S2 Chapter 14: Human Digestive System

WA3 Revision

Definition of digestion

Digestion is the breaking down of large, insoluble and complex food molecules into small, soluble and simple molecules which can be absorbed into the body cells.

Physical digestion involves..

the mechanical break-up of food into smaller pieces to increase the surface area for enzymes to digest it.

Chemical digestion involves…

enzymes to break down large, insoluble and complex molecules into small, soluble and simple molecules through the action of enzymes so that it can be absorbed into the bloodstream.

the three common classes of enzymes

carbohydrases, proteases, lipases

carbohydrases digest

carbohydrates into simple sugars

proteases digest

proteins into amino acids

lipases digest

fats into fatty acids and glycerol

Process of digesting carbohydrates

carbohydrates (starch) into maltose into glucose (by carbohydrases)

Process of digesting proteins

proteins into polypeptides into smaller polypeptides into amino acids (by proteases)

Process of digesting fats into fatty acids and glycerol

fats into fatty acids and glycerol (by lipases)

Examples of carbohydrases & place of origin

salivary amylase (mouth), pancreatic amylase (pancreas), maltase (small intestine)

Examples of proteases & places of origin

protease (from stomach, pancreas and small intestine)

Examples of lipases & places of origin

pancreatic lipase (pancreas), intestinal lipase (small intestine)