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Chapter 14 Digestive System
Elsevier items and derived items © 2009 by Saunders, an imprint of Elsevier Inc.
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Pretest True or False The pancreas is an accessory organ of the digestive system. Peristalsis consists of rhythmic waves of contractions that propel food particles through the digestive tract. The buccinator muscle connects the tongue anteriorly to the floor of the mouth. The total number of primary teeth is 32. Saliva moistens and lubricates the food. Elsevier items and derived items © 2009 by Saunders, an imprint of Elsevier Inc.
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Pretest, cont. True or False
The esophagus provides a passageway for food between the pharynx and stomach. The first part of the small intestine is the duodenum. Hepatocytes are liver cells. Iron is stored in the liver. The function of the gallbladder is to produce bile. Elsevier items and derived items © 2009 by Saunders, an imprint of Elsevier Inc.
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Introduction to the Digestive System
Includes: a. Digestive tract Also called: Alimentary canal Gastrointestinal (GI) tract Consists of a long continuous tube Extends from mouth to anus Includes: mouth, pharynx, esophagus, stomach, small intestine, large intestine Elsevier items and derived items © 2009 by Saunders, an imprint of Elsevier Inc.
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Introduction to the Digestive System, cont.
b. Accessory organs Tongue and teeth Salivary glands, liver, gallbladder, and pancreas Secrete fluids into digestive tract Elsevier items and derived items © 2009 by Saunders, an imprint of Elsevier Inc.
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Introduction to the Digestive System, cont.
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Introduction to the Digestive System, cont.
Functions of the Digestive System Food undergoes three types of processes in the body: Digestion Absorption Metabolism Digestion and absorption: occur in digestive tract After nutrients are absorbed: are available to all cells in the body Used by the cells in metabolism Elsevier items and derived items © 2009 by Saunders, an imprint of Elsevier Inc.
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Introduction to the Digestive System, cont.
Preparation of food for use by the body’s cells: a. Ingestion: the taking in of food b. Mechanical digestion: food broken into smaller particles Chewing (mastication) Churning and mixing actions in stomach Elsevier items and derived items © 2009 by Saunders, an imprint of Elsevier Inc.
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Introduction to the Digestive System, cont.
c. Chemical digestion Carbohydrates, proteins, and fats: transformed into smaller molecules Can be absorbed and used by the cells Hydrolysis: water is used to break down the complex molecules in food Digestive enzymes: speed up the hydrolysis process, which is otherwise very slow Elsevier items and derived items © 2009 by Saunders, an imprint of Elsevier Inc.
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Introduction to the Digestive System, cont.
d. Movements Deglutition: swallowing Mixing movements: occur in the stomach (smooth muscle contractions) Mix food particles with enzymes Peristalsis: rhythmic waves of contractions Propels food particles through digestive tract e. Absorption: food molecules pass through lining of the small intestine into blood f. Elimination: food molecules that cannot be digested are eliminated from body Defecation: removal of indigestible wastes (feces) through the anus Elsevier items and derived items © 2009 by Saunders, an imprint of Elsevier Inc.
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General Structure of the Digestive Tract
Long continuous tube: 30 feet long Opens to outside at both ends (mouth and anus) Four layers or tunics: a. Mucosa: innermost tunic Lines lumen of digestive tract Consists of: epithelium, loose connective tissue, smooth muscle In certain regions: mucosa develops folds Increase surface area for absorption Cells in the mucosa secrete: Mucus, digestive enzymes, hormones Elsevier items and derived items © 2009 by Saunders, an imprint of Elsevier Inc.
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General Structure of the Digestive Tract, cont.
b. Submucosa: thick layer of loose connective tissue Contains blood and lymphatic vessels Carries away absorbed nutrients Contains nerves that form a network: submucosal plexus Provides autonomic nerve impulses to the muscle layers of the digestive tract Elsevier items and derived items © 2009 by Saunders, an imprint of Elsevier Inc.
