Bile is a yellowish-green fluid produced by the liver. It is a digestive fluid that aids in breaking down fats in the small intestine.
How Bile is Made and Stored
The liver continuously produces bile, making approximately 400 to 800 milliliters (about 14 to 27 fluid ounces) per day in adults. Bile is primarily composed of 97–98% water, along with bile salts, bilirubin, cholesterol, fats like lecithin, and inorganic salts.
After its production, bile travels from the liver through a network of small bile ducts that merge into larger ones, leading to the common hepatic duct. Bile then flows into the pear-shaped gallbladder, a small organ located beneath the liver. The gallbladder stores and concentrates bile by absorbing water and electrolytes. When food, particularly fatty meals, enters the small intestine, hormones like cholecystokinin signal the gallbladder to contract, releasing the concentrated bile into the duodenum, the first section of the small intestine.
The Essential Roles of Bile
Bile plays a role in the digestion and absorption of fats. Bile salts act as detergents to emulsify large fat globules from food into smaller, microscopic droplets. This emulsification increases the surface area of fats, making them more accessible for digestion by pancreatic lipase enzymes. Without bile salts, most dietary lipids would pass through the body undigested and be excreted.
Bile also aids in the absorption of fat-soluble vitamins, specifically vitamins A, D, E, and K, as well as beta-carotene. These vitamins are incorporated into micelles formed by bile salts around digested fats, allowing them to be absorbed by the intestinal walls.
Beyond digestion, bile helps eliminate waste products. It serves as a route for the excretion of bilirubin, a yellowish byproduct from the breakdown of old red blood cells. Excess cholesterol and certain drugs or toxins metabolized by the liver are also secreted into bile and removed from the body through feces. A process called enterohepatic circulation ensures that about 95% of bile salts are reabsorbed and returned to the liver for reuse, with the remaining small fraction excreted. This recycling mechanism helps maintain a stable concentration of bile salts.
When Bile Goes Wrong
Imbalances in bile composition or its flow can lead to various health issues. Gallstones are hardened deposits of bile that form in the gallbladder. These stones often consist of excess cholesterol (about 4 out of 5 gallstones) or bilirubin (about 1 in 5 gallstones) that crystallize within the bile. Symptoms can include sudden and intense pain in the upper right abdomen, back pain, nausea, or vomiting, especially after fatty meals.
When gallstones or other issues block the bile ducts, bile can back up into the liver, leading to a condition called jaundice. Jaundice causes a yellowing of the skin and the whites of the eyes due to the accumulation of bilirubin in the bloodstream. This blockage can also result in dark urine and light-colored stools. Cholestasis refers to the slowing or stoppage of bile flow, which can originate either within the liver or due to obstructions in the bile ducts. Prolonged cholestasis can lead to inflammation in the liver, gallbladder, or pancreas, and may result in nutritional deficiencies due to impaired fat-soluble vitamin absorption.