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Digestion Pre IB Biology
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Digestion Pre IB Biology

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  • 1. NUTRITION AND DIGESTION
  • 2. Stages of Food Processing 1. Ingestion: The act of eating. Usually involves placing food in mouth or oral cavity. 2. Digestion: Macromolecules are too large an must be broken down into small molecules so they can be absorbed and utilized by the body. Involves two processes: Mechanical: Chewing and churning. Chemical: Enzymatic breakdown of food.
  • 3. Stages of Food Processing
  • 4. Stages of Food Processing 3. Absorption: Cells lining the digestive cavity and take up food into the bloodstream delivering throughout the body. 4. Elimination: Undigested food materials are discharged from body.
  • 5. Nutrients • The substances in food that an organism needs and uses for its life functions.
  • 6. Nutritional Needs of Animals The diet of animals provides: 1. Fuel (chemical energy) to power body activities. 2. Organic raw materials to make animal’s own macromolecules. 3. Essential nutrients or substances that the animal cannot make for itself and must obtain prefabricated from food: – Essential amino acids – Vitamins – Minerals
  • 7. Nine Amino Acids are Essential Nutrients  Adult humans cannot make nine of the 20 amino acids needed to make proteins. – Complete proteins: All essential amino acids are present (Example: Meat, milk, eggs, and cheese). – Incomplete proteins: Deficient in one or more amino acid. Most plants are incomplete sources of amino acids (Example: Rice, corn, and wheat). • Vegetarian diets must carefully balance protein sources.
  • 8. Essential Amino Acids Are Not Synthesized by Humans Most Vegetables are Incomplete Protein Sources
  • 9. Function of Nutrients 1. They act as a fuel to provide energy for the life activities of cells. 2. They supply chemicals needed for growth and repair of cells. 3. They regulate the metabolic processes needed for the proper functioning of the cell.
  • 10. Six Types of Nutrients 1. Carbohydrates 2. Proteins 3. Lipids 4. Vitamins 5. Minerals 6. Water
  • 11. Carbohydrates • Main source of energy for body functions. Ex: bread, pasta, and fruits
  • 12. Lipids • Supply of energy • Part of cell membrane • Storage form of excess food in the body. Ex: butter, bacon, and nuts
  • 13. Proteins • Used for growth and repair of body tissue. Ex: meat, milk , eggs, and fish
  • 14. Water • Solvent in which chemical reactions take place. • Aids in the transport of materials in the body.
  • 15. Minerals • Make up the body structures. Ex: Calcium- make up bone and teeth or Iron- part of hemoglobin (red blood cells)
  • 16. Vitamins • Needed for normal metabolism. Ex: vegetables, fruits, and meats
  • 17. • Carbohydrates, proteins, an d lipids need to be digested by the body in order to be absorbed into the blood. • Vitamins, minerals, and water do not need to be digested and are easily absorbed into the blood.
  • 18. Digestive Tract • Also known as the GI tract • Consists of a one-way digestive tract. • Food is moved through the tract by slow, rhythmic muscular contractions called peristalsis.
  • 19. Parts of the Human Digestive System Alimentary canal: Long tube like structure. • Mouth • Tongue • Pharynx (throat) • Esophagus • Stomach • Small intestine • Large intestine • Rectum • Anus
  • 20. Digestive glands: Produce enzymes, bile, and other substances important for digestion. • Salivary glands • Pancreas • Liver • Gallbladder
  • 21. Human Digestive System
  • 22. Human Digestive System Mouth: – Ingest and mechanically break down food. – Digestion: Saliva lubricates and starts to digest food. • Starch is digested by salivary amylase – Other enzymes in saliva kill bacteria.
  • 23. Mouth: Ingestion, Mechanical Breakdown, and Early Digestion of Food
  • 24. Salivary glands
  • 25. Part of the Human Digestive System Pharynx (Throat): – Throat opens into both the trachea (respiratory system) and esophagus (digestive system). – As food enters pharynx, swallowing reflex is triggered: Esophagus: – Muscular tube that conveys food to stomach. – Peristalsis: Wavelike involuntary muscle contractions squeeze food through alimentary canal (towards the stomach).
  • 26. Swallowing Reflex and Esophageal Peristalsis
  • 27. Swallowing Signal to open
  • 28. Stomach: – Stores food (can stretch to accommodate up to 2 liters of food and water). – Gastric juice contains hydrochloric acid (HCl), enzymes (pepsin), and mucus. – Protein digestion starts in stomach with pepsin. – Food is churned in stomach with gastric juice to form chyme. – Food remains in stomach from 2 to 6 hours, after which it is released into the small intestine.
  • 29. Stomach: Food Storage and Digestion
  • 30. Stomach lining & gland
  • 31. Gastric ulcers: – Open lesions in stomach wall. – Until recently believed to be caused by stress or diet. – Now we know that most are caused by a bacterium Helicobacter pylori. – Can be treated and cured with antibiotics.
  • 32. H. pylori causes Gastric Ulcers
  • 33. Small Intestine: – Huge surface area, about 300 square meters. – Most digestion and absorption occurs here. – Pancreas and liver empty digestive enzymes and bile into the small intestine. • Pancreatic amylase: Breaks down starch • Trypsin and Chymotrypsin: Break down proteins • Lipases: Break down fats • Peptidases: Break down proteins • Nucleases: Break down DNA and RNA • Bile: Helps fat digestion by emulsifying fats.
  • 34. Small Intestine is Site Most Enzymatic Digestion
  • 35. Small intestine – 6 meters long (19.8 ft) a. Duodenum – the first part of the small intestine – secrete digestive enzymes, used to complete the breakdown process of carbs, proteins, and fats
  • 36. b. Jejunum and Ileum – the second and third region of small intestine – function mainly in the absorption of nutrients
  • 37. C. Villi Very large surface area for absorption due to: • Large circular folds (villi) • Tiny cell surface projections (microvilli). D. Capillaries drain nutrients from small intestine and then sends them to first to liver and then rest of body.
  • 38. Large Intestine (Colon): – 1.5 m long and 5 cm wide (diameter) – Most water absorption occurs here (up to 90%). – Undigested remainder of food is converted into feces. – Site of bacterial synthesis • Vitamin K • Folic acid • Biotin • Several B vitamins – Appendix: Small fingerlike projection. Involved in immunity. Rectum: – Stores feces until ready to eliminate
  • 39. Large Intestine: Water Absorption and Formation of Feces
  • 40. Human Digestive System Digestive Glands: Liver: – Produces bile which is stored in gallbladder. – Bile is released into the small intestine after a meal. – Bile contains no enzymes, but helps emulsify fat particles. – Has many other functions. Pancreas: – Produces several digestive enzymes which are emptied into small intestine. – Enzymes digest starch, protein, fats, and nucleic acids.
  • 41. Digestive Glands: Liver and Pancreas Empty Contents into Small Intestine

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