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General Structure of the Digestive Tract, cont.
c. Muscle layer (muscularis) Inner circular layer: contraction causes decrease in diameter of the tube Outer longitudinal layer: contraction causes shortening of the tube Myenteric plexus: network of autonomic nerve fibers between muscle layers Controls movements and secretions of digestive tract (along with submucosal plexus) Elsevier items and derived items © 2009 by Saunders, an imprint of Elsevier Inc.
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General Structure of the Digestive Tract, cont.
d. Serosa or adventitia: outermost layer Adventitia: above the diaphragm Composed of connective tissue Serosa: below the diaphragm Layer of epithelium covering the connective tissue (visceral peritoneum) Secretes serous fluid for lubrication a) Allows abdominal organs to move smoothly against each other Elsevier items and derived items © 2009 by Saunders, an imprint of Elsevier Inc.
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General Structure of the Digestive Tract, cont.
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Components of the Digestive Tract
Mouth Receives food by ingestion Breaks food into small particles by mastication Mixes food with saliva Elsevier items and derived items © 2009 by Saunders, an imprint of Elsevier Inc.
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Components of the Digestive Tract, cont.
Lips and Cheeks Functions Helps hold food in mouth Keeps food in place for chewing Formation of words for speech Elsevier items and derived items © 2009 by Saunders, an imprint of Elsevier Inc.
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Components of the Digestive Tract, cont.
Lips Folds of skeletal muscle Covered with a thin, transparent epithelium Reddish color: blood vessels underlying the epithelium Contain numerous sensory receptors Determine temperature and texture of foods Elsevier items and derived items © 2009 by Saunders, an imprint of Elsevier Inc.
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Components of the Digestive Tract, cont.
Cheeks Main component: buccinator muscle Covered by skin and subcutaneous tissue Oral cavity: lined with mucous membrane Stratified squamous epithelium Provides protection against abrasion from food particles Elsevier items and derived items © 2009 by Saunders, an imprint of Elsevier Inc.
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Components of the Digestive Tract, cont.
Palate Forms roof of oral cavity Separates oral cavity from nasal cavity Anterior portion: hard palate Supported by bone Elsevier items and derived items © 2009 by Saunders, an imprint of Elsevier Inc.
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Components of the Digestive Tract, cont.
Posterior portion: soft palate Consists of skeletal muscle and connective tissue Ends in a projection: uvula During swallowing: soft palate and uvula move upward Directs food away from nasal cavity and into oropharynx Elsevier items and derived items © 2009 by Saunders, an imprint of Elsevier Inc.
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Components of the Digestive Tract, cont.
Tongue Consists of skeletal muscle 2. Root: major attachment for tongue Anchored to hyoid bone 3. Frenulum linguae: connects tongue to floor of mouth 4. Papillae: tiny projections on dorsal surface of tongue Provide friction for manipulating food in mouth Contain the taste buds Elsevier items and derived items © 2009 by Saunders, an imprint of Elsevier Inc.
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Components of the Digestive Tract, cont.
5. Lingual tonsils: embedded in posterior surface of tongue Provide defense against bacteria that enter mouth 6. Tongue muscles Manipulate food in the mouth for mastication Move food around to: Mix it with saliva Shape it into a ball-like mass: bolus Direct it toward the pharynx for swallowing Elsevier items and derived items © 2009 by Saunders, an imprint of Elsevier Inc.
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Components of the Digestive Tract, cont.
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Components of the Digestive Tract, cont.
Teeth 1. Primary (deciduous) teeth Appear at approximately 6 months of age Continue to develop until about 2½ years of age Contain 10 teeth in each jaw: total of 20 teeth 2. Secondary (permanent) teeth 6 years of age: primary teeth begin to fall out Replaced by secondary teeth Contain 16 teeth in each jaw: total of 32 teeth Elsevier items and derived items © 2009 by Saunders, an imprint of Elsevier Inc.
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Components of the Digestive Tract, cont.
Types a. Incisors: chisel-shaped and have sharp edges Used for biting food b. Cuspids (canines): cone-shaped and have points Used for grasping and tearing food c. Bicuspids (premolars) and molars: flat surfaces with rounded projections Used for crushing and grinding food Elsevier items and derived items © 2009 by Saunders, an imprint of Elsevier Inc.
