2.3 HUMAN DIGESTIVE SYSTEM

2.3 HUMAN DIGESTIVE SYSTEM

Learning outcome•  explain what digestion is.• identify the parts of the digestive system.• describe the flow of food particles in the alimentary

canal.• state the functions of the organs in the digestive

system.• describe the process of digestion in the alimentary

canal.• list the end products of digestion of carbohydrate,

protein and fats.

Digestion

• Process of breaking down complex food to simple molecule for absorption into the blood circulatory system.

• 2 stages:– Physical digestion – big pieces of food are

broken down into smaller pieces by teeth– Chemical digestion – enzymes break up

complex food molecules into smaller molecules.

Enzyme

• What is enzyme????– Protein that speed up the process of digestion.

• Characteristic of enzymes– required in small quantities– Not destroyed at the end of digestion– Act only specific foods– Function best at normal body temperature (37

celcius). It destroyed at high temperature.– Specific enzyme act only in specific acidic or alkaline

conditions.

Digestive system• What must you know????• Organ that involve in digestive system..

– Mouth, oesophagus, stomach, pancreas, bile duct, gall bladder, liver, small intestine, large intestine, large intestine, anus

• Alimentary canal start from mouth, oesophagus, stomach, small intestine, large intestine and the end at anus.

• Process of peristalsis – food that pushed along the alimentary canal by contract and relax of muscular walls

Mouth (physical digestion)• Food chewed and broken up into small pieces by the teeth.• Small pieces of food have wide surface are for the saliva to

act upon.• The salivary gland secrets saliva that is alkaline and contains

salivary amylase• Salivary amylase convert starch into maltose

Salivary amylase

Starch maltose

Oesophagus• No digestion take place. Why???• Food from mouth pushed through oesophagus(gullet)

into the stomach by the alternating muscular contraction and relaxation of the oesophagus

• Process peristalsis.

Stomach• Food mixed with gastric juice• What is gastric juice???

– Juice that secreted from the cell at stomach wall.– Contain Hydrochloric acid and enzyme rennin and

pepsin

Hydrochloric acid

• Function of hydrochloric acid– Providing and acidic medium for enzymic action– Killing bacteria found in food– Neutralising the alkaline property of saliva and

stopping the action of salivary amylase

Cont…• Pepsin

– Digest protein into peptones

Protein Peptone

• Rennin– Coagulates milk in the stomach to help in the

enzymic action of pepsin

Liquid milk protein Solid milk proteinRennin

Pepsin

Small intestine• The duodenum is first part of the small

intestine– Receive bile and pancreatic juices

Bile• Bile produced by liver and stored in the gall

bladder.• Bile flows from gall bladder into the

duodenum through the bile duct.• Function of bile:

– Emulsification of fat– Preparation of an alkaline medium for enzymic action

Pancreatic juice• Produced by pancreas cell• Contain 3 type of enzyme

– Pancreatic amylase(digest starch)• Starch maltose

– Protease( digest peptones)• Peptones amino acods

– Lipase• Fat fatty acids+ glycerol

Pancreatic amylase

Protease

lipase

• Small intestine also produce enzyme maltase that digest maltose into glucose

• Digestion is completed in the small intestine• It ready to be absorbed into the blood stream

through the thin wall of the small intestine

Large intestine

• Absorb water

• Undigested food is expelled from the body through the anus as faeces

End products of digestion• The end product must in simple forms that

readily absorbed into the small intestine through villi

Class of food Final product of digestion

Carbohydrate Glucose

Starch maltose glucose

Protein Amino acid

Protein peptones amino acid

Fat Fatty acid and glycerol

Large fatty globules small droplet fatty acid and glycerol

amylase maltase

pepsin protease

bile lipase

The end