Gallbladder Anatomy and Role in Digestion

The gallbladder is also known as the cholecyst in the vertebrates. The gallbladder is a small hollow organ where bile is stored and concentrated before it is released into the small intestines. In human beings, there is a pear-shaped gallbladder that lies just beneath the liver. The structure and the position of the gallbladder are not the same in everyone as it will differ in other animal species. The liver is responsible for the production of the bile and the gallbladder is responsible for receiving and storing the bile from the liver. The gallbladder receives the bile from the liver with the help of the common hepatic duct and releases it via the common bile duct into the duodenum. Duodenum is where the bile helps in the digestion of fats. 

The functioning of the gallbladder can be affected by the gallstones which are formed by the materials that cannot be dissolved which are usually cholesterol or bilirubin which are the product of the haemoglobin breakdown. The gallstones will cause significant pain particularly at the upper right corner of the abdomen. The gallstones are often treated with the removal of the gallbladder called a cholecystectomy. Cholecystitis is the condition in which there is an inflammation of the gallbladder and it is caused by many reasons which could be from the impact of gallstones, infection, and any autoimmune disease. 

In this article, we are going to discuss in a detail the gallbladder function, the structure of gallbladder, gallbladder anatomy, gallbladder location and the use of gallbladder.

Gallbladder Definition

The gallbladder is a pear-shaped hollow structure that is located on the right side of the abdomen and under the liver. The primary function of the gallbladder is to store and concentrate the bile which is a yellow-brown digestive enzyme produced by the liver. The gallbladder is a part of the biliary tract and it can store up to 50 ml.

When the liver produces the bile, the gallbladder serves as a reservoir for bile while it is not being used for digestion. The gallbladder’s lining absorbent lining concentrates the stored bile. A hormone called cholecystokinin is released when the food enters the small intestine, this hormone then signals the gallbladder to contract and secrete bile into the small intestine through the common bile duct. By breaking the fats the bile helps in easing the digestive process. The bile is also responsible for draining the waste products from the liver into the duodenum which is a part of the small intestine. 

Gallstones could be formed in the gallbladder when there is an excess of cholesterol, bile salts, or bilirubin. When the stored bile crystallizes, the gallstones which are generally small and hard deposits are formed inside the gallbladder. The person who had gallstones in the gallbladder will rarely see any symptoms in the initial stages until the gallstones reach a certain size or if the gallstone obstructs the bile ducts. The only method by which the gallstones could be treated is to surgically remove the gallbladder. 

Structure of the Gallbladder

• The gallbladder is a hollow organ that sits below the right lobe of the liver and is grey-blue in colour. In adult human beings the gallbladder size and measures are up to ten centimeters in length and four centimeters in diameter when it is fully distended. 

• The gallbladder is known for receiving and storing bile from the liver and the total capacity of the gallbladder is about 50 milliliters. 

• The gallbladder is a pear-shaped organ with its tip opening into a cystic duct. The gallbladder is divided into three sections or parts which are the fundus, body, and neck. 

• The fundus has a rounded base and angled in such a way that it faces the abdominal wall. The body lies on the surface of the lower liver. The neck is continuous and tapers with the cystic duct which is a part of the biliary tree. The gallbladder fossa is found beneath the junction of the hepatic segments IVB and V.The fundus and the body of the gallbladder lies against the gallbladder fossa. 

• The common hepatic duct unites with the cystic duct to become the common bile duct. At the neck junction of the gallbladder and the cystic duct, there is an out-pouching of the gallbladder wall which forms a mucosal fold known as the Hartmann’s pouch.

• Below a diagram is given with the parts of gallbladder

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Gallbladder Anatomy

• There are a number of layers that are responsible for composing the gallbladder wall. The innermost surface of the gallbladder is lined by a single layer of columnar cells which has a brush border of microvilli. These are very similar to the intestinal absorptive cells. 

• Under the epithelium, there is an underlying lamina propria, a muscular layer, serosa, and an outer perimuscular layer. The gallbladder does not have muscularis mucosae and the muscular fibers are not arranged in distinct layers, unlike the intestinal tract. 

• The mucosa is the inner portion of the gallbladder wall and it consists of a lining of a single layer of columnar cells. These columnar cells have a small hair-like attachment called microvilli. The microvilli sit on a thin layer of connective tissue called the lamina propria. The mucosa is very curved and it has been collected into tiny outpouchings called rugae. 

• There is a muscular layer that sits beneath the mucosa which is formed by the smooth muscle which has fibers that lie in longitudinal, oblique, and transverse directions, and they are not arranged in separate layers. 