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Components of the Digestive Tract, cont.
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Components of the Digestive Tract, cont.
Parts of a tooth a. Crown: visible portion of the tooth covered by enamel b. Root: portion embedded in the sockets (alveolar processes) of the mandible and maxilla c. Neck: small region in which the crown and root meet Adjacent to the gingival (or gum) Tooth structures a. Pulp cavity: central core of tooth b. Pulp: consists of connective tissue, blood vessels, nerves Located in pulp cavity Elsevier items and derived items © 2009 by Saunders, an imprint of Elsevier Inc.
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Components of the Digestive Tract, cont.
c. Root canal: term used to describe pulp cavity located in root of the tooth d. Apical foramen: opening in root of the tooth for nerves and blood vessels e. Dentin: surrounds pulp cavity and forms bulk of tooth f. Cementum: thin layer of calcified connective tissue Surrounds dentin in root of the tooth Attaches root to the periodontal ligaments g. Periodontal ligaments: firmly anchor root in the alveolar process h. Enamel: surrounds dentin in crown of the tooth Hardest substance in the body Elsevier items and derived items © 2009 by Saunders, an imprint of Elsevier Inc.
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Components of the Digestive Tract, cont.
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Components of the Digestive Tract, cont.
Salivary Glands Secrete saliva into oral cavity Mixed with food during mastication 2. Parotid glands: largest of the salivary glands Located on each side of head: just in front of ear 3. Submandibular glands: located in floor of mouth 4. Sublingual glands: also located in floor of mouth, anterior to the submandibular glands and under the tongue Elsevier items and derived items © 2009 by Saunders, an imprint of Elsevier Inc.
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Components of the Digestive Tract, cont.
From Jarvis C: Physical examination and health assessment, ed 5, St. Louis, 2008, Saunders Elsevier items and derived items © 2009 by Saunders, an imprint of Elsevier Inc.
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Components of the Digestive Tract, cont.
5. Saliva Contains water, mucus, and amylase (enzyme) Functions: Cleansing action on the teeth Moistens and lubricates food during mastication and swallowing Dissolves certain molecules so that foods can be tasted Begins chemical digestion of starches Elsevier items and derived items © 2009 by Saunders, an imprint of Elsevier Inc.
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Components of the Digestive Tract, cont.
Pharynx Connects nasal and oral cavities to larynx and esophagus 2. Nasopharynx: posterior to nasal cavity Contains the pharyngeal tonsils (adenoids) Passageway for air No digestive system function Elsevier items and derived items © 2009 by Saunders, an imprint of Elsevier Inc.
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Components of the Digestive Tract, cont.
3. Oropharynx: posterior to oral cavity Region where food enters when it is swallowed b. Fauces: opening from oral cavity into oropharynx c. Palatine tonsils: masses of lymphoid tissue located near the fauces Elsevier items and derived items © 2009 by Saunders, an imprint of Elsevier Inc.
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Components of the Digestive Tract, cont.
4. Laryngopharynx: lower region of pharynx Opens into both the esophagus and larynx Pathway of food through pharynx: Food is forced into pharynx by tongue When food reaches the fauces: sensory receptors initiate swallowing reflex Uvula elevates: prevents food from entering nasopharynx Epiglottis drops downward: prevents food from entering larynx Directs food into esophagus Peristaltic movements: propels food from pharynx into esophagus Elsevier items and derived items © 2009 by Saunders, an imprint of Elsevier Inc.
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Components of the Digestive Tract, cont.
Esophagus Collapsible muscular tube Passageway for food between pharynx and stomach Located behind trachea and in front of vertebral column Elsevier items and derived items © 2009 by Saunders, an imprint of Elsevier Inc.
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Components of the Digestive Tract, cont.
Mucosa has glands that secrete mucus Keeps lining of esophagus moist and well lubricated Eases passage of food through esophagus 5. Esophageal sphincter (also called cardiac sphincter) Controls movement of food between esophagus and stomach Elsevier items and derived items © 2009 by Saunders, an imprint of Elsevier Inc.
