Bile LQ: What does it do?

Learning outcomes All: must give the two uses of bile Most: can explain what bile does to lipids Some: can explain how bile increases the surface area of lipids Grade 6: explain how surface area increases digestion and explain the terms emulsification micelle and increased digestion

Chewing breaks up large chunks of food into smaller chunks Why do we chew our food? Chewing breaks up large chunks of food into smaller chunks Chewing mixes in saliva… … which contains amylase. Amylase is an enzyme which breaks down starch into simple sugars. Amylase Sugars (maltose) Starch molecule

Solid lumps of food can only be digested from the outside If we break large lumps of food down into smaller pieces… Lump of food Chewing Enzymes … we increase the surface area for the enzymes to work on This will speed up the rate of chemical digestion by the enzymes

Progress check What is the function of the teeth? What enzyme is produced in the mouth? What is the purpose of chewing your food? How does this help amylase do its job?

The lining of the stomach produces gastric juice The stomach is a muscular bag which mashes food into a watery paste called chyme The lining of the stomach produces gastric juice Pepsin & Hydrochloric Acid Gastric juice contains: - water - hydrochloric acid which kills microbes in the food and provides the optimum pH for… - pepsin, an enzyme which breaks down proteins into amino acids

Progress check What does pepsin break down? What does the stomach lining produce? What two functions does hydrochloric acid have in the gut? What is the protein broken down into?

Pepsin Amino acids Protein molecule

The lining of the small intestine produces enzymes Once the stomach has reduced the food to a smooth paste, it passes into the small intestine Pancreas Digestive Enzymes Pepsin & Hydrochloric Acid The lining of the small intestine produces enzymes More enzymes are added by the pancreas The enzymes in the small intestine have an optimum pH of 6 - 8 Why is this a problem?

Liver The pancreas produces sodium bicarbonate Bile Gall Bladder The pancreas produces sodium bicarbonate The liver produces bile salts… … which are stored in the gall bladder until they are needed Sodium bicarbonate and bile salts are alkali… … so they neutralize the stomach acid

Progress check Why are bile and sodium bicarbonate added to the small intestine? What happens to the digested food in the small intestine?

The contents of the small intestine are mostly water GLYCEROL Lipase Fat molecule Fatty acids The contents of the small intestine are mostly water Fat (e.g. Vegetable oil) Digestive enzymes are water soluble, but… Surface where fat and water meet … fats do not dissolve in water, so… … lipases can only digest fats at the surface of fat droplets Lipase enzyme particles Water

Adding bile salts cause fats to emulsify in water (emulsify-to become an emulsion, two liquids mixed together) Micelle Add bile Shake Water Emulsion The fat forms tiny droplets called micelles which will stay suspended in water and not separate out This massively increases the surface area for the lipase enzymes to work on

Progress check Why does the lipid have to be made into smaller pieces before it can be digested? What is the term that describes the breaking down of lipids? (think “e”) What is a small piece of lipid called? What does this process increase? (think “s” “a”)

Bile 6 mk Q answer Emulsifier – means to make two liquids mix together e.g. oil and water Bile acts upon fats Bile is produced in the liver and stored in the gall bladder Increases surface areas of fat droplets so it can be digested easier by enzymes Lipase enzyme digests the fat into fatty acids and glycerol