta the last part of the biliary tree we're talking about here. The last part of the biliary tree that conducts our bile until it finally reaches the GI tract. And the part of the GI tract that bile is released into is the duodenum. The duodenum or the first part of the small intestine. In the duodenum the bile is finally going to get to see some fat and start doing its job by emulsifying or making the fat easier to absorb. Now the fat isn't absorbed in the duodenum. In fact the bile salts with our new emulsified fat from our food will travel along to the ileum. Now you remember the ileum's the last part of our small intestine. And this is where we're going to have our bile salts and our fats that were just emulsified absorbed. So this is where the absorption process occurs. The ileum is where absorption of our bile salts and our fats occur. The duodenum is where bile is secreted into the GI tract. So bile is secreted into the GI tract. Now we talked about what happens to fats once they're absorbed in the ileum when we talked about the small intestine. But what happens to our bile salts? Well the bile salts, after they've been absorbed in the ileum, are actually gonna circulate right on back to the liver to undergo this process all over again. So if we were to review all the different pit stops that our bile takes in this process. Number one is that bile is made in the liver. Then once it's made number two it's going to go through the common hepatic duct and then flow to the cystic duct to be stored in the gallbladder until we receive cholecystokinin as a signal to tell the gallbladder to contract and then from there bile is squeezed out of the gallbladder, re-enters the cystic duct. I guess you can say this is the fifth place it would go. Re-enters the cystic duct and goes into the common bile duct. The common bile duct is the last part of the biliary tree which will then release its contents into the duodenum. And so finally our bile has reached the GI tract. The bile salts will then do their job to emulsify the fats that we've eaten. And then we'll have our bile salts get re-absorbed in the ileum before it heads back to the liver where it gets reused. So we reuse some of the existing bile salts in the liver. And that's how our biliary tree works.