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General anatomy of the Digestive System Introduction Structure of the digestive system A tube that extends from mouth to anus Accessory organs are attached Functions Ingestion Movement Digestion Absorption Defecation include Overview of Digestive System Histological Organization Same basic arrangement of tissues from esophagus to anal canal Four layers (from innermost to outermost) Mucosa Submucosa Muscularis Serosa 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 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 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 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 2 sets Deciduous (20) Permanent (32) Held in sockets Gingiva = gums Structure Crown Root Neck Composition Dentin Enamel Cementum Dental caries Wisdom teeth Teeth 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 Stomach 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 Histology of the Stomach Mucosa is simple columnar epithelium with goblet cells Mucosa is folded to form gastric pits Gastric glands secrete gastric juice Gastric Gland Several kinds of cells produce substances that form gastric juice Mucus cells Chief cells Parietal cells Enteroendocrine cells Functions of the Stomach Mechanical Food reaches pylorus Chemical digestion Digestion of proteins Absorption digestion No food Water, electrolytes Some drugs Alcohol 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 A Villus 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 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 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 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 Accessory Organs Liver Pancreas Gall bladder The Liver Performs many lifesustaining 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 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 Functions of the Liver bile – the primary digestive function Produces 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 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 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