2.31 understand the role of bile in neutralising stomach acid and emulsifying lipids

- The liver cells produce a liquid called bile which is stored in a sac underneath the liver called the gall bladder.
- Bile can pass from the gall bladder down the bile duct and as shown in the diagram below, it then mixes with the contents of the duodenum (small intestine) soon after the acidic chyme leaves the stomach.

What is in bile?
- Bile is alkaline, which neutralises the stomach acid that enters the duodenum. This ensures that enzymes in the small intestine aren't denatured and working at their optimum pH.
- Bile also contains bile salts. These are what helps with the digestion of lipids in the duodenum.

Emulsification of lipids
- In the duodenum, lipid molecules will exist as large droplets.  Large droplets of fat/oil will have a reduced surface area for lipase to bind to and so the rate of digestion of the lipid would be slow.
- Bile salts interact with the lipid droplet causing a few large droplets to be broken down into dozens of tiny droplets.  This is called emulsification and while it does not chemically alter the lipid, it does make it easier for lipase to break it down.  Lipase and bile salts together break down lipids much faster than lipase alone.