Spotlight on the gall bladder
Monday, 5 October 2020
The gallbladder is a small, but really important organ of the digestive system, and because GI problems, can be as a result of a number of pieces of a larger puzzle, I’d like to use this blog to discuss a number of the functions of the gallbladder, bile and bile acids.
What is bile?
The manufacturing of bile takes place in the liver and is transferred to the gallbladder which acts as a reservoir to hold the bile until it is needed for digestive and immune processes.
Bile is a fluid made up of water, electrolytes and a host of organic molecules including bile acids, cholesterol, phospholipids and bilirubin that flows through the biliary tract into the duodenum of the small intestine.
The gallbladder stores and concentrates bile during the fasting state. Typically, bile is concentrated five-fold in the gall bladder by absorption of water and small electrolytes - virtually all of the organic molecules are retained.
When chyme from an ingested meal enters the small intestine, acid and partially digested fats and proteins stimulate secretion of two hormones cholecystokinin and secretin.
Cholecystokinin: The name perfectly describes its effect - cholecysto = gallbladder and kinin = movement. The most potent stimulus for release of cholecystokinin is the presence of fat in the duodenum. Once released, it stimulates contractions of the gallbladder and common bile duct, resulting in delivery of bile into the gut.
Secretin: This hormone is secreted in response to acid in the duodenum - it stimulates biliary duct cells to secrete bicarbonate and water, which expands the volume of bile and increases its flow out into the intestine.
It’s a perfect example of a dance between our hormones and digestive system.
There are two fundamentally important functions of bile:
If this process does not happen as well as it should, fats and oils may then become rancid in the stomach because they are not being properly broken down, this often causes constipation, flatulence and a decrease in digestive capabilities.
So what are bile acids?
Bile acids are derivatives of cholesterol made in the liver. Cholesterol, absorbed as part of the diet or synthesised in the liver is converted into the bile acids cholic and chenodeoxycholic acids. Two amino acids (glycine or taurine) are then “stuck” on - which is termed conjugated, which makes them less toxic. These conjugated bile acids have a key role in absorption of fats.
Large amounts of bile acids are secreted into the intestine every day, but only relatively small quantities are lost from the body. This is because approximately 95% of the bile acids delivered to the duodenum are absorbed back into blood within the ileum (the last section of the small intestine).
The remaining 5% reach the large intestine and form Secondary bile acids (BA): deoxycholic acid, lithocholic acid, which are synthesised in the intestinal lumen by action of bacterial flora. Diets high in fat (this includes the popular ketogenic diet!) increase secondary BAs, such as deoxycholic acid (DCA) and lithocholic acid (LCA), which are risk factors for inflammation in the colon and cancer. In direct contrast, a fibre rich whole grain carbohydrate diet is associated with anti-inflammatory and anticancer effects. These effects may be due to the increased production of the short chain fatty acids (SCFAs) acetate, propionate, and butyrate during dietary fibre fermentation in the colon by gut flora.
Bile as an antimicrobial
Bile also has an antimicrobial effect, mainly due to this detergent-like effect on cell membranes. This very action helps to keep bacterial counts in the small intestine lower, and prevents SIBO.
When bile acids enter the ileum, the final section of the small intestine, they bind to a receptor known as the farnesoid X receptor (FXR). One of the roles FXR plays is in the secretion of antimicrobial peptides. When bile acids bind to FXR in the ileum, antimicrobial proteins get secreted to prevent bacterial growth.
Bile acids and Motility
Bile acids modulate several gastrointestinal functions including electrolyte secretion and absorption, gastric emptying, and small intestinal and colonic motility.
The MMC is a pattern of electromechanical activity seen in the gastrointestinal smooth muscle during the periods between meals, and so is thought to serve a "housekeeping" role and sweep residual undigested material through the gut. A malfunctioning migrating motor complex predisposes to the growth of bacteria in the small intestine, which can cause bloating and poor motility in of itself. Bile plays a large role in both motility of the MMC as well as sweeping away bacteria that may begin to grow. It seems even to be involved in initiating the MMC.
There are 3 phases of the migrating motor complex when looking at it from a motility perspective.
Bile has to empty into the duodenum before phase 3, strong pulses commence. These forceful phase 3 contractions in the stomach force open the pyloric sphincter separating the stomach and duodenum and deposits the acidic stomach contents into the duodenum. Now the peristaltic contractions carry the bile through the gut. Along the way, the antimicrobial effects of bile acids kill unwanted bacteria and waves of muscular contraction sweep them into the colon.
In the ileum, bile acids bind to receptors that release antimicrobial peptides and send the bile acids back to the liver for recycling. All the while, the gallbladder refills for the next cycle.
Stress and the Gallbladder
As we can see from this image, stress, by way of its impact on the autonomic nervous system - paralysed many actions of the gut and vagus nerve. There are 2 arms of the autonomic nervous system that work together called the sympathetic and the parasympathetic nervous systems.
The sympathetic system is the fight or flight mode while the parasympathetic system is often referred to as rest and digest. These 2 arms work together like the brake and accelerator of your car. When we are in Sympathetic mode - right from the top to the bottom of the digestive system, actions and roles are put “on hold” - and inhibition of the gallbladder contraction to release bile is just one!
This flow chart, from Dr Kharrazian shows the impact this situation can have:
So now we have more of an insight into the mechanisms, we can apply some targeted nutritional interventions.
I hope this blog has given you some insight into this small, but crucially important organ.
In health, Tanya