CHAPTER 2CHAPTER 2

THE ALIMENTARY CANAL: THE ALIMENTARY CANAL: DIGESTION AND ABSORPTIONDIGESTION AND ABSORPTION

Copyright © 2010, 2005, 1998 by Saunders, an imprint of Elsevier Inc.

22Copyright © 2010, 2005, 1998 by Saunders, an imprint of Elsevier Inc.

Components of the Components of the Alimentary TractAlimentary Tract

Oral cavityOral cavityEsophagusEsophagusStomachStomachSmall intestineSmall intestine

DuodenumDuodenumJejunumJejunumIleumIleum

Large intestineLarge intestineCecumCecumColonColonRectumRectum

Accessory organs:Accessory organs:Salivary glandsSalivary glandsLiverLiverGallbladderGallbladderPancreasPancreas

33Copyright © 2010, 2005, 1998 by Saunders, an imprint of Elsevier Inc.

Digestion of FoodDigestion of Food

Mechanical actionsMechanical actionsBreak up and mix foods, Break up and mix foods,

permitting better blending with permitting better blending with the chemicalsthe chemicals Chewing Chewing PeristalsisPeristalsis

Chemical actionsChemical actionsReduce foodstuffs to absorbable Reduce foodstuffs to absorbable

moleculesmolecules EnzymesEnzymes

44Copyright © 2010, 2005, 1998 by Saunders, an imprint of Elsevier Inc.

Process of Nutrition: Oral CavityProcess of Nutrition: Oral CavityFood choices influenced by Food choices influenced by

the three sensory perceptions: the three sensory perceptions: SightSightSmellSmellTasteTaste

The oral cavity is the “port of The oral cavity is the “port of entry” where receptors for the entry” where receptors for the sense of taste or sense of taste or taste buds taste buds are locatedare locatedTaste bud consists of 30–100 Taste bud consists of 30–100

cellscells

55Copyright © 2010, 2005, 1998 by Saunders, an imprint of Elsevier Inc.

Process of Nutrition: Oral CavityProcess of Nutrition: Oral CavityMechanical digestionMechanical digestion

Begins w/biting and Begins w/biting and chewing foodchewing food Smaller food pieces Smaller food pieces

provide more surface provide more surface area for digestive area for digestive enzymes to functionenzymes to function

Saliva containing Saliva containing mucus causes food to mucus causes food to stick together into a stick together into a bolus; lubricates the bolus; lubricates the mass for swallowingmass for swallowing

Chemical digestionChemical digestionSalivary amylaseSalivary amylase

Allows large molecule Allows large molecule carbohydrates, which are not carbohydrates, which are not fermentable by plaque acids, fermentable by plaque acids, to be hydrolyzed into shorter to be hydrolyzed into shorter chains that are fermentablechains that are fermentable

From Thibodeau GA, Patton KT: Anatomy & Physiology, ed From Thibodeau GA, Patton KT: Anatomy & Physiology, ed 6. St. Louis: Mosby, 2007.6. St. Louis: Mosby, 2007.

66Copyright © 2010, 2005, 1998 by Saunders, an imprint of Elsevier Inc.

Process of Nutrition: EsophagusProcess of Nutrition: EsophagusNo digestion occursNo digestion occursThe bolus passes The bolus passes

back to the pharynx back to the pharynx under voluntary under voluntary controlcontrolThe process then The process then

becomes involuntarybecomes involuntary

Peristalsis moves the Peristalsis moves the food rapidly to the food rapidly to the stomachstomach

From Thibodeau GA, Patton KT: Anatomy & Physiology, ed From Thibodeau GA, Patton KT: Anatomy & Physiology, ed 6. St. Louis: Mosby, 2007.6. St. Louis: Mosby, 2007.

77Copyright © 2010, 2005, 1998 by Saunders, an imprint of Elsevier Inc.

Process of Nutrition: StomachProcess of Nutrition: StomachStomach secretionsStomach secretions

Chief cells produce pepsinogen Chief cells produce pepsinogen Parietal cells release HCl to make gastricParietal cells release HCl to make gastric

contents acidic (1.5-3 pH)contents acidic (1.5-3 pH) Halts the action of salivary amylaseHalts the action of salivary amylase Aids in absorption of minerals like calcium, iron, zincAids in absorption of minerals like calcium, iron, zinc Kills or inhibits growth of food bacteriaKills or inhibits growth of food bacteria

Secrete intrinsic factor to aid absorption of vitamin BSecrete intrinsic factor to aid absorption of vitamin B1212

Pepsinogen and HCl work together to begin hydrolysis of Pepsinogen and HCl work together to begin hydrolysis of proteinprotein

Gastric lipase to digest short and medium chain FAGastric lipase to digest short and medium chain FAStomach empties in 1–4 hrs depending on amount and Stomach empties in 1–4 hrs depending on amount and

types of food eatentypes of food eaten

From Thibodeau GA, Patton From Thibodeau GA, Patton KT: Anatomy & Physiology, ed KT: Anatomy & Physiology, ed

6. St. Louis: Mosby, 2007.6. St. Louis: Mosby, 2007.

88Copyright © 2010, 2005, 1998 by Saunders, an imprint of Elsevier Inc.

