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Chapter 3 Digestive System and Nutrition 1 Outline • • The Digestive Tract – Mouth – Pharynx – Esophagus – Stomach – Small Intestine – Large Intestine – Accessory Organs Nutrition – Eating Disorders 2 The Digestive Tract • • • Roof of the mouth composed of two parts. Anterior hard palate. Posterior soft palate. Tonsils help protect against infection. Three pairs of salivary glands send juices through ducts to the mouth. – Saliva contains bicarbonate and salivary amylase. 3 Digestive Tract 4 The Digestive Tract • • Teeth used to chew food into pieces small enough to swallow. – Each tooth has two main divisions. Crown. Root. Tongue mixes chewed food with saliva and forms a bolus in preparation for swallowing. 5 Adult Teeth and Mouth 6 The Pharynx • The pharynx receives air from the nasal cavities and food from the mouth. – Swallowing is a reflex action that occurs in the pharynx. Soft palate moves to close off nasopharynx, and the trachea moves under the epiglottis to cover the glottis. 7 Swallowing 8 The Esophagus • The esophagus is a muscular tube that passes from the pharynx through the thoracic cavity and diaphragm into the abdominal cavity. – Rhythmic peristalsis pushes food along the digestive tract. – Sphincters encircle tubes and act as valves. 9 The Wall of the Digestive Tract • Layers. – Mucosa - Mucus membrane layer. – Submucosa - Submucosal layer. – Muscularis - Smooth muscle layer. – Serosa - Serous membrane layer. 10 Wall of the Digestive Tract 11 The Stomach • Stomach stores food and aids in digestion. – Columnar epithelial lining contains gastric pits leading into gastric glands. Produce gastric juice containing enzyme pepsin. – Walls of stomach have folds which help churn and mix food and gastric juices. Chyme leaves the stomach and enters the small intestine. 12 Stomach Anatomy 13 The Small Intestine • The small intestine is the primary site for nutrient absorption. – Receives bile from liver to emulsify fat. – Walls contain villi which increase surface area and thus absorptive capability. Nutrients are eventually transported into the cardiovascular system and fats are transported into the lymphatic system. 14 Small Intestine Anatomy 15 Regulation of Digestive Secretions • Secretion of digestive juices is promoted by the nervous system and by hormones. – Hormones are produced by one set of cells and affect a different set of cells. Gastrin. Gastric inhibitory peptide (GIP). Secretin. Cholecystokinin (CCK). 16 Hormonal Control of Digestive Secretions 17 The Large Intestine • • The large intestine absorbs water, salts, and some vitamins, and stores fecal material. Cecum is blind end of large intestine. – Colon. Ascending. Transverse. Descending. Sigmoid. – Rectum. – Anus. 18 The Large Intestine • • • Polyps are small growths arising from the epithelial lining. – May increase likelihood of colon cancer. Can be removed surgically. Diarrhea is caused by infection of the lower intestinal tract and nervous stimulation, and results in increased peristalysis. Constipation can be caused by a lack of water and fiber, and leads to dry, hard feces. 19 Three Accessory Organs • • • The pancreas secretes insulin and glucagon that regulate blood glucose levels. The liver maintains homeostasis by maintaining blood glucose levels, producing bile, and detoxifying blood. – Disorders. Jaundice. Cirrhosis. The gallbaldder stores excess bile. 20 Digestive Enzymes • Digestive enzymes are hydrolytic enzymes that break down substances into nutrient molecules. – Glucose and amino acids are absorbed into blood capillaries of the villi. – Fatty acids and glycerol reform within epithelial cells and enter lacteals as lipoprotein droplets. 21 Nutrition • The body requires three major classes of macronutrients to supply energy and optimum cellular metabolism. – Carbohydrates. – Protein. – Fat. 22 Food Guide Pyramid 23 Carbohydrates • Carbohydrates are digested to simple sugars, which are, or can be converted to, glucose. – Quickest, most readily absorbed source of energy for the body. – Complex carbohydrates should make up the bulk of the diet. 24 Proteins • Adequate protein formation requires twenty different amino acids, including eight essential amino acids. – Body is unable to produce essential amino acids. – Amino acids are not stored in the body, and thus a daily supply is needed. 25 Lipids • Fat and cholesterol are both lipids. – Intake of fat increases weight gain, and increases the risk of cardiovascular disease and cancer. Plaque deposits contain saturated fats and cholesterol. For optimal cardiovascular health, less than 30% of calories should come from fat and less than 10% from saturated fat. 26 Vitamins and Antioxidants • Vitamins are inorganic compounds used by the body for metabolic purposes, but cannot be produced in adequate quantities. – Antioxidants are vitamins that defend the body against free radicals. Molecules that carry an extra electron. 27 Minerals • The body also requires minerals. – Macrominerals are present at a minimal level of 5 grams each. Calcium, Potassium, Sodium, Magnesium, Phosphorus, Sulfur, Chloride. – Microminerals are present at levels under 5 grams each. Iodine, Copper, Mangenese, Zinc, Iron. 28 Calcium and Sodium • • Calcium counteracts osteoporosis and generally strengthens bones. Sodium helps maintain osmotic balance, but too much sodium can intensify hypertension. – How do you reduce sodium intake? 29 Eating Disorders • Obesity. – Most often defined as body weight 20% or more above ideal weight. Most likely caused by a combination of hormonal, metabolic, and social factors. Increases risk of heart disease. 30 Eating Disorders • • Bulimia Nervosa. – Habit of eating to excess and then purging by artificial means. Alters blood composition leading to heart rhythm problems and kidney damage. Anorexia Nervosa. – Morbid fear of gaining weight. Self-induced starvation. 31 Review • • The Digestive Tract – Mouth – Pharynx – Esophagus – Stomach – Small Intestine – Large Intestine – Accessory Organs Nutrition 32 33