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YEAR 8 SCIENCE The Digestive System and Nutrition Digestive System Processes Five Processes • Mechanical processing and movement: chewing, mixing • Secretion: fluid, digestive enzymes and hormones, bile, acid, alkali, mucus • Digestion: breaking down food to smallest absorbable units • Absorption: through mucosa, into blood or lymph vessels • Egestion: undigested material eliminated Overview of Digestive Pathway 1. Mouth 2. Oesophagus 3. Stomach 4. Small Intestine (Duodenum, Jejunum, Ileium) 5. Large Intestine (Colon, Rectum, Anus) Digestive System The Mouth Mouth: begins digestion (Physical & Chemical) • Teeth Incisors, canines, premolars, molars • Tongue skeletal muscle, moves food in mouth, taste • Saliva • Source: Salivary glands • Composition: Salivary amylase, bicarbonate. Pharynx and Oesophagus • Pharynx • Common passageway for air and food • Participates in swallowing • Oesophagus: connects pharynx to stomach • Structure: mix of skeletal and smooth muscle • Mucus secreting cells: assist passage of food • Food motility: gravity and peristalsis Motility: Peristalsis The contraction of the muscles within the esophagus causing food to be pushed into the stomach Stomach Function (Chemical digestion) Functions: - Food storage - Chemical Digestion of Fats and some proteins - Delivery of Gastric juices Gastric Juices • Hydrochloric acid: produces a pH of about 2, breaks down large bits of food, creates suitable conditions for enzyme activity • Pepsinogen: begins protein breakdown • Mucus: protects stomach lining from acid Stomach Contraction (Mechanical Digestion) Produces Chyme Product of mixing food with the gastric juices Stomach contractions Propel Chyme from the lower Oesophageal sphincter to pyloric sphincter (Muscular bands that act as valves to stop back flow) Small intestine Structure Duodenum Jejunum ileum Small Intestine Functions (Digestion & Absorption) Duodenum Break down of Long protein chains and Lipids Jejunum Break down of Carbohydrates & Completion of Protein Digestion Neutralization acid from stomach Absorption: 95% of food nutrients absorbed here Slide 14.10B Villi: Structure within the intestines Villi are like little hairs that line the intestines, they provide a large surface area for absorption of nutrients In the diagram you can see there are circulatory path ways inside the Villi waiting to take nutrients absorbed into the Villi around the body Absorption of Nutrients • Proteins and carbohydrates: Diffusion / active transport into the blood • Lipids: broken down and reassembled • Water: osmosis • Vitamins and minerals: assorted means Slide 14.14C Large Intestine = Large Intestine: Function and Structure Functions - Absorbs nutrients and water - Eliminates waste • Structure: • Caecum (Cellulose Break down), appendix • Colon: ascending, transverse, descending, sigmoid • Rectum, anus . Accesory Organs: Aid Digestion and Absorption • Pancreas • Secretes digestive enzymes and sodium bicarbonate • Liver • Produces bile (acts as emulsifer – begins fat breakdown) • Hepatic portal system: drains blood from digestive tract • Metabolic functions: storage, synthesis, chemical processing • Gallbladder: stores Bile Slide 14.12 Overview of Chemical Digestion