The cystic duct is the duct that (typically) joins the

gallbladder In vertebrates, the gallbladder, also known as the cholecyst, is a small hollow Organ (anatomy), organ where bile is stored and concentrated before it is released into the small intestine. In humans, the pear-shaped gallbladder lies beneath t ...

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 measures (sources differ) 2–4 cm/2–3 cm in length (though its length has been known to range from 0.5 cm to 9 cm), and 2–3 mm in diameter. It is often tortuous. It is the distal continuation of the neck of the gallbladder, from where it is directed inferoposteriorly and to the left/medially (this occurs in half of individuals). It typically terminates by uniting with the common hepatic duct to form the

bile duct A bile duct is any of a number of long tube-like structures that carry bile, and is present in most vertebrates. The bile duct is separated into three main parts: the fundus (superior), the body (middle), and the neck (inferior). Bile is requ ...

(usually anterior to the right hepatic artery). It usually joins the common bile duct from the right lateral side (forming an oblique angle between the two), and at such a distance that the bile duct is twice as long as the common hepatic duct. It often fuses with the common hepatic duct before actually opening into it after a variable distance (this arrangement may have the purpose of directing bile flow distally instead of back towards the liver).

Structure

The inner surface of the cystic duct features spiral, crescentic mucosal folds - the spiral folds of cystic duct. 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.

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 Microvilli (: microvillus) are microscopic cellular membrane protrusions that increase the surface area for diffusion and minimize any increase in volume, and are involved in a wide variety of functions, including absorption, secretion, cellula ...

upon their apical surfaces. The subepithelial layer consists of elastic connective tissue and is highly vascular; vessels that are adjacent to the epithelial

basement membrane The basement membrane, also known as base membrane, is a thin, pliable sheet-like type of extracellular matrix that provides cell and tissue support and acts as a platform for complex signalling. The basement membrane sits between epithelial tis ...

are fenestrated, possibly to facilitate ion and fluid exchange with the bile as is the case in the gallbladder itself. The outer fibromuscular layer contains

smooth muscle Smooth muscle is one of the three major types of vertebrate muscle tissue, the others being skeletal and cardiac muscle. It can also be found in invertebrates and is controlled by the autonomic nervous system. It is non- striated, so-called bec ...

continuous with that of the gallbladder; some of the smooth muscle extends into the spiral valves.

Relations

It usually lies next to the cystic artery.

Variation

The cystic duct may rarely be doubled. An accessory hepatic duct may join the cystic duct. A pathological diverticulum known as the Hartmann’s pouch may be present at the junction of the neck of bladder and the cystic duct. Length The duct may sometimes be extremely short (making cholecystectomy risky) or may rarely be altogether absent (so that the gallbladder is directly attached to the bile duct). Shape While most often tortuous, it may occasionally be curved, straight, or S-shaped. 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), or it may instead unite with the a hepatic duct. Occasionally, the cystic duct may first run alongside the common hepatic duct for some distance within the hepatoduodenal ligament before joining it. It sometimes join the common hepatic duct at its anterior, posterior, or medial side (in the latter case by passing posteriorly around the common bile duct to join it from the other side). It may spiral around the common hepatic duct before joining it. Very rarely, the cystic duct opens into the

duodenum The duodenum is the first section of the small intestine in most vertebrates, including mammals, reptiles, and birds. In mammals, it may be the principal site for iron absorption. The duodenum precedes the jejunum and ileum and is the shortest p ...

Function

Bile can flow in either direction between the gallbladder, and the common bile duct and hepatic duct. In this way, bile is stored in the gallbladder in between meal times. The hormone

cholecystokinin Cholecystokinin (CCK or CCK-PZ; from Greek ''chole'', "bile"; ''cysto'', "sac"; ''kinin'', "move"; hence, ''move the bile-sac (gallbladder)'') is a peptide hormone of the gastrointestinal system responsible for stimulating the digestion of fat a ...

, 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 sphincter of Oddi (SO) (also hepatopancreatic sphincter or Glisson's sphincter), is a sphincter, a muscular valve that, in humans and some animals, controls the flow of bile and pancreatic juice out of the gallbladder and pancreas respective ...

. The bile duct was once thought to possess a

sphincter A sphincter is a circular muscle that normally maintains constriction of a natural body passage or orifice and relaxes as required by normal physiological functioning. Sphincters are found in many animals. There are over 60 types in the human bo ...

ic 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.

Clinical significance

Gallstone A gallstone is a stone formed within the gallbladder from precipitated bile components. The term cholelithiasis may refer to the presence of gallstones or to any disease caused by gallstones, and choledocholithiasis refers to the presence of ...

s 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 Biliary colic, also known as symptomatic cholelithiasis, a gallbladder attack or gallstone attack, is when a colic (sudden pain) occurs due to a gallstone temporarily blocking the cystic duct. Typically, the pain is in the right upper part of t ...

, is sometimes referred to as a gallbladder "attack" because of its sudden onset. During a

cholecystectomy Cholecystectomy is the surgical removal of the gallbladder. Cholecystectomy is a common treatment of symptomatic gallstones and other gallbladder conditions. In 2011, cholecystectomy was the eighth most common operating room procedure performed i ...

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

Additional images

File:Digestive system showing bile duct.svg, Digestive system diagram showing the cystic duct File:Gray1095-gall_bladder.png, The gall-bladder and bile ducts laid open. File:Bilebladder.png, The portal vein and its tributaries. File:Slide10CHA.JPG, Cystic duct.Visceral surface of liver.

References

External links

* - "The gallbladder and extrahepatic bile ducts." * - "Stomach, Spleen and Liver: The Gallbladder and the Bile System" * (, ) {{Authority control Digestive system Hepatology Gallbladder