Edexcel IGCSE Biology: Double Science 复习笔记 2.5.10 Humans: Bile

Edexcel IGCSE Biology: Double Science 复习笔记 2.5.10 Humans: Bile

Bile Production

 

  • 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 production and secretion

 

 

Exam Tip

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: 

     

    1. 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

       

    2. 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-and-emulsification

 

Bile salts break large lipid droplets into smaller ones with a larger surface area

 

 

Exam Tip

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.

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