CHAPTER 2 THE ALIMENTARY CANAL: DIGESTION AND ABSORPTION Copyright © 2010, 2005, 1998 by Saunders, an imprint of Elsevier Inc.

2 Components of the Alimentary Tract Oral cavity Oral cavity Esophagus Esophagus Stomach Stomach Small intestine Small intestine Duodenum Duodenum Jejunum Jejunum Ileum Ileum Large intestine Large intestine Cecum Cecum Colon Colon Rectum Rectum Accessory organs: Accessory organs: Salivary glands Salivary glands Liver Liver Gallbladder Gallbladder Pancreas Pancreas

3Copyright © 2010, 2005, 1998 by Saunders, an imprint of Elsevier Inc. Digestion of Food Mechanical actions Mechanical actions Break up and mix foods, permitting better blending with the chemicals Break up and mix foods, permitting better blending with the chemicals Chewing Chewing Peristalsis Peristalsis Chemical actions Chemical actions Reduce foodstuffs to absorbable molecules Reduce foodstuffs to absorbable molecules Enzymes Enzymes

4Copyright © 2010, 2005, 1998 by Saunders, an imprint of Elsevier Inc. Process of Nutrition: Oral Cavity Food choices influenced by the three sensory perceptions: Food choices influenced by the three sensory perceptions: Sight Sight Smell Smell Taste Taste The oral cavity is the “port of entry” where receptors for the sense of taste or taste buds are located The oral cavity is the “port of entry” where receptors for the sense of taste or taste buds are located Taste bud consists of 30–100 cells Taste bud consists of 30–100 cells

5Copyright © 2010, 2005, 1998 by Saunders, an imprint of Elsevier Inc. Process of Nutrition: Oral Cavity Mechanical digestion Mechanical digestion Begins w/biting and chewing food Begins w/biting and chewing food Smaller food pieces provide more surface area for digestive enzymes to function Smaller food pieces provide more surface area for digestive enzymes to function Saliva containing mucus causes food to stick together into a bolus; lubricates the mass for swallowing Saliva containing mucus causes food to stick together into a bolus; lubricates the mass for swallowing Chemical digestion Chemical digestion Salivary amylase Salivary amylase Allows large molecule carbohydrates, which are not fermentable by plaque acids, to be hydrolyzed into shorter chains that are fermentable Allows large molecule carbohydrates, which are not fermentable by plaque acids, to be hydrolyzed into shorter chains that are fermentable From Thibodeau GA, Patton KT: Anatomy & Physiology, ed 6. St. Louis: Mosby, 2007.

6Copyright © 2010, 2005, 1998 by Saunders, an imprint of Elsevier Inc. Process of Nutrition: Esophagus No digestion occurs No digestion occurs The bolus passes back to the pharynx under voluntary control The bolus passes back to the pharynx under voluntary control The process then becomes involuntary The process then becomes involuntary Peristalsis moves the food rapidly to the stomach Peristalsis moves the food rapidly to the stomach From Thibodeau GA, Patton KT: Anatomy & Physiology, ed 6. St. Louis: Mosby, 2007.

7Copyright © 2010, 2005, 1998 by Saunders, an imprint of Elsevier Inc. Process of Nutrition: Stomach Stomach secretions Stomach secretions Chief cells produce pepsinogen Chief cells produce pepsinogen Parietal cells release HCl to make gastric Parietal cells release HCl to make gastric contents acidic (1.5-3 pH) Halts the action of salivary amylase Halts the action of salivary amylase Aids in absorption of minerals like calcium, iron, zinc Aids in absorption of minerals like calcium, iron, zinc Kills or inhibits growth of food bacteria Kills or inhibits growth of food bacteria Secrete intrinsic factor to aid absorption of vitamin B 12 Secrete intrinsic factor to aid absorption of vitamin B 12 Pepsinogen and HCl work together to begin hydrolysis of protein Pepsinogen and HCl work together to begin hydrolysis of protein Gastric lipase to digest short and medium chain FA Gastric lipase to digest short and medium chain FA Stomach empties in 1–4 hrs depending on amount and types of food eaten Stomach empties in 1–4 hrs depending on amount and types of food eaten From Thibodeau GA, Patton KT: Anatomy & Physiology, ed 6. St. Louis: Mosby, 2007.

