Digestive System

Functions Digestion – breakdown Absorption

Organization Alimentary Canal - Gastrointestinal (GI) Tract Mouth to anus 30 feet long

Organization (cont’d) Accessory Organs Found either within the alimentary canal or outside it and communicate with it by way of ducts Teeth, salivary glands, tongue, pancreas, liver, and gallbladder

Mucous Membranes System lined with mucous membrane Kept moist for lubrication and absorption

Tunics Walls of alimentary canal from esophagus to large intestine lined with 4 basic layers (tunics)

Tunics (cont’d) Mucosa Innermost layer lines lumen of organ Submucosa Nerves, blood vessels, glands

Tunics (cont’d) Muscularis externa Smooth muscle Inner circular layer Outer longitudinal layer Combined contraction causes peristalsis

Tunics (cont’d) Serosa Outermost Visceral peritoneum Continuous w/ parietal peritoneum Mesentery Greater and lesser omentum

Digestive Processes Ingestion Propulsion Peristalsis Segmentation

Digestive Processes (cont’d) Mechanical digestion Chewing, churning, etc. Prepares food for further breakdown by enzymes

Digestive Processes (cont’d) Chemical digestion Large food molecules broken down to building blocks by enzymes Carbohydrates  monosaccharides Proteins  amino acids Lipids  fatty acids and glycerol Absorption Elimination - Defecation

Digestive Organs

Mouth Lips and cheeks Palate – roof Tongue – floor Forms bolus (ball) of food Attached to hyoid bone and styloid process of skull Frenulum

Mouth (cont’d) Teeth Digestive processes of mouth Deciduous (baby) teeth Permanent teeth Digestive processes of mouth Food ingestion Mechanical – mastication (chewing) Chemical - starches

Salivary Glands Parotid glands Near ears Mumps Submandibular gland Inside jaw Sublingual gland Under tongue Digestive processes Chemical breakdown of starches

Pharynx/Esophagus Pharynx Esophagus Digestive processes Gullet Conducts food to the stomach Digestive processes Food propulsion Swallowing – deglutition Peristalsis

Stomach Cardioesophageal sphincter Cardiac region Fundus

Stomach (cont’d) Body Pylorus Pyloric sphincter or valve

Stomach (cont’d) When full, can hold about 4L of food When empty, collapses inward on itself Large folds – rugae

Stomach (cont’d) Walls have 3rd muscle layer – oblique Allows churning and mixing of food

Stomach (cont’d) Gastric glands produce: HCl, pepsin, rennin, mucus (protects stomach from digesting itself), gastrin, and intrinsic factor Chyme – semifluid; passes on to the sm. intestine

Stomach (cont’d) Digestive processes Mechanical – churning Chemical – proteins Propulsion - peristalsis

Small Intestine Major digestive organ 6m long Three subdivisions: Duodenum Jejunum Ileum

Small Intestine (cont’d) Microvilli, villi, and circular folds Increase surface area for enhanced absorption

Small Intestine (cont’d) Pancreatic juice and bile enter duodenum

Small Intestine (cont’d) Digestive processes Food digestion (chemical) of carbohydrates, proteins and lipids completed here Absorption of water and end products of digestion also completed here Mechanical – bile – emulsifies Propulsion - peristalsis

Large Intestine Subdivisions Cecum Appendix Colon Rectum Anal Canal

Large Intestine (cont’d) Digestive processes Food breakdown Bacteria metabolize remaining nutrients to produce vitamins (K & some B) Reabsorbs these vitamins, bile salts, and water Propulsion Peristalsis and mass movements Elimination – defecation - remainder of undigested food– feces

Pancreas Pancreatic juice Contains enzymes that break down all categories of food Secreted into the duodenum in an alkaline fluid (neutralizes acidic chyme)

Liver Largest gland of body Produces bile Emulsifies fat Enters duodenum through bile duct

Gallbladder When food digestion is not occurring, bile backs up into gallbladder to be stored

Homeostatic Imbalances

Homeostatic Imbalances Appendicitis Inflammation of appendix If ruptures, spread infection throughout peritoneal cavity – peritonitis – life-threatening Gallstones If bile stored too long in gallbladder or too much water is removed – cholesterol crystallizes Heartburn Cardioesophageal sphincter fails to close tightly – gastric juices backs up into esophagus

Homeostatic Imbalances (cont’d) Hiatal Hernia Superior part of stomach protrudes slightly above diaphragm Gastric juice flows into unprotected esophagus Ulcers Erosion of mucosa of any part of GI tract exposed to secretions of stomach Duodenal ulcer 3x more common than gastric ulcer Bacteria Helicobactor pylori now believed to be major cause of ulcers

Homeostatic Imbalances (cont’d) Emesis Vomiting Like a reverse peristalsis Caused by irritation of stomach or disturbance of equilibrium Diverticulitis Diverticula (mucosa protrusions thru colon walls) become inflamed. May be caused by chronic constipation and low-fiber diet

Homeostatic Imbalances (cont’d) Diarrhea Food rushed thru large intestines before water can be absorbed Constipation Food remains in large intestine for extended time – too much water is absorbed Hepatitis Inflammation and death of liver tissue Usually caused by viruses May be caused by chemical toxins

Homeostatic Imbalances (cont’d) Colitis Inflammation of colon and rectum May be chronic (usually inherited) or acute (caused by irritation of bowel due to diet or infection)

Homeostatic Imbalances (cont’d) Cancer Stomach and pancreatic Highly metastatic Usually fatal Colon Common Fatal if not treated early