Process of Nutrition: Process of Nutrition: Small IntestineSmall Intestine

DigestionDigestionAcidic chyme from the stomach stimulates the release Acidic chyme from the stomach stimulates the release

of pancreatic enzymesof pancreatic enzymes CHOs: pancreatic amylaseCHOs: pancreatic amylase Protein: trypsin, chymotrypsin, carboxypeptidaseProtein: trypsin, chymotrypsin, carboxypeptidase Fat: lipaseFat: lipase

Microvilli in intestinal wall produce:Microvilli in intestinal wall produce: Lactase, sucrase, and maltase: CHOsLactase, sucrase, and maltase: CHOs Aminopeptidase and dipeptidase: proteinsAminopeptidase and dipeptidase: proteins Lipase: fatsLipase: fats

Bile produced by the liver and stored in the gallbladder Bile produced by the liver and stored in the gallbladder aids in emulsification of fatsaids in emulsification of fats

99Copyright © 2010, 2005, 1998 by Saunders, an imprint of Elsevier Inc.

Process of Nutrition: Process of Nutrition: Small Intestine–AbsorptionSmall Intestine–Absorption

Means of transport (3–10 hr transit time)Means of transport (3–10 hr transit time)ActiveActive

Carrier systems require energy, e.g., intrinsic factorCarrier systems require energy, e.g., intrinsic factor Pumps require energy, e.g., absorption of glucose, Na, K, Pumps require energy, e.g., absorption of glucose, Na, K,

Mg, P, I, Ca, Fe, and amino acidsMg, P, I, Ca, Fe, and amino acids Pinocytosis: engulfing of small drops of intestinal contentsPinocytosis: engulfing of small drops of intestinal contents

Allows for absorption of whole proteins, such as immunoglobulins Allows for absorption of whole proteins, such as immunoglobulins in breast milkin breast milk

PassivePassive DiffusionDiffusion

1010Copyright © 2010, 2005, 1998 by Saunders, an imprint of Elsevier Inc.

Process of Nutrition: Process of Nutrition: Small Intestine–AbsorptionSmall Intestine–Absorption

DuodenumDuodenum ElectrolytesElectrolytes Minerals (Fe, Ca, Mg, Zn)Minerals (Fe, Ca, Mg, Zn)

JejunumJejunum Water-soluble vitamins (C, Water-soluble vitamins (C,

thiamine, riboflavin, Bthiamine, riboflavin, B66, folic acid), folic acid) Mono- and disaccharidesMono- and disaccharides

IleumIleum ProteinProtein Fat-soluble vitaminsFat-soluble vitamins Fat/cholesterolFat/cholesterol Vitamin BVitamin B1212

From Thibodeau GA, Patton KT: Anatomy & Physiology, From Thibodeau GA, Patton KT: Anatomy & Physiology, ed 6. St. Louis: Elsevier, 2008.ed 6. St. Louis: Elsevier, 2008.

1111Copyright © 2010, 2005, 1998 by Saunders, an imprint of Elsevier Inc.

Process of Nutrition: Process of Nutrition: Large IntestineLarge Intestine

Cecum (proximal portion) Cecum (proximal portion) WaterWaterElectrolytes: Na and KElectrolytes: Na and K

ColonColonAdditional digestion of materials occursAdditional digestion of materials occurs

Several nutrients are formed by bacterial synthesis during the Several nutrients are formed by bacterial synthesis during the process including vitamins K and Bprocess including vitamins K and B1212, thiamine, riboflavin, thiamine, riboflavin

Intestinal flora ferment CHO and fiberIntestinal flora ferment CHO and fiber

RectumRectumAnal canalAnal canal

1212Copyright © 2010, 2005, 1998 by Saunders, an imprint of Elsevier Inc.

Dental Hygiene ConsiderationsDental Hygiene Considerations

Assess nutritional status of patients with gustatory Assess nutritional status of patients with gustatory or olfactory disorders for changes in dietary habitsor olfactory disorders for changes in dietary habits

Monitor quality and quantity of food intake for Monitor quality and quantity of food intake for patients with difficulty chewing and swallowing foodpatients with difficulty chewing and swallowing food

Heartburn: result of regurgitation Heartburn: result of regurgitation (gastroesophageal reflux) of stomach contents into (gastroesophageal reflux) of stomach contents into the esophagusthe esophagusOver an extended time, chronic problems with vomiting or Over an extended time, chronic problems with vomiting or

reflux can result in sensitive teeth and superficial or deep reflux can result in sensitive teeth and superficial or deep tooth erosion especially on lingual and occlusal surfacestooth erosion especially on lingual and occlusal surfaces

1313Copyright © 2010, 2005, 1998 by Saunders, an imprint of Elsevier Inc.

Practical ApplicationPractical Application

A patient has had a A patient has had a gastric bypass that gastric bypass that removes the lower removes the lower portion of the portion of the stomach and much of stomach and much of the duodenum and the duodenum and jejunumjejunumGive a rationale for Give a rationale for

which nutrients might which nutrients might be affectedbe affected

From Mahan LK, Escott-Stump S: Krause’s Food and From Mahan LK, Escott-Stump S: Krause’s Food and Nutrition Therapy, ed 12. St. Louis: Saunders, 2008.Nutrition Therapy, ed 12. St. Louis: Saunders, 2008.