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Components of the Digestive Tract, cont.
Stomach Receives food from esophagus Located in the upper left quadrant of abdomen Average capacity: 1.5 liters Elsevier items and derived items © 2009 by Saunders, an imprint of Elsevier Inc.
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Components of the Digestive Tract, cont.
Structure 1. Cardiac region: small region around stomach opening from esophagus 2. Fundus: most superior region Balloons above cardiac region to form a temporary storage area 3. Body: main portion of stomach Curves to the right creating 2 curvatures Lesser curvature: concave Greater curvature: convex Elsevier items and derived items © 2009 by Saunders, an imprint of Elsevier Inc.
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Components of the Digestive Tract, cont.
4. Pyloric region: narrow region as body approaches the exit from the stomach 5. Pyloric sphincter: acts as a valve between the stomach and small intestine Muscular layer in wall of stomach Mixes food with enzymes and other fluids b. Rugae: longitudinal folds in the wall of the stomach Allow the stomach to expand Elsevier items and derived items © 2009 by Saunders, an imprint of Elsevier Inc.
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Components of the Digestive Tract, cont.
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Components of the Digestive Tract, cont.
Gastric Secretions 1. Exocrine gastric glands: composed of mucous cells, parietal cells, and chief cells Secrete gastric juice 2-3 liters produced each day 2. Exocrine gastric gland secretions a. Mucous cells secrete: Thick and alkaline mucus: forms protective coating for stomach lining Thin and watery mucus Mixes with the food Creates a fluid medium for chemical reactions Elsevier items and derived items © 2009 by Saunders, an imprint of Elsevier Inc.
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Components of the Digestive Tract, cont.
b. Parietal cells secrete: Hydrochloric acid Kills bacteria Provides an acidic environment for the action of enzymes in the stomach Intrinsic factor: aids in the absorption of vitamin B12 c. Chief cells secrete: Pepsinogen: inactive form of the enzyme pepsin Hydrochloric acid: converts inactive pepsinogen into the active enzyme pepsin Begins chemical digestion of proteins Elsevier items and derived items © 2009 by Saunders, an imprint of Elsevier Inc.
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Components of the Digestive Tract, cont.
3. Endocrine cells Secrete the hormone gastrin Functions in the regulation of gastric activity Churning action of stomach wall muscles: Breaks food into smaller sizes Mixes them with gastric juice Produces a semifluid mixture: chyme Chyme leaves the stomach through the pyloric sphincter Enters the small intestine Elsevier items and derived items © 2009 by Saunders, an imprint of Elsevier Inc.
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Components of the Digestive Tract, cont.
Regulation of Gastric Secretions Regulation of gastric secretions: accomplished through neural and hormonal mechanisms Gastric juice: produced all the time Amount varies on the basis of certain factors Elsevier items and derived items © 2009 by Saunders, an imprint of Elsevier Inc.
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Components of the Digestive Tract, cont.
Regulation of gastric secretions Divided into cephalic, gastric, and intestinal phases 4. Cephalic phase: anticipates food and prepares stomach to receive it Triggered by sensory input: Thinking about food Seeing, smelling, or tasting food Elsevier items and derived items © 2009 by Saunders, an imprint of Elsevier Inc.
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Components of the Digestive Tract, cont.
Sensory input: stimulates centers in the medulla oblongata Sends impulses through vagus nerve to stomach Causes an increase in the secretion of gastric juice Increases secretion of the hormone gastrin Gastrin enters blood and circulates back to stomach Increases activity of gastric glands Elsevier items and derived items © 2009 by Saunders, an imprint of Elsevier Inc.
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Components of the Digestive Tract, cont.
5. Gastric phase: begins when food reaches the stomach Presence of food in the stomach: stimulates reflexes that result in gastrin secretion Gastrin: stimulates secretion of gastric juice (contains hydrochloric acid and pepsinogen) Hydrochloric acid Acidifies stomach contents Activates pepsinogen into pepsin Pepsin: breaks down proteins Elsevier items and derived items © 2009 by Saunders, an imprint of Elsevier Inc.
