The Digestive System Chapter 24

Introduction Structure of the digestive system Functions include A tube that extends from mouth to anus Accessory organs are attached Functions include Ingestion Movement Digestion Absorption Defecation

Overview of Digestive System FG25_01.JPG Title: Components of the Digestive System Notes: This figure introduces the accessory organs and major regions of the digestive tract, together with their primary functions. Keywords: digestive system, components, oral cavity, teeth, tongue, liver, gallbladder, large intestine, salivary glands, pharynx, esophagus, stomach, pancreas, small intestine Human Anatomy, 3rd edition Prentice Hall, © 2001

Histological Organization Same basic arrangement of tissues from esophagus to anal canal Four layers (from innermost to outermost) Mucosa Submucosa Muscularis Serosa Human Anatomy, 3rd edition Prentice Hall, © 2001

Movement and Mixing of Digestive Materials Peristalsis Coordinated motion of two muscular layers Circular muscles contract, then longitudinal muscles Segmentation Mixing of food Circular muscles in two areas contract Longitudinal muscles alternately contract & relax Human Anatomy, 3rd edition Prentice Hall, © 2001

Human Anatomy, 3rd edition The Oral Cavity Structure Lined with stratified squamous epithelium Lips surround the opening Roof is formed from the hard & soft palate Tongue dominates the floor Functions Take in food Prepare food for digestion Human Anatomy, 3rd edition Prentice Hall, © 2001

Human Anatomy, 3rd edition The Tongue Structure Skeletal muscle covered with mucosa The lingual frenulum connects the tongue to the floor of the mouth Surface Papillae Functions Maneuvers food Human Anatomy, 3rd edition Prentice Hall, © 2001

Human Anatomy, 3rd edition Salivary Glands Found outside mouth Ducts carry saliva to mouth 3 pairs Parotid glands Submandibular glands Sublingual glands Saliva Functions Keeps mucous membranes moist Lubricates food Dissolves food Begins carbohydrate digestion Human Anatomy, 3rd edition Prentice Hall, © 2001

Human Anatomy, 3rd edition Teeth 2 sets Deciduous (20) Permanent (32) Held in sockets Gingiva = gums Structure Crown Root Neck Composition Dentin Enamel Cementum Dental caries Wisdom teeth Human Anatomy, 3rd edition Prentice Hall, © 2001

The Pharynx and Esophagus Food enters the esophagus from the pharynx The esophagus is a muscular tube behind the trachea Food is moved by peristalsis from the pharynx to the stomach Cardiac sphincter separates esophagus from stomach Human Anatomy, 3rd edition Prentice Hall, © 2001

External Anatomy of the Stomach FG25_10A.JPG Title: The Stomach and Omenta Notes: (a) Surface anatomy of the stomach, showing blood vessels and relation to liver and intestines. (b)Radiograph of stomach and duodenum after swallowing barium solution to increase contrast. (c)Radiograph of pyloric region, pyloric valve, and duodenum. Keywords: stomach, surface, lesser curvature, gastroepiploic artery, greater curvature, omentum, hepatoduodenal ligament, hepatogastric ligament, duodenum, pylorus, rugae, pyloric sphincter, fundus, body Human Anatomy, 3rd edition Prentice Hall, © 2001

Human Anatomy, 3rd edition The Stomach Same 4 basic layers When the stomach is empty, the mucosa lies in large folds Rugae Pyloric sphincter separates stomach from small intestine Human Anatomy, 3rd edition Prentice Hall, © 2001

Histology of the Stomach Mucosa is simple columnar epithelium with goblet cells Mucosa is folded to form gastric pits Gastric glands secrete gastric juice Human Anatomy, 3rd edition Prentice Hall, © 2001

Human Anatomy, 3rd edition Gastric Gland Several kinds of cells produce substances that form gastric juice Mucus cells Chief cells Parietal cells Enteroendocrine cells Human Anatomy, 3rd edition Prentice Hall, © 2001

Functions of the Stomach Mechanical digestion Food reaches pylorus Chemical digestion Digestion of proteins Absorption No food Water, electrolytes Some drugs Alcohol