8Copyright © 2010, 2005, 1998 by Saunders, an imprint of Elsevier Inc. Process of Nutrition: Small Intestine Digestion Digestion Acidic chyme from the stomach stimulates the release of pancreatic enzymes Acidic chyme from the stomach stimulates the release of pancreatic enzymes CHOs: pancreatic amylase CHOs: pancreatic amylase Protein: trypsin, chymotrypsin, carboxypeptidase Protein: trypsin, chymotrypsin, carboxypeptidase Fat: lipase Fat: lipase Microvilli in intestinal wall produce: Microvilli in intestinal wall produce: Lactase, sucrase, and maltase: CHOs Lactase, sucrase, and maltase: CHOs Aminopeptidase and dipeptidase: proteins Aminopeptidase and dipeptidase: proteins Lipase: fats Lipase: fats Bile produced by the liver and stored in the gallbladder aids in emulsification of fats Bile produced by the liver and stored in the gallbladder aids in emulsification of fats

9Copyright © 2010, 2005, 1998 by Saunders, an imprint of Elsevier Inc. Process of Nutrition: Small Intestine–Absorption Means of transport (3–10 hr transit time) Means of transport (3–10 hr transit time) Active Active Carrier systems require energy, e.g., intrinsic factor Carrier systems require energy, e.g., intrinsic factor Pumps require energy, e.g., absorption of glucose, Na, K, Mg, P, I, Ca, Fe, and amino acids Pumps require energy, e.g., absorption of glucose, Na, K, Mg, P, I, Ca, Fe, and amino acids Pinocytosis: engulfing of small drops of intestinal contents Pinocytosis: engulfing of small drops of intestinal contents Allows for absorption of whole proteins, such as immunoglobulins in breast milk Allows for absorption of whole proteins, such as immunoglobulins in breast milk Passive Passive Diffusion Diffusion

10Copyright © 2010, 2005, 1998 by Saunders, an imprint of Elsevier Inc. Process of Nutrition: Small Intestine–Absorption Duodenum Duodenum Electrolytes Electrolytes Minerals (Fe, Ca, Mg, Zn) Minerals (Fe, Ca, Mg, Zn) Jejunum Jejunum Water-soluble vitamins (C, thiamine, riboflavin, B 6, folic acid) Water-soluble vitamins (C, thiamine, riboflavin, B 6, folic acid) Mono- and disaccharides Mono- and disaccharides Ileum Ileum Protein Protein Fat-soluble vitamins Fat-soluble vitamins Fat/cholesterol Fat/cholesterol Vitamin B 12 Vitamin B 12 From Thibodeau GA, Patton KT: Anatomy & Physiology, ed 6. St. Louis: Elsevier, 2008.

11Copyright © 2010, 2005, 1998 by Saunders, an imprint of Elsevier Inc. Process of Nutrition: Large Intestine Cecum (proximal portion) Cecum (proximal portion) Water Water Electrolytes: Na and K Electrolytes: Na and K Colon Colon Additional digestion of materials occurs Additional digestion of materials occurs Several nutrients are formed by bacterial synthesis during the process including vitamins K and B 12, thiamine, riboflavin Several nutrients are formed by bacterial synthesis during the process including vitamins K and B 12, thiamine, riboflavin Intestinal flora ferment CHO and fiber Intestinal flora ferment CHO and fiber Rectum Rectum Anal canal Anal canal

12Copyright © 2010, 2005, 1998 by Saunders, an imprint of Elsevier Inc. Dental Hygiene Considerations Assess nutritional status of patients with gustatory or olfactory disorders for changes in dietary habits Assess nutritional status of patients with gustatory or olfactory disorders for changes in dietary habits Monitor quality and quantity of food intake for patients with difficulty chewing and swallowing food Monitor quality and quantity of food intake for patients with difficulty chewing and swallowing food Heartburn: result of regurgitation (gastroesophageal reflux) of stomach contents into the esophagus Heartburn: result of regurgitation (gastroesophageal reflux) of stomach contents into the esophagus Over an extended time, chronic problems with vomiting or reflux can result in sensitive teeth and superficial or deep tooth erosion especially on lingual and occlusal surfaces Over an extended time, chronic problems with vomiting or reflux can result in sensitive teeth and superficial or deep tooth erosion especially on lingual and occlusal surfaces

13 Copyright © 2010, 2005, 1998 by Saunders, an imprint of Elsevier Inc. Practical Application A patient has had a gastric bypass that removes the lower portion of the stomach and much of the duodenum and jejunum A patient has had a gastric bypass that removes the lower portion of the stomach and much of the duodenum and jejunum Give a rationale for which nutrients might be affected Give a rationale for which nutrients might be affected From Mahan LK, Escott-Stump S: Krause’s Food and Nutrition Therapy, ed 12. St. Louis: Saunders, 2008.