The 6 th International Junior Science Olympiad Training Programme

Transcription

1 The 6 th International Junior Science Olympiad Training Programme KEEPING HEALTHY SECTION 2: DIGESTIVE SYSTEM Notes to Teachers Learning Objectives: Processes of nutrition in human (0.25 hr) General plan of the human digestive system Roles of various parts of the alimentary canal and accessory glands (1 hr) Structure and care of teeth (0.5 hr) Absorption digested products Absorption of water soluble and fat soluble substances, Structure of small intestine in relation to absorption (0.5 hr) Assimilation of digested products (0.5 hr) Importance of dietary fibre (0.25 hr) Time Allocation: 3 hrs Dr. K.M. Leung 1 2 Learning Outcomes After studying this topics students will be able to: 2.2 COMPONENTS OF THE HUMAN DIGESTIVE SYSTEM List the 5 processes of nutrition Relate the structures of the alimentary canal to their functions Describe the roles of accessory glands in digestion of food Describe the structure of teeth List different measures for preventing tooth decay Explain how digested products passes from the small intestine to the bloodstream List the routes and transport of absorbed food substances Describe the role of the liver in assimilation Describe the importance of dietary fibre 3 1. Alimentary Canal / Digestive Tract tubular structure for the passage of food, digestion of food and absorption of the digested products 2. Associated Glands glands linked to the alimentary canal for secreting digestive juices 4 Cellulose is broken down by cellulase but which cannot be secreted from the digestive system of mammals. Cellulase is being secreted from some symbiotic bacteria which live in the gut of herbivorous mammals. 5 6

2 2.3.3 DIGESTION OF LIPIDS Site of Enzyme Site of Digestio Products of Digestio Secretio Pancreas Small intestine Fatty acids + Glycerol Intestinal glands Small intestine Fatty acids + Glycerol 7 8 B. TYPES OF TEETH A. STRUCTURE OF TOOTH 3. Premolars Premolars have 1 or 2 blunted points of cusps, for crushing & grinding 1. Incisors 1. Incisors sharp & chisel shaped, for cutting and bitting 9 4. Molars 4. Molars have 4 cusps, for crushing & grinding 2. Canines 2. Canines long, curved, pointed, for grasping and killing prey, tearing flesh i 10 carnivores C. DENTAL HEALTH n Dental formulae of human: Milk set: Permanent set: Tooth Decay caused by chemical actions of bacteria ithe mouth ofood debris plaque, sticky thifilm of bacteria, food debris and saliva is formed othe tooth surface. sugar Æ acid by bacteria acid dissolves enamel and makes small holes. acid irritates the nerve ithe pulp cavity causing toothache 12

3 2.4.3 OESOPHAGUS PHARYNX tubular structure connecting the pharynx to the stomach no digestive enzyme secretio food mass is passed dowthe stomach through peristalsis Peritalsis: rhythmic contractioand relaxatioof the muscles ithe wall of the alimentary canal STOMACH A. FUNCTION OF STOMACH mechanical digestion: by churning (peritalsis istomach) to break dowfood mass into small pieces. 3 layers of muscles: oblique, circular and longitudinal muscle to give more powerful peristalsis 15 chemical digestioby gastric juice enzymes gastric glands to the lumeof the stomach 16 extracellular digestio gastric juice is secreted from gastric glands which are located othe stomach wall

4 C. INTESTINAL JUICE secreted from the intestinal glands / crypts of Lieberküh various enzymes are present to finish the final step of digestio LARGE INTESTINE Large intestine = caecum + appendix + colo+ rectum (anus is the exit of alimentary canal) fat soluble substances, chylomicrons (fatty acids and glycerol recombined and coated with proteii epithelial cells of villi) Water soluble substances e.g. amino acids, water soluble vitamins, water, mineral salts blood capillaries of villi lacteal of villi hepatic portal vei thoracic duct (a lymphatic duct) liver hepatic vei vena cava left subclaviavei heart to various tissues via blood circulatio 21 C. STRUCTURE OF SMALL INTESTINE IN RELATION TO ITS FUNCTION ASSOCIATED GLANDS SALIVARY GLANDS 23 3 pairs of salivary glands Saliva contains water, mucus, NaCl, NaHCO 3, and amylase Water and mucus isaliva facilitate swallowing. 24

5 2.7.2 PANCREAS LIVER secretes pancreatic juice pancreatic juice is discharged into the duodenum through the pancreatic duct. also secretes hormones to regulate the level of blood glucose 25 A. STRUCTURE OF LIVER the largest gland of the body reddish brown in colour, just below the diaphragm 26 References for Further Studies: Biology (6th ed.); EP Solomon, LR Berg & DW Martin; Thomas Learning Inc.; 2002 Mammals: Structure & Function; CJ Clegg; John Murray; 1998 Essentials of anatomy and physiology (4th ed.); RR Seeley, TD Stephens & P Tate; McCraw Hill Higher Education;