Human Anatomy, 3rd edition The Small Intestine About 18 feet long The duodenum About 8 inches long Common bile duct & pancreatic duct empty here The jejunum About 8 feet long Most digestion occurs here The ileum About 9.5 feet long Most absorption occurs here Ends in the ileocecal valve Human Anatomy, 3rd edition Prentice Hall, © 2001

Histology of the Small Intestine The lining is folded into circular pleats Plicae circulares The mucosal surface is folded into villi The epithelial cell membranes are highly folded into microvilli Intestinal glands are found in the crypts at the base of villi Secrete intestinal juice Human Anatomy, 3rd edition Prentice Hall, © 2001

Human Anatomy, 3rd edition A Villus FG25_15C.JPG Title: The Intestinal Wall Notes: (a) Characteristic features of the intestinal lining.(b) The organization of villi and the intestinal crypts.(c) Diagrammatic view of a single villus. (d)Panoramic view of small intestine wall. (e)Villi photomicrographs from jejunum. Keywords: villi, intestinal crypts, mucosa, muscularis mucosae, submucosa, muscularis externa, serosa, lacteal, lymphoid nodule, intestinal glands, submucosal plexus, lymphatic vessel, myenteric plexus, plica, goblet cell, lacteal, brush border Human Anatomy, 3rd edition Prentice Hall, © 2001

Functions of the Small Intestine Chyme is further broken down Proteins Carbohydrates Fats Most absorption is in the small intestine

The Large Intestine (Colon) About 4.5 feet long Mesocolon supports Begins with the cecum Appendix is attached Ascending colon Transverse colon Descending colon Sigmoid colon Colon connects to rectum Rectum connects to anal canal Empties to the exterior through the anus Human Anatomy, 3rd edition Prentice Hall, © 2001

Histology and Functions of the Large Intestine Mucosa - simple columnar epithelium Completion of absorption Formation of feces Lots of mucus glands Expulsion of feces from the body Human Anatomy, 3rd edition Prentice Hall, © 2001

Digestion in the Large Intestine Mechanical Regulated by the ileocecal valve Mixing and peristalsis Mass peristalsis Chemical Mucus secreted No enzymes Bacteria – prepare chyme for elimination Human Anatomy, 3rd edition Prentice Hall, © 2001

Feces Formation & Defecation Chyme is now solid or semi-solid - feces Large intestine absorbs any more water and electrolytes from feces Defecation Mass peristalsis pushes fecal material into rectum Rectum stretches Defecation reflex Human Anatomy, 3rd edition Prentice Hall, © 2001

Accessory Organs Liver Pancreas Gall bladder

Human Anatomy, 3rd edition The Liver Performs many life-sustaining functions Location – under the diaphragm on the right Connected to the diaphragm by the falciform ligament Divided into lobes Right lobe Left lobe Caudate lobe Quadrate lobe Human Anatomy, 3rd edition Prentice Hall, © 2001

Human Anatomy, 3rd edition Histology of the Liver Outside is a capsule Composed of tiny lobules Each lobule is surrounded by liver cells and sinusoids Hepatocytes Kupffer cells Bile ducts run between liver cells Human Anatomy, 3rd edition Prentice Hall, © 2001

Functions of the Liver Produces bile – the primary digestive function Composition Water Bile salts Cholesterol Pigments Bilirubin Digestive function Emulsification of fats

Other Functions of the Liver Absorbs and stores iron, vitamins A, D, E, B7, K Detoxifies toxins and hormones Metabolizes proteins, carbohydrates, and lipids Removes bacteria from the blood Produces plasma proteins Removes worn-out and damaged red blood cells

Human Anatomy, 3rd edition The Gallbladder Location – underside of right lobe of liver Function – concentrate and store bile Collected from liver Hepatic ducts Adds bile to duodenum Cystic duct Common bile duct Gallstones Human Anatomy, 3rd edition Prentice Hall, © 2001

Human Anatomy, 3rd edition The Pancreas Location – in the curvature of the duodenum Connected to the duodenum by the pancreatic duct Produces pancreatic juice Functions Exocrine - digestion of all nutrient groups Endocrine – control blood glucose level Human Anatomy, 3rd edition Prentice Hall, © 2001