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From Wikipedia, the free encyclopedia

Biliary tract
Diagram showing the position of the perihilar bile ducts CRUK 357.svg
Ducts of the biliary tract
Details
FunctionFacilitate movement of bile, which aids in fat absorption
Identifiers
MeSHD001659
Anatomical terminology

The biliary tract, (biliary tree or biliary system) refers to the liver, gall bladder and bile ducts, and how they work together to make, store and secrete bile. Bile consists of water, electrolytes, bile acids, cholesterol, phospholipids and conjugated bilirubin. Some components are synthesised by hepatocytes (liver cells), the rest are extracted from the blood by the liver.

Bile is secreted by the liver into small ducts that join to form the common hepatic duct. Between meals, secreted bile is stored in the gall bladder. During a meal, the bile is secreted into the duodenum to rid the body of waste stored in the bile as well as aid in the absorption of dietary fats and oils.

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  • ✪ Biliary tree anatomy

Transcription

Voiceover: I think we have a pretty good idea of how the liver works. One of the things I kind of touched on when we were talking about our hepatic lobule is that we have bile that's produced in the liver and flows out through the common hepatic duct. 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. 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 actually absorb our fat. Bile salts help us emulsify fat. They allow us to turn fat into micelles, which can then be absorbed in the ilium. So let's take a step back and get a better idea of how our biliary tree really works. So 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. This is the common hepatic duct that comes out of the liver. Bile that leaves from the liver after its produced has to go somewhere to be stored. Where is it stored? Well, one of the first places that it's going to go is this duct right here. This guy is called the cystic duct. This is the cystic duct. 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 sort of 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. When bile just comes into our gallbladder and it's 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 a removal of the gallbladder. Cholecystokinin will cause our gallbladder to contract. 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 going to have bile flow through is going to be another duct altogether. This guy is called the common bile duct. The common bile duct. This is sort of 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. 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 abosrb. 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 ilium. Remember, the ilium is the last part of our small intestine. This is where we're going to have our bile salts and our fats that were just emulsified absorbed. This is where the absorption process occurs. The ilium is where absorption of our bile salts and our fats occur. The duodenum is where bile is secreted into the GI tract. Bile is secreted into the GI tract. We talked about what happens to fats once they're absorbed in the ilium when we talked about the small intestine. What happens to our bile salts? The bile salts, after they've been absorbed in the ilium, are actually going to circulate right on back to the liver to undergo this process all over again. 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. Then from there, bile is squeezed out of the gallbladder, re-enters the cystic duct. I guess you could 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. 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 ilium before it heads back to the liver where it gets reused. We reuse some of the existing bile salts in the liver, and that's how our biliary tree works.

Contents

Structure

The biliary tract refers to the path by which bile is secreted by the liver then transported to the duodenum, the first part of the small intestine. A structure common to most members of the mammal family, the biliary tract is often referred to as a tree because it begins with many small branches which end in the common bile duct, sometimes referred to as the trunk of the biliary tree. The duct, the branches of the hepatic artery, and the portal vein form the central axis of the portal triad. Bile flows in the direction opposite to that of the blood present in the other two channels.

The system is usually referred to as the biliary tract or system, [2]and can include the use of the term "hepatobiliary" when used to refer just to the liver and bile ducts.[3] The name biliary tract is used to refer to all of the ducts, structures and organs involved in the production, storage and secretion of bile.[4]

The tract is as follows:

Function

Bile is secreted by the liver into small ducts that join to form the common hepatic duct. Between meals, secreted bile is stored in the gall bladder, where 80%-90% of the water and electrolytes can be absorbed, leaving the bile acids and cholesterol. During a meal, the smooth muscles in the gallbladder wall contract, leading to the bile being secreted into the duodenum to rid the body of waste stored in the bile as well as aid in the absorption of dietary fats and oils by solubilizing them using bile acids.

Clinical significance

Pressure inside in the biliary tree can give rise to gallstones and lead to cirrhosis of the liver.

The biliary tract can also serve as a reservoir for intestinal tract infections. Since the biliary tract is an internal organ, it has no somatic nerve supply, and biliary colic due to infection and inflammation of the biliary tract is not a somatic pain. Rather, pain may be caused by luminal distension, which causes stretching of the wall. This is the same mechanism that causes pain in bowel obstructions.[citation needed]

An obstruction of the biliary tract can result in jaundice, a yellowing of the skin and whites of the eyes. [5]

References

  1. ^ Standring S, Borley NR, eds. (2008). Gray's anatomy : the anatomical basis of clinical practice. Brown JL, Moore LA (40th ed.). London: Churchill Livingstone. pp. 1163, 1177, 1185–6. ISBN 978-0-8089-2371-8.
  2. ^ Biliary+tract at the US National Library of Medicine Medical Subject Headings (MeSH)
  3. ^ Dorland's (2012). Dorland's Illustrated Medical Dictionary (32nd ed.). Elsevier. p. 846. ISBN 978-1-4160-6257-8.
  4. ^ Dorland's (2012). Dorland's Illustrated Medical Dictionary (32nd ed.). Elsevier. p. 1946. ISBN 978-1-4160-6257-8.
  5. ^ "Definition: biliary tract from Online Medical Dictionary".
This page was last edited on 25 February 2019, at 00:32
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