The choledochus is a small tube about six centimeters long, with an average caliber of 5-7 mm, used to transport bile and pancreatic juices to the intestine. The choledochus, in fact, opens in the lumen of the second half of the duodenum, pouring its own content into this initial stretch of small intestine.
Above, the common bile duct represents the continuation of the common hepatic duct; we are therefore talking about two contiguous segments of a unitary channel, which is called the choledochus when the cystic duct, coming from the gall bladder, merges with the hepatic one coming from the liver (see figure). For this reason the common bile duct is also known as the common bile duct.
Below, before opening into the duodenum, the common bile duct merges with the greater pancreatic duct, which carries the digestive juices rich in enzymes produced by the pancreas.
At the melting point between the choledochus and the pancreatic duct a short unitary channel is formed, with a slightly enlarged shape, which is called the ampulla of Vater. This duct does not open directly into the duodenum, but undergoes control of a sphincter structure composed of smooth muscle fibers, called Oddi's sphincter. Thanks to the presence of this valve, bile and pancreatic juice do not continuously pour into the intestine, but they do it especially at mealtimes. It is in fact the presence of food in the pylorus and in the intestinal lumen that stimulates the opening of the aforementioned sphincter.
Choledochus and digestion
Bile and pancreatic juices are fundamental for the digestive processes that take place in the duodenum; these, in turn, represent an essential prerequisite for the correct absorption of the nutrients introduced with the diet.
Bile is continuously secreted in the bile canaliculi and channeled into the hepatic ducts. The closure of Oddi's sphincter between one meal and another favors its storage in the gall bladder; after meals, the presence of food in the earliest tracts of the duodenum causes the gallbladder to contract and the bile thus expelled, together with the newly formed bile, to be introduced through the common bile duct in Vater's Ampolla; ultimately, bile enters the duodenum (together with the pancreatic juice) due to relaxation of Oddi's sphincter.
Diseases of the common bile duct
With regard to the pathological conditions affecting the common bile, obstructive disorders linked to the presence of a calculus formed in or coming from the gallbladder are particularly common. This condition, known as choledocholithiasis, is typically accompanied by jaundice (yellowish coloring of the skin and ocular sclerae), dark urine and pale stools; in these cases, the concomitant presence of fever and chills suggests infectious complications (ascending cholangitis). The congenital anatomical alterations of the common bile duct, such as dilatations or atresias, and in situ neoplasms are of much more limited incidence.
