Body Function – Digestion – Year 10 Human Biology 2015

Definitions Mechanical Digestion Chemical Digestion Physically breaking up large particles into small particles Chemical Digestion Chemically breaking up larger molecules into smaller molecules

Digestive Process Six basic activities are carried out by the digestive organs Ingestion of food Mechanical digestion of food Chemical digestion of food Movement of food along alimentary canal Absorption of food into blood and lymph Elimination of food that is not absorbed

What is happening at each stage shown in this diagram?

Mechanical Digestion - Mouth Food enters the mouth Teeth break down the food into smaller pieces Four different types of teeth perform different functions of mechanical digestion 4 incisors 2 canines 4 premolars 6 molars

Mechanical Digestion - Stomach Waves of muscular contraction move along the muscular stomach wall Stomach has three layers of muscle allowing is to moved food around like a food processor Food is churned and mixed with gastric juices Food is converted into a thick, soup-like substance called chyme

Stomach and Liver Relationships

Chemical Digestion - Enzymes Enzymes speed up the chemical reaction Enzymes are proteins Enzymes decrease the amount of energy required to start a reaction Enzymes allow the reactions to continue at a rates that suits the body’s requirement Enzymes are specific

Chemical Digestion - Mouth Salivary glands secrete saliva into the mouth Saliva contains mucous and salivary amylase Salivary amylase is an enzyme that breaks down starch molecules into smaller units Saliva has many functions

Mouth and Oesophagus

Chemical Digestion - Stomach Stomach contains mucosa that resists gastric juices Gastric glands secrete gastric juices containing hydrochloric acid, mucous and digestive enzymes Proteins and fats begin to be broken down in the stomach with the help of these gastric juices

Chemical Digestion – Small Intestines Small intestines contain three important fluids – pancreatic juice, bile and intestinal juice Pancreatic juice is secreted from the pancreas and contains enzymes Enzymes in pancreatic juice are Pancreatic amylase Trypsin (pancreatic protease) Ribonuclease and deoxyribonuclease Pancreatic lipases

Chemical Digestion – Small Intestines Pancreatic amylase breaks starch into disaccharides, namely maltose Trypsin breaks the bond between amino acids in proteins into peptide chains Ribonuclease and deoxyribonuclease digest RNA and DNA Pancreatic lipases break down fats into fatty acids and glycerol

Defecation Defecation is the removal of waste products The product that is defecated by the body is called faeces Faeces consist of Food waste eg. Fibre, undigested food Bile pigments Some excess water

Faeces Faeces-shaped Ice-Cream in a toilet “cone”

Toilet Dining!

Movement of Materials Food passes from the mouth to the stomach through the oesophagus in 5-6 seconds Food remains in the stomach for 2-8 hours but most has left within 4 hours High carbohydrate foods leave after a few hours High protein foods take a little longer High fat foods take the longest time to leave the stomach

Movement of Materials Food passes from the stomach to the small intestines Movement through the small intestines is fairly slow It may take up to 5-6 hours to move food through the small intestines Nutrients are absorbed during this process

Small intestines

Movement of Materials Food then passes to the large intestines Movement is very slow through this organ Water is absorbed during the slow movement Food may be in the large intestines for 12-24 hours Food basically “rots” in the large intestines!

From Eating to Defecation From the time food enters the mouth until such time as it is excreted as waste, it is in our body for: UP TO 36 HOURS Therefore you may be defecating (mainly fatty) food that you ate nearly one and a half days ago! Carbohydrates take about 12-15 hours Proteins take about 26-28 hours

Energy Requirements The body needs energy for: Growth and repair of tissue Maintaining body temperature Maintaining normal body functions Contraction of muscles in physical activity

Work to be completed Label the diagram on Digestion Complete the Unit Review Questions.