The layers of the gallbladder conform to the basic pattern seen in the histology of other structures in the gastrointestinal tract, except that rather than having 4 layers (mucosa, submucosa, muscularis and serosa/adventitia), it has 3 layers (mucosa , muscularis and serosa/adventitia). There is a distinct absence of a submucosa.
Basic Histologic Makeup of Gastrointestinal Tract
32347 tube colon small bowel lung bronchus bronchi esophagus stomach large bowel bile duct ureter tube principles Courtesy Ashley DAvidoff MD Davidoff art mucosa submucosa muscularis adventitia serosa histology
Histological Makeup of the Gallbladder Wall
The gallbladder wall has 3 major layers; mucosa muscularis and serosa/adventitia. It lacks a distinct submucosa, but also lacks a muscular layer in the mucosa (muscularis mucosa ). The lamina propria functions as a submucosa to house blood vessels and lymphatics but it is tucked intoo the folds of the gallbladder, and is rapidly within a short distance frrom the fiolds followed by the muscularis layer.
There is also a difference in the wall of the gallbladder that abuts the liver and the wall that abuts the peritoneal cavity.
Ultrasound examination of the gallbladder is performed in the fasting state and it is therefore distended. When the gallbladder is distended, the three layers cannot be distinguished. When the gallbladder is contracted, three distinct layers representing echogenic mucosa hypoechoic muscularis and echogenic serosa adventitia become obvious.
1632H5~1.8s gallbladder wall layers mucosa submucosa muscularis serosa thick walled contracted USscan ultrasound Courtesy Philips Medical Systems copyright 2008
The folds of the mucosa that project toward the lumen are frond-like in form and are quite irregular and non uniform when viewed in comparison to the folds of the small bowel for example. The mucosa consists of a tall columnar epithelium with basal nuclii and pale cytoplasm (due to sulfomucins) and lack goblet cells. In the neck however mucus secreting goblet cells are found. The mucosal layer secretes mucous to protect the gall bladder from the relatively alkaline bile it stores. (pH 7.6 -8.6)
Deep to the epithelium, the lamina propria contains abundant capillaries and larger blood vessels. The epithelial layer and the lamina propria comprise the mucosa.
Next there is a smooth muscle layer called the muscularis externa appearing as irregular layers of smooth muscle, connective tissue and elastic tissue. The inner components align longitudinally and the outer align diagonally so that they spiral around the gallbladder.
The peritoneum covers the gallbladder on its free surface and so in that location a serosa is formed. There is no peritoneum in the gallbladder fossa and so in this region it is called an adventitia.
In 10% of people aberrant vestigial ducts of Luschka project from the liver into the wall of the gallbladder without connecting to the gallbladder lumen. There are also larger accessory ducts that communicate with the cystic or hepatic ducts.
Rokitansky Aschoff Sinuses
The Rokitansky-Aschoff sinuses are diverticula or pockets in the wall of the gallbladder that may be microscopic or macroscopic. They are thought to be an acquired abnormality caused by increased intraluminal pressure resulting in mechanical stresses on a mucosa and outward bulging of the mucosa..
Structurally they are characterized as outpouchings of the gallbladder mucosa into and sometimes extend beyond the gallbladder muscle layer. They are not of themselves considered abnormal, but they seem be associated with elevated pressures in the gallbladder possibly as a result of normal and hypercontractile states and are also associated with chronic cholecystitis and cholelithiasis which may have similar pathogenetic mechanisms.
The diverticula do not cause functional impairment.
No clinical impairment is therefore implicated but they are associated with the hyperplastic cholecystoses (adenomyomatosis and cholesterolosis) as well as gallstone disease. Sometimes calcific concretions accumulate within the diverticulum.
When the diverticula are large the diagnosis is usually accomplished by ultrasound, and less commonly by CT or MRI.
Treatment is only considered when a patient presents with right upper quadrant pain and no other cause can be found. In some patients symptomatic relief has been accomplished with cholecytectomy.
04743c01s gallbladder contracted outpouchings diverticula prominent Aschoff Rokitansky sinuses hyperplastic cholecystosis hyperplastic cholecystoses adenomyomatosis oral cholycysogram post fatty meal courtesy Ashley Davidoff MD copyright 2008
82006c04.8s liver gallbladder blood supply hepatic artery cystic artery cystic arterioles wall edema hyperemic mucosa red = hepatic artery green = lumen of the gallbladder CTscan Courtesy Ashley Davidoff MD Copyright 2008