• The muscle fibres present in the muscular layer contract to expel the bile from the gallbladder. The gallbladder has Rokitansky–Aschoff sinuses which are considered to be its distinctive feature. Rokitansky–Aschoff sinuses are deep outpouching of the mucosa which can extend through the muscular layers. The muscular layer is surrounded by a layer of connective and fat tissue. 

• The surfaces which are not in contact with the liver and the outer layer of the fundus of the gallbladder are covered by a thick serosa that is directly exposed in the peritoneum. The blood vessels and lymphatics are present in the serosa and the surfaces which are in contact with the liver are covered in connective tissue. 

Gallbladder Function

• The gallbladder is also called the gall and its main function is to store bile which is needed for the digestion of fats present in the food. Bile is produced by the liver and flows through the small vessels into the large hepatic ducts and finally through the cystic duct into the gallbladder where it is finally stored. At a particular instant of time, the gallbladder can store up to thirty to sixty milliliters of bile. 

• In the digestive tract, if the food enters that has fat in it, there is a stimulation that is sent to secrete the cholecystokinin (CCK) from I cells of the duodenum and jejunum. The gallbladder responding to the stimulation from the cholecystokinin then contracts and releases its contents into the common bile duct which eventually gets drained into the duodenum.

• The emulsification of the fat in the partly digested food is done by the bile and in a way, bile assists the absorption process. Bile mainly consists of bile salts and water and also bile helps in eliminating bilirubin which is a product of haemoglobin metabolism from the body. 

• The bile which is secreted by the liver and then stored and concentrated in the gallbladder is not the same bile that is secreted by the gallbladder. During the storage of bile in the gallbladder, the bile is concentrated three to tenfold by the removal of some electrolytes and water.

• Through the active transport of sodium and chloride ions across the epithelium of the gallbladder, osmotic pressure is created that causes water and other electrolytes to be reabsorbed.

Gallbladder Conditions 

• Gallbladder Cancer: It is very rare to see cases of gallbladder cancer but cancer can affect the gallbladder. Gallbladder cancer is very difficult to diagnose and it is usually found at the late stages only when the symptoms start to appear. The symptoms of gallbladder cancer may resemble those of gallstones. 

• Gallstones: The gallstones are also called cholelithiasis. For reasons unknown, the substances present in the bile can get crystallized in the gallbladder resulting in the formation of the gallstones. Gallstones cause a lot of pain, nausea, and vomiting

• Gallstone Pancreatitis: the ducts that drain the pancreas are blocked by the impacted gallstones. It is a very serious condition as there is an inflammation of the pancreas.

• Cholecystitis: Cholecystitis is caused due to the infection of the gallbladder which is often caused due to the gallstones in the gallbladder. Cholecystitis is known to cause severe pain and fever and when the infection of the gallbladder continues or cannot be stopped then the only treatment that could be done to stop the infection is surgery. 

Gallbladder Treatments

• Antibiotics: during cholecystitis, there may be infection present in the gallbladder. Though the antibiotics completely treat cholecystitis, they can prevent the infection from spreading. 

• Gallbladder Surgery: It is also called (cholecystectomy, a surgery that removes the gallbladder using either laparoscopy or the laparotomy method.

• Chemotherapy and Radiation Therapy: When gallbladder cancer is treated through the surgical method, the patient may have to go through chemotherapy and radiation therapy to prevent cancer from returning. 

Different Gallbladder Tests

There are many tests that are helpful in determining the conditions that are affecting the gallbladder. 

• Abdominal Ultrasound: It is a test in which a probe on the skin bounces high-frequency sound waves off structures in the belly. Ultrasound is a very good test that is found to be very effective in detecting gallstones and also to check the gallbladder wall.

• Abdominal X-Ray: X Rays in the abdomen are used to check other diseases and though it does not treat any gallbladder condition the X-ray is found to be very effective in detecting the gallstones in the gallbladder. 

• Endoscopic Ultrasound: Through the mouth to the intestine, a tiny ultrasound probe on the end of the flexible tube is inserted. Endoscopic ultrasound has been found to be very useful in detecting gallstone pancreatitis and choledocholithiasis.

• Endoscopic Retrograde Cholangiopancreatography (ERCP): In ERCP a flexible tube is inserted through the mouth through the stomach to the small intestine, this way the doctor can see the gallbladder clearly and the conditions that are affecting its proper function. ERCP is mainly used to detect gallstones in the gallbladder. 

• Magnetic Resonance Cholangiopancreatography (MRCP): An MRI scanner is used to provide high-resolution images of the pancreas, the bile ducts, and the gallbladder. The images from the MRCP are then used to treat the condition and eventually become the guide for future treatments.