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Components of the Digestive Tract, cont.
6. Intestinal phase: regulates entry of chyme into small intestine Triggered by: passage of chyme through pyloric sphincter into duodenum Distention and the presence of acid chyme in duodenum: Stimulates secretion of intestinal hormones Inhibit gastric secretions Initiate responses in medulla: inhibit gastric secretions Help prevent excess acid chyme from entering small intestine Elsevier items and derived items © 2009 by Saunders, an imprint of Elsevier Inc.
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Components of the Digestive Tract, cont.
When chyme is neutralized and moves away from duodenum: Inhibitory responses stop Gastric secretion is again stimulated Elsevier items and derived items © 2009 by Saunders, an imprint of Elsevier Inc.
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Components of the Digestive Tract, cont.
Stomach Emptying Peristalsis in the stomach Pushes chyme toward the pyloric region As chyme accumulates, pyloric sphincter relaxes Small amount of chyme is pumped into small intestine Within 4 hours after a meal: stomach is empty Elsevier items and derived items © 2009 by Saunders, an imprint of Elsevier Inc.
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Components of the Digestive Tract, cont.
Rate of stomach emptying Liquids pass through quickly Solids stay until mixed with gastric juice Carbohydrates move through rather quickly Proteins take a little longer Fatty foods: may stay as long as 4-6 hours Elsevier items and derived items © 2009 by Saunders, an imprint of Elsevier Inc.
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Components of the Digestive Tract, cont.
Small Intestine Extends from pyloric sphincter to ileocecal valve Functions: Finishes process of digestion Absorbs nutrients Passes residue to large intestine Elsevier items and derived items © 2009 by Saunders, an imprint of Elsevier Inc.
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Components of the Digestive Tract, cont.
Structure 1. Plicae circulares: circular folds in the wall of the intestines Increase surface area for absorption 2. Villi: finger-like extensions of the mucosa Project from the circular folds Further increase the surface area for absorption Each villus: Surrounds a blood capillary network and a lymph capillary (lacteal) Functions: absorption of nutrients Elsevier items and derived items © 2009 by Saunders, an imprint of Elsevier Inc.
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Components of the Digestive Tract, cont.
4. Intestinal glands: between adjacent villi Surface epithelium on the villi: Contains tiny hairlike extensions: microvilli Form a brush border: increase surface area for absorption Elsevier items and derived items © 2009 by Saunders, an imprint of Elsevier Inc.
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Components of the Digestive Tract, cont.
Three regions of the small intestine: a. Duodenum: begins at pyloric sphincter and ends at jejunum Receives chyme from the stomach Receives secretions from liver and pancreas b. Jejunum: middle portion c. Ileum: last portion 7. Mesentery: extensions of peritoneum Suspend intestines from the abdominal wall Elsevier items and derived items © 2009 by Saunders, an imprint of Elsevier Inc.
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Components of the Digestive Tract, cont.
Secretions of the Small Intestine Large amounts of watery fluid: secreted by intestinal glands Keeps chyme in a liquid form Appropriate environment for chemical reactions Fluid medium for absorption of nutrients Mucus Protects intestinal wall from acid chyme and digestive enzymes Elsevier items and derived items © 2009 by Saunders, an imprint of Elsevier Inc.
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Components of the Digestive Tract, cont.
Digestive enzymes: located in microvilli a. Peptidase: acts on proteins b. Maltase, sucrase, and lactase: act on disaccharides (double sugars) c. Intestinal lipase: acts on fats 4. Enterokinase: enzyme that activates a protein-splitting enzyme (trypsinogen) from the pancreas Elsevier items and derived items © 2009 by Saunders, an imprint of Elsevier Inc.
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Components of the Digestive Tract, cont.
Large Intestine Begins at ileocecal junction and ends at the anus Ileocecal junction: where ileum enters the large intestine 2. Ileocecal sphincter and ileocecal valve Circular band of smooth muscle fibers at ileocecal junction Elsevier items and derived items © 2009 by Saunders, an imprint of Elsevier Inc.
