Introduction to Bile
The consumed food gets digested with the help of several glands and these glands are called digestive glands. These glands produce various types of juices for the breaking down of food into smaller particles, and they are salivary glands present in the mouth, gastric glands present in the stomach, the pancreas, and the liver. In this article let us learn about what is bile? Where is bile produced and stored? How does it play the main role in the process of digestion?
What is Bile?
Bile is derived from the Latin word “Bilis” which is maybe a dark-green to yellowish-brown fluid produced by the liver of most vertebrates that helps in the digestion of lipids within the intestine. In humans, bile is secreted from the liver continuously and is stored and concentrated within the gallbladder. After the consumption of food, this stored bile is discharged into the duodenum to perform the process of digestion.
Bile Contents
The composition of hepatic bile is as follows,
97–98% of water
0.7% bile salts
0.2% bilirubin
0.51% fats such as cholesterol, fatty acids, and lecithin
200 meq/l of inorganic salts
The two main pigments of bile are bilirubin, which is orange-yellow, and its oxidized form is biliverdin, which is green in color. When these two pigments are mixed, they are liable for the brown color of feces. About 400 to 800 milliliters of bile is produced per day in the adult citizenry.
Role of Bile in the Process of Digestion
The liver secretes bile or gall that acts as a surfactant to some extent, that helps to emulsify the lipids in food. Bile salt consists of anions that are hydrophilic on one side and hydrophobic on the other side. Consequently, they have a tendency to aggregate around droplets of lipids such as triglycerides and phospholipids to make micelles. In the micelles, the hydrophobic sides are faced inwards to the fat, and the hydrophilic sides facing outwards. The hydrophilic sides of the micelles are charged and these charged micelles sides are required to prevent the fat droplets from re-aggregating into larger fat particles that are coated with bile. In the case of humans, the micelles that are present in the duodenum have a diameter of around 1–50 μm.
The dispersion of food fat into micelles provides a greatly increased area for the action of the enzyme pancreatic lipase, which actually digests the triglycerides, and is in a position to reach the fatty core through gaps that are present in between the bile salts. A triglyceride is formed into two fatty acids and a monoglyceride is absorbed by the villi that are present on the walls of the intestine. After being transferred across the intestinal membrane, the fatty acids reform into triglycerides by the process called re-esterification, before being absorbed into the systema lymphatica through lacteals. In the absence of bile salts, most of the lipids that are obtained from food would be undigested and excreted in feces.
The liver, the place where is bile released, increases the absorption of fats, it's a crucial part of the absorption of fat-soluble substances, like vitamins A, D, E, and K. A byproduct of red blood cells that are recycled by the liver produces bilirubin, along with the digestive function it acts as a route for excretion of the bilirubin. Bilirubin derives from hemoglobin by glucuronidation.
Microscopic View of Bile
Use of Bile in Human Body
Aid digestion by breaking down fats,
allowing fat-soluble vitamins to be absorbed
waste products to be eliminated
Laxative Action by inducing peristalsis
Cholagogue Action by acting as a stimulant in and of itself
Bile Helps to Maintain a Suitable pH
Bile mucin acts as a lubricant and a buffer.
Regurgitation of bile in the stomach aids in the neutralisation of gastric acidity, preventing acid damage to the gastric mucosa.
More to Know
Bile tends to be alkaline on average.
The pH of bile juice is 7.50 to 8.05 which is said to be more than that of the corresponding gallbladder bile acid pH is 6.80 to 7.65.
Bile within the gallbladder becomes more acidic the longer an individual goes without eating, though resting slows this fall in pH.
As an alkali, it also has the function of neutralizing excess stomach acid before it enters the duodenum, the primary section of the tiny intestine.
Bile salts also act as bactericides, destroying many of the microbes which will be present within the food.
Conclusion
The fluid that is made and released by the liver is considered bile. The main and important function of the bile is to help in the digestion of fats into fatty acids. In the absence of bile, the consumed fats or the vitamins that are required to dissolve the fat get accumulated in the colon of the intestine where it causes several complications.
FAQs on Bile
1. What is bile and what are its primary functions in the human body?
Bile is a greenish-yellow digestive fluid that is produced by the liver and stored in the gallbladder. It has two main functions: firstly, it aids in the digestion and absorption of fats and fat-soluble vitamins in the small intestine. Secondly, it helps the body excrete waste products like bilirubin, which is a byproduct of red blood cell breakdown.
2. Where is bile produced and where is it stored?
Bile is continuously produced by the liver's hepatocytes (liver cells). From the liver, it is transported to the gallbladder, a small organ situated just beneath the liver. The gallbladder's role is to store and concentrate the bile, releasing it into the small intestine when fatty food enters.
3. What are the main components of bile?
Bile is a complex mixture consisting of several key components. The primary constituents include:
- Water (which makes up about 95% of its volume)
- Bile salts (such as sodium glycocholate and sodium taurocholate)
- Bile pigments (primarily bilirubin and biliverdin)
- Cholesterol
- Phospholipids (like lecithin)
- Electrolytes
4. Explain the importance of bile salts in the digestion of fats.
Bile salts are essential for fat digestion through a process called emulsification. They act like a detergent, breaking down large, water-insoluble fat globules into much smaller, microscopic droplets. This action dramatically increases the surface area of the fat, allowing the fat-digesting enzyme, pancreatic lipase, to access and break down the fats much more effectively.
5. Why is the alkaline nature of bile crucial for digestion in the small intestine?
The alkaline pH of bile (typically 7.5 to 8.5) is critical because it neutralises the highly acidic chyme that moves from the stomach into the duodenum (the first part of the small intestine). This neutralisation is important for two key reasons: it protects the intestinal lining from acid damage and it creates the optimal alkaline environment required for the digestive enzymes in the small intestine to function properly.
6. How does the structure of bile salts enable them to emulsify fats?
Bile salts have an amphipathic structure, meaning one end of the molecule is hydrophobic (attracted to fat) and the other end is hydrophilic (attracted to water). The hydrophobic end attaches to the fat droplet, while the hydrophilic end faces the surrounding watery environment. This unique structure allows them to surround tiny fat droplets, preventing them from merging back into large globules and keeping them suspended for enzyme action.
7. What is the key difference between the roles of bile and pancreatic juice in digestion?
The primary difference lies in their mode of action. Bile does not contain any digestive enzymes; its function is mechanical, focused on the physical breakdown (emulsification) of fats. In contrast, pancreatic juice is a rich source of powerful digestive enzymes, including lipase (for fats), amylase (for carbohydrates), and trypsin (for proteins), which perform the chemical breakdown of food molecules.
8. What would be the impact on digestion if a person's gallbladder was surgically removed?
If the gallbladder is removed, the liver continues to produce bile, but it can no longer be stored and concentrated. Instead, bile trickles directly and continuously into the small intestine. This means the body cannot release a large amount of concentrated bile in response to a fatty meal. Consequently, the individual may find it difficult to digest large quantities of fat at one time and is often advised to consume smaller, low-fat meals to avoid digestive discomfort.
