Gallbladder – Definition, Location, Functions


Gallbladder Diagram

The gallbladder or cholecyst is a small, hollow, pear-shaped organ located beneath the liver. Its primary function is storing and concentrating bile, a digestive fluid that the liver produces. The gallbladder releases bile into the small intestine to aid in the digestion of fats. Common problems associated with the gallbladder include inflammation (cholecystitis), gallstones (cholelithiasis), and bile duct obstruction.

  • The gallbladder is an organ that collects bile from the liver, concentrates it, and releases it into the small intestine to aid in fat digestion.
  • Bile also removes waste products from hemoglobin metabolism, mainly from old red blood cells.
  • Diet and eating habits influence gallstone formation. Both rapid weight gain and rapid weight loss increase the risk of gallstones.
  • While a gallbladder is not essential for human survival, removal carries some risks.

Location, Appearance, and Structure

The gallbladder rests in a depression beneath the right lobe of the liver. It is a grayish to greenish organ that typically measures about 7-10 cm in length and 4 cm in diameter, with a capacity of 30-50 mL of bile. The gallbladder consists of three parts: the fundus, body, and neck. The neck tapers and connects to the cystic duct, which merges with the common hepatic duct, forming the common bile duct.

Variations in Size, Shape, and Location

The size, shape, and location of the gallbladder often vary among individuals. Occasionally, a person has two or even three gallbladders. Some gallbladders are larger or smaller than the average. There are also anatomical variations, such as the presence of a folded fundus (Phrygian cap) or multiple cystic ducts. In rare cases, the gallbladder is absent, a condition known as agenesis of the gallbladder.

Is the Gallbladder Necessary?

The gallbladder is not essential for human survival. Its primary function is storing and concentrating bile and then releasing it into the small intestine to aid in the digestion of fats. Without a gallbladder, bile is less concentrated and continuously trickles into the intestine, rather than being released in larger amounts when needed. This affects the digestion and absorption of fats, but most people adjust over time. Eating smaller, more frequent meals and avoiding very fatty or greasy foods minimizes digestive discomfort.

Comparative Anatomy

Most vertebrates have a gallbladder, but it is absent in certain species, including horses, deer, rats, and some birds. The absence of a gallbladder in these animals likely relates to their diet and the continuous secretion of bile into the intestine. Invertebrates lack a gallbladder.

Embryological Origin

The gallbladder originates from the endodermal layer of the embryonic gut. It develops from a diverticulum of the primitive gut tube around the fourth week of gestation. This diverticulum gives rise to the hepatic duct, cystic duct, and gallbladder.

Microanatomy

The gallbladder wall consists of several layers:

  • Mucosa: The innermost layer, lined with simple columnar epithelium and possessing numerous folds (rugae) to increase surface area.
  • Lamina Propria: A thin layer of connective tissue beneath the epithelium.
  • Muscularis: A layer of smooth muscle that contracts to expel bile.
  • Perimuscular Layer: A connective tissue layer that provides structural support.
  • Serosa: The outermost layer, which covers the gallbladder except where it is attached to the liver.

Functions of the Gallbladder

  1. Storage of Bile: The gallbladder stores bile produced by the liver. Components of bile include bilirubin and biliverdin, which come from hemoglobin metabolism. So, bile is an effective means of removing the waste products of this metabolism from the body.
  2. Concentration of Bile: It absorbs water and electrolytes from the bile, concentrating it up to tenfold.
  3. Release of Bile: In response to hormonal signals (mainly cholecystokinin) triggered by the ingestion of fats, the gallbladder contracts and releases bile into the small intestine via the common bile duct.

The gallbladder may also play role in protection against cancer. Removal of the organ mainly increases the risk of right-sided colon cancer, but it also potentially increases the risk of other types of cancer.

Bile: Composition and Role in Digestion

Bile is a yellow-green fluid composed of bile salts, cholesterol, bilirubin, electrolytes, and water. Liver hepatocytes produce bile, which then flows through bile canaliculi, hepatic ducts, and into the gallbladder for storage. During digestion, bile emulsifies fats, breaking them into smaller droplets for easier enzymatic breakdown by lipases. The average human produces about 500-1000 mL of bile daily.

Common Gallbladder Issues

The most common issues with the gallbladder are inflammation, gallstones, and problems with bile movement. Gallbladder cancer is rare, yet potentially deadly.

