Edexcel IGCSE Biology: Double Science 复习笔记 2.5.10 Humans: Bile
Bile is an alkaline substance produced by cells in the liver
Before being released into the small intestine bile is stored in the gallbladder
Bile production and secretion
Bile contains bile salts, it is these molecules which emulsify the fats, however you can use both terms interchangeably.
The Role of Bile
Bile has two main roles:
Neutralising the hydrochloric acid from the stomach
The alkaline properties of bile allow for this to occur
This neutralisation is essential as enzymes in the small intestine have a higher (more alkaline) optimum pH than those in the stomach
Breaking apart large drops of fat into smaller ones (and so increasing their surface area)
This is known as emulsification
The more alkaline conditions and larger surface area allows lipase to chemically break down the fat (lipids) molecules into glycerol and fatty acids at a faster rate
Bile salts break large lipid droplets into smaller ones with a larger surface area
Emulsification is the equivalent of tearing a large piece of paper into smaller pieces of paper.This is an example of mechanical digestion, not chemical digestion – breaking something into smaller pieces does not break bonds or change the chemical structure of the molecules which make it up, which is the definition of chemical digestion.