Cystic duct

Template:Short description Template:Use American English Template:Infobox anatomy Template:Bile ducts and pancreas The cystic duct is the duct that (typically) joins the gallbladder and the common hepatic duct; the union of the cystic duct and common hepatic duct forms the bile duct (formerly known as the common bile duct). Its length varies.

Anatomy

The cystic duct typically<ref name=":022" /> measures (sources differ) 2–4 cm<ref name=":133">Template:Cite journal</ref><ref name=":224">Template:Cite book</ref>/2–3 cm<ref name=":022" /> in length (though its length has been known to range from 0.5 cm to 9 cm<ref name=":133"/>), and 2–3 mm in diameter.<ref name=":022" /><ref name=":224" /> It is often tortuous.<ref name=":133"/><ref name=":224" />

It is the distal continuation of the neck of the gallbladder, from where it is directed inferoposteriorly and to the left<ref name=":022" />/medially<ref name=":224" /> (this occurs in half of individuals<ref name=":133"/>). It typically<ref name=":022" /> terminates by uniting with the common hepatic duct to form the bile duct (usually anterior to the right hepatic artery).<ref name=":022">Template:Cite book</ref> It usually joins the common bile duct from the right lateral side (forming an oblique angle between the two),<ref name=":224" /> and at such a distance that the bile duct is twice as long as the common hepatic duct.<ref name=":133"/><ref name=":224" /> It often fuses with the common hepatic duct before actually opening into it after a variable distance<ref name=":224" /><ref name=":133"/> (this arrangement may have the purpose of directing bile flow distally instead of back towards the liver<ref name=":133"/>).

Structure

The inner surface of the cystic duct features spiral, crescentic mucosal folds - the spiral folds of cystic duct.<ref name=":224" /><ref name=":133"/>

The inner surface of the proximal cystic duct exhibits a network of submicroscopic convoluted folds (rugae), whereas that of the distal cystic duct exhibits submicroscopic parallel longitudinal folds.<ref name=":133"/>

Histology

The epithelial lining of the inner surface of the duct is similar to that of the gallbladder and consists mostly of columnar epithelial cells with short microvilli upon their apical surfaces.<ref name=":133"/>

The subepithelial layer consists of elastic connective tissue and is highly vascular; vessels that are adjacent to the epithelial basement membrane are fenestrated, possibly to facilitate ion and fluid exchange with the bile as is the case in the gallbladder itself.<ref name=":133"/>

The outer fibromuscular layer contains smooth muscle continuous with that of the gallbladder; some of the smooth muscle extends into the spiral valves.<ref name=":133"/>

Relations

It usually lies next to the cystic artery.Template:Citation needed

Variation

The cystic duct may rarely be doubled.<ref name=":022" /><ref name=":133"/>

An accessory hepatic duct may join the cystic duct.<ref name=":022" /><ref name=":224" />

A pathological diverticulum known as the Hartmann’s pouch may be present at the junction of the neck of bladder and the cystic duct.<ref name=":022" />

Length

The duct may sometimes be extremely short (making cholecystectomy risky)<ref name=":022" /> or may rarely be altogether absent (so that the gallbladder is directly attached to the bile duct).<ref name=":022" /><ref name=":224" /><ref name=":133"/>

Shape

While most often tortuous, it may occasionally be curved, straight, or S-shaped.<ref name=":133"/>

Termination

The cystic duct may unite with the common hepatic duct so that the common hepatic duct is either very short or very long (and the bile duct in turn very long or very short, respectively),<ref name=":224" /> or it may instead unite with the a hepatic duct.<ref name=":133"/>

Occasionally, the cystic duct may first run alongside the common hepatic duct for some distance<ref name=":022" /><ref name=":224" /> within the hepatoduodenal ligament<ref name=":224" /> before joining it.<ref name=":022" /><ref name=":224" /> It sometimes join the common hepatic duct at its anterior, posterior, or medial side<ref name=":224" /><ref name=":133"/> (in the latter case by passing posteriorly around the common bile duct to join it from the other side).<ref name=":022" /> It may spiral around the common hepatic duct before joining it.<ref name=":224" />

Very rarely, the cystic duct opens into the duodenum.<ref name=":133"/>

Function

Bile can flow in either direction between the gallbladder, and the common bile duct and hepatic duct.<ref name=":133"/> In this way, bile is stored in the gallbladder in between meal times. The hormone cholecystokinin, when stimulated by a fatty meal, promotes bile secretion by increased production of hepatic bile, contraction of the gall bladder, and relaxation of the Sphincter of Oddi.

The bile duct was once thought to possess a sphincteric function, however, it is now known that bile flow through the cystic duct proceeds unimpeded and is instead regulated by other mechanisms at other points of the biliary system.<ref name=":133"/>

Clinical significance

Gallstones can enter and obstruct the cystic duct, preventing the flow of bile. The increased pressure in the gallbladder leads to swelling and pain. This pain, known as biliary colic, is sometimes referred to as a gallbladder "attack" because of its sudden onset.

During a cholecystectomy, the cystic duct is clipped two or three times and a cut is made between the clips, freeing the gallbladder to be taken out.

See also

• Accessory bile duct

Additional images

• Digestive system showing bile duct.svg

  Digestive system diagram showing the cystic duct

• Gray1095-gall bladder.png

  The gall-bladder and bile ducts laid open.

• Bilebladder.png

  The portal vein and its tributaries.

• Slide10CHA.JPG

  Cystic duct.Visceral surface of liver.

References

<references />

External links

• Template:SUNYAnatomyFigs - "The gallbladder and extrahepatic bile ducts."
• Template:SUNYAnatomyLabs - "Stomach, Spleen and Liver: The Gallbladder and the Bile System"
• Template:NormanAnatomy (Template:NormanAnatomyFig, Template:NormanAnatomyFig)