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Components of the Digestive Tract, cont.
Characteristics Mucosa Large numbers of goblet cells No villi Longitudinal muscle Limited to three distinct bands: teniae coli Run the entire length of colon Contraction creates a series of pouches: haustra 3. Epiploic appendages: pieces of fat-filled connective tissue Attached to outer surface of colon Elsevier items and derived items © 2009 by Saunders, an imprint of Elsevier Inc.
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Components of the Digestive Tract, cont.
Regions of the Large Intestine 1. Cecum: blind pouch that extends from ileocecal junction a. Vermiform appendix: attached to cecum No function in digestion 2. Colon: longest portion of large intestine a. Ascending colon b. Transverse colon c. Descending colon d. Sigmoid colon: S-shaped curve of the colon Elsevier items and derived items © 2009 by Saunders, an imprint of Elsevier Inc.
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3. Rectum Mucosa is folded to form longitudinal anal columns 4. Anal canal a. Anus: opens to the outside Internal anal sphincter: under involuntary control External anal sphincter: under voluntary control Elsevier items and derived items © 2009 by Saunders, an imprint of Elsevier Inc.
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Components of the Digestive Tract, cont.
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Components of the Digestive Tract, cont.
Functions of the Large Intestine Functions: Absorption of fluid and electrolytes Elimination of waste products Chyme that enters large intestine: Contains materials that were not digested or absorbed in small intestine Residue that remains: becomes the feces Elsevier items and derived items © 2009 by Saunders, an imprint of Elsevier Inc.
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Components of the Digestive Tract, cont.
Sluggish mixing and peristaltic movements More likely to occur after a meal Result of reflexes initiated in small intestine As rectum fills with feces: defecation reflex is triggered Mucus: only secretory product in large intestine Protects intestinal wall against abrasion and irritation from chyme Helps hold particles of fecal matter together Elsevier items and derived items © 2009 by Saunders, an imprint of Elsevier Inc.
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Accessory Organs of Digestion
Liver Largest gland in the body Location: right hypochondriac and epigastric regions of abdomen Just beneath diaphragm Elsevier items and derived items © 2009 by Saunders, an imprint of Elsevier Inc.
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Accessory Organs of Digestion, cont.
Structure of the Liver Divided into two major lobes and two minor lobes 2. Falciform ligament: attaches liver to abdominal wall Separates right lobe from left lobe (major lobes of liver) 3. Caudate lobe and quadrate lobe (minor lobes of liver) 4. Porta a. Hepatic artery and hepatic portal vein: enter liver b. Hepatic ducts: exit liver Elsevier items and derived items © 2009 by Saunders, an imprint of Elsevier Inc.
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Accessory Organs of Digestion, cont.
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5. Liver lobules: functional units of the liver Consist of hepatocytes (liver cells) Radiate outward from central vein Central veins of adjacent lobules unite to form hepatic veins Drain into inferior vena cava Elsevier items and derived items © 2009 by Saunders, an imprint of Elsevier Inc.
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Accessory Organs of Digestion, cont.
c. Bile canaliculi: tiny channels interwoven with the liver cells Carry bile (produced by hepatocytes) Toward periphery of the lobule Merge to form right and left hepatic ducts Ducts combine: form the common hepatic duct Transport bile out of the liver Elsevier items and derived items © 2009 by Saunders, an imprint of Elsevier Inc.
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d. Sinusoids: venous channels that separate the plates of hepatocytes Carry blood from periphery of lobule toward the central vein Lined with special phagocytic cells: Kupffer cells Remove foreign particles from the blood e. Portal triads: located around the periphery of lobule Consist of: Branch of hepatic portal vein Branch of hepatic artery Branch of a hepatic duct Elsevier items and derived items © 2009 by Saunders, an imprint of Elsevier Inc.
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Accessory Organs of Digestion, cont.
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Accessory Organs of Digestion, cont.
Functions of the Liver 1. Secretion: produces and secretes bile 2. Synthesis of bile salts a. Bile salts facilitate fat digestion and the absorption of fats and fat-soluble vitamins 3. Synthesis of plasma proteins: synthesizes albumin, fibrinogen, globulins, and clotting factors 4. Storage Glucose in the form of glycogen Iron Vitamins A, B12, D, E, and K Elsevier items and derived items © 2009 by Saunders, an imprint of Elsevier Inc.
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5. Detoxification Alters chemical composition of toxic compounds: makes them less harmful Changes configuration of certain drugs (e.g., penicillin) Excretes them in the bile for removal from body 6. Excretion Hormones, drugs, cholesterol, bile pigments Excreted in the bile Elsevier items and derived items © 2009 by Saunders, an imprint of Elsevier Inc.
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7. Carbohydrate metabolism Removes excess glucose from the blood and converts it to glycogen for storage Breaks down glycogen into glucose when more is necessary 8. Lipid metabolism Breakdown of fatty acids Synthesis of cholesterol Conversion of excess carbohydrates and proteins into fat Elsevier items and derived items © 2009 by Saunders, an imprint of Elsevier Inc.
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Accessory Organs of Digestion, cont.
9. Protein metabolism Converts amino acids into different amino acids (as needed for protein synthesis) 10. Filtering a. Kupffer cells: remove bacteria, damaged red blood cells, and other particles from blood Elsevier items and derived items © 2009 by Saunders, an imprint of Elsevier Inc.
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Accessory Organs of Digestion, cont.
Bile 1 liter of bile produced by liver cells each day Yellowish-green fluid Composed of water, bile salts, bile pigments, and cholesterol a. Bile salts Act as emulsifying agents Break large fat globules into tiny fat droplets Increase surface area of the fat Allow for more efficient enzyme action in fat digestion Facilitate absorption of fat-soluble vitamins Elsevier items and derived items © 2009 by Saunders, an imprint of Elsevier Inc.
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Accessory Organs of Digestion, cont.
b. Bile pigments: produced in the breakdown of hemoglobin from damaged red blood cells Responsible for the color of the urine and feces Principal bile pigment: bilirubin c. Cholesterol: product of lipid metabolism Elsevier items and derived items © 2009 by Saunders, an imprint of Elsevier Inc.
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Accessory Organs of Digestion, cont.
Gallbladder Pear-shaped sac Attached to liver by cystic duct Cystic duct joins the hepatic duct from liver Forms the common bile duct Empties into duodenum Elsevier items and derived items © 2009 by Saunders, an imprint of Elsevier Inc.
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Accessory Organs of Digestion, cont.
When gallbladder contracts: Bile ejected from gallbladder into cystic duct Function: store and concentrate bile When chyme with fatty contents enters duodenum: a. Cholecystokinin stimulates gallbladder to contract Permits bile to flow from gallbladder into duodenum Through cystic duct and common bile duct Elsevier items and derived items © 2009 by Saunders, an imprint of Elsevier Inc.
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Pancreas Elongated and flattened organ Located along posterior abdominal wall 3. Head: right side of pancreas 4. Tail: left side of pancreas Elsevier items and derived items © 2009 by Saunders, an imprint of Elsevier Inc.
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Accessory Organs of Digestion, cont.
Endocrine functions a. Islets of Langerhans: secrete insulin and glucagon into the blood 6. Exocrine portion: consists of pancreatic acinar cells Secrete digestive enzymes into tiny ducts between the pancreatic cells Ducts merge to form pancreatic duct Extends the full length of the pancreas Empties digestive enzymes from the pancreas into duodenum Elsevier items and derived items © 2009 by Saunders, an imprint of Elsevier Inc.
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Pancreatic juice contains digestive enzymes: a. Pancreatic amylase: acts on starch and other complex carbohydrates b. Trypsin: breaks down protein Secreted in an inactive form: trypsinogen Activated by enterokinase when it reaches duodenum c. Pancreatic lipase: breaks fats into fatty acids Elsevier items and derived items © 2009 by Saunders, an imprint of Elsevier Inc.
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Accessory Organs of Digestion, cont.
When acid chyme enters the duodenum: Intestinal mucosa: produces secretin (hormone) Secretin: stimulates pancreas to produce a fluid with bicarbonate ions Neutralizes the acids in the duodenum Proteins and fats in chyme: Stimulate intestinal mucosa to secrete cholecystokinin Cholecystokinin: Stimulates pancreas to produce a pancreatic juice Contains digestive enzymes Enter duodenum from pancreatic duct Elsevier items and derived items © 2009 by Saunders, an imprint of Elsevier Inc.
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Chemical Digestion Relies on hydrolysis: water is used to split molecules Reactions proceed at a slow rate Digestive enzymes: speeds up hydrolysis reactions Do not alter the reactions: make them occur more rapidly Elsevier items and derived items © 2009 by Saunders, an imprint of Elsevier Inc.
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Chemical Digestion, cont.
Carbohydrate Digestion Starches and other complex carbohydrates Broken down into disaccharides: by salivary amylase and pancreatic amylase Disaccharides: sucrose, maltose, and lactose Elsevier items and derived items © 2009 by Saunders, an imprint of Elsevier Inc.
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Chemical Digestion, cont.
Disaccharides: broken down into monosaccharides (simple sugars) By enzymes from the small intestine: sucrase, maltase, and lactase Maltose: yields two molecules of glucose Sucrose: yields one molecule of glucose and one of fructose Lactose: yields a molecule each of glucose and galactose End products of complete carbohydrate digestion a. Glucose, fructose, and galactose Elsevier items and derived items © 2009 by Saunders, an imprint of Elsevier Inc.
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Chemical Digestion, cont.
Protein Digestion Pepsin Secreted by gastric glands as pepsinogen (inactive) Activated by hydrochloric acid to pepsin (active) Trypsin Secreted by pancreas as trypsinogen (inactive) Activated by enterokinase to trypsin (active) Elsevier items and derived items © 2009 by Saunders, an imprint of Elsevier Inc.
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Chemical Digestion, cont.
Pepsin and trypsin break down proteins Into shorter chains of amino acids: peptides Peptidase enzymes from the small intestine and pancreas Break peptide bonds to produce amino acids Absorbable end products of protein digestion Elsevier items and derived items © 2009 by Saunders, an imprint of Elsevier Inc.
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Chemical Digestion, cont.
Lipid Digestion Small intestine: only place where lipid (fat) digestion occurs When fat enters duodenum: emulsified by bile Pancreatic lipases: break down fat into monoglycerides and fatty acids Elsevier items and derived items © 2009 by Saunders, an imprint of Elsevier Inc.
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Absorption Each day: Approximately 10 liters of food, beverage, and secretions enter digestive tract Less than 1 liter enters large intestine 9 liters or more are absorbed in small intestine Elsevier items and derived items © 2009 by Saunders, an imprint of Elsevier Inc.
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Absorption, cont. Absorption When chyme reaches large intestine:
Takes place along entire length of small intestine Most occurs in jejunum When chyme reaches large intestine: All that remains is some water, indigestible materials, and bacteria Elsevier items and derived items © 2009 by Saunders, an imprint of Elsevier Inc.
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Posttest True or False The taking in of food is known as mastication.
Mechanical digestion breaks down food into smaller particles through the mixing actions of the stomach. The hard palate and uvula direct food away from the nasal cavity and into the oropharynx during swallowing. Cuspids are teeth that have sharp edges used for biting food. The cardiac sphincter acts as a valve between the stomach and small intestine. Elsevier items and derived items © 2009 by Saunders, an imprint of Elsevier Inc.
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Posttest, cont. True or False
The intrinsic factor aids in the absorption of vitamin B12 from the digestive tract. Chyme is a semifluid that results when food is broken down in the stomach. The large intestine functions in the absorption of nutrients. Bile emulsifies fat into small fat droplets. The end product of protein digestion is glucose. Elsevier items and derived items © 2009 by Saunders, an imprint of Elsevier Inc.
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