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Digestion Chapter 3
Digestion • Process of making food into a form that can be taken into the body.
Alimentary Canal • The passage that connects the mouth all the way to the anus.
Breakdown of Food • Physical breakdown of food. • Chemical breakdown of food.
Physical Breakdown of Food • Physically breakdown food from large pieces into small pieces in the mouth. • 4 kinds of teeth: • Incisors • Canines • Premolars • Molars
Incisors • At the front of the mouth. • Chisel-shaped. • Biting soft food.
Canines • Pointed • Tearing tougher food. • Used as extra incisors. (humans)
Premolars and molars • They have cusps with grooves. • Crushing and grinding food.
Chemical Breakdown of Food • Chemically breakdown big molecules into small molecules. • Start from the mouth and continue along the alimentary canal. • Carbohydrates, fats and protein are made from large molecules. • Large molecules do not dissolve in water and cannot pass through the wall of the digestive system. • Small molecules do dissolve in water and do pass through the wall of the digestive system.
Enzyme (amylase) Enzyme (amylase) Large molecules (starch) Smaller molecules (maltose)
Enzymes • Made from protein. • Speed up chemical reactions. • Belong to a group of chemical substances called catalysts. • Catalysts – substance that speedup chemical reaction without being changed or used up.
Along the Alimentary Canal Starch sugar • Mouth • Salivary glands produce saliva. • 3 salivary glands (sublingual, parotid, submaxillary). • Saliva is deliver to the mouth via ducts (tubes). • consists 99% water, mucin and enzyme amylase. • Mucin coats the food and makes it easier to swallow. • Amylase breakdown starch molecules into sugar molecules.
Oesophagus/ gullet • Connecting the mouth to the stomach. • Bolus – pellet of chewed food. • Swallowing cause the bolus to slide down the oesophagus. • Peristalsis – wave of muscular contraction to move food along the alimentary canal. • Bolus move through oesophagus via peristalsis.
Stomach • Stomach wall produces hydrochloric acid and pepsin. • Pepsin – enzymes that digest the protein. • Hydrochloric acid kills bacteria in the food and provides acidic environments that pepsin needed. • The food is prevented from leaving the stomach by a valve. • When food is break down into a creamy liquid the valve opens, allow the liquid food to pass into the small intestine.
The duodenum, liver and pancreas • Duodenum is part of the small intestine. • 2 tubes open into duodenum. • One tube carries bile from gall bladder. • Bile is made in liver and break down fat into small droplets. • Another tube comes from pancreas. • Pancreas produced pancreatic enzymes (a juice containing enzymes) that digest proteins, fats and carbohydrates. • The mixture of liquids then pass into small intestine.
Small Intestine • Wall of small intestine makes enzymes that complete food digestion. • Protein amino acids • Carbohydrates sugar • Fats fatty acid and glycerol • These small molecules are soluble and can pass through the wall of small intestine. • Then carried by the blood to all cells of the body.
Large Intestine • Indigestible parts of the food pass from small intestine to large intestine. • Caecum - first part of large intestine. - attached to colon. • Colon - second part of large intestine. - water and some dissolved vitamins are absorbed into the body. - the remaining semi-solid substances form the faeces. • Rectum - last part of large intestine. - stored faeces. • Faeces are removed from the body through the anus. (egestion / defecation)
colon caecum rectum appendix anus
Catalyst • a substance that increases the rate of a chemical reaction without itself undergoing any permanent chemical change. • a substance that speed up the chemical reaction without being used up or change its structure. • Therefore enzyme is a type of catalyst
Properties of enzyme • Specific to substrate • Made of protein • Affects by temperature and pH • Does not used up in a reaction • Enzyme is a catalyst
This is the Lock and Key theory. • The active site act as lock and the shape is complementary to the shape of the substrate (key). • This makes the enzyme very specific. • Each enzyme can only catalyse one substrate at one time. And only specific shape of substrate can bind to it.