  1. Cholecystitis: Inflammation of the gallbladder, often due to gallstones blocking the cystic duct. Symptoms include severe abdominal pain, fever, and nausea. Treatment typically involves antibiotics, pain management, and possibly surgery.
  2. Gallstones: Solid particles that form from bile components. They can be cholesterol stones (more common) or pigment stones (made from bilirubin). Gallstones cause pain, nausea, vomiting, and jaundice if they block bile ducts.
  3. Biliary Dyskinesia: Abnormal gallbladder motility, leading to pain and digestive issues.
  4. Gallbladder Cancer: A rare but serious condition that often presents late with symptoms similar to other gallbladder diseases. Sometimes cancer only gets detected following gallbladder removal for one of the other issues.

Gallstones

Gallstones form when there is an imbalance in the substances that make up bile, such as excess cholesterol or bilirubin, or insufficient bile salts. There is a significant association between certain dietary patterns, dieting behaviors, and the development of gallstones.

  • High-Fat Diets: Diets high in saturated fats and cholesterol increase the risk of cholesterol gallstones. Excessive dietary cholesterol supersaturates bile, potentially causing stone formation.
  • Low-Fiber Diets: Diets low in fiber slow down digestion and alter bile acid metabolism, increasing the likelihood of gallstone formation.
  • High-Calorie and Rapid Weight Gain: Consuming high-calorie foods and gaining weight rapidly contributes to gallstone development.
  • Low-Calorie and Rapid Weight Loss: Rapid weight loss, particularly through very low-calorie diets or crash dieting, creates an imbalance in bile salts and cholesterol, increasing the risk of gallstones. During rapid weight loss, the liver secretes extra cholesterol into bile, potentially causing stone formation.
  • Fasting and Skipping Meals: Fasting or skipping meals concentrates bile with cholesterol, as the gallbladder is not regularly emptied. This promotes the formation of gallstones.
  • High Sugar Intake: Diets high in sugar and refined carbohydrates increase the risk of gallstones.
  • Obesity: Obesity is a well-established risk factor for gallstones, as it is associated with higher cholesterol levels in bile.
  • Weight Cycling: Repeated cycles of weight loss and gain (yo-yo dieting) increases the risk of gallstones, particularly cholesterol stones.
  • Alcohol: Moderate alcohol consumption has a protective effect against gallstones, but excessive alcohol intake can have other detrimental health effects.

Symptoms of gallstones include pain in the upper right abdomen, back pain between the shoulder blades, nausea, vomiting, and jaundice.

Diagnosis of gallstones involves ultrasound, CT scans, or MRI. Blood tests are useful for detecting infection or inflammation.

Treatment options include medications to dissolve stones, lithotripsy to break them up, and cholecystectomy (surgical removal of the gallbladder).

Complications of Gallstones and Gallbladder Removal

Complications from gallstones include acute cholecystitis, pancreatitis, and cholangitis (infection of the bile ducts). Cholecystectomy (gallbladder removal) is a common recommendation for recurrent or severe cases, and can be performed laparoscopically or through open surgery. There is some risk of bile duct injury from surgery, which is serious and potentially fatal. Following a normal surgery, bile flows directly from the liver to the small intestine. This causes changes in digestion, but usually does not produce significant long-term issues. That being said, around 30% of patients experience some degree of indigestion after gallbladder removal. There appears to be an increased risk of cancer following gallbladder removal, but factors such as diet, genetics, and overall health also influence cancer risk.

References

  • Choi, Y.J.; Jin, E.H.; et al. (2022). “Increased Risk of Cancer after Cholecystectomy: A Nationwide Cohort Study in Korea including 123,295 Patients”. Gut Liver. 16 (3): 465–473. doi:10.5009/gnl210009
  • Meilstrup, J.W.; Hopper, K.D.; Thieme, G.A. (1991). “Imaging of gallbladder variants”. AJR Am J Roentgenol. 157 (6): 1205–8. doi:10.2214/ajr.157.6.1950867
  • Mu, L.; Li, W.; Ren, W.; Hu, D.; Song, Y. (2023). “The association between cholecystectomy and the risk of colorectal cancer: an updated systematic review and meta-analysis of cohort studies”. Transl Cancer Res. 12 (6): 1452–1465. doi:10.21037/tcr-22-2049
  • Nagral, Sanjay (2005). “Anatomy relevant to cholecystectomy”. Journal of Minimal Access Surgery. 1 (2): 53–8. doi:10.4103/0972-9941.16527
  • Standring, S.; Borley, N.R., eds. (2008). Gray’s Anatomy : The Anatomical Basis of Clinical Practice. Brown JL, Moore LA (40th ed.). London: Churchill Livingstone. ISBN 978-0-8089-2371-8.