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Chemical Digestion Honors Biology Facilitator: Mr. Lee Room 320 Objective • Distinguish between mechanical digestion & chemical digestion Chemical Digestion • Gastric fluid carries out the chemical digestion in the stomach – Pepsinogen is converted into the enzyme pepsin at a low pH – Pepsin breaks down proteins Chemical Digestion… • Formation of Chyme: – When food enters the stomach the cardiac sphincter closes – Food stays in the stomach about 3-4 hours – Chyme is the mixture of particles of food and gastric fluids – Peristalsis forces the chyme into the small intestine (pyloric sphincter regulates the flow) Liver • Stores glycogen and breaks down toxins • Secretes bile: – Needed in digestion of fats – Helps to increase the surface area of fats, aids digestive enzymes • Excess bile is stored in the gallbladder Pancreas • It produces hormones that regulate blood sugar levels • Secretes pancreatic fluid • Changes the pH of the chyme from acidic to a base • Contains digestive enzymes that help complete the breakdown of nutrients in chyme – Disaccharide to monosaccharide – Fats to fatty acids & glycerol – Proteins to amino acids Small Intestine • Chyme passes through the pyloric valve and enters the duodenum (1st part of the small intestine) • Most of the chemical digestion and absorption of the food occurs in the small intestine • Most nutrients are absorbed into the circulatory and lymph systems Small Intestine… • Absorption in the Small Intestine: – Three parts of the small intestine are: • Duodenum • Jejunum • Ileum – Villi are folded surfaces in the small intestine that are adapted for absorption of nutrients – By the time the food leaves the small intestine it is just about nutrient-free Large Intestine • Four major parts: – – – – Ascending colon Transverse colon Descending colon Sigmoid colon (leads to the rectum and anal canal) • Minerals and vitamins that are produced by bacteria are absorbed • Most of the remaining water is absorbed • Mucus lines the walls for lubrication Digestive System Rap Review • Distinguish between mechanical digestion & chemical digestion: – Mechanical digestion involves the physical grinding of food – Chemical digestion involves breaking down food particles by chemical reactions Learn